Hey guys, I just recently got my first G35 the other day and have been battling the cooling system since day one. First off, it's a 2004 G35X and it does not have a blown head gasket. I went and had it checked out right away. Anyways, I'm losing coolant and I havent noticed any leaks. I'll top it off, go for a 5 minute drive and the reservoir will have drained about 50%. I have driven further and it will just keep draining. I have changed the thermostat and pressure tested it. It seems to hold at about 12-13psi. I have burped the radiator multiple times with a spill free funnel and the bubbles never stop. I've ran it for over an hour and they just won't stop. I tested the thermostat in boiling water before install and it worked just fine. However, the only time I've noticed the thermostat open up is when I remove the radiator fan relay and let it idle for a few minutes. Not sure if that's normal? I've ran it for hours with the fan on and the lower hose is always cold. My coolant levels have also dropped over night while the car is off. Never all the way when it's off though. Sorry for the ranting but I just want to paint a detailed picture for you guys. Any suggestions you guys could give would be extremely helpful. Thanks!

 

Update:

I topped off the reservoir last night when the engine was cold, I took a look this morning and it hadn't gone down at all. So the coolant isn't leaking, it's burning?

 

coolant doesn't burn but if you're losing coolant its likely being 'consumed' via your engine and going out the tail pipe. Leak-down test and compression test would be your next steps.

 

^^^ This and an oil analysis to see what's in the oil. Anti-freeze shows up pretty readily.

 

Doesn't it evaporate when it boils though? Wouldn't the only way the engine could 'consume' the coolant be through a blown head gasket?

 

Generally speaking, yes, that's true. (But stranger things have happened.) How was it determined that your head gasket(s) are fine? Did you (or shop) do the compression, leakdown as prescribed, along with an oil and/or coolant analysis (although if you're losing fluid that fast and refilling, exhaust contamination in the coolant might not be obvious or show up easily). These are the primary "diagnostic tools" that will properly identify (or rule out) head gasket malfunction.

 

likely ... leak down & compression and prepare yourself for machined heads and new head gaskets. Replace your water pump while things are apart.

 

The mechanic performed a combustion leak test. Also I've checked my oil, it's not discolored and I don't put out white smoke. It doesn't overheat either which blows my mind with how much coolant I'm losing. Plus it doesn't leak when the block is cold, which I would think if it was a head gasket it would constantly be leaking, not just when it's hot? Correct me if I'm wrong because I'm pretty clueless when it comes to this.

 

I figured it out! It ended up needing a low temp thermostat and a new radiator cap. Now the coolant levels are steady again.