Ok so it's been two days since my heads/cam/longtube install. Along with all that I installed a 160 thermo and had a tune by TSP. Everything was going fine and the car was running at 175ish-185ish the previous couple days. I went to the gas station and as soon as I started to leave the service ABS/traction light flashed. I headed on to school and parked it. After returning from my class and attempting to drive back home the car started running hot 220+, then it got really hot 240+, then I just parked it and shut it down. I can't get it to STOP running hot now. At idle it creeps up to 225+ and then I just turn it off. The resevoir bubbles and gurgles for another 3-5 minutes after I turn the car off, (this is with the cap off). I tried switching back to the stock thermostat and it kept doing the same thing. I am kinda stumped as to what is going on with the car.

It ran fine for two days and now all of a sudden this. I don't get it.

 

Is your radiator fan coming on?

 

Yes both fans are coming on at the set time.

 

You may possibly still have an air pocket in there somewhere, you wouldnt think it would be there after a couple days though...just throwin out possibilites.

 

I would try completely draining and refilling the system first. I use a lisle funnel that keeps the fill level higher than the radiator cap to help force the air out. It works well for me.

 

What about the water pump? Might be dead. Before you do that, check if you have anything stuck in front of the radiator as the C5 likes to suck in things off of the road.

 

Pressure test the system and the cap. I see lots of bad caps. Hell most new ones don't hold pressure. It could be a head gasket.

 

The stat might be getting stuck as well.

 

could it be a wrong head gasket. Ya know the differences in years. I dont know too much about it but its an idea.

 

ya but if it was blocking passages you would think that it would have happend on the first fire up...did you torque the heads down properly? cause it could be a head gasket leaking that lets the exhuast leak through the gasket each time the cylinder hits. this is what happend on my old mans northstar. i know different motor but its all aluminum like ours. so if the heads werent TQ properly then you may have this prob. see if you can smell any hydrocarbons in the coolant. just an idea. oh yea i ran fine and would just overheat like a ****

 

I have already swapped thermostats twice now and that wasn't the problem. I am almost positive it isn't a head gasket because the oil is fine, no white smoke, and no loss of coolant. Also the head gaskets were torqued down EXACTLY as per the write-up on LS1HowTo. I even have the little lines you are supposed to draw on the top of the bolts. I am starting to lean towards the water pump. I might just buy one today and install it to see if that fixed it.

 

well the motor that i had the oil was fine too. it would only leak exhuast gas through the gasket when the cylinder would fire. other wise it was fine. no loss of coolant and no white smoke. what would actually happen is that exhuast gas would make the coolant get too hot and thats why is would over heat. oh yea and at idle it was ok but when you start driving it thats when it would happen. could be your water pump though also i guess. i havent taken the water pump apart to see if it fails then it actually doesnt pump an water. i dont know how the impeller is make and all that but it is possible i suppose

 

yes I agree with the above check the cap my buddy just boughta cap from the local chevy dealer the otherday and fired up a freshly biult motor to dyno. car seemed to be running at temp. but then a head gasket blew after scratching our heads for a while wondering what went wrong we tested the cap and the it didn't hold 1 pound of pressure so I would try the things that you wouldn't normally think of

 

I let it idle with the cap off and it still creeps up. I think that rules out the cap. I am going to pick up the water pump in a couple minutes and install that to see if it helps any. This is really frustrating.

 

It will overheat with the cap off. That is what we are trying to tell you. The caps are supposed to be rated at 18 lbs, but most new caps don't hold that pressure. The coolant system relies on pressure to maintain temperature. I would at least pressure test the system and cap before spending a bunch of money on a pump you may not need. Could just be a 10 dollar cap that needs replacing.

 

I'm still thinking gasket's. I hope it's something simple like the cap. What bolts did you use on your heads?

 

You sure your 2 radiator hoses that go to the throttle body and overflow are in the right places. They are the two that are right under the radiator cap. Its easy to put the top on the bottem and the bottem on the top.

 

Ok I have NO idea how to really explain this. I bought a new water pump today and as I was going to install it I decided to try to let it air itself out one more time just to see what would happen. Car started up.....I let it sit for a full 17 minutes. It never got above 174 degrees!!! I drove it around the block and no over heating, then I took it farther, and it was fine!


I left the car in the garage with the radiator cap off, I honestly have NO idea what exactly happened but the car is fine. I drove it around all afternoon and night. I modulated the throttle, went from freeway to inside the city and all sorts of stuff. Everything seems fine for now!

 

Cool. Hope it is fine now. Maybe you busted it's bubble letting it sit!

 

sweet