ahspros

Smoke from 928 under air filter box.

I am having some oil smoke coming out from under the air filter box. This is a 1986.5 with 80,000 on the clock. I do not see any oil on the floor/ground and no drips from engine. Going to remove the filter box for a look see. Any ideas as to what I should be looking for?

ahspros

Crumpler

Were you doing any cleaning beforehand? The burn off of cleaning products can be pretty freaky when you fire the engine back up.

9two8

Rocker/ valve cover gasket oil leak ?

Mongo

I wonder if the hose to the heater valve has sprung a leak. Is it possible to 'smell' the smoke? It's easy to tell if the smoke is oil related. A 'sweet' smell usually means antifreeze.

ahspros

I found the source of the oil smoke. Rear main oil seal. Just had this replaced about <1,000 back.

ahspros

worf928

Hmmm...

Keep looking. It's pretty hard for the rear main to leak onto the exhaust enough to produce smoke and not leave a puddle. Cam cover gaskets on the other hand...

5-speed or auto? Stock catalytic converter?

dr bob

Pardon my bluntness, but... You'll be looking for oil, and more particularly what might be causing it to smoke that high up on the engine.

Under the intake manifold there is a web of crankcase vent hoses, for instance. They connect to the cam covers on either side, and also to the oil filler neck at the top front of the engine. Look down on the side of that filler neck to see the hose connection there. Oil vapors are ultimately drawn into the engine intake at a port in the side of the rubber connecting bellows at the throttle body and the intake plenum underneath the organ pipes. The hoses, if original, have endured over thirty years of heat, oil exposure, and vibration. They crack, split, tear, fall off, etc, depending on the immediate local conditions. When one of those leaks, oil will get loose in the valley ofunder the intake.

The plastic oil filler neck has a gasket where it connects to the block, below and slightly behind the coolant bridge at the front of the valley on top of the engine. The plastic cracks, and also distorts enough with age and heat to cause the gasket underneath to leak. The crank whips up a massive oil fog right under the filler, so any leaks there are sure to be oily.

The cam covers are sealed with a rubber o-ring style gasket, and there are vents, plugs and seals around openings for the ventilation elbows, spark plug wells and hold-down bolts. RESIST THE URGE to just tighten down on those bolts to add pressure to the gasket. The hold-down bolts are shouldered and sit tight against the bosses in the head already. They are 6mm steel bolts, with a recommended tightening torque not to exceed about 7 lbs/ft. They break rather easily on removal it turns out. (sorry...) So don't weaken them by 'just snugging them up', or you risk a lot of drilling to get the steel stubs out of the aluminum heads. Instead, plan on complete removal and replacement of all the rubber and plastic bits.

At the rear end of the heads there are plastic cam bore end plugs, each with its own seal. Leakage there and/or at the cam covers at the rear will allow oil to fall on to the exhaust and make the smoke you ask about.

Conclusions:
Oil in the valley, on its own, doesn't usually have a heat source enough to make smoke. There's a drain hole at the rear of the valley that might get oil onto the exhaust, but it usually shows up on the bellhousing and the floor if that's the path. The cam cover gaskets and seals, and the cam end plug seals, are the most likely sources of oil onto something hot enough to make smoke. You can use the digital test (fingers...) to reach around the rear of the heads with engine cold, looking/feeling for oil seepage there. If you don't find any, then th air cleaner housing comes off for a better look underneath. At the same time, oil from leaking vent hoses in the valley will be visible just looking between the pipes on the intake.

James Bailey

The oil drain hole in the V was a later "improvement" not present on early blocks. Not sure exactly when it was added or why ?? Draining oil into the bell housing might be O K on automatics but sure is questionable when there is a clutch in there !!

ahspros

This is a 86.5 auto. I ran the motor for 20 minutes and oil did drip on the garage floor with no smoke. The oil spot right at the end of the engine.
The smoke is only when driving then smokes when coming to stop.

ahspros

dr bob

Your mission then is to get the car up high enough to see where it's dripping, clean above that, then run it a little to ID the source. In the meanwhile, a good flashlight and some mark-1 eyeballs should be able to see into the valley for oil sitting in there.

On the automatic cars, there's a plastic inspection plug in the bottom of the bellhousing. Pop that out, and reach in with a finger to find any oil around the hole. If it's wet, pull the whole air cleaner box and do the same look-and-feel test on the top of the bellhousing. If that area is wet, oil is coming from the valley and draining out the back. If the top of the bellhousing is dry but there's oil inside that plug hole at the bottom, the rear main seal is leaking. Oil there can drip onto the exhaust, making the smoke you see coming up under the air cleaner housing.

Mrmerlin

also to note the new rear main seals have changed,
and the side of the seal has changed ,
a bit of material has been removed this combined with the relief slot made for seal removal could combine to create a leak

vanster

The wonderful thing about an 85-86.5 is that the airboxes an the intake tubes are NLA. As you most know they are unique. Don't take anything for granted. Find the culprit and fix it! Trust me!