A few months ago, my front passenger side window started fogging up. In the past few weeks, my front winshield fogs up instantly when the outside temp is below 50 degrees.

I don't have the recirc. button pushed in, so I think it's a heater core problem.

Short of replacing the Heater Core, can I check any hoses (without taking my dash off) for leaks?

What does it smell like? Antifreeze smell is rather unique. Are the mats smelly?

I'll bet the valve is leaking OR you have rain water leaks.
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http://www.fidalgo.net/~brook4/oilslubesfilters.html

Check the mats to see if they are wet on driver's or pass. side. You can check the heater hoses by removing the underdash cover on driver's side, then the plastic panel beside your right leg. Hoses and heater valve are right there. If the windows are fogging, and esp. if they do it worse when you run the blower, it does sound like a heater core leak. One sure sign is if you go to wipe the windows clear and the fogging just smears around - rather like it was greasy. That's glycol, my friend, and you are likely in for the dreaded heater "core-ectomy".

Also, are any of the floor mats in the car wet (esp passenger side?)

Monitor your coolant level.

The same thing can be caused by moisture getting into debris in the air intake or the heater core itself. It stays wet until you run the fan for a while.
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Chris Herbst
1992 945, 71k
independent volvo shop tech

I'll check my carpet to see if it's wet. If it is wet, what should I check for?

My coolant has been slowly leaking for about a year, but the window fogging has been an issue since March.

My temp gauge spikes up to hot (4 minutes after starting the car), then settles in the middle until I start the car again. Is this all realated???

>My temp gauge spikes up to hot (4 minutes after starting the car), then >settles in the middle until I start the car again. Is this all realated???

This reminds me of my '84 244GL, when I got it delivered from the junkyard. I thought it had a cracked head. (the engine cooughed & wheezed so much because the intake system was destroyed in the crash, I didn't know the state of the engine)

I took the chance that maybe the cooling system was blocked somewhere (fluid was very dirty, and I found no water in the oil). Flushed it a couple of times then idled it using plain water (not winter yet)

It was nerve-racking watching that needle rise into the red. It did an about-face, though and has worked normally now for the 10,000 miles I have driven it.

Have you done a thorough flush of the engine block, heater core & radiator? Remove the T-stat first. That way you can force water from the top of the engine down through the draincock.