[Miteymek]

I have a 1994 GMC C 1500 that originally came out of a van which I believe was a 1989.It is TBI.Last week I noticed it had blown a head gasket but had no signs of overheating.I removed the engine and decided to refresh the complete engine so that I know what I have.I had the block bored 30 over.I replaced all the gaskets and seals. I installed a mild cam.After installing in the truck I started and adjusted the lifters.While I was adjusting the lifters I noticed it was getting hot.I checked the gauge and it was around 215.I shut the truck off and checked the temp. with a temp gun.It was correct. I changed the waterpump and thermostat while doing the overhaul.I replaced the radiator just to make sure.It seems like it is only getting hot on the back of the heads.The radiator is never as hot as the back of the heads.I checked the belt routing and the waterpump is rotating the correct direction. I removed the intake and checked the gasket.The new gasket has only a pin hole in the rear ports.The intake manifold has an open port that goes all the way through. I ran the engine 3 different times to make sure there was no air,I thought.Any body got any ideas?Thank You.

[pacman350]

freshly rebuilt motors tends to run a little wormer because everything is still tight and hasn't broke in yet. more friction means more heat once the motor starts wearing and loosin up a little it should run cooler.

[spinn]

Did you pressure test the cooloing system? The temp will run away if not holding pressure.

Something else, After those first few heat cycles, retorque the bolts. My water neck happened to be steel and the manifold aluminum. The two different expanding metals can create a leak.

[cobalt327]

Originally Posted by Miteymek

I have a 1994 GMC C 1500 that originally came out of a van which I believe was a 1989.It is TBI.Last week I noticed it had blown a head gasket but had no signs of overheating.I removed the engine and decided to refresh the complete engine so that I know what I have.I had the block bored 30 over.I replaced all the gaskets and seals. I installed a mild cam.After installing in the truck I started and adjusted the lifters.While I was adjusting the lifters I noticed it was getting hot.I checked the gauge and it was around 215.I shut the truck off and checked the temp. with a temp gun.It was correct. I changed the waterpump and thermostat while doing the overhaul.I replaced the radiator just to make sure.It seems like it is only getting hot on the back of the heads.The radiator is never as hot as the back of the heads.I checked the belt routing and the waterpump is rotating the correct direction. I removed the intake and checked the gasket.The new gasket has only a pin hole in the rear ports.The intake manifold has an open port that goes all the way through. I ran the engine 3 different times to make sure there was no air,I thought.Any body got any ideas?Thank You.

Make sure the engine has plenty of ignition timing advance while it's running to break in the cam. You must not idle the engine even for just a minute, so set the timing using a dial back timing light or make a timing tape so you can see what the timing is at w/the engine running at 2000-plus rpm. You can give it 32-34 degrees (not counting the vacuum advance), no problem. Won't hurt to connect the vacuum advance, because the engine is running w/o a load, so there won't be detonation from excessive timing unless you were to go WAY up there. But 32 degrees w/o to as much as 45 degrees w/the vacuum advance hooked up is OK. Placing a large fan in front of the radiator can help.

[Miteymek]

Originally Posted by pacman350

freshly rebuilt motors tends to run a little wormer because everything is still tight and hasn't broke in yet. more friction means more heat once the motor starts wearing and loosin up a little it should run cooler.

I thought that also but it is running up around 230 to 240 only at the back of the haeds.I removed the intake and checked the water flow and it seems fine.I am going to pressure check it tonight with plugs removed because I have noticed alot of white smoke.

[Miteymek]

Originally Posted by cobalt327

Make sure the engine has plenty of ignition timing advance while it's running to break in the cam. You must not idle the engine even for just a minute, so set the timing using a dial back timing light or make a timing tape so you can see what the timing is at w/the engine running at 2000-plus rpm. You can give it 32-34 degrees (not counting the vacuum advance), no problem. Won't hurt to connect the vacuum advance, because the engine is running w/o a load, so there won't be detonation from excessive timing unless you were to go WAY up there. But 32 degrees w/o to as much as 45 degrees w/the vacuum advance hooked up is OK. Placing a large fan in front of the radiator can help.

The radiator is not getting hot at all.It is running hot only on the rear of the engine.The temp. sensor is on the rear of the head and I did check it with and temp. gun to make sure.It also does not have vacuum advance.I did idle the truck for awhile yesterday.Is it going to hurt it?It gets hot quick also.Lots of white smoke.It was not like this before the rebuild.

[Miteymek]

Originally Posted by spinn

Did you pressure test the cooloing system? The temp will run away if not holding pressure.

Something else, After those first few heat cycles, retorque the bolts. My water neck happened to be steel and the manifold aluminum. The two different expanding metals can create a leak.

I am going to pressure test tonight with plugs removed to check for leakage into the cylinders.Then I will run with tester on it.