Accidentally posted in the LT forum because someone had a similar issue, but I'd like to ask here too. I recently bought an '02 z/28 with an MTI built 427. Right after I bought the car it started idling rough. The car has a conservative tune, so after talking with the previous owner, just figured the plugs are fouled.... no big deal. I was able to replace the driver side without a problem and it drove and sounded better, for one day. Didn't bother me since I still had the passenger side to do.

Fast forward a week. I haven't really driven the car hard until a saturday night. Right after doing a quick run against an evo, the temperature gauge pegs. I quickly shut it down and check for leaks- none. Oil- looks good (just did an oil change with 10-40 RP). Let it cool off and attempt to drive it again.... make it like a mile before the temp gauge pegs again. This time I check the coolant and notice it's low, I can still easily see it though. Top it off, maybe takes a 1/4 of a jug of 50/50. I drive home and don't touch the car for a week.

Fast forward another week. This last saturday I decide to drop the car off at National Speed Inc in Wilmington, NC. Go out to the car and check the coolant level before heading out... I can't see it at all! The car didn't get hot at all driving the 8 miles or so from where I had to shut her down the previous week. WTF. So I top her off, cross my fingers and start the 1.5 hour drive. I kept my eye on the temp gauge the whole drive and she never moved from right below 210... with the heat on full blast and off. When I got to National Speed I check the coolant level again and come to find there is hardly any loss at all. I didn't even add anything.

The car is running an SLP low temp tstat. There has never been any coolant in the reserve tank, talking with the previous owner, he says he's never had any in there too. I noticed a wet spot on the control arm (?) on the passenger side of the engine which is near the reserve overflow tank, maybe a leak???

What confuses me is the good amount of coolant loss from 8 miles of driving vs hardly any after over 100 miles. There are no leaks on the ground. Don't notice a smell. I haven't done a pressure test, but the coolant loss and rough idle lead me to believe it's a HG. Any ideas would be much appreciated.

 

My friends 427 did this a few years back. It overheated at the track. We let it cool off, added coolant, and it drove fine home. Then it pegged the temp gauge again a few days later. Pulled the heads and sure enough it had lifted the passenger side head gasket.

I would get yours pressure tested. Also, you could have a weak radiator cap that is letting too much coolant leak into the overflow tank when you shut it off.

 

I dropped it off, so I assume they'll do a pressure test during the diagnostic... The thing is, the overflow tank is empty. The very tip is wet, but it's not even close to being at the correct level. Even the previous owner said that even after putting coolant in the overflow... it would "disappear."