"Low Coolant" warning

Hi everyone,

I hope everyone had a great Valentine's day. Here in Seattle, we've had a warm winter and are headed for an early spring, but my car isn't so happy.

My "Low Coolant" warning has been coming on intermittently and I was wondering if the engine was overheating yesterday, even though the reservoir is full and I can't add any more coolant. (Meaning, it didn't boil over and the gauge was in the usual zone, but it was hot and I'm not sure I can rely on a temperature gauge if the coolant really is not there.)

What does the warning mean? The radiator was replaced about a year ago and the heater works fine. The car is a '96 2.0L turbo convertible.

Hi
Not sure if you've resolved the problem by now (over the last 7 weeks). But if you have not, the following may be of some use.

Your coolant reservoir (reservoir tank, expansion tank, coolant tank, header tank, water pressure bottle). Is the highest part in the coolant system and is a good indicator for the rest of the system.

Usually if the coolant level (when cold) is on or slightly over the KALT/COLD mark, marked on the reservoir, then all is well with the rest of the system. If any air is trapped within the system, it usually travels quickly around with the pumped water until it finally reaches the coolant reservoir to be replaced with coolant. This in turn causes the water level in the reservoir to drop, as does a water leak within the system.
Sometimes air has been known to get trapped in the heater system, but as yours is working this is not the case.

Inside the reservoir tank is a float that will trigger a switch if the coolant level drops below a min level. This will bring on the "coolant low" on your dashboard.
It could also be triggered if the coolant level is close to the minimum amount, and the car is parked facing up a steep hill. The switch and float device are on the front of the coolant reservoir.
I usually fill mine (when coolant is cold and on level ground) to just below the max line. The coolant level will rise in the tank when the engine is up to temperature, but will be within the normal working levels, because even though it's above the max line, the level is to be read when the coolant is cold.
Another possibility could be the float might be clogged or sticking due to the condition of the coolant. If a "leak-stop" additive has been added it could be having an affect on the float mechanism.

I've looked on various sites and so far have not been able to find anything relating to the float or switch being available on their own as a spare part. It looks as though a complete reservoir may be needed. Perhaps a trip to a scrap yard would be the least expensive route, although the part appears to be common throughout the years and ranges, it seems not to be reflected in the price.
reservoir tank. Part number 4356390 item#8 on the link
1996 Saab 900 Parts - Saab Parts Distribution - Your Saab Parts Source!

It could be a clogged float assembly,switch fault, switch plug corrosion or trapped wire.
Check the wiring for bad insulation bare wires etc. and the connection to the switch for water ingress. Or if you think the float is clogged or at fault, you could remove the reservoir and clean it out by putting water and some crushed ice in and giving it a good shaking.
Some people have said dry rice instead. but not too sure that you could get it back out as easy. If you think its the float being fouled by something, then perhaps a drain and flush of the cooling system as well at the same time would be a good idea. The mixture should contain at least 40% anti-freeze, but not more than 70%.

In your thread you said the coolant reservoir was full and you could not add any more coolant. Did you mean it was up to the KALT/COLD line, or to the actual top of the reservoir neck. If it's up to the neck it has too much in and needs emptying to the correct level. Not sure it would have any effect on the float, I've never done it.
The temperature gauge is a thermocouple type, so as the temperature rises, it's resistance changes. If this type fails they tend to go open or short circuit , all or nothing, rather than inaccurate.
Hope this is of some use to you.
Cheers for now.
Dave.

I have had this problem on my 2000 9-3 with 120,000 miles for two years. I tried to clean the sensor in the coolant reservoir, but it did not make any difference. The coolant level always is OK and the car is not overheating. I just ignore the light and consider it part of the car's character.

Quote:

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Originally Posted by JTRI

I have had this problem on my 2000 9-3 with 120,000 miles for two years. I tried to clean the sensor in the coolant reservoir, but it did not make any difference. The coolant level always is OK and the car is not overheating. I just ignore the light and consider it part of the car's character.

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Thanks for the replies. I agree--if I know it's actually OK, I'd rather live with it than put in a different old switch. In fact, it just stopped giving the false warning on its own.

Bad luck--I got a coolant leak after I'd learned to ignore the low coolant warnings, and ended up with an expensive overheat and blown head gasket. These bargain cars can be expensive.

The sensor mounted on the coolant reservoir can only be purchased new as part of a complete reservoir assembly for about $140. I found a pretty clean-looking one in a junkyard while looking for something else, but I haven't got around to installing it yet.

Quote:

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Originally Posted by Dave 2 93s

Or if you think the float is clogged or at fault, you could remove the reservoir and clean it out by putting water and some crushed ice in and giving it a good shaking.
Some people have said dry rice instead. but not too sure that you could get it back out as easy. If you think its the float being fouled by something, then perhaps a drain and flush of the cooling system as well at the same time would be a good idea.

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For future reference, adding to this old thread. A low coolant level warning in the SID was a pretty regular occurrence at startup on my 01 Viggen, coolant level was always where it should be however and no other cooling issues. Had my local Saab indy look at it, diagnosed as likely sensor issue with the expansion tank, sensor not available as a separate part, quoted me a couple hundred bucks parts+labor to replace the tank. Read Dave's advice herein and decided to pull and clean the expansion tank as part of a DIY cooling system renewal project - intrigued with the idea that I might be able to fix this. Upon removal and inspection I was absolutely horrified at the amount of crap/crud that was in this tank!! Picture below and the debris on the napkin is what was collected in a strainer in my kitchen sink (yes, wifey gave me the evil eye more than once) after my initial rinsing the tank out.
Attachment 17260Attachment 17261

My best attempt to document the crud built up on the float mechanism inside. This too is after my initial rinse, before cleaning.
Attachment 17262

Dried the rinsed out tank in the sun. Wife had uncooked rice (not minute rice, you need the hard stuff that takes 20 minutes to cook) in the pantry and decided to use that as the abrasive media. Added about 1 cup of the rice to the tank, put plastic bags with rubber bands over the various holes in the tank, began shaking...
Attachment 17263

Lots of shaking, hoping that it wouldn't hurt the float mechanism on the inside, doesn't seem to have. Emptied first batch of rice out, still not as clean as I'd like and so ran another batch. Once satisfied with the extent of my crud removal, I took a magnetized screwdriver and cleaned/scraped the metal particles off of the float's magnetic tip. Washed and reinstalled the tank along with the rest of my cooling system refresh. Looks almost new now and happy to report that it seems to have fixed the sensor malfunctioning - no more warnings in the SID.

Great write up and thanks for the rice tip. Considering all of that crud in there.. I might have run some flush treatment mixed with distilled water thru her on a 20 minute drive or so.. (in Nevada, maybe 10.. lol)..., and then do your rice trick to clean out the reservoir and fix the sensor. I actually found that the magnet for my sensor had fallen inside the reservoir and had to find a way to reattached it in mine after getting the low coolant fault some years ago. Took a minute, but it still works.

I recommend a vacuum based tool for refilling, but also draining and testing the entire system for like $60 bucks or so.. takes all of 5 to 10 minutes to refill under vacuum.