So I was trying to slap together an engine last week and ran into an overheating issue. I put together a '76 350 and used the FelPro Blue head gaskets which I thought I had read here would work for any '68-'80 Buick 350. The engine is together and runs but after the thermostat cycles a couple times the temp will not drop back down and climbs up past 230 and starts pushing the coolant out the overflow. I tried two different radiators, new thermostat, new radiator cap and it has a new water pump on it as well. I can feel the upper hose and know I have coolant flowing pretty good once the thermostat opens. The oil still looks good, there's no water leaking into the oil pan. Any ideas on where to look next?
I would say check the timing. A lean mixture will also cause excessive heat. I don’t remember what the symptoms are for an upside down head gasket? Anyone remember? I thought it leaked coolant into the valley pan.
Yeah, reading through the old posts the upside down head gasket leaked coolant out the side of the block and it's not doing that. I've also verified timing and made sure the carb is providing a good amount of fuel, it's an 800 cfm carb from a 455 but I don't think that would make it overheat. It almost seems like the coolant system is getting pressurized somehow, that's why I was thinking it may be a head gasket issue.
good detail! I have dyno proof that the 455 800 cfm Q jet carb on a 350 will add WAY too much idle air. AFR was way off at idle and into transition.
Does it do this just sitting there Ken? Did not seem to be an issue when you were driving it last week. I thought you mentioned it was staying around 190*.. If the radiator and fan clutch are working correctly, then the heat being released off the radiator at the temps your talking about should have the clutch fan locked up tight, and it should be roaring. The guard should be coming over from the air base looking for their jet.. If it is not, then either the radiator is not radiating enough heat into the thermostatic fan clutch to get it to lock up, or the fan clutch is trying to lock up, but just can't because all the juice ran out of it.. If you a have a non contact thermometer, check the temp of the fan clutch as best you can.. At this point, that is your most likely cause if this happens just sitting still/low speed driving. if it happens with normal driving, then it can be timing and air/fuel issues.. since I set the timing, it's not that, unless it got bumped somehow. Not all q-jets have bypass air, I believe the one we put on yours does not. Primary metering between the two carbs is very similar. JW
Jim, It took several miles of driving it before the problem appeared, the temp had been staying at 190 when we were running it. I did not hear the fan roaring now that you mention it, even when the temp was climbing, and yes it will happen just idling in place. I verified timing and dwell and both were we had left them. I did stick a set of fatter secondary rods in the carb, but that shouldn't have affected how things are at idle. I think I'll swap out the fan clutch and put a regular fan on it and see how it reacts, that seems to be the most likely suspect!
Also last time my HG went it would spike the temp gauge within a minute of running and pressurize the snot out of the system.
Upside down head gasket = water dumping out on the floor when you try to fill up the radiator. Air bubble in system? Timing too retarded?
Check and make sure your radiator hoses aren't collapsing. I ran into that issue on my 455 recently. The lower hose should have the coiled wire spring inserted. I even had my upper collapse as well. I am running the TA high flow pump though, but I suspect it was collapsing even before with the standard water pump. This is on my 66 Skylark with a 455, but it may be happening to you. The hose manufacturers say the newer hoses don't need the springs due to better materials now days, but I didn't find that to be true.
Also be sure to run the engine with the rad cap off, wait till the thermostat opens then shut it off, top off rad, and put the cap on. Then it’s air free.
