PontiacBonnevilleClub.com

'90 Buick LeSabre. 122,XXX miles, inherited from mom and stepfather - always well serviced. Have driven for 4 years, 50,000 miles of my own. So, heater has always been marginal. mode and mix doors seem to be working OK. 195 Thermostat has been replaced twice with no improvement.

I attached a small indoor/outdoor thermometer to the upper rad hose to get a feel for what the stat was doing. Also tried it on the heater hose going to the core. So far it looks like the stat isn't regulating. It opens after a couple of miles of driving and seems to stay open so that the hose temp gets up to maybe 140 and then drops to as low as 110, never getting up to proper temp. In town at low speeds, it heats up to off the scale (160 max on this digital thermometer), but drops down to the lower range on the highway. As the weather cools, the temps are lower yet. The heater hose temp is only about 110 to 120 like it's way over cooling. Air temp is 110 max at the AC vent with a small dial type thermometer (when in vent mode - haven't put a sensor in the heater outlet).

These engines have the stat on the flywheel end of the motor, unlike all other motors I have worked on. Is there any trick to getting the stat to regulate at specified temp? Blocking off part of the rad is an obvious fix of sorts, but I'd like to get it working as it was designed.

I'm not sure if monitoring the temp of the upper hose is a valid test. Wouldn't the hose temp drop when the thermostat closes? Does this car have a temp gauge in the dash?

Honestly, replacing your thermostat won't do much if there's a bunch of crap in the cooling system plugging portions. Do a thorough reverse flush of the system.

Mechanical Mike wrote:I'm not sure if monitoring the temp of the upper hose is a valid test. Wouldn't the hose temp drop when the thermostat closes? Does this car have a temp gauge in the dash?

Yea, the hose is a poor measure of system temp. If you can get a fix on the thermostat housing, that would be beter.

Without looking at it, i would venture to guess that the coolant system needs a good flushing. Restricted flow through the heater core on older cars is a really common reason for low heater performance.

Asymetric wrote:

Mechanical Mike wrote:I'm not sure if monitoring the temp of the upper hose is a valid test. Wouldn't the hose temp drop when the thermostat closes? Does this car have a temp gauge in the dash?

Yea, the hose is a poor measure of system temp. If you can get a fix on the thermostat housing, that would be beter.

Without looking at it, i would venture to guess that the coolant system needs a good flushing. Restricted flow through the heater core on older cars is a really common reason for low heater performance.

I agree. I would start by reverse flushing the heater core. That will let you know if you have a plugged up core and might improve it enough to make it functional again.

I've done a thorough flush of the heater core in both directions. No restrictions. The purpose of putting the sensor on the upper hose was to simply see if the stat was cycling. It does not seem to be. It appears to be stuck open. I drive 100 miles every day and outside temps are 30 to 40 when I start out. Upper hose temp warms slowly from the time I leave the driveway and continues until I've been on the highway for several miles, maxing out at 130 or so. when I get into town, it gradually rises to off scale (160), coming back on scale and cooling to 130 again when back on the highway. The heater inlet hose temp follows loosely, but somewhat cooler, but going off scale also in town. The vent temp never goes over 110, but I'm beginning to suspect my dial gage sticks at that temp. Heater output is OK in town, but marginal on the highway. We're not really into the cold weather here yet and I don't think that at 10 and below, it will be up to snuff. As you probably know, the heaters in GM cars (all US cars that I know of) use 100% outside air all the time. I used to be a factory tech and trainer for AC and cooling systems for Nissan, so I got to be pretty familiar with the concepts. Individual models can sometimes be pretty peculiar, though.

Next step is to try yet a different stat. I know it's properly installed. It only fits one way. I drilled a small hole in the valve itself to make sure it was not trapping air. I've run into that in other cars. It puzzles me that the heater hose temp is lower than the top hose temp. Most cars are designed to send the hottest water in the block to the heater first.

There is no temp gage on this car's dash. I did lose the coolant last summer once and before I got to where I could do something about that, the overtemp light came on, so I know that much works.

Any more thoughts?

Are you using the seal around the thermostat and the o-ring on the housing. There is actually 2 seals on the LN3. One is an o-ring that goes around the thermostat housing to seal it to the intake manifold. There is another seal that goes around the thermostat to keep the coolant from by-passing the thermostat.

Try another thermostat & don't drill it. I'd go with the Stant Superstat. You can check thermostats in a pan of boiling water with a meat thermometer. It should open slowly at 190- 195 & when removed from the heat it should close fully right around the same temp. Just for fun you might want to check the old & new thermostats at the same time. After the engine has warmed up & cooled back down check the coolant level in both the reservoir & the radiator.

The O-rings are both there.

A new stat is definitely in order. Thanks, I'll use the Stant Superstat.

I'll report the results.

Use a thermometer and heat up some water in a pan on the stove to check your thermostat is functioning property..

Never use the engine as the test dummy for the "does it work" test..
That's a waste of coolant and time..

I've had 3 delco therms fail in a row brand new in the box from the dealer..
Quality has gone down over the years on some OEM parts and sensors..

So the current situation is -

I bought a new stat. No one in this town carries Stant, but at the CarQuest store they said their best one is made by Stant, so that's what I got. Checked it and the existing stat in the pan of water on the stove. Using 2 thermometers, small dial type from Robinaire and a K-D radiator testing liquid-in-tube type. Both thermometers tracked together, both stats operated identically in both rising and dropping temp.

The parts man said the new stat should have a seal which he sold me (for $4) which seals the edge of the flange. It's a flat ring seal with a groove on the ID to engage the flange edge. (Wish I could post photos. It would be a lot more clear.) Well, there was no way I could get it all to fit together with that seal on it. I'd have to shorten the spigot on the outlet to get it to seat. With the seal on the stat, I could get it into the recess in the manifold, but could not seat the outlet. That one bolt design may work OK with new parts, but it's a lousy one for service. Can't develop any clamping force.

So I reassembled it with the new stat and the old seals. (The new stat has a slightly thicker flange than the old one.) Still, I cannot get the outlet to seat squarely, so it leaks. I tried the old stat, and still I cannot get the outlet to seat squarely. I think I may have bent the boss where the bolt hole is, although I'm pretty cautious about over tightening things - especially aluminum parts. Doesn't look bent by eyeball.

The inner seal may be somewhat swelled up and preventing the assembly from fully seating. The outer O-ring is no longer round in section and should be replaced. Think the local parts houses would have them in stock? No chance. Gotta order them in. You'd think I was working on a Bugatti or something.

Currently I have it assembled with only the outer O-ring in place and no inner seals. So I'm sure it is leaking past the stat. The outlet is also leaking, but not so much I can't drive it. It just smells bad. I have a new outlet on order and will use all new seals. The water temps on the road still follow the pattern which I have been trying to correct, that is over cooling and not much heat from the heater. Today the air temp was high 30s to low 40s. On the highway, the upper hose temp was steady at 97. (These are Fahrenheit degrees we're talking here.) In town it would get up to 155 and the heater put out useful heat. Back on the highway, the temps would drop and the heater is useless.

I have same problem in my 91 buick pa, 3800seriesI with dual a/c. where i live, temps have been this winter low ZERO F, thats like -30 celcius. so i have been really experiencing cold in the car. replaced thermostat, acquired core, not replaced yet.
my problem is that engine does heat up to 120F according to gauge, but the heater does not heat the cockpit. i hardly can keep my windshield clean from steaming. i found out in FSM that heater can be set to override- so i placed it to maximum heat. but you cant do it with out FSM, its complicated although it starts only with pressing off-and warm buttons simultaneously

Impala, please start your own topic, this one is aging, and your solution may not be the same. There's no need for everyone to read through someone else's stuff to finally see yours.

NoShowCar, you MUST use that seal you paid 4 bucks for. That's why your car won't heat up. You're bypassing the thermostat without that seal.

To the OP...

Next time you have it all apart snap a pic of everything you have for seals as well as the Thermostat housing.. There were slight differences from 88 to 89-90 and 91

I know you have a 90, but would like to know what all you were sold.. If the thermostat is a 44mm it should be correct for your application.. Being a 90 you should only have an O ring for the thermostat housing and a rubber gasket for the bottom of the housing... IIRC there should be no gasket on the thermostat its self.. Let me correct that, I should have said around the thermostat

The OE replacement, ACDELCO 131-115, 195 degree thermostat, has a rubber seal (gasket) mounted on the circumference of the thermostat.

Please continue this in your post.