Hi all,

I just picked up a 2009 c6 Z06 and unfortunately noticed some cooling issues on the way home. About halfway through the drive I noticed the coolant temps were in the 240s (on the highway with ambient temps in the mid 40s) and then creeped into the 250s right as I was getting home. I got the message warning that the car was running hot. It didn't max out the gauge, but it was in the 250s for about a minute until I could get somewhere safe to turn the car off (Luckily just a block from where I live). The oil temps were fine the whole way (180-200). Today I noticed the coolant in the resevoir was low and the previous owner told me a few months ago he had to top it off. The car has aftermarket valves and guides, catless long tubes, and is tuned. I did a deep dive on the forums and think I might know what's going on but want to ask for other people's advice. Thinks I have looked into so far:
- I filled up the coolant resevoir a couple times today while letting it idle. It took about 2/3rds of a gallon. Temps initially were climing to 240+ at idle, but after adding the coolant they seemed to be stable at ~223 or so while idling. I'm not sure if I the system is still down on coolant, it got dark on me so I stopped.
- The fan turns on when it's supposed to.
- I didn't see any obvious debris on the radiator.
- I was worried it might be bad head gaskets, but neither the oil or the coolant is milky/frothy. There is a bit of white smoke coming from the tailpipes at idle, but it just smelled like exhaust and the car got VERY wet on the drive home two days ago and rained on it again yesterday (I have not driven it since getting home, just let it idle for maybe 5-10 minutes total). There was a bit of water in the tail pipes (tasted like dirty water at least, not coolant, yuck), so I think that's why the small amount of smoke...Hopefully. Head gaskets were also replaced about 4,000 miles ago when the valves/valveguides were done.
- The inlet hose ,I think that's what it's called, the large diameter hose connected to where the thermostat sits did not heat up to the touch like the other coolant lines after letting it idle and having coolant temps reach 220+.
- The water pump appears to be fine, but I haven't gotten under the car to get a really good look for leaks in. I haven't been able to identify the reason for low coolant, I didn't see any puddles below the car, but I'm thinking this is a slow leak since the previous owner had to top it off months ago. Somewhat embarassingly I looked at the coolant resevoir and misremembered how full it was supposed to be when I was inspecting the car, the level was low in hindsight but didn't change hardly at all after driving home.

I'm thinking the thermostat may be stuck shut or maybe there is air in the system? I'm hoping it's not coolant escaping into the cylinders in one way or another. I was thinking I would try pressure testing the coolant system and replacing the thermostat. Maybe doing a compression test is warranted because of the disappearing coolant and smoke? Any other advice? Thanks for the help!

 

Little update. I added another 1/5 of a gallon this morning as the resevoir was still low.. Car idled at 208 and I drove it around and it ran at like 198. The smoke from the tailpipe went away after I drove it around a bit. I think the coolant had just gotten wildly low. Maybe a line had collapsed allowing there still to be coolant in the resevoir? The ratio of water to antifreeze was also high so I wonder if that facilitated some coolant evaporating on my drive home, exacerbating the issue. I'm happy to see temps coming down, and starting to think it's probably not the thermostat. I think the system needs to be pressure tested, flushed, and refilled. Seems like it had a slow leak that was flying under the radar for a long time. Open to any other suggestions.

 

I suspect either a leak or consumption, coolant doesn’t usually just disappear

I’d also run the heater and cycle coolant through the heater core, try and eliminate any bubbles in the system



.

 

Thanks for the reply, I tried turning the heat on. Coolant level went down a bit again after driving around and the white smoke returned at idle... I can't find anywhere that it's leaking coolant. Starting to think it might be consumption... I think it's time I figure out a shop I can take it to. Hopefully it's just a leak I'm missing, but we will see.

 

These cars dont have a heater core valve

 

I presure tested the system this morning and the water pump bagan leaking. It is only leaking under pressure, which is why I hadn't been able to find it yet. That seems to be my issue. I'm very happy it's something relatively inexpensive that I can tackle.