Please help. Heater output problems 94 SLS

[What job]

Good day,

I am at a loss folks. My daughters 94 SLS is having heater problems.

First the car takes a very long time before any heat starts to come out of the floor vent. I thought this may be caused by a bad / open thermostat. After removing the thermstat and testing it I found it doesn't open even at +200f. Now I'm confused because the engine doesn't seem as if it is running hotter than normal. No over heating problems.?

I haven't replaced the thermostat yet so I have no running temperatures for the engine but as best I recall the last time I checked with lazer the engine was running around 195-200f. Now I'm wondering if a stuck closed thermostat can cause this problem?

Does anyone know if the thermostat not opening on a 4.6 could cause the heater to not flow right or if I have missed some thing else.

Here is another thing that is not making sense to me. I drove the car home last night about a 100 mile trip. The heat was ok but it was also +25f or so outside. The daughter said at +10 to -5f the car has no heat at all.

Here is the strange part. When ever I climbed a hill the heater was putting out great heat. I mean hot and this was at the rear outlet in the console. When I was going down hill the heat would get cooler. Maybe 110-120f. This is just by feel of the air on my hand the temperature may have been higher but it didn't feel much more than warm.

I really need some input before I tear the whole car apart in search of the cause. I'd rather find the cause instead of replacing a lot of parts that are not bad if you know what I mean.

Also the parts house tells me they only make a 180 thermostat for this engine. Is this true? Where I am located it will drop to-40f at times. Will a 180 thermostat be able to keep up?

I'm at a loss guy's so any ideas on what to look for / test are very welcome.

Thanks much for any input.

[PAUL T]

I think there is a 190 or 195 degree thermostat. If the concentration of the coolant is 50/50 mix and the coolant level is topped off, then I would say you have a partially blocked heater core. I flushed mine out recently and it made all the differance. I took the heater hoses loose below the power steering pump and attached a water hose to one hose and an extension hose to clear the car on the other hose and flushed one way then switched hoses and flushed the other way. I put everything back together and it works fine now. It is not easy to get these hoses loose, I had to fabricate a hooked screw driver to break the seal and loosen the hose from the fitting.

[Ranger]

I am almost sure that the OEM stat was at least 190, if not higher. The fact that temp output varies with attidude makes me think there may be air in the core. Is the purge line clear and flowing?

[The Fred]

I would have a hard time believing that OEM is 180F

It heats when you climb a hill not so good coming down?

With the stat just taken out?

So when you climb the hill it works harder, you're not going as fast so less airflow= better heat... coming down going faster less work more air coming through=less heat

Purge the system of any air and try a 195F stat or what ever it calls for

[What job]

Thanks for all the ideas.

I replaced the thermostat and the heater seems to be working now. At least at 25f we have at this time. Even so it does feel as if the heat is better than it was last night.

Looking at the old thermostat there are holes drilled arount the surface area that would block the water flow from the radiator to the engine. The new thermostat doesn't have these holes but is sealed except for a small hole with some type of little valve in it. I think this is to allow the air to exit the block.

Just a guess I really do not know but I think the water from the radiator was passing the thermostat enough that the water temp never got as hot as it needed to be. This to me would explain the engine getting hotter going up hill then cooling back down on the down hill side.

Almost the same as a stuck open thermostat would act.

Anyway thanks to all that had ideas and if this new thermostat doesn't do the trick I will try some of these ideas.

On another note, I check the old t-stat and as far as I can tell the new one is the same. There aren't any markings as to the temp rating of either one of these units. Only a 54mm on both. What this means I haven't a clue. Any ideas out there?

The manual calls for 180-192 t-stat. Seems cold to me but time will tell.

Thanks again guy's.

[Cadillac Jim]

The only thermostat for my 1997 ETC is a 180 degree, even for California, year-round. It's important that you get the correct thermostat for the Northstar because the cooling system works differently than those for many other cars, in that the thermostat is in the cooled water return line from the radiator, not the water pump outlet for hot water to the radiator. The thermostat is operated by water on the engine side but flow is from the radiator to the engine. This gets us to the last point, that the thermostat must not be installed backward.

[jorghenry]

Could you not check the coolant temp in the console??? This would indicate the temp of the coolant,,,the fans will come on arnd 234F.

,,,feel the temp on the inlet & outlet lines on the right back of the eng. room.

Also you can sqeeze and get a feel of the flow rate. It seems you are not getting enough hot water into your heater core assuming your blowers are doing ok. Also note that there is a blower fan inside your center console to supply hot air from the rear vent. Also when you climb up you have a better flow into the heater core due to the inclination of the car. Hence also check your coolant level.

From what you say, it seems you are getting heat with the motor revving high, if so

points to a flow discrepency to your heater core. You may have a restricted/clogged inlet /outlet hose or flow control valve if not a bad impellar in your water pump not giving sufficient flow rate ,,,

Just another angle.

[Cadillac Jim]

I just checked my 1997 FSM checklists for engine not coming up to temperature and it mentions only these three items:

• Low coolant level.
• Stuck or improper thermostat.
• Stuck bypass valve (!!!).

I can't find the bypass valve mentioned anywhere else. It's the valve from the thermostat housing to the metal bypass hoses that go behind the engine.

[What job]

Again these are all good points and well taken.

I don't think the t stat can be installed but one way. Then again if someone tried hard enough I guess they could get it in wrong.

I'm not sure on the coolant level. The system did take a little less than a quart on the refill over what was drained out. I think the over flow tank holds that much so it may have been a tad low but not enough to cause this problem. Then again it may have had a small role.

Guy's I have another question. Does anyone know what these special pellets are that the manual says must be added anytmie the cooling system is serviced or great damage can be done to the engine?

I am not close to any dealers and am wondering if there is an after market product that I could find at a parts house.

Are these pellets a type of stop leak / sealer or what? If it is stop leak and has been added to this system everytime it was serviced from new then I may start looking at a blocked heater core as part of the heater problem.

I did notice this car has a new radiator in it so now I'm thinking the system may be full of crud and this is the reason the radiator was replaced.

I did flush the core awhile back when I first bought this car last fall and it did seem to have good flow. Would the core flow well if it had a blockage in some of the passages?

Again thanks for all the help.

[JimD]

The aftermarket equivalent to the GM product is Bar's Leaks Golden Seal. I like the powder product and I use two tubes when servicing my cars. You can usually find it at WalMart and other places.

The purpose is simply to provide a little insurance against nuisance leaks. And it would be hard to use too much of it.

[Ranger]

The barsleaks that JimD mentions has a product code of G12BP. The tabs are HDC. It is the exact same thing you will get from the dealer.

No, the core would not flow well if it had a blockage, but the sealant tabs should not cause any blockage, or we all would be having problems.

[MAC]

According to GM's 1994 Service Manual (p. 6B1-4) the thermostat should begin to open between 192-199 degrees F and should be fully open at 219 degrees. My Eldorado calls for a 195 F thermostat. The thermostat should be tested in a pan filled with 50/50 mixture of water and antifreeze. And the thermostat should not rest at the bottom of the pan due to the uneven concentration of heat at that point in the pan.

[Cadillac Jim]

The 1997 FSM page 6-180 says that the normal operating range of the thermostat is 188 F to 206 F. The thermostat test it to use a mark on the thermostat housing with a temperature stick for 206 F and if coolant flows before it melts, the thermostat is opening OK. If it opens before a mark from a temperature stick for 188 F melts, it is opening early or stuck open.

The special tool number for a set of temperature sticks is J 24731. I would bet that you can get temperature sticks or test strips from an auto parts store.

The Rock Auto thermostat lookup for my 1997 ETC gives 180 F thermostats by Stant, part number 14228, and Gates, part number 33808. The AC/Delco part number is 131128 {replaces 131-117 #12559807) but it doesn't give a temperature. There is no mention of a separate thermostat for CA. Newcadillacparts.com gives one thermostat for the 1997 ETC but doesn't give a part number. I don't have a part number for the dealer OEM thermostat.

My thinking is that you should get one from the dealer using your VIN and don't sweat the small stuff.

[kcd1184]

Recently did the coolant drain and refill with tabs. Replaced with aftermarket thermostat also. Didn't run in the right temp range, so I replaced with oem thermostat from caddy dealership. #12559807--195 degree. Runs around 204 most of the time. Ran 201 with the old original thermostat. The aftermarket place using what they had listed on their computer, had given me a 185 thermo. (wouldn't crack 195 degrees most of the time) MY Gm mechanic friend said you will hurt your motor with too cool of a thermostat. Side by side there was quite a visual difference. The aftermarket one really looked light weight compared to the oem one.

Kent

[What job]

Again many thanks.

I'm wondering about this OEM part compared with the after market part. I'm sure the one I removed was after market as well as the replacement one. Both of these were very heavy duty t-stats in my opinion. Not anyting like I'm use to seeing out of a Chevy, Ford ,etc. If the OEM is built even better than these it must be one heck of a piece of hardware.

I'm now concerned the engine will not running hot enough with this 180 t-stat since it can and does get very cold here.

I guess I had best call the dealer and find out just what is going on.

It will be just my luck that I need to make a 200 mile trip and then tear into this thing again.

That new car for the kid is looking better all the time.

Thanks again for all the help guy's.

[MAC]

Speaking of thermostats, I see that RockAuto and AutoPartsGiant sell only a 180-degree thermostat for my Eldorado. I don't think I am, but perhaps I'm a bit confused thinking that I have a 195-degree. My Eldo generally runs at 196-201 degrees during these cooler temperatures. Anyway, I want the OEM recommended thermostat so maybe I'll just buy a new ACDelco 180-degree. At the moment I'm using a Stant.

[adallak]

What's wrong with Stant? It actually may be the company making private lable thermostats for ACDelco. Do they look different?

[MAC]

What's wrong with Stant? It actually may be the company making private lable thermostats for ACDelco. Do they look different?

I must say that I haven't had a problem with Stant since I bought it about 3 years ago. It looks like OEM--At least there is no major difference.

[What job]

Speaking of thermostats, I see that RockAuto and AutoPartsGiant sell only a 180-degree thermostat for my Eldorado. I don't think I am, but perhaps I'm a bit confused thinking that I have a 195-degree. My Eldo generally runs at 196-201 degrees during these cooler temperatures. Anyway, I want the OEM recommended thermostat so maybe I'll just buy a new ACDelco 180-degree. At the moment I'm using a Stant.

I'm not following you Mac.

Do you now have a 180 and are running at the higher temps?

You have started me thinking the engine was made in a way that the 180 t-stat makes the engine run at a higher temp just by where it is located.

Can this be the case? Could the T-stat be installed in such a way it kept the engine temp higher than the rated opening of the t-stat?

I just can't see why there are so many folks that have 180 t-stats and the amount of parts houses that only sell the 180 if the car infact needs a 190-195 to run at the correct temperature.

Now I'm confused.

[adallak]

What's wrong with Stant? It actually may be the company making private lable thermostats for ACDelco. Do they look different?

I must say that I haven't had a problem with Stant since I bought it about 3 years ago. It looks like OEM--At least there is no major difference.

Mine was from Stant and worked perfectly for six years. I replaced it with a cooler one (180) BBF gave to me. Still keep the old one "jus in case".

[Cadillac Jim]

The outside temperature and season aren't a factor in the thermostat. A 180 degree thermostat will keep a Northstar with properly functioning cooling system at about 185 degrees or warmer, and a 195 degree thermostat will keep a Northstar at about 200 degrees or warmer. If the dealer takes your VIN when he looks up the part number on a Cadillac parts microfiche or CD-ROM, you are good to go.

[BodybyFisher]

Speaking of temps, today I was driving in traffic and when I got moving again, I looked down and my temp was 190.... I was shocked the car was running for an hour. I have never seen a low coolant temp like that on my car.... Anyone have an idea why? It was 40 out.

[MAC]

Speaking of temps, today I was driving in traffic and when I got moving again, I looked down and my temp was 190.... I was shocked the car was running for an hour. I have never seen a low coolant temp like that on my car.... Anyone have an idea why? It was 40 out.

I have experienced the same thing. Once I saw my temp dip to 187. I think it may have to do with the thermostat not closing fast enough to keep the temperature up to normal. You may notice it will happen when temps are in the 212 range and above and once you start to move the radiator will cool the water so quickly that the thermostat can't respond fast enough. Anyway, that's my theory.

[BodybyFisher]

Interesting, thanks MAC, glad to see its not just me

[kcd1184]

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