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I ran the car at Sebring a bit this past weekend (instructed at a track day) and had problems with blowing coolant past the radiator cap. This wasn't a problem at the track before, although it was high 80s in the morning and low 90s in the afternoon, probably 10F warmer than last time. The coolant temps didn't go up above normal (stock gauge, but seems pretty linear). Oil temps were only slightly higher than last time, when oil temps (sender in the pan) went over 210 I backed off a little to let the car cool down.

I have a 16 lb cap on the reservoir with a vent lever. A guy pitted near me with an E30 M3 had a 20 lb cap, I tried that and it stopped the coolant from blowing out. However, the upper radiator hose was rock-hard after coming off the track, so I went back to my old cap, figuring it might be better to blow a bit of coolant out (I could just refill it, and the sensor tells me when the reservoir is low), than blowing a hose or radiator because of the higher pressures. At lunch, I picked up another cap at an auto parts store. They said a 13 lb cap was stock, but they had another 16 lb cap so I bought that. The new 16 lb cap let coolant escape just like the old one, so I guess there's nothing wrong with the old one.

I did a compression test the day before the track event and numbers were from 198 - 205, pretty even. No coolant in oil, no oil in coolant. Under normal conditions, it doesn't spit coolant, so I don't think the head gasket is bad.

So, my question is, what cap should I be running? Is a 20 lb cap safe? Radiator and hoses are in good condition.

BTW, the car ran well at the track. The tires didn't like the additional heat very much, and got a little greasy and had a little higher wear in the afternoon. No brake problems, just a slightly soft pedal. Brake pads (Ferodo DS2500 on E34 M5 brakes) now have about 2.5 hours of track time on them, and are still less than half worn.

In the morning, I was staying ahead of a viper but he must have either not known what he was doing or not been trying hard. I was faster in the corners, and he didn't gain much down the straights. I chased a track-prepped Porsche 914 (gutted, roll bar, probably 6 cyl and track tires) off the track; well, he wouldn't point me by, and got a little crazy trying to stay ahead of me and lost it in the carousel, I knew he was gone when he entered the turn too fast and way off-line. He didn't hit anything and was back on the track later on. I caught up with an //M Coupe (with same motor as new M3) driven by a novice, he ran down the next straight without pointing me by and I stuck with him, not bad for having about the same power and a bunch more weight. He was a good guy and pointed me by on the next straight, though.

All in all, it was a very fun day. I took a couple friends with me and gave them rides at the track, both were very impressed. They also rode with others and had a great time as well. For those of you near a Chin Motorsports event, you should check it out even if you're not driving. For $20, you can ride with any solo driver.

Sounds like a fun time. As for the radiator cap, be very careful. My temperature gauge was a little flaky when we put the turbo on. It would jump around from time to time, but I thought it was reading accurately. Well, when we did the install, the thermostat got put in backwards accidentally. Wouldn't have been a huge deal except apparently the gauge wouldn't read above half (12 o'clock). So the car was driven approximately 10-15 miles on the highway. The only indication of something amiss was that suddenly the motor started knocking due to the ridiculous heat induced thinning of the 20W50 Mobil1!!! The bottom end miraculously survived apparently unscathed, but the head wound up warped.

Long story short, don't trust the life of your engine to the stock temp gauge. Get something else in there to confim or deny that your coolant is the proper temperature. Get a real gauge in there or, if you have a pyrometer like I've noticed a fair number of track junkies do these days, fire it in the inlet hose to the radiator or the radiator itself when the cap starts spitting coolant, make sure you're not getting hot and not realizing it.

Jeremy


[Edit by Jeremy on [TIME]1120101197[/TIME]]