After the heads and cam swap on my friends car (FSANE) his car has been overheating. We've changed the thermostat four times. Coolant is going through the block because it is coming back into the radiator via the throttle body. There are absolutely no leaks at all. Coolant is not getting into the oil either (no milkshake). The fans are coming on and staying on too. The car is fine on the highway, but sitting in traffic it overheats. We let the car idle still for a good twenty minutes and it was fine, but after long drives and sitting in traffic it overheats.

We have no f*cking idea whatsoever what hte problem is. It doesn't appear to be anything mechanical. I think it may have something to do with the tuning/computer, but I don't knwo what. The fans seem to work fine. Any help you guys can give me would be greatly appreciated, because the car has to be driveable from New York to Ohio by the end of the week.

Thanks

 

Are you sure you bled the system enough? What you can do is with the car cool, take off the radiator cap (replacing this may be a good idea too, they go bad), and look at the coolant level in the radiator. Then revving the engine up and down, keep sure to keep the coolant to the very top. Keep watching until the level dosent go down and all the bubbles are gone. Good luck!

 

Like he said, it sounds like you need to get the air out.

 

I read in your post that coolant is returning to the radiator from the steam/vent line from the block/tb.

Doublecheck the two hoses that connect to the top of the radator near the radiator cap to assure both are installed correctly. Even though you can see coolant returning to the radiator with the cap off, doesn't necessarily mean the hoses are attached correctly. If coolant is returning through the hole in the radiator cap housing, it's wrong and the hoses are attached backwards.

Make sure the steam vent return line hose is attached to the inlet tube (3/8 inch) on the radiator. It's the inlet tube just below the overflow outlet tube (3/8 inch) which runs to the overflow tank (radiator cap overflow hole).

Apparently these hoses do get reattached incorrectly by professional installers (at least that's what happened when my ATI charger was installed by someone who had installed at least 20 ATI systems).

The car will cool and run OK in traffic, but as soon as you let it idle it will puke coolant out of the overflow tank. Reason why is because steam generated in the block, has nowhere to go, because the hose is attached to the overflow outlet tube and is blocked at the radiator cap rather being returned to the radiator and recyled back to the block (the lower inlet tube).

In addition, coolant in the radiator will never stay full, because as soon as the coolant reaches the level of the lower inlet, it will run into the overflow tank (hose is attached incorrectly).

In addition, there are kits to check for hydrocarbons in the coolant, if you have a leaking headgasket. Pellets (Caddy Pellets) sold by GM dealers can sometimes seal leaking head gaskets.

Good luck.
HTH

 

You're a genius dude. I think that was it. Thank you so incredibly much. I would have never thought that switching those two hoses would make such a difference. We actually knew that they were on wrong, but didn't think it mattered.

Thanks again!