VehiGAZ

Hi all,

I did my first DE this weekend at Lime Rock with PCA. Wheeee! It was more challenging than I expected, though - my street-driving skills were useless.

I had an overheating problem late in the day, and I wanted to get some input on the potential causes. Here are the facts of the case:

I had about a half a tank of 93 octane in the car on arrival, and I topped off in the morning with about 13.5 gallons of 110 octane race gas. Seemed like a good idea at the time...

It was very hot all day - my temp gage in the paddock read about 100*F before each afternoon session. It was about 90-95*F on the track. I was fine for the first 3 sessions, but it overheated at the end of the last two sessions (around 2:30 and 4:00 in the afternoon). I got the "engine temp too hot" message and a warning light on the temp gauge both times. I was driving everything but the front straight in 3rd gear, topping out around 6000 rpm or so, so it was fairly demanding on the engine, but not too bad. The cooling flaps were opening as they were supposed to. The radiator fins are clean and mostly straight.

I checked my service records when I got home and found that the last time I know the coolant was changed was in 2004 (maybe 6k miles since then). It could have been changed since then, but I can't be sure.

I took it for a spirited test drive yesterday afternoon, maybe 85*F or so weather, and it ran hotter than normal, but didn't get to the warning stage.

My questions...
Would 110 octane race gas make the engine run significantly hotter?
Should any cooling fans stay on after shutting off the engine?
Is 4 year old coolant too old?


Thanks!!

Gary Knox

Well, 110 octane gasoline will burn slightly "slower" than 93 octane (thus, allowing use in higher compression engines). PERHAPS this is a bit like having slightly retarded timing - which I seem to recall can result in an engine running slightly warmer. That's my only thought (please someone correct me on the timing issue if I'm wrong!!!!).

If you enjoyed Lime Rock, I can't recommend Watkins Glen too highly. It is a MUCH more 928 oriented track than Lime Rock.

Gary Knox
West Chester, PA
'89 S4 5 spd
'94 GTS auto

VehiGAZ

All in good time, Gary...

123quattro

Race gas will have NO affect on coolant temperature. I'd say your radiator is not doing it's job.

hinchcliffe

Hmmmm, you should try Watkins in October. Shouldn't overheat up here.....

hacker-pschorr

Was it VP-110? IIRC that leaded gas, not good for O2 sensors & CATS.

If you did run leaded gas you could have burned up the cats causing them to clog, that could cause the engine to run hot.

Sharkbody

I'm assuming the 112 was B32 or some equivalent. It's probably the coolant system. That kind of race gas has enough lead in it to turn you into the tin man. Unless you're running 12/1 comp. or thereabouts, I'd stay away from it. There are milder forms of competition fuel that are also unleaded. The cat argument has some merit as well. G

123quattro

Leaded fuel will typically kill an oxygen sensor in about 25,000 hours. It will kill a catalyst in short order. If the catalyst clogged, you would know immediately. The brick melts nearly instantaneously and back pressure goes through the roof. Engine power on that bank gets effectively cut to zero output. My 92 SHO had a clogged cat on one back. It was such a huge restriction that the engine couldn't hit the rev limiter at WOT when in neutral.

pcar928fan

Clearly you do not understand the point of race gas and as noted most race gas is still leaded which is VERY, VERY bad for a catalyst equipped car!

Octane is a SPARK/Ignition INHIBITOR! Its point is to allow for MUCH HIGHER compression ratios before the mix explodes out of time w/ the engine causing pinging and death to a motor. UNLESS your car is Turboed or Supercharged there is absolutely NO POINT what-so-ever to using fuels with an octane rating above 93! That is what your car was designed to run on! The light pressure Turbos and S/C's don't even require higher octane fuel to run well...

Doubt that was the cause of your overheating, but DON'T RUN RACE GAS IN YOUR STREET CAR, IT IS A WASTE OF MONEY!!! Though race gas does smell better when burned, but I think that goes back to the whole lead issue actually!

VehiGAZ

It was only 13 gallons of the 110 octane fuel (not sure what spec but I didn't see any "CONTAINS LEAD" signs on the pump, either) mixed in with about 9 gallons of normal 93 octane pump gas. I've only used less than half of that mixture, as well. I will stay away from it from now on, that's for sure.

Am I ok to burn the rest of it? Or should I consider having it drained?

Anyway, back to my original questions...
Is 4-year-old coolant too old?
Should my fans stay on for a while after shutting off the engine?

Adam Geist

I change my coolant in all my cars every two years regardless of the mileage. Cheap insurance against cooling system corrosion.

Your cooling fans will remain running after shutting the engine off if your under the hood temps are high. On my '86.5, this after shutdown circuit runs through a resistor that cuts the fan speed roughly in half.

hacker-pschorr

Same here, except on the track car I flush out the coolant every spring.

mark kibort

your system might need to be burped. see that you overflow tank is more than halfway filled.
check the radiator for temp. touch the top and bottom either in front or in the back, and it should be hot to the touch. cool spots can indicate clogged water passages.

why are you running 13 gals of race gas? weight is the enemy on the track. I would NEVER touch the the track with any more than 1/3 of a tank. (unless you plan on being on the track for more than 30 mins at a time.) As was said, yes, no need to run race gas as your motor is not tuned for it to utilize it. in fact, it then can produce a reduction in power.

mk

VehiGAZ

Yes, that is fair to say. I'm a noob to the track - what can I say? I know better already...

Does anyone have any hard advice about burning off the rest of the gas vs. draining it?

VehiGAZ

Hmm... After getting a high-engine-temp alarm, wouldn't it be fair to expect that the fans should have stayed on when I shut off the engine after coming off the track?