Where's the oil going?

I've got a 1978 B200 Dodge van. 318ci auto trans, 362,000mi. I've got
about 200,000 miles on a good engine rebuild. Two years ago I replaced
the timing chain, water pump and front end. I've used Castrol 20/50
and changed every 3k since the rebuild. It runs smoothly and DOES NOT
smoke. I've tried going down a steep hill in low gear and then
accelerating at the bottom of the hill and still couldn't get it to
smoke. I don't see any oil on the ground under the van. It is "using"
1 quart every 400 miles. I switched to Castrol hi mileage 20/50 about
2600 miles ago and haven't noticed any change yet. Does anyone have
any idea where the oil is going?
TIA,
-cadjak

 

With or without catalytic converter?

And yet...

Could easily be a pressure leak that doesn't show up until you're on the
highway, at which point the oil leak takes a path that leaves minimal or
no stains on the vehicle itself. One of the prime suspects for this kind
of leak is the oil pressure sender. They can even still work as they leak
under pressure. Other common leak points include the oil filter mount and
others which I'm sure Steve L will comment on in greater detail
eventually.

-Stern

 

With a catalytic converter and I have replaced the oil pressure
sender, which was leaking a few weeks ago.
-cadjak

 

Then it's quite possible the engine *is* burning oil. The catcon will
consume and "invisible-ize" a great deal of oilsmoke so you'll never see
it. Go do a cylinder leakdown test on all 8 cylinders.

-Stern

 

Probably a good idea to check the PCV system real well too. If that's
it, the solution is likely very simple and cheap (replace or clean hoses
and PCV valve).

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")

 

Or simply drop the cat and start the engine. It WILL be noisy, but a
heavy oil burner will make visible smoke with the cat out of the way.

My '88 New yorker was using a fair quantity of oil, and showing NO
smoke. I pulled the crossover pipe, and when I started the engine
there were huge billows of blue smoke. Valve guides were very sloppy.
Cat was also dead and had to be replaced to pass E-Test.

 

Ooo! Be careful. Unhitching the exhaust under the hood has caused many a
fire, one I've seen myself.

--Geoff

 

You don't need to run it long enough to even get anything hot. Bad
valve guides allow oil to run down into the cyl when the engine is
shut off, and that oil makes a cloud of blue smoke immediately on
startup.

 

Changed the plugs, cap, rotor and PCV. 2 of the plugs were a bit furry
with deposits, but I've sen worse. Found a small leak at the rear main
$eal. I think I'm burning some and leaking some. The rear main is too
expensive to tackle on a van with this many miles. As long as the oil
consumption doesn't get worse, I'll keep adding oil. Anyone here
selling a low mileage, cream puff, Ram Wagon?
-cadjak

 

At a quart per 400 miles? Yick. Why not just swap in a good used low-miles
engine? It's sure to improve your fuel economy as well as your oil
economy.

-Stern