Silicone Brake Fluid

911 and Porsche World

Porsche recommends that the brake fluid be replaced every two years. Porsche also goes on to recommend that we use only polyglycol, DOT 3 or DOT 4 fluids and not DOT 5 silicone fluid. Furthermore they say that we should not add or mix DOT 5 silicone type brake fluid with the brake fluid in your car as severe component corrosion may result. Such corrosion could lead to brake system failure. 

For the model year 1993 and forward the brake systems in all Porsche models were filled with an improved type of brake fluid, ATE type 200. ATE Type 200 fluid was a new improved DOT 4 fluid with a higher dry boiling point, a higher wet boiling point which extended the life of the fluid and resulted in longer change intervals (every 3 years). This same brake fluid is sold on the aftermarket as ATE Blue and is a superior normal DOT 4 brake fluids. 

Brake fluid comes in DOT 3, DOT 4 or DOT 5 ratings. The DOT standards for brake fluids were established in 1972. When the National Highway Traffic Safety Administration, Department of Transportation (NHTSA) set up the requirements for brake fluids they determined that there was a need for two grades of fluid until an all-weather fluid was developed with viscosity and boiling point characteristics suitable for all braking systems. In order to provide added protection against vapor locking and fade in severe braking service, DOT 4 fluid is recommended. But in such applications it is important to note that the same higher viscosity that helps eliminated vapor locking and fade may result in poorer system performance in very cold weather Also, it should be noted that the high boiling points are sacrificed in the DOT 3 fluid for low viscosities for use at low temperatures. These differences between the viscosities of the DOT 3 and DOT 4 fluids are necessary to cover the specified operating temperature ranges and as such make it necessary to maintain both DOT 3 and DOT 4 brake fluids. 

DOT 5 fluid is supposed to be the all-weather fluid that is mentioned in the preceding paragraph and it can be used as a replacement for both DOT 3 and DOT 4 brake fluids. They test all three fluids for a great number of different characteristics, however, the most interesting characteristics to us are the equilibrium reflux boiling point (dry boiling point), the wet equilibrium reflux boiling point (wet boiling point) and the kinematic viscosities (viscosity at cold temperatures). Dry boiling point: These are the minimum boiling temperatures allowed for the various grades of fluid (this test simulates the boiling point when the fluid is new). 

DOT 3 401° F
DOT 4 446° F
DOT 5 500° F 

Wet boiling point: These are the minimum boiling temperatures allowed for the various grades of fluid when wet (this test is a simulation of the boiling point after the absorption of moisture from air) 

DOT 3 284° F
DOT 4 311° F
DOT 5 356° F 

NOTE: These are the minimum requirements and there are brake fluids available that will exceed these minimum requirements. 

Kinematic viscosities: All brake fluids (DOT 3, DOT 4 and DOT 5) must meet a minimum viscosity test of not less than 1.5 centestokes at 100° C (212° F) and must not be more than the following to meet their various classifications (the larger numbers indicate higher kinematic viscosities just like with motor oils). 

DOT 3 1500 Centestokes at minus 40° F
DOT 4 1800 Centestokes at minus 40° F
DOT 5 900 Centestokes at minus 40° F. 

There are some advantages to silicon brake fluid over conventional polyglycol brake fluids. It is permanent, it does not absorb moisture, it does not boil, it helps prevent corrosion rather than causing it, it will not damage paint if it is spilled on the paint and it helps lubricate seals and other components in the brake system. 

The disadvantages, though minor, can still be very annoying. Silicon brake fluids are slightly compressible, or at least they appear to be because of their affinity for air, which results in a different pedal feel from that of a system which uses a conventional non-compressible polyglycol fluid. Because of silicon brake fluid's affinity for air and their surface tension characteristics they tend to cling to any air bubbles which get into the braking system making the system very difficult to bleed properly. 

The brake fluids required for our Porsches by Porsche AG are either DOT 3 or DOT 4 in new and unused condition (that means that the can should be sealed so that there is no moisture in the fluid). Porsche recommends that we changed the brake fluid every two years (three years with the new ATE type 200 brake fluid) because the conventional polyglycol fluids are hygroscopic and will absorb moisture. When the fluid absorbs moisture, two things happen: the boiling temperature goes down and the absorbed moisture is corrosive to the brake components. Minimum wet boiling point is specified for DOT 3 is 284° F and for DOT 4 is 311° F and because these fluids are hygroscopic they commonly will approach these minimum limits. In contrast DOT 5 silicon fluids have a wet boiling temperature of 356° F and because they are not hygroscopic they will never approach the wet boiling limit. 

The silicon brake fluids are DOT 5 and as such are required to be compatible with all conventional DOT 3 and DOT 4 fluids in order to comply with the federal regulations for DOT 5. There are also other DOT 5 brake fluids that while they are synthetic are not silicone based and as a result are more similar to the conventional DOT 3 and DOT 4 brake fluids that we are familiar with. 

Silicon brake fluid is inert and is supposed to be the only universally compatible brake fluid. However silicon is not miscible and will not mix with other types of brake fluids. Although the silicon fluids can be used with conventional polyglycol fluids, they will not mix and the conventional fluid still in the brake system can continue to absorb any moisture in the system components. 

To gain maximum benefits for the silicon brake fluids the complete brake system should be completely disassembled and cleaned before adding the silicon brake fluid. Then because of the silicon brake fluid's affinity for air, it is recommended that a pressure bleeder be used for bleeding the system. 

I have had personal experience with silicon brake fluid in both street and racing cars. And indeed have experienced difficulties getting the systems properly bled. Even when we were sure we had properly bled the brake system, the brake pedal always had a strange, soft feel to it. We attempted to use silicon brake fluid in a Porsche 935 race car at Daytona in 1981 for the twenty four hour race because of the problems we have in Florida with the high humidity lowering the boiling point of the brake fluid. It probably would have achieved our objective; however, the drivers didn't like the pedal feel and requested that we change it back to conventional fluid. The spongy pedal thing gets worse with heat and in our experience with it at Daytona the driver, Bobby Rahal, told us if we didn't take it out we would have to drive the car ourselves; it was scaring him to death. At that time there was no chicane on the back strait away and they would come into the braking area for Turn one at about 200 mph before braking. At that point they were committed to turn one, which was a little like threading a needle and the soft brake pedal was very unsettling to say the least. Rahal said that the pedal would get worse each lap as the brakes got warmer. We returned to conventional brake fluid and won that years 24-hour race. 

In street cars the silicon fluid has advantages which may outweigh its disadvantages, particularly for older cars that do not get driven very much. Moisture absorbed by conventional polyglycol brake fluid cause serious corrosion of metal parts and deterioration of rubber seals and hoses in the brake system. However, in order to take advantage of that attribute the brake system must be completely free of any polyglycol brake fluid. If any polyglycol brake fluid remains in the system any moisture in the system will be attracted to those small pockets of polyglycol brake fluid causing corrosion

Unleaded Fuels

911 and Porsche World

When we started to convert to unleaded fuels here in the United States in the late seventies everyone was concerned about what was going to happen to our cars with out lead to lubricate the valve guides and cushion the valves on the valve seats. 

One of the first things that I did was check with Porsche and they said that all of the cars from the SC forward had sintered iron seats made of a material that they call Pluko. They said that all of these cars would be fine and that they weren't sure about the earlier cars, but that if there was a problem the could provide Pluko seats for the earlier cars as well. 

Next I checked with a friend, Tim Wusz, who was the Senior Engineering Associate Fuels Technology, Unocal Science & Technology Division then, and who is one of the authorities here in the US on what the effect would be when they took the lead out of the gas over here in the late seventies and early eighties. Tim Wusz said that the only cars that would have problems with the removal of lead were some early American cars that used the cast iron of the blocks or the heads as the material for the valve seats and had very soft seats. Wusz assured me that our cars would run fine on the unleaded fuels that would be available and suggested that I have our valve seats tested for their hardness. 

Unleaded fuel is really no problem at all - lead was the work of the Devil. Lead did do a few things for us, but it may have actually done more harm than good. Lead in gasoline contaminated our oil, it fouled our plugs and it loaded up our oil control rings. Modern cars that run on unleaded fuels last longer, run better, and go further between services. We often see the modern Porsches of the unleaded era run for well over two hundred thousand miles without requiring major mechanical work. 

However, besides acting as an octane booster tetraethyl lead acts as a shock absorber between the exhaust valves and valve seats. The concern we enthusiasts have is for the potential of excessive valve seat recession or pound-in because of being run without leaded fuels. The reason that lead is so important to these older cars with "soft" seats is that the lead acts as a lubricant between the valves and the valve seats, cushioning the valve each time it seats to prevent exhaust valves and/or seats from recessing or pounding-in. In older Porsches, with their softer seats and valves there is some cause for concern. The newer cars, from 1977/78 on were designed so they could run on unleaded gasoline. In 1978, when Porsche started to use catalytic converters to meet the emissions standards requiring the use of unleaded gasoline, they changed the valve seat material to an sintered iron material that they call Pluko. Just how hard are "soft" seats and how hard do they have to be to prevent recession or pound-in. Really soft seats are cast iron seats with a hardness of from Rockwell 12 to 25. Seats with a Rockwell hardness of 45 to 50 are probably hard enough in most cases to provide for satisfactory protection. 

I have hardness tested the exhaust seats used in a number of our different Porsche cylinder heads. I checked the following heads with the following results:

1. 1966 911 head RA 65
2. 1969 911 head RA 54
3. 1976 911 head RA 64
4. 1.8 914 head RA 59
5. 1.7 914 head RA 44
6. 1962 356 head RA 64
7. 356C/912 head RA 58

None of these seats can be considered "soft" seats and as such they should not cause any problems with unleaded gasolines. Additionally all of the Porsche engines built since 1964 have some form of valve rotators. Their favorite is to use the ATE style keepers which do not hold the valve tightly, so that the valve is free to rotate. This has served them well and only the 924 engines had a separate valve rotator. So we should be able to use unleaded gasoline without any additional changes. However, the best way to keep track of what is happening until we are sure, will be with more frequent checks of the valve clearances. Obviously, if the valve clearance changes over a short period of time, some changes will have to be made to the exhaust valves and/or seats. 

It is also interesting to note that when lead was introduced to gasoline in 1923 there was very similar concern about the effect on the engine's valves and valve seats because of the addition of lead to gasoline as there is today with the removal of lead from the gasoline. At the time the engine designers felt that the lead caused a serious service problem with the spark plugs and exhaust valve damage caused by the corrosive effect of lead oxide. The designers forged ahead and used lead as an additive because of leads superiority over all other antiknock additives of that era. With higher octane gasoline the engine designers could use higher compression ratios to achieve major gains in both power and fuel economy. During this period of automotive history the designs and materials used in high-compression engines made tremendous improvements over a very short period of time. These included special alloy exhaust valves, and seats and sodium cooled valves all to combat valve and valve seat erosion, caused not by the removal of lead, but the addition of lead to the gasoline. With the introduction of lead to gasoline the octane number was increased from about 50 to todays 90+ for high octane unleaded gasolines making possible a boost in compression ratios from 4 to 1 up to the 9+ to 1 used by all of our modern Porsche engines. Because of advanced catalytic cracking methods and other octane boosting additives the gasoline companies find it easier to make high octane unleaded gasolines today than they did sixty years ago so the removal of lead from our gasoline hasn't caused much problems. 

Engines that are run on unleaded gasoline burn cleaner and will run much longer between tune-ups than cars that are run on leaded gasolines. All modern normally aspirated Porsches (4, 6 and 8 cylinders) have a recommended service interval of 15,000 miles including the oil change intervals and the turbocharged cars have a recommended oil change interval of 7,500 miles. Bosch has 30,000 and 50,000 mile spark plugs and the unleaded fuels are largely responsible for these extended service intervals. It also looks like engines that have been run on unleaded fuels will last longer than those run on leaded fuels, it is not uncommon for 911 SC engines to run for 175,000 to 200,000 miles without requiring any major maintenance. 

I have offered to write an article for 911 & Porsche World, which would include most of the above information, but Chris didn't seem too interested, perhaps I should ask the Post. 

Porsche never really wanted to say much beyond what I mentioned about the seat material. PCNA has never really said anything about the potential effect of unleaded fuels. Here in California the leaded fuels have been gone for most of this decade and we have really seen no negative effects are a result of the absence of lead. 

To your point about the amount of power used, my expert said that the only to examples that he could think of where people might have problems were Power boats where you run at full power for extended periods of time and possibly with one of the old VW busses heavily loaded pulling a very long very steep grade. Everyone will worry about the potential problem until sometime in the future when it dawns on everyone that everything has gone on as normal and that the cars have had no problems. Everyone will pretty much have to experience that for themselves as they have over here. Young people over here don't know any better and think unleaded fuels are just fine.

Daytona with Joel

911 and Porsche World

This year I went to the Daytona 24-hour race with a good friend, Joel Reiser, who just started racing this past year. I have known Joel Reiser for ten years or so, we met because we are both Porsche enthusiast and share the interest in modifying Porsches for more performance. He contacted me because he had read my suggestions for modifying the 911SC engines in my Porsche 911 Performance Handbook and had some questions. He contacted me to find out how to modify a 911 SC that he owned at the time and he and I became great friends. 

Over the years Joel got involved in the Porsche Club of America Drivers Education events held at the different tracks in the north eastern United States and in Canada. He has run PCA drivers education events for the past eight year and instructed for the past five. Joel kept buying newer and better cars to participate in the club events, but he also continued to modify all of his cars. I tried to talk Joel into running in some of the club races, but because of the modifications that he made to his cars they were always unfavorably classed so he never ran any of the club races.

Then last fall he ordered a factory 993 RSR which was delivered in late December 1997 as a 1998 model. His first event with this car was a test session in June, which was the first time he had ever driven on slicks. A couple weeks later he entered his first PCA club race in the RSR at Mosport July 27, 1998 where he placed second in GT2R. Joel told me he had a fantastic time an that the thrill of passing the other guy was a lot more fun that he thought it would be. He said that passing cars added a whole new dimension to cars for him. 

In early July Joel also bought Jochen Rohr’s GT1 car which he immediately started racing. He raced it in the 50/50 at Watkins Glen and four top ten finishes in the Canada Challenge Cup races at Mosport. Joel’s racing carrier was limited to these races before entering the Daytona 24-hour race in January. 

After Joel got the GT1 car he met Tony Callas who had a great deal of experience with GT1 Porsches, a lot of that experience with the car that Joel bought from Jochen Rohr, both with Rohr and the previous owner the Roock Brothers. Tony has been involved in racing since he was a kid starting with his father, racing their 910 and RSRs. Tony moved to California in 1985 working for several prestigious Porsche shops before starting his own Callas Rennsport in 1992. The past few years Callas has worked for several name teams including the New Zealand New Hardware team in 1996. I first met Tony Callas at Daytona 1996 when he was with the New Hardware team. He has also worked for Rohr Motorsport, Roock Racing and Champion racing. Tony was a member of the Rohr GT1 team that won their class at Daytona in both 1997 and 1998 and won the GT1 class at the Petit Le Mans with the Champion team. He was alto the lead engineer for the Rohr Motorsport team when they won the GT1 championship in 1997 with the Porsche GT1 car. 

Joel and Tony Callas hit it off personally and decided to do more together than just the GT1 racing. Joel shipped his car from his home in NY to Tony Callas’s shop in California with the idea that they would run the car in some of the west coast PCA club races. Instead they decided to race the car in the January 24-hour race and started making plans toward that end in November. 

They started rounding up drivers for the race and planned a test session at Willow Springs December 21, 1998. By then three drivers had been selected, Joel, Grady Wilingham and Johnny Mowlem. 

Joel is 39 years old the Chief Technical Officer of Matamor Software Solutions which is headquartered in Rochester, NY. Metamor is one of the teams sponsors. Grady Willingham is 35, from Birmingham Alabama and entering his seventh season of racing. Grady has class wins at Sebring, Road Atlanta and Road America. Grady has raced at Daytona the past three years scoring victories in all three races. He has also claimed a victory in his class in the HSR/Rolex Enduro at Road Atlanta in 1995. Johnny Mowlem was referred to Tony Callas by his friend Allan McNish. Mowlem is 29 years old from Great Britain in his ninth season as a professional racer. Most of his experience has been in formula cars, with a change to the Pirelli Porsche Cup series in 1996. In 1996 he recorded a class victory and a second overall, he was back Cup racing again in 1998 where he wan first overall. The Daytona 24-hour race was his first endurance race. 

After the test session they were lucky to add David Murry to the driver line up for the race. Murry who is 41 and lives in Atlanta, GA and is the most experienced of the driving team. Murry has been racing since 1981 and has recorded three championships, the most recent SCCA’s World Challenge drivers championship. 

This was Johnny Mowlem’s first endurance race so I was interested in his impressions of the race. He said that in the test at Daytona early in January he was impressed with being there. He said that the green grass in front of the pits is like a putting green and then behind that you see a wall with Daytona on it and all of the grandstands behind that, it really makes a big impression. He said that at most road courses like Le Mans and there is no real land mark that you can look at and say well, that’s Le Man, whereas Daytona is so obviously Daytona. Was really excited to be there. When they asked him to qualify the car during one of the qualifying sessions he said he was really honored that they would ask him with David Murry on the same team with so much more experience at Daytona. 

He said that it was nice to work with David Murry, because David was so helpful. It gave him a lot of confidence to be able to run the same sort of time as David. Johnny and David were able to work together on the setup of the cars and then to be able to go out and qualify the car was simply fantastic. Johnny told me that he never ever thought that they would finish the race, not that he didn’t’ think that they would finish, but he said he just never thought about them finishing. He said he just assumed that they wouldn’t finish, until he got back from resting read to drive again at about eleven in the morning, twenty two hours into the race and the car was second in class and eighth overall in the race. He said he remember thinking then maybe we are going to finish and do well. He didn’t realize that the car had stalled already and David had gotten it back to the pits and saved their position.

Johnny got in and drove for the last hour an a half in very slippery rainy conditions. The team wanted to leave David Murry in the car because he was used to driving the car in the rain there as he was in the car when the rain started. However, to leave Murry in until the end would exceed the four hours continuous driving allowed by the rules so the team had to change drivers. Johnny was anxious about getting in while it was raining with the car in a good position for fear he might have a problem learning the wet track. He felt that it was going to take two or three laps to get to know the track without throwing it into the wall. The O7 closing down on their second place car and he was concerned that he might loose second position while he learned the track in the wet. There was a lot of pressure on him to do well and maintain their second position. During that last hour one of the Ferraris in the CanAm class went by him that had problems earlier but was again running well and passed them for eighth overall dropping them to ninth overall. 

Johnny said that at the end of the day Joel has the enthusiasm and commitment to do the job properly, Tony Callas is unbelievably good as a crew chief, particularly when it came to dealing with the car. He said he enjoyed it so much even though he was so tired at the end of the race and had sores on his hands. It was so much to take in, but he felt so happy for Joel and Tony that he didn’t really feel any happiness for himself until he got home and had time to think about it. Afterwards he said he thought about it and thought wow that it really good for his career as a race drive. He said that when he got home people were ringing him up and telling him you have done yourself so much good. He said that at the end of the race he was just happy for the guys and happy that the race was over, because there is nothing worse than being the one that is sitting in the car when it stops.

He said it was a wonderful experience for him, it worked out absolutely perfect. It was such an adventure to start out they rang him up about the twelfth of December and two weeks later he was in California testing at Willow Springs and a month later they were finishing second in the race at Daytona. That is like the sort of stories you have in a comic books. 

He said that David Murry was very helpful. When he knew he was going to be driving with David Murry he told Allan McNish, and Allan told him that he was a perfect guy for him and that he would help him and not try to hurt him. And he will be a really good guy to learn about 24-hour races from. Johnny said that everything McNish said was true, he was a great guy and he gave him a lot of advice and helped him the whole way through. He said he told him that when he got out of the car not to hang around the pits, even if it is day time, but to go back to the motor home and lay down even if he couldn’t sleep. Lay down, relax, drink, eat bananas and don’t start getting caught up in the race because it will catch up with you. He said he was glad that he took Murry’s advice, because if he had stayed in the pits until nine or ten at night and then had to do night driving he would have been finished. He said that advice like that was very helpful for him because David Murry really knows what he is doing. He said that this was his first ever 24-hour race and that he was happy to have started with this team and David Murry. 

David Murry said that the teams plan was to qualify the primary number 02 car for the race. But that between the early January test at Daytona and the race Joel Reiser had purchased a second RSR that the team planned to qualify and then start in the race, but not run the entire race. With the two cars they would have more time for all four drivers to become familiar with the track and the 993 RSRs. They didn’t have enough time to race prepare the second car nor the crew to run the two car in the race. The new number 92 RSR is red and was fitted with basically the same spring rates and set up as theyhad on the primary car. Joel Reiser and Grady Willingham spent most of their time driving the red number 92 car to get more track experience while Johnny Mowlem and David Murry worked on setup in the number 02 car getting it ready to run in the race. Thursday was practice and qualifying so they didn’t have much time to get everything done before it was time to qualify, which is why having the two cars was a real benefit for the team. 

During qualifying on Thursday David Murry took the white number 02 car out on a light fuel load to qualify it. I took Murry awhile to get a couple of clear laps and qualify and by then he had run out of fuel, but by the checkered flag he had qualified fifth. The plan had been to have Johnny Mowlem qualify the red number 92 car, but they were experiencing ABS problems and the car did not get out during the Thursday session. Thursday David Murry said that the had a chance to change the set up on the white number 02 again and it was better. It was a two hour session and everyone got some time in the primary number 02 car during the night practice.

Friday the plan was for Johnny Mowlem to qualify the number 02 car and David Murry to qualify the red number 92 car to make sure that it was in the race just in case something happened to the primary car at the start of the race. The red number 92 car was again troubled with some brake problems and team manager Tony Callas most of the final qualifying session to solve the problem. They just got the car out at the end of the session in time for one lap of qualifying. The one lap was good enough to qualify the car for the race so both cars were qualified for the race. 

David Murry said that it is really hard to understand what it takes to do well in a long race until you have done one - or more. Joel and Johnny had never done an endurance race before and he was surprised at how quickly that they they figured it out. Murry started the race 6th in GT3 and by the end of his first driving sting he was in 4th place. Johnny Mowlem started the red car and ran it for about 20 minutes before retiring it. Then Johnny took over the primary car from Murry and when he turned it over to Grady Willingham he was 3rd in GT3. David Murry said that they were looking pretty good after the first round of driving, but it was very early. Grady drove his stint and turned the controls over to Joel Reiser. They did that same rotation again through all four drivers and were still 4th. It was going to be a tough battle. The Alex Job Porsche had led from the pole and was very strong. There car was more extensively developed than the Reiser/Callas car so they weren’t able to run quite as fast a pace as the lead car, but even so they soon found themselves 2nd in the GT3 class with the G&W #07 very close behind. 

Murry said that in the morning, around 9 AM with four hours of the race to go it began to rain. The rain came down very fast and hard, hard enough for USRRC to go full coarse yellow. David Murry knew the track conditions and drove most of the rest of the race. He couldn’t finish the race because that would put him over the 4-hour straight driving limit that USRRC has set. The plan was to put Johnny Mowlem in for the last hour plus to finish the race. The team was confident that Johnny could finish the race. He was "very" quick and would adapt to the conditions instantly. Johnny an incredible job to finish 2nd in GT3 and 9th overall. The #07 car had an axle break just before the finish but fixed it to finish 3rd in GT3. 

I spent most of my time at Daytona either out photographing the cars on the track or hanging out in the pits taking photos of the various GT3 teams doing their pit work. The Reiser/Callas Rennsport team was a well organized team with good team members and most of their stops went well. Tony Callas’ dad Mike was on the crew and about dawn I was talking with him and he said that he remembered why he had quit racing before. All of the leading GT3 teams did well, but they all had minor problems in the last few hours of the race that because the each had their own problems had little effect on the outcome of th e race. The lead Alex Job car, number 23, had and axle fail that they had to replace. The third place G&W Motorsports, number 07, car had a similar problem. While the second place Reiser/Callas Rennsport, number 02 car, had an oxygen sensor fail and the car died out on the course. Fortunately David Murry was able to get the car running again and return to the pits where Tony Callas could diagnose and repair the car and get it under way again.