Mysterious Oil Consumption ???

[318idol]

I have a 1991 318i with 150,000 miles on it. Recently, the profile gasket failed (for second time, I assume). The engine got slightly hot, but not enough to damage anything. No blown head gasket, no warped head.

The shop that did the repair - a very reputable shop with years of experience with this car and engine -- suggested I have the head rebuilt while it was off. Good idea. So the head was totally rebuilt, new valves, guides, etc. The "new" engine runs like a champ, smooth, quiet, plenty of power.

However...

Before the the repair the engine used essentially NO oil, like one quart every 3-4,000 miles. I have always run Mobil 1 10-40. Since the new head was installed, oil consumption is insane, like one quart every 500-600 miles.

WTF?

There is no smoke out the tailpipe and no leaks. I have no idea what is going on. The shop has no idea either. You'd think with the new head and valve guides it would be using even less oil.  If it was burning that much oil, wouldn't it shoot out a blue smoke plume worthy of Jame's Bond's smoke screen gadget?

I wondered if the overheating, slight as it was, somehow compromised the oil control rings -- but, if so, where is the smoke?

I'm considering changing to regular oil (non synthentic) and see what happens.

Any ideas?

This is a really sweet car, perfect paint and a host of upgraded components.

Thanks for any and all suggestions.

Gary

[keflaman]

I know you said there are no external leaks, but if the O-ring (#8, http://bmwfans.info/parts-catalog/E30-2-doors/USA/318is-M42/L-M/jul1990/browse/engine/lubrication_system_oil_filter/) behind the filter canister fails you'll lose a lot of oil. It will follow the block webbing behind the coolant pipe and coat the undercarriage beneath the driver's seat.

That's all I got!

[DesktopDave]

Kef is right, definitely check the oil filter housing for leaks. They all leak there. Considering how much oil mine leaks, I'd assume a quart gone every 600 miles is unlikely but possible. It also only leaks when the motor is running, so you may not see a lot of oil pooled where the car is parked.

I'd also pull the intake to see if you have a lot of blow-by. If your rings aren't sealing well, you might see a good bit of oil in the intake pipe, sent from the cam cover breather.

Coolant is OK, right?

[deansweet]

I'd suggest adding a dye to the oil system then either park in the garage and shut a;; forms of light and or wait til after the sun falls down.
That dye combined with a black light make it so easy to see where even the smallest leak is evident,.

I used this to find a very small leak of coolant.

Oil filter housing only take an hour or two to swap out. Make sure you have a in/lbs torque wrench as the bolts that hold the housing to block are kind of easy to strip.

Dean

[318idol]

Thanks for the tips guys.  Where would I look for oil if that O-ring is leaking? I see no oil underneath the car and a quick glance from above shows no oil or wetness on the side of the block adjacent to the oil filter housing. I will jack it up and look more closely...

Gary

[keflaman]

If you look behind, and slightly aft, of the oil filter housing there is a section of webbing under the plastic coolant pipe. Oil will pool in that area, but if you aren't seeing oil under the car I doubt this is your problem.

[318idol]

Not sure how reliable the Metric Mechanic website it, but:

http://www.metricmechanic.com/product-info/engine-information/engine-wear/

According to them, just rebuilding the head increases oil consumption. Seems counter intuitive.

I would be open to rebuilding an M42 block and use the new head. Can you use an M42 head on an M44 block? Which are more available?

[DesktopDave]

I've heard similar stories from racing mechanics. They re-do the valves after the pistons & bottom end breaks in...they claim a 5% power improvement from improved valve sealing. I figured it was a smallblock thing, but it make sense in general.

I'm told the heads are physically interchangeable, but the M42 has higher specs on most parts. The M44 has a lot of differences in terms of engine electronics. The crank sensor mounts to the side of the block, cam sensor is apparently on the other cam, etc.

I'd be looking for a late production M42 block...something built in '94 or '95. '96 is too late, that's when the M44 took over.

[aguyther]

Well OP, you're not the only one with this problem. I bought a super clean 318is with a rebuilt motor from a trusted source and cannot figure out why I am consuming so much oil. No leaks, nothing comes out of the tail pipe, etc. can't figure it out. Motor was properly broken in and everything.

Edit: Maybe it could be blow-by? Dear god I hope not. I have a long crank at times even with a pretty new starter in the car, and my oil does look a little blacker than it should. 

[sfinsf]

If my little M42 didnt need oil on a regular basis I would definitely worry. Seems like they have a nasty habit of eating it up. I've come to expect it. My M50 and M20 have no where near the consumption levels.