I have to relay my favorite british car engineering story - related to oil
consumption/loss. Most of you have probably heard it before.
Anyone here have to fully dismantle an MGA motor?? If you notice, they do
leak. There are two major oil leak sources. First, the non-pcv valve.
It's really quite efficient - an inverted U tube that vents at the bottom
of the car. Shouldn't get anything but fumes in it, but on occasion some
oil comes out. The open end of the tube is cut at an angle to act like a
venturi - which draws out crankcase pressure very efficiently. The second
location is the backplate. The early motors don't really have a rear main
seal so much as they have a spiral slinger (that creates positive
crankcase pressure - hence the previous part). When the slinger didn't do
the job of keeping oil off the clutch, a clever engineer designed a groove
in the engine back-plate. That way when the oil gets past the seal, it
will leak on the ground, rather than into the clutch. It seems to work
well. I always see a little oil when I stop.
This is one of many reasons that a leak isn't really a problem - it's
"normal seepage." The problem is when you have no more normal seepage -
that means you are out of oil, and you've waited too long to add more.
> What? You think they didn't know how to control oil consumption
> then? It wasn't the Dark Ages. ;^) If the engine is in good shape
> internally and doesn't leak, it shouldn't require that oil be added
> between changes. Your 130K-mile B needs a rebuild.
> Bob Donahue wrote:
>> Remember, this is a British engine designed 50 years ago. Don't expect
>> the low oil consumption of modern cars. IMHO - AFTER the rings have
>> bedded in, anything over 500 miles per quart is OK. I keep scrupulous
>> records of gas and oil consumption on my vehicles. My B with 130k on the
>> odometer (with no engine rebuild yet) gets between 500 to 1000 miles per
>> quart. (I seem to get worse oil consumption with highway driving.)