Ryan1992M

Hey guys, just bought a 1996 Z28. Drove it home friday, and everything went well. Had to drive about 70 miles on the highway to take it home, and it stayed right in the middle of the temp guage. Saturday rolls around, and I got stuck in traffic for about 15 min, and I notice the temp gauge creeps up the 3/4 and then cools down a bit. Did this until I started moving, and then cooled down to around 1/2 gauge.

Now I heard these engines run hot, but something doesnt seem right. I figured maybe the fans werent coming on, so last night I let it idle in my driveway to see if I could hear the fans kick on. Car got right up to 3/4 gauge and then coolant started bubbling out of the overflow tank so I shut it off. I didnt hear the fans kick in at all, and it was obviously too hot for normal operating temps because the coolant started boiling over in the overflow tank.

Decided to replace the coolant fan #2 relay. Had my mechanic look at it today, he plugged his scan tool into it and jumped the fans so they are working. Afterwards, it seemed to crawl up to 3/4 on the gauge and then cool down a little. The SES light also came on friday night, and it scanned p0174 and another code (p0171 i think?), so with that as well, my mechanic seems to think the car is running so hot because the cats are clogged and the car cant release all the heat its generating.

Does any of this sound plausible? I cant imagine that these cars run 3/4 of the way up the gauge as normal, but I dont know. Moving, the car cools ok. But maybe within a minute or two of stopping, it moves right back to under redline. Any help in this area is much appreciated.


Thanks,
Ryan

Ryan1992M

By the way, the coolant light comes on randomly. I bought this car from a dealer, and I asked them to have that fixed by the time I took the car home. They replaced the coolant temp sensor in the water pump, but it didnt fix the coolant light coming on in the dash. Just wanted to mention that incase its relevant.

shoebox

Perhaps you need a new radiator cap, but the temperatures are more normal than abnormal. The temps are normally going to go up when you stop moving. Since you noticed the temp also come back down when not moving, that seems to indicate your fans are working. You should check the coolant level in the radiator when the engine is cool. It should be right to the top.

You might want to read this.

Was it the "low coolant" light coming on in the dash? The temp sensor in the water pump has nothing to do with that.

Ryan1992M

thanks for the reply. Yes, it was the low coolant light in the dash. Coolant levels seemed normal when I checked them.

Im bringing it back to the dealer to have it taken care of, I just wanted to get an idea of what it could be before I brought it in. Could clogged up cats be a plausible culprit tho? I have never heard of clogged up cats overheating a car, but I dont know. Thanks for the help

96 Z 28

I had similar temps where sitting in traffic the car just got hot... Factory Fan settings are set @ 226 Deg before they even come on at all....

Best option I found was to swap to a 160 Deg Thermostat and have the car reprogrammed (adjust fan temps + tuning)

I used a company that used PCMForLess Tunes and my car never gets over 1/3 in traffic with a 160 Deg T-stat and tune.

Give them a call - and make sure of you do go to a 160 Deg T-Stat it's LT1 Specific (4th Gen LT1 S=T-Stat).

Injuneer

Does the engine feel really down on power? It would feel that way if the cats were plugged. Your mechanic can check for plugged cats by attaching a pressure gauge to the pre-cat O2 sensor bung on each bank of the engine.

Sounds like it may be running hot because it's running lean. A correctly running engine and a properly maintained cooling system will not exhibit the problems you are experiencing. I would solve the problem before resorting to a lower temp t'stat and reprogrammed PCM. For starters check the plugs for a lean condition. Check the fuel pressure.

Ryan1992M

I do think that its running lean, like I said I got that SES light and one of the codes was 0174, which is lean in one of the banks. Just didnt know that would contribute to the engine running hot, but i will definitely bring that up tomorrow when I bring it back to the dealer.

Thanks a ton guys, all this info is very helpful

Injuneer

Ask the dealer if he is familiar with the correct procedure for bleeding the air out of the LT1's "reverse flow" cooling system. Air in the system, and it's going to overheat. Did you read Shoebox's "this" link in post #3?

Injuneer

If you actually got both the codes you listed they are both for a severe lean condition on both banks of the engine. The PCM is adding ~22% more fuel than normal using the long term fuel corrections, and that did not cure the lean condition, so the short term fuel corrections started adding even more fuel, and when those corrections reached ~8%, the codes set for both banks.