I replaced my intake manifold and throttle body gaskets along with new knock sensors and wiring harness last night, truck started right up today was a little high at idle at first and seemed to drive ok but temperature all of a sudden started climbing towards the 240 range. i pulled over a couple times on the way back and coolant didnt seem to be cycling thru engine so removed thermostat on the side of the road and still overheated any ideas what might have gone wrong???

 

Probably still have air in the motor. You need to get all the air out. Sometimes that takes a while.

 

Thank you, i noticed coolant back flowing from reservoir so I drained it second time but still happened. I ran out of coolant gonna wait till parts store opens tom to get catch pan and couple more gallons. Are there any tricks to getting ALLthe air out or just have to repeat few times?? Thank you again for response was worried I messed something up during install.

 

I doubt it. I leave the radiator cap (assuming that you have one, some cars dont anymore as its on the over flow-tank) at half turn and run it till its hot, with the heater wide open. Let it cool down and refill to the brim. That usually does the trick. The air is trapped up in the head(s) and you need the water pump and lots of coolant to get the air all out of the system.

I keep checking it for a few days just in case, but its never really been a problem for me. I always make sure I run the heater hot in the summer to keep the coolant from stagnating, once every week or so. I also use NAPA brand coolant corrosion inhibitor between changes. The last thing I want to do is change a heater core out, and rip the dash apart.

I lucked out changing my late father's 1988 C-2500 heater core out. The heater box had a outlet cover on the bottom with screws, and I managed to wiggle it out. It was hell getting to the screws in the back, but I managed to get them out with a flex coupler with 1/4 inch ratchet and sockets. Lots of work, but better then pulling the A/C lines out and having to recharge the A/C system, if I pulled the dash-heat/AC box out. Too that old rig used R-12 Freon, not R-134a, so there is that too.

Had to take the rubber floor mat out to get the room to get the bottom cover off but it was doable. The heater wasn't bad, per se'. It was Chevy trying to use plastic tanks and outlet pipes on the core. The crimped-on seals started leaking. Thankfully Chevrolet changed back to an all aluminum heater core and plumbing, so that's what I replaced it with.