99 SW2 Overheat, blows cold inside, ???

[ww2steel]

Hello everyone, first post! I have read a lot about this on here and understand the system much better now! ...but still confused!

My personal experience - Owner of a 99 SC2 since new. Just bought this SW2. 11 years parts, ASE, manager at a parts store, worked at the Saturn dealer briefly, but that was all 8+ years ago. I have only a small amount of hands on knowledge with the SX cooling systems.

Okay, the problems, I'll try to be concise. This one, if it's a single fault, really has me puzzled! Okay, three times now on really cold days and once on a warm day over the span of three months the car has overheated. (Car is a daily driver.) Gauge slowly climbs to red, I do a precautionary stop, and then the engine begins boiling. I crack the cap and steam/ fluid vents freely until I tighten it back down. On the really cold days (didn't try on the first OH, which was the warm day) there was absolutely NO heat. Blows cold, not lukewarm, I mean -7° ambient air this morning. The engine's boiling, car's venting, but there's no heat (when the engine is running, of course).

Serpentine belt rotates normally. Next time it overheats I'll verify fan operation; this morning when it overheated it was turning very slowly. Though I did it accidentally (because I thought it was off since I didn't hear it) I was able to put my hand into the fan without it being uncomfortable. I wouldn't do it on purpose because I don't want to damage it. The fan does NOT operate when the AC is engaged, but the compressor didn't either. (temp sensor? It was very cold today.) However, a bad fan will have nothing to do with a lack of heat inside the car. (Heat always works fine when the engine is not about to overheat.)

The weirdest thing... sitting at a light you can cut the ignition off, wait a moment as if resetting a computer, restart, and sometimes - instantly - heat comes rolling out and the engine temp stays / goes where it normally is (at the ¼ mark, roughly). I can’t remember what my 99 SC2 temp usually indicated. I totaled it a few months ago (had it since new) .

If I understand correctly this is like my other cars and the thermostat doesn't block the heater hoses, so a hot engine that is circulating should give heat. The only thing I can think of that can this can cause this is an intermittently failing water pump or a blockage that prevents circulation (can't be ice, it did it on a hot day). I read that this pump can fail in such a way that the belt will still turn. Is that correct? Can it fail intermittently like this, especially with 2000+ miles on the car between failures? I bet the car was doing this when I bought it, but it was not disclosed... possibly the reason the original owner sold it!

Thanks a bunch, I'm 1300 miles from home and really can't afford to do explorative surgery!

Mike

[bumpdraft]

My only experience with your symptoms was in a 1981VWDasherDiesel with 20+:1 compression:

Engine Compression leaks into cooling system and blows water away from cylinder head.
It caused temperature gage to spike at random.
Drive at highway speeds for a while until heater started blowing cold (especially when exiting highway/slowing down). Shut off the engine for a while and everything was fine.
^This happened in deep, cold winter far from home.

[hoseppi]

Are you sure you have the proper coolant mixture. If the system is diluted the mixture will freeze in the hoses, thereby preventing proper circulation.Oops, I reread your post and saw that you said it happened on a hot day also...so much for my theory. Still, I think you should feel the hoses and make sure you are getting proper circulation.

[alordofchaos]

Originally Posted by ww2steel

If I understand correctly this is like my other cars and the thermostat doesn't block the heater hoses, so a hot engine that is circulating should give heat

You are correct; thermostat is up front.

Post 3 here shows coolant flow. Heater core is bypass so there should always be coolant flow in the core

only thing I can think of that can this can cause this is an intermittently failing water pump or a blockage that prevents circulation (can't be ice, it did it on a hot day).

Did you do a flush on the system when you got this car? First things I thought of as well were intermittent blockage and such.

The fan on the S-series is not multispeed, sounds like yours is dying or dead (when it comes on, it is really noticieable - or should be). If you provide direct power to the fan, it should be roaring. You are correct that the fan will not come on using the AC button when temps are below 40F ambient.

Either way, a 1/4 reading on the temp gauge is low. You may need to replace the ECTS, thermostat, or both.

[Highmile]

Start with the most basic stuff first....

Is the cooling fan running when it gets to about 3/4 on the temp gauge? Definately should be running by the time it gets close to the red.

If so, replace thermostat with a high quality part. It's cheap and fairly easy to replace and could keep you from going further.

Sounds like the radiator is ok since it doesn't do it all the time...

do you have a slow coolant leak somewhere. Check the level when cold ever day or two for a couple of weeks to find out.

When you do check it cold is there still pressure in the cooling system that could indicate compression leaking into the cooling system? (head gasket or cracked head).

Highmile
447k '95 SL1

[ww2steel]

Thanks for the posts!

Yes, there is a VERY slight leak coming from the front of the engine just below the... water pump. At least they're cheap.

The water pump solves the OH/ no heat problem, but can that actually happen intermittently? A stuck partially open Tstat would cause the low running temp. On my SC I did have the plastic temp sensor do their normal thing, I will see if this has a brass one. Air/ fuel mix seems fine though and I know from the SC when that goes bad it throws off the mixture. On all three cold days I was driving it when it did it and all of the days the roads were crappy limiting speed to 25mph or less, maybe the OH is caused by the fan since I always otherwise drive on the highway and just wouldn't know the fan was bad until the restricted speed days. But if it was only the fan then why no heat only on those overheat occasions??? My plan for now is that I'm out of town for work for another month and I'm going to drive it (since the screw ups are rare) until the problem makes itself obvious or at least persistent so I can troubleshoot. Once I get home I'll replace the fan, Tstat, Water pump, and temp sensor. Hopefully that will take care of everything so if something acts up in the future at least I'll get faults one at a time. Hopefully it'll make it another month. I hate buying used cars!

[busting_tranny]

are you letting the car run for a while when refilling with fluid? i had a pesky air pocket that caused mine to overheat with no heat.

[ww2steel]

I apologize for the revival of the old post but I am hoping that this may help someone else. Since I am the O.P. please understand I am trying to follow up. The original problem as a recap: whenever I drove <~35mph the car would overheat AND while overheating I never got any heat in the car. Part 2 has never been resolved BUT to the slow driving part…

I checked the fan a long time ago and it cycled on and turned. I finally happened to be looking at it when it turned on and the motor cut on but it took the fan itself a moment to spin up. I was able to easily stop the fan with minor drag on the outside edge of the surround. Long story short, I pulled the motor and the roll pin locking the fan to the motor had sheared so the fan was barely turning. This caused it to overheat which caused the loss of coolant, which MAY have formed a bubble in the heater core/ hoses/ whatever. Regardless, after replacing the motor with a spare (nothing wrong with the motor, I still have it, but I didn’t have a spare roll pin) ALL of the cooling system problems have disappeared.

Hope this helps someone else out there! It’s literally a 10 cent fix. (Unless you take it to a shop where you pay for their ignorance!)