C5 runs hot, tested literally everything, help
Advanced
Joined: May 2025
Posts: 54
Likes: 14
From: Howard, Ks.
Interesting set-up you have there. My air cleaner is on the inlet of my super charger. , Im thinking I must be right as I just put out 590 rwh on my 2Kvert W/6 gears. Just curious are you using yours to blow on the radiator to keep the temp. down. ........................................ ........................................ ...................................lol
Racer
Joined: Mar 2007
Posts: 250
Likes: 30
From: Central Texas
Today I wanted to test if the AC compressor or another part of the AC system maybe had an internal issue and was causing excess head at the condenser, (I know it's unlikely but I just wanted to try). So I simply took off the AC belt and drove the car. It didn't make a difference. The car got to 221 after driving for about 15 minutes, with some slight fluctuation. I had another idea while driving, to see what happens if I get the car up to 50-60 mph (with plenty of air flow) and then I just coast. So I tried that after the car got to 221 and I found that when I did that the car would cool down pretty quickly. Well not super fast or anything but at a normal rate, which before the temps would just stay there. Any ideas of what this could indicate?
Tech Contributor
Joined: Jan 2007
Posts: 19,492
Likes: 1,178
From: Dyer, IN
The next time it starts heating like this, roll down your windows, turn the heat up, and give it occasional revs to push water through. Mine has a 160 thermostat and a 3" radiator, but since it needs the fans upgraded, does NOT like heavy traffic. So far, that's been my temporary (until the fans are added next month) trick for cooling it below 200, while waiting for all of the refugees to put their cell phones down, stop videoing the highway construction barrels, etc., and drive. It's been as far as 235, and that's when that trick really seems to help. It's temporary, but hopefully that helps a little until you're able to get it taken care of.
Last edited by lucky131969; Jun 9, 2026 at 07:03 PM.
Thread Starter
Heel & Toe
Joined: Oct 2025
Posts: 15
Likes: 2
From: Tampa, Florida
The problem is not when the car is idling, it's when the car is cruising. It seems to me that I don't have an airflow problem, because I have an air dam and when I coast the car at speed with the transmission in neutral and the engine idling the car cools down. However if I'm just cruising at 50 mph in 5th gear at around 2000-2500 rpm the temps don't move at all, where they should be dropping since there is plenty of air going through the radiator. I'm not sure what this could be. Maybe the water pump isn't flowing enough water at rpms higher than idle? I replaced the water pump on this car already, however I replaced it with a used one that I had in the shop. What are the odds that both the original and this replacement water pumps were both bad?
Racer
Joined: Mar 2007
Posts: 250
Likes: 30
From: Central Texas
the 160° thermostat is meaningless once the engine gets up the operating temperature. Trying to drive the temperature of the engine that's designed to run over 200° is pointless too, especially for a street car. You don't need upgraded fans .....you need to evaluate your cooling system and confirm your fan settings in the tune. You also need to confirm that the splitter is intact so you're getting air through the radiator when the vehicle is in motion.
