I have had this happen before with another 240 some years back but I cannot remember what the cause was. Here is what happens...... we are driving up a slight grade, then there is a bit of detonation like rattle coming from the engine and then a huge cloud of noxious white smoke. I thought maybe it was a bad knock sensor so I pulled one of another car but it didn't fix the problem. Can anyone point me in the right direction?
Thanks,
Len
--
Two 1989 245 Volvos and three Land Rovers a 1969 IIA, a 1991 RRC SWB and a 1995 RRC LWB!

Huge cloud of noxious white smoke...

Usually white smoke out the exhaust is a sign that coolant is getting into a combustion chamber. Your post does not specify the source of the smoke, exhaust or ???

Is the car running OK otherwise?

There is a "quick and dirty" chack for a head gasket break. Do it when first starting an overnight-cold engne. It is not a precise test.

Remove the expansion tank cap. Leave the hood up and get in to the car. Situate yourself (or have a helper) so that you can see the open top of the expansion tank. Start the engine and watch.

If you see coolant welling up out of the tank, there is a head gasket failure. Combustion pressure is getting into the cooling system.

As an engine heats up, parts expand and thus a small gasket break may get compressed tight enough to temporarily close the leak.

The next check for a head gasket/valve problem is a compressoin test.

The above is based on the white smoke coming from the exhaust.

Good Luck,

Bob

:>)

There is a very brief rattle(sounds just like pinging/detonation) and then the smoke will come out of the exhaust for a second or so. This white/gray cloud is huge and dense. The engine runs great otherwise, has good power and still gets very good mileage. The rattle/smoke only happens when the engine is under a load while accelerating or going up a grade. I just noticed that the exhaust pipe tip is black sooty looking like it is running rich. The weather has just started getting cold here and I wonder if my temperature sending unit to the ECU is bad? Is there a way to test the sending unit? I will also check the preheating tube and the airbox.
Thanks,
Len
--
Two 1989 245 Volvos and three Land Rovers a 1969 IIA, a 1991 RRC SWB and a 1995 RRC LWB!

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First test would be the poor man's check for a bad HG, remove the spark plugs, do any of them look like they have been sandblasted clean? If yes, you've got a water leak into that (those) cylinder(s). Head gasket at a bare minimum would be called for.

Sometimes, oil smoke can look more white than blue, so I would definitely check the spark arrestor and plumbing to make sure they aren't plugged up, replace as needed.

Hope that helps.

jorrell
--
92 245 250K miles, IPD'd to the hilt, 06 XC70, 00 Eclipse custom Turbo setup...currently taking names and kicking reputations!

My 92 240 had a black and sooty exhaust pipe, but blew out black smoke. I changed the o2 sensor and problem was solved. The car had some codes, can't remember exactly what they were.