Cold-running 1992 5.7L Buick Roadmaster

[Jon]

Car has been a stone axe for the last 282,000 miles. Thanks to Terry Dyson, found a coolant leak, guessed it was the intake manifold. My father is a mechanic of 40+ years, so he did the work. Car always ran a little warm. Now, it runs cold. Barely breaks 160. I put a new thermostat in (a Stant SuperStat, 192-195 OEM everything). Temp comes up slowly, just barely above 160 (indicated, and guage has always been accurate), and the (like the superstats are supposed to) hovers around that temp. Ambient temps are in the 20's (F), and I don't get doodly for heat out of the heater until it's good and warmed up.

RPM helps -- since he Buick is geared /really/ tall (1400 RPM at 70). So if I'm cruising about at 1200 RPM, I don't much heat. If I put it in drive (instead of OD), I get plenty of heat, although the guage doesn't move. When we did the t-stat, and were burping the system, we both noticed that flow from the heater core back into the radiator is not very good.

It's not consuming any AF that I can tell, and the oil looks /perfect/ (it's had Mobil 1 it's entire life).

A few days ago, with about 100 miles on the new t-stat (t-stat replacement was about 150-200 miles ago), temp came up to 250-260 indicated for, oh, 10 seconds then /rapidly/ came down -- we both think it was a stuck air bubble. Since then, it's been just fine, but low temp. Pre-repair, temps would hover in the 195 range pretty easily, but she'd ping like there was no tomorrow, even with 93+ octane. Post-repair, no ping (except perhaps a very slight ping for a split second from the cruising to acceleration transition). Lastly, the EGR hoses were clogged completely, although the EGR valve looked just fine when cleaned.

I have plans on hooking up an "OTC 2000" to it, when I get a chance, but it might be some time. The onboard computer should have compensated by now.

So. That's alot of information, hopefully everything ya'll need to help me out. Does anybody have any ideas?

 

[Chris142]

I would remove the t-stat, suspend it in a pan and boil it. See when it opens. You can use a meat thermometer.

I work at a radiator shop and seem to been getting a lot of brand new bad Stant t-stats, both regular and superstats. Although most of the bad ones I see are stuck shut. They are lasting a week at most.

Another possibility is a siezed fan clutch. It should not matter to a system with a t-stat but it does sometimes.

If it's pumping the coolant slow to the heater could the impellers be rusted or corroded off? How about a plugged heater core? You can remove the hoses, with a garden hose and some pipe back flush the core.

I have an old truck thet even with a 195* stat it wont get over 150 in the winter......I put cardboard in front of 1/2 of the radiator to get it up to temp.

 

[Jon]

quote:

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Originally posted by Chris142:
I would remove the t-stat, suspend it in a pan and boil it. See when it opens. You can use a meat thermometer.

I work at a radiator shop and seem to been getting a lot of brand new bad Stant t-stats, both regular and superstats. Although most of the bad ones I see are stuck shut. They are lasting a week at most.

Another possibility is a siezed fan clutch. It should not matter to a system with a t-stat but it does sometimes.

If it's pumping the coolant slow to the heater could the impellers be rusted or corroded off? How about a plugged heater core? You can remove the hoses, with a garden hose and some pipe back flush the core.

I have an old truck thet even with a 195* stat it wont get over 150 in the winter......I put cardboard in front of 1/2 of the radiator to get it up to temp.

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I would be surprised to see if it was the t-stat because the original t-stat (the one that worked for 282,000 miles) *also* showed temps at or near 160 (on the gauge).

Fan Clutch? Why would that have gone "bad" during or immediately after the intake manifold gasket replacement?

I'm trying to fit the observations and theories in with the facts, and nothing much jives. The cold-running behavior started with the intake manifold gasket replacement. Thinking that the t-stat have given up during the replacement, we put a new one in with no fix. Indeed, the new t-stat appears to be working just perfectly, but at the wrong temperature (that temperature doesn't vary from 160 indicated by very much at all).

This is frustrating! Would anybody consider flushing (or backflushing) the system? I *do* have a hose adapter installed on the heater core return hose, so theoretically a shop could hook up a drain hose to that, pop the radiator cap off, and run the engine, replacing fluid lost through the drain via the cap.

It's so weird.

 

[Jon]

Follow up.

Of course with summer I didn't care if the temp never broke 160, the can did and still does run PERFECTLY.

A few months ago, when it first started getting cold again, I broke down and checked things.

I put in a new t-stat and everything is back to normal.