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1998tegPosted - 01 Jan 2017 : 23:26:22
Hello, and happy new year!

With apologies for raising the well-discussed issue of temperature control, I'd welcome some wisdom on the unusual symptoms I've been seeing lately.

A little while ago I had a new triple-core radiator fitted, with a new water pump and thermostat too. Since then the temperature gauge has been all over the place.

After getting hot and sitting at the N position, it will slowly rise until it gets to half or just over half way between the N and the red zone. But then it will suddenly drop back to N. This cycle repeats pretty much whatever I'm doing on the throttle.

I can't believe this is what it should be doing. Any ideas? Might it be air in the system?

Thanks, Phillip
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1998tegPosted - 08 Jan 2017 : 15:08:25
melle: thank you for a very re-assuring reply. I shall try to trust that everything is just fine - but I might change to a lower-rated thermostat when it's next convenient. I'll also do the heater trick in case there's any residual air in the system.
mellePosted - 06 Jan 2017 : 11:46:14
1998teg: What you experience is just the thermostat opening, nothing unusual. Your engine probably has a thermostat with an opening temp of about 89degC fitted, replace with a "colder" (82/83degC) thermostat if it bothers you. I never bleed the cooling system using the bleed valve on the heater box and I've never had issues. Just put the heat on max for a mile or so after filling the system, works a treat.

Zagato: Replace the bolts with studs once you're at it.

Derek: I think it's nigh on impossible to fit the thermostat in the wrong position.
ZagatoPosted - 06 Jan 2017 : 08:13:57
Mine did as you describe also before it came off the road. I need to put a new thermostat in, just scared of sheering off the probable seized bolt, gonner start soaking it in plus gas now and undo it in the summer lol!

9000 Aero
1998tegPosted - 05 Jan 2017 : 22:13:29
Good suggestions all, thank you.

Regarding the sudden fall; I wouldn't describe it as a flicker. From the N position the temperature rises slowly and steadily up to a point whereupon it will fall back to the N at a much faster rate.
FliptopPosted - 04 Jan 2017 : 14:30:17
Also check the wire on the temp sensor on the stat housing - they can get loose (it's just a spade connector on a round terminal) and vibrate, causing the needle to flicker.

Running and bodging Saabs since the dark ages...
pchristyPosted - 04 Jan 2017 : 09:38:31
When you say the needle suddenly moves, do you mean its flickering? If so that suggests an electrical fault rather than the cooling system.

I had the same on mine, and traced it to the multi-pin connector on the back of the instrument. Giving this a wiggle - or better, remove and replace it - should provide a cure. Its a poor earth caused by slight corrosion on the pins. If you watch carefully, you can see it affects the fuel gauge as well, but not so noticeably.

"Duct tape is like the Force: It has a light side and a dark side, and it binds the Universe together!"
DerekPosted - 03 Jan 2017 : 12:38:19
The orientation of the thermostat is apparently critical if you go by the manual. The domed cross bar on the top can be pressed down and distorted by the lid when bolted down. This will effect how it opens and closes. This distortion might correct itself when you take the lid back off. I've not read of anyone having this problem so they must be going by the book or just lucky. However the garage may not know about this and so might have put it in the wrong position. It may be that only certain brands of thermostat have a problem. Cross bar should be across the car (at right angles to the crank) for peace of mind.
green96v4Posted - 02 Jan 2017 : 12:50:53
Hi Phillip

My temp gauge has always sat just above N and wouldn't the movement be just the thermostat opening and closing? (it could be that your temp gauge wasn't moving as much before as the old rad/pump/stat were sludged up with old age and now the new parts are allowing the waterways to "breathe" easier?)
1998tegPosted - 02 Jan 2017 : 11:28:57
Thanks for the suggestions. The work was done at a garage so I can't vouch for the bleeding. It's something I'll check when I can.
UK_SubPosted - 02 Jan 2017 : 10:58:55
Did you bleed the system using the bleed valve situated on the heater box?
Betsy67Posted - 02 Jan 2017 : 07:01:58
Think I would start by putting the old thermostat back in and see what happens. Could it be in upside down ?

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