been about 400 miles since oil change and is about 3/4 of qt low. no leaks seen. its a 2001 dodge dakota 3.9l any ideas on cause?

 

One that's been noted on AllPar is using a non-Mopar PCV valve.

I'd check that out first.

Also, being a 1995, I'd check the plenum gasket. With the motor OFF, open the throttle body all the way and see if there's any oiliness visible. If there is, most likely the plenum gasket has failed.

The plenum gasket can be just replaced, but it'll fail again. Hughes has a kit that fixes it right.

(The problem is the intake is aluminum, the plenum belly pan is steel, and the two expand/contract at a different rate, causing the gasket to tear after time.)

RwP

 

It may not be low at all. How long do you wait after turning off the engine to check the oil? You can get the most accurate reading by checking oil first thing in the morning with the truck on a level surface. Also since the filter is mounted on an angle it will hold a lot of oil by itself when the engine is off. The missing 3/4 of a quart may be in the filter.

Jimmy

 

been about 500 miles its now a little over a quart low and oil is getting dark

 

With detergent oil, I'd expect it to start getting darker at 500 miles.

And 500/quart isn't BAD on a high mileage motor (don't like it, but it's not bad. Not good, either.)

Did you check the plenum gasket, by looking down into the throttle body while the motor isn't running, and seeing if it's oily? It should be bone dry there - any oil, and I'd blame the plenum gasket FIRST.

If not, well ... If you love the truck, I'd find a good core motor and get it rebuilt, or locate a good crate built motor, to replace the current one.

If it's not the plenum gasket or a bad PCV valve hung open, then you've got some gaskets or seals leaking (which would spot something under the truck at that rate), valve seals leaking (which it would burn off), or bad rings (again, would burn off).

IF you grab a core out of the boneyard to rebuild, grab a 1993 if at all possible, with the larger manifolds, and use the 1993 Y-pipe / exhaust when you drop it back in. That's good for about 5 to 10 ponies all by itself.

Other choice would be to go with headers, and get it breathing free with those.

(If you do headers, don't worry, just grab a Magnum 3.9 ... or consider this a chance to pop a 5.2 or 5.9 in its place if it's 2WD!)

RwP

 

Best way to check the plenum gasket:

1) Disconnect and plug breather hose going from valve cover to airbox.
2) Pull PCV valve out of other valve cover.
3) With engine running, gently put your finger on PCV valve hole in valve cover.
4) Pressure=good plenum gasket, vacuum=bad plenum gasket.