Thread: GM 3400 overheat

My son has a 98 Transport with 3400. He installed a new thermostat. It overheated shortly thereafter. Must have been fairly severe because it actually burst the plastic side-rail on the radiator. We installed a new radiator. Now it looks like it is still overheating. Heater blows hot. OBD-2 reader says it was 215*. Steam began to pour out of top of engine under the plastic cover. Second thing. When I press the gas and hold it steady, it sounds like I am pumping it. Checked with reader and the spark advance is at about 20* to 30*. No error codes thrown. Any ideas guys?

Originally Posted by ericspecullaas

Ok I run this engine you have a crap ton of air in the system. Also are your fans turning on? They cause most of the over heating problem. What happens is the ground gets ruated out or fails for what ever reason make sure when you see it about half way to kick on the ac and max heater that way it wont blow. Also have you done the head gasket yet they are known to fail and cause air to enter the system. And make sure you put thw gtp radiator in it will help keep the temps down as well

Thanks for ideas.

Bleeding air tips?
Any ideas on the pulsing engine thing? Isn't the spark advance reading way out of whack? It almost sounds like the computer is limiting the engine. I press half down on gas and the engine rythmically bounces between 2500 to 1000 rpm.

OK I may have the overheat thing fixed. Thanks for the tips on bleeding. What about my timing at 22*? Did my timing belt/chain jump?

OK, Thanks 55DP, Then I am wondering what is causing the engine to "pull back" when I step on the gas? Ex. Idle smooth, then I step on the gas, it revs up, then pulls back to idle, then revs up, then pulls back. All the while I have my foot on the gas steady. It's as if I am pumping the gas pedal in a rythmic manner.