99 Blazer, 4.3 W. The first part of this insanely long drawn out saga is at this thread; the second part is here, and the third is there. Just so you know what's been going on. Now here comes part four.

So I had the mechanic replace the manifold gasket AND the lower manifold. (That's another $370 in parts and $632 in labor, if anyone's keeping score.) He said the spider isn't bad yet; whatever. He also flushed the cooling system and changed the oil; he said that the rear water passages in the head were unbelievably stuffed up with crud: there's a place on the underside of the manifold near the back that caps a water passage, and it had about an inch thick stack of crud attached to it when he pulled it off. Hope he got that all out. He also said that it was running about 210 at idle, which in my experience is kinda hot; it used to run about 195, but in the past couple years it's been getting very hot if I drive uphill with the A/C on. (Which in my '88 never goes above 200 no matter what you do.)

In any case I tried driving it about 15 miles today, mostly on level ground (no mountains here in Jersey to speak of), with the A/C on. About halfway there on the Parkway, the gauge starts creeping to the right, maybe 240 or so, and when I shut the A/C and turned the heater on I got nothing but cold air. When I got off the highway, it went almost all the way to the top, and the Check Gauges light went on. When I put it in Neutral and revved the motor, it didn't get any lower, if anything it got even hotter; only way to get the temp down was to start moving again, which means that I was kinda uptight every time I got to a red light. At my destination I shut it off, opened the hood and checked the hoses; the rad was full (lever-type cap, I lifted it and it shot liquid into the overflow, which was also up to the full line), upper rad hose was hot, couldn't get to the lower hose so who knows. Heater top hose was hot, lower one not so much. Thermostat is relatively new (changed a few months ago).

I let it sit for an hour or so, then with heart in mouth started it up to drive home. Whaddaya know, there's heat coming from the heater, and the temp gauge stayed at 210 or a little over. I kept the heat on for the whole trip back; the air started getting a little bit cool halfway there, but no overheating this time.

So I don't know what the hell to do anymore. I called mechanic, he said it sounds like a flow problem, and I should drop it off, but I'd like some opinions from the experts here first. Is he barking up the wrong tree? Is there still cr@p in the water passages that hasn't been flushed out? and if so, how do we get it out without tearing down the block, if it comes to pulling cylinder heads I'm washing my hands of this POS once and for all. Yeah I know I've said that before, I really mean it this time. (voice from peanut gallery: Suuure you do...) Air bubbles? Could the water pump be bad?? Maybe even the damn sensor is lying??? One thing I know, at least the fan's turning, cos I can see it. (Although I've no idea if the clutch is any good either.) What bugs the hell out of me is, why is it sometimes over heating and sometimes not?? I freaking hate intermittent faults.

(edit to add: one more possibility, I read somewhere about the lower hose actually getting sucked shut and collapsing.)

Any suggestions?

Thanks in advance.

 

Just a long shot but did you try putting a new red cap on. About that hose getting sucked shut Don't really c that happining seeing that there is a heavy spring inside of the hose.

 

I had an issue some years back very similar but with a 396. After the smoke cleared (being sarcastic) and pooched the engine, bad waterpump. Since a shop did the gaskets and flushed the system, did he ok the radiator about no gunk or clogs? Flowing freely? If mine I'd do water pump and Tstat. Any oil/water mix that you can tell? Any signs of possible blown head gasket?

 

ecmusicman: This whole shenanigan started when I put a new radiator cap on. The original GM cap was a 15 pound cap, but they claimed 16 pounds was the correct one according to the almighty computer, so that's what they sold me. This apparently raised the pressure enough to start the whole cascade of leaks, or at least to blow out a previously weak area in the gasket.

Vahomboy: My mechanic did say it sounded like a flow problem, but he said also that the chances of a water pump going out without also creating a leak were very small. Head gaskets are probably OK given that there's no water in the oil or the exhaust; mechanic said I should keep an eye on that. Thermostat is almost new.

In any case, he sent me to the dealer to get the cooling system power flushed and new coolant put in. We did this (another $120). The dealer's mechanic said he did pull some air out, so there might have been some pockets causing air binding. I forgot to ask them how much sludge they sucked out of there, so I couldn't say if there were other blockages. I drove it the 65 miles to work today and it didn't go over 210°, so it appears to be fixed for now בלי עין הרע. (that's hebrew for knock wood)

Although the damn gauge is wrong. If there are 16 lines between 100 and 260, then the center point should be 190, but it actually says 210. Mathematically it doesn't make sense.

 

Gauges don't have to be linear.

Sounds like you got it fixed. Air can be a pain in the 4.3.