Please help. Heater output problems 94 SLS

[JimD]

I'm getting a little confused. Are you people saying that there can be more than one correct temp thermostat for a 94 ELDO or whatever?

Kent

Not really. A GM dealer parts counter can provide the 'correct' OEM thermostat based on your VIN.

An aftermarket parts house can sell you a thermostat that 'should' work; but you will be doing the testing.

[kcd1184]

To be more specific, are you saying that two seperate 94 Eldos might require different thermostat tempts???

Kent

[Ranger]

Not likely Kent. I would bet that they all require the same thermostat. I'm guessing 190 or 195 is the correct one. I just checked the '99 FSM and while it does not give thermostat tempurature, it does say that the operating rang is 188 - 206.

[WarrenJ]

My '95 Eldorado consistently ran at 180 degrees on the highway. My current '98 is equally consistent under the same conditions, but at 196 degrees.

Regards,

Warren

EDIT: The '95 had a Delco thermostat, dealer supplied. The '98 is an unknown.

[KHE]

A 180 degree thermostat is not the correct stat for the Northstar. It is designed to use a 195 degree thermostat.

[What job]

Good day to all,

The search goes on. I put about 2 hours into checking the on line part houses this morning. Most offered the 180 t-stat. Some offered a gates model that was listed as the OEM part but none of the sites had any information on what temp it opened at.

I did find out from reading of all things the owners manual the t-stat operates between 192-199 degrees. At least this is the range give for it to open.

The manual even has the part number listed for the t-stat AC type 131-66/3531407.

So at this point I guess I need to call a dealer and see just what this t-stat is.

Once again thanks for all the input.

[WarrenJ]

Good Grief! Whouda thunk something as simple as a 'stat would create such consternation?

FWIW, I always felt the heat in my '95 (with the 180 'stat?) wasn't quite up to par. I always meant to look into that, but the time has passed.

Regards,

Warren

[Cadillac Jim]

I'm the one who put the seemingly contradictory information in post #13, where I said that Rock Auto sells a 180 degree thermostat for the 1997 model year, and that the 1997 FSM says that the coolant temperature range is 188 F to 206 F.

More information from the 1997 FSM, page 6-243. ECT (engine coolant temperature? Available on the DIC Info list by adding 64 to the override word): 90 C to 110 C (194 F to 230 F). The engine coolant temperature (ECT) sensor is on the left (rear) head at the front (driver's side), which is, arguably, the hottest point on the engine.

I'm not sure that there is a contradiction here. The thermostat senses temprature near the input side of the water pump. This water is mixed, including warm water from the heads and less warm water from the sleeve water jacket. When this tempearture hits about 185 degrees, the thermostat opens up and lets some radiator-cooled water into the mix, and when the mix hits about 180 degrees it closes until things warm up again. Instrumentation by a user, posted on this board, show that the thermostat is constantly opening and closing, and our experience is that the egine maintains a more or less constant temperature over an amazing range of conditions. I think it's entirely possible that an intake-side thermostat with a nominal rating of 180 degrees could maintain a head temperature of 195 degrees.

Then, there's the obvious: get the thermostat from a Cadillac dealer, using the VIN number from your insurance card or registration, and don't worry about the small stuff.

[kcd1184]

Perfect

[MAC]

I'm not going to look for a 180-degree. The Guru addressed this issue and stated that wide temperature swings can be a factor in facilitating "thermal fatigue," which could cause engine problems including head gasket failure, particularly for Northstars with over 100,000 miles. However, he was not too concerned about temperature swings as he also mentioned that when the fan is activated at 225 the engine will cool evenly and thus mitigate the effects of thermal fatigue.

For the most part my Eldorado is very stable as far as temperature range. This is likely one reason why I have over 215,000 miles on the original engine and I remain impressed with how well it continues to run. Even while standing coolant temps do not quickly jump to 225 degrees and above. What I do see from time-to-time are swings from 212 and higher down to 192 (sometimes 35-40 degree swings). Obviously the result of an efficient cooling system and an apparent slow adjusting thermostat. If anything, maybe it's time for a new ACDelco 195-degree thermostat. If a Northstar calls for a 195-degree thermostat then don't lower it to a 180-degree since a lower temp thermostat will only create greater temperature swings. I want to minimize temperature swings as much as reasonably possible. Will a new 195-degree thermostat change anything? Perhaps not--However, I think it's a reasonable expenditure considering the high mileage on my Northstar. Actually, the lower temperature dips are a recent phenomenon so it could indicate it's time for a new thermostat.

[Cadillac Jim]

MAC, please consider using your VIN number at a Cadillac dealer to get your thermostat. I don't see how you can go wrong doing that, and I would expect that the Guru won't contradict me here.