Hey Guys,

I've got an '04 6mt coupe that is having a temp issue. After about 15 minutes of driving the temp gauge starts going up above normal. It doesn't seem to matter what speed I'm at. I can hear the fans kick on and I have verified that they are both working. The radiator looks clean. I have traced the coolant lines and I do not see any leaks. The coolant reservoir is still at the proper level. However, the temp immediately falls back to normal with the heat on for just a minute. I'm thinking this could mean that I have a bad thermostat.

Would the heater allow coolant to bypass my thermostat or does this sound like a different issue? Just wanted your perspectives before I replace the t-stat. I appreciate any advice!

 

Either you have:

Bad thermostat
Air in the system
Bad water pump
A blockage in the heater core

How long have you had the car, how many miles does it have and have you done any work on the cooling system lately? The thermostat is easy to check. Just remove it from the car, put it in a pot of boiling water and if it opens it's good. If you've done any work on the cooling system my money's on the air, our cars can be a pain in the azz to bleed completely. If the water pump isn't making any noise or leaking my guess is it's not the issue but you never know.

 

This should be a Sticky, we've seen this same question frequently for years! It doesn't just apply to our cars either, the possibilities apply to all water cooled engines foreign and domestic!
Gary

 

I've had the car since Fall 2014 and it has 109k miles. I've never done work on the cooling system. I was expecting the water pump to leak if it was bad, but I guess you never know. I'll pull the tstat and update the thread.

 

Gotta pressure test the system. Could be just a hairline crack somewhere or a pinhole leak undetectable without pressure. If you pressure test the system (you can rent the tool for free from AutoZone) and the cap and there are no leaks, then change the thermostat. If it's still overheating, run the car with the radiator cap off and look at the coolant when the car gets up to temp. If the coolant isn't flowing, yer water pump is next.

It's most likely not the water pump, as that's fairly rare, but there has been a case or two of pump blades rusting off; most likely due to people using too much water or undistilled water in their mixture.

 

I doubt it's the water pump, since it's driven by the timing chain. The only way I know of how it goes bad is if an impeller rusts off or the bearings go bad, but you never know I'm sure there are other weird failures out there. The bearings went bad in mine and you will know when that happens.

How do the hoses feel when the car is running? Is one really hot and the other cold?

I'd test your thermostat first.
Run the car with the radiator cap off and look at the coolant for flow.
Check the coolant level in the radiator.
You might need to pressure test it in order to see any leaks that only occur when the system is pressurized.
Is there any debris on the radiator, bent fins, or it could be blocked internally.
Worst comes to worse you could take out the water pump, but I wouldn't recommend that for the novice. You need to mess with the timing chain a little bit.

 

Sorry for the late follow up. I convinced myself that the tstat must have been the culprit, so I went ahead and replaced it. Happy to report no problems since.