DigitalWidgets

Last month I had the opportunity to attend a local autocross "practice" event. Basically a 40 sec course you could run as many as you could get in for the day. By late afternoon, the "crowd" was thinning out and I was just doing run after run with maybe 3-4 mins in between (i.e. finish a run, just hop back in line and go again after a handful of cars).

At one point I had done like 8-10 runs in a row. I had the windows open, and AC turned off. I had the interior fan running, but eventually it started blowing out very hot air (like the heater was on...but maybe even hotter). Soon I could smell a bit of coolant and temp gauge was rising to 230 range, so I figured I had beat on the car enough and took a break (hood open, car off).

My question is: Is it best to just stop and open the hood, or would I have been better off to perhaps just take a leisurely cruise around the facility perimeter road to keep air flowing through the engine bay (and I guess also over the brakes)? I ask, because I notice that the temp is really high after a restart in these situations, but will typically come back down fairly quickly while idling for the next run.

Any input, comments or suggestions appreciated!

hklvette

The jump in temperature you see after a restart is almost certainly due to heat-soak, which won't happen if you keep air moving. Not sure if one method is better than the other, but keeping air moving isn't a bad thing. I'm curious what your oil temperature was in that situation.

Gordy M

When you autocross with re-runs or at practice, you will greatly increase your temps, but like hklvette said it is your oil temps that you should be looking at. I always put the oil temp on the DIC and monitor it whether autocrossing or doing HPDE. When I finish a run, I immediately turn on the A/C or, if I can stand it, the heater. This helps cool the water temp and the oil temp. You will find with repeated runs the oil temps will run about 245F otherwise. By running the A/C or heat you should be able to get the oil temps closer to 225F.

ltborg

+1.

I also turn the AC on once off course as this kicks the cooling fans on sooner. Usually if I let the car sit for a minute or two with the AC on (ie. cooling fans on), the coolant temp drops quickly. I wait until the coolant is below 200 or so to shut the car off. I've seen times where cars are shut off too early, the coolant heats up from the residual heat in the block, and then overflows (or over-expands, whatever you want to call it).

Regardless of coolant temperatures, I cool the car off if the oil gets over 260.

If you use a water sprayer on your tires, you can also spray the radiator to help it cool off faster.

DigitalWidgets

Great info here!

I didn't know about the AC kicking on the cooling fans...interesting fact that would have probably been useful had I known. I didn't really think about idling a bit just to keep the coolant circulating.

I'm still an absolute rookie, so I haven't started carting out the water sprayer, and other tools of the trade etc. I pretty much just arrived and drove (I did inflate the tires all around to 35 psi per a suggestion here and peeked at them in the DIC a few times).

The oil temperature in the DIC sounds like a prudent measure as well. In my typical daily driving I'm seeing in the 220-225 range. Thanks for the temps (245 and 260)...I have no idea where the danger zone would start, so that's a great piece of info.

ltborg

You can also install a switch to kick the fans on whenever you want, although that might technically be against the rules depending on what organization you run with.

Solofast

If you are at a test session or an event where you don't have to go right back to the grid, it's a good idea to drive around at 30-40 mph. The car cools very quickly and there is a good amount of airflow through the engine compartment at those speeds.

For testing we generally run in three lap segments. That is, start with the car and most importantly the tires relatively cool, and then make three runs, taking tire temps and doing a quick data system reset after each run, and making notes on the quality of your driving and what was good and bad about how the car behaved on the run. That way you get data on cold, warm and hot tires. After the three runs bag it for 15 or 20 minutes while you make changes. That way the car doesn't overheat, and neither do the tires.

TedDBere

If I turn off the engine between runs the hood comes up.

If I keep the engine running the A/C comes on to kick on the extra fan.

If the engine is really hot I turn on the A/C until the temp comes down and then I turn it off and pop the hood between runs.

I too keep the oil temp on the DIC and won't take a run until it's over 120 degrees...fwiw.

Good luck.

bsalie99

I have an c5 Z05 with a warmed over LS3 installed. I was seeing high temps when I got the car. I investigated and found that the rad was damaged by a accident of the prev owner. I had a Griffen 4 core alum rad installed. Now the car runs at 197( thermostat temp) almost all the time and got up to 206 one day of 15 back to back 60 sec autox runs with the AC running. I boiled away the brake fluid, but the coolant was fine, and the racing Rad was less expensive then a GM replacement