Cold running 5.7L '92 Roadmaster

Recently, I had my (otherwise fine running) 1992 Buick Roadmaster's intake manifold gasket replaced, because it was consuming coolant at this location. With 282,000 miles on the vehicle, I had yet to experience a
system failure worse than an alternator.
The problem is that, since the repair, the vehicle has run VERY cool. I replaced the thermostat with a 65359 (I think) Stant 'superstat' from NAPA. 195 degree OEM etc... After burping the system, the temperature rarely got above 160 (the temp gauge is actually quite accurate). I thought I had gotten a bad one (rare), so I replaced it. No change.
Only with ambient temperatures above 40F *and* 2/3 of the radiator blocked off do I get heat out of the heater much more than ambient. Today, with temperatures between -5F and 10F, I get barely enough temperature to defog the windows, and the temp. gauge reads between 150 and 160F.
What could be wrong? How can I diagnose this?
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"J. Nelson" wrote

The first thing I would do is to install a "GM" thermostat just to make sure. I've had to many problems with the relatively few aftermarket t/stats that I've used over the years.
Then we can go from there.
Ian
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wrote:

Just bought a '92 Roadmaster, and I have the same problem - but I did a flush and fill. That seemed to clear out debris from the system.
I used a radiator flush, then let that drain, and refilled the system. The heater did come back to life, but the temp is still in the 140F - 160F range.
Either that fixed it, or I got really lucky :)
. Vuarra
Quid quid latine dictum sit altum videtur. (That which is said in Latin sounds profound.)
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Today I had the system flushed. What came out was discolored, but not too bad for 282K miles. It took about an hour, mostly because the vehicle is slow to heat up. By the time I left, the heating system seems to work quite a bit better than it did, although I say that very tentatively at this point.
I guess we'll see, but your advice was key in my decision making. Thanks!
On Wed, 07 Jan 2004 00:35:10 -0500, Vuarra wrote:

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Well, it sounds as if you've done the right thing for installing a new thermostat, I'm assuming the heat output was substantially greater before the head gasket was replaced.
The first thing I would do would be to throw that aftermarket t-stat in the garbage and shell out the extra $4 and go buy a genuine GM one. I know, I know, the aftermarket ones meet the GM requirements but you can never be too safe. I went through 2 bad aftermarket thermostats trying to track down a no heat problem and I'll be darned if BOTH of those t-stats weren't bad.
In a last ditch effort (since I was SURE it wasn't the thermostat) I decided, what the heck, buy a GM part, couldn't be any worse then the luke warm temp of my car at that point...and WHAM! what a difference!! Instant heat, perfect operating temperature, stable...beauty!
Cheap insurance,
Shane Williams Toronto, Canada

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