I have just changed the spark plugs in my 91 940GL B230F. They are shown in the photos below. In the first pic you can see the 3rd plug is very different from the others. The second pic is a close up of that plug. This plug is shiny and damp. Is it likely my car is burning coolant? The engine runs roughly when started from cold after sitting overnight or all day at work. The coolant reservior tank holds pressure when the engine is cold. I can remove the cap and there is a hissing sound. The coolant needs to be topped up about once a month but it usually doesn't take very much. Has anyone seen plugs this colour before? I'd welcome some opininons.

Thanks

Brad

I dont think so, something is going on there but almost every case of
blown headgaskets I have seen involved spark plugs with an OBVIOUS greenish
hue on ceramic of the tip area. this said, these cars seemed to actually be OK and running decently until the headgasket just blew ! (I am in the service
business). I hav'nt topped up my coolant in over a year, that does bother me.
You need to find out that problem & repair.

have you ever done a heater control valve ? (see faq on used car purchase PM)
I lost my 1st 740 to a heater control valve, fortunately I got it running and traded the car off.
--
Kevin P Walsh, Casper WY. '91 945 SE turbo 170,000 miles / paid for

Start the car from cold, turn it off the instant you verify it is running rough, pull that plug, examine it carefully by sight and smell for coolant or excess fuel. You might then swap two plugs. The three white plugs look very lean to me, especially in winter conditions.

I should add that I am in Australia and it's the middle of summer here. Temperatures in the low to mid 30's (Celsius).

Brad

Brad, for a really objective compression check, with all four plugs out , do it and record pressures. Remember rule #1. NEVER do a compression check on a cold engine. If you are somehow interrrupted between say #2 & #3....warm it up again two minutes. Don't forget..if all plugs are out you will not get confusing results.If you have a constant-pressure-release at the top of the opened expansion tank(which I've seen many times), it's time for a weekend under the hood.
I happen to agree that the only "normal" plug is the one with the "tanning-bed" look. Too clean = too hot or too many baths.

I thought the other plugs looked a little too clean but the other one was moist (not saturated) and didn't smell like fuel. I did a compression check a while back just for the sake of it but I think I may have stuffed it up so I will try again. How long should I let the engine turn over during the check? 2 or 3 times? 8 or 9 times?

Thanks

Brad

I'm certainly not the expert, but I've followed the recommendations in: Compression Test Help Needed from the archives; maybe others with more expertise than me can comment.

In a nutshell:
- prop the throttle open so the engine isn't starved for intake air
- only crank from the starter test connector, so fuel doesn't get pumped/injected
- do four compression strokes
- record psi after the first and after the fourth stroke

--
David Armstrong - '86 240(350k km?), '93 940T(270k km), '89 240(parts source for others) near

The "perfect" plug should look tan/light brown but not glazed.

It's the 3 other white plugs that don't look right to me--usually white indicates running too hot.
--
Norm Cook Vancouver BC; 1989 745T 202,000KM

Nope, those are all normal.
There's certainly something odd with one plug, alright.
Could be lots of things: leaky injector, bad rings, etc., but burning coolant usually makes plugs cleaner.

I had been thinking it might be a leaky injector - fuel dripping into the cylinder all night then the engine tries to burn it off a gut full of fuel and runs like crap. But the plug doesn't smell like fuel though, it smells like stagnant water. Perhaps it could be oil...
I'll take the plugs to my Volvo mechanic also and see what he thinks.

Brad