Thermostat failure 1996 850

parkbro · Post by **parkbro** » 02 Feb 2008, 20:42

As the temperature cooled this winter I noticed my heater wasn't as warm as it should have been. I also notice the temperature gauge would climb to 3 oclock postion on morning warm ups but would soon fall to 4 and sometimes even 5 oclock once I began traveling at highway speed. I diagnosed the problem to be that my thermostat may be stuck in the open position. I purchased a new 87* Valnet thermostat from FCP Groton and installed.
I am happy to report I now have continuous heat and no flucuation in my temperature gauge. But.....I noticed my gauge rises and sits at a bit higher then the 3 oclock (mid-way point) it sits at more like 2:55 oclock.
Whether I'm sitting at idle for a long period or traveling on highway it sits at this position.

Is this nomal?

Also, I am noticing a light hissing sound coming from the green radiator cap (this is after the car has set and cooled for a few hours) it is not leaking any coolant around the cap but simply a light hiss.

Could my radiator cap not be sealing as tight as it should, thus not creating the correct system pressure and causing a slight high temperature reading?

Suggestions when changing thermostat: The night before changing thermostat spray the (2) T40 bolts which holds on housing with PB blaster / Liquid Wrench. Spray onto bolt while the engine is warm
(not hot) and repeat a second and thrid time. The following morning use either a long (5") T40 bit. I used a short T40 bit slipped into a 1/4" drive socket + a 6" 1/4" drive extension + a 1/4" racket. This allows you the necessary clearance to get around the fuel rail. Make sure the T40 bit is not worn and fits the bolt snuggly and while pressing down turn the rachet at the same time. I was able to break these (2) bolts without a problem. I also purchased (2) new replacement bolts. I hope this helps and good luck with your thermstat change.

Post by **JRL** » 02 Feb 2008, 20:59

Yeah, it's OK but you should buy a new cap

Post by **MadeInJapan** » 02 Feb 2008, 21:01

I agree with JRL...Murphy's law, the cap will just get worse and worse and they're known to do this after awhile when they need replacing.

Post by **Ozark Lee** » 02 Feb 2008, 21:02

you should buy a new cap

Particularly if it is a grey cap. The good cap is a greenish blue color and it works very well.

...Lee

Post by **MadeInJapan** » 02 Feb 2008, 21:04

It's $5.00 here. http://www.fcpgroton.com/volvo850cooling.htm
Last time I checked my dealer wanted about $15 for one.

parkbro · Post by **parkbro** » 02 Feb 2008, 21:16

Thanks guys for all your feedbacks. I have absolutely enjoyed this site and what a resource for anyone that likes to maintain their own vehicle.