1996 4.0L Consuming 1 qt. of Oil Every 300 Miles

[admsvcs]

I have no discernable leaks. The rear main is moist, but does not drip. No sign of oil underneath the truck. I did a compression test and all cylinders were within 5 lbs of each other (155 to 150). I see no smoke from the exhaust, only a few drops of water. Does anyone have any idea how I could be going through so much oil with the typical telltale signs? Is 150 lbs. compression too low?

 

[shaun5664]

Is it a high mileage vehicle? I have a 96 explorer with the 4.0 and it has 325,000 on it and I burn about a quart of oil every 2 and a half weeks. The rings could be getting worn on the pistons and that could be the cause. They will let oil get on top of the pistons and could be burning that way.

 

[bigcrunch]

Check you PVC valve? clogged?

 

[admsvcs]

Mileage = 140,000. The PVC valve was in good shape. I also checked the tightness of the bolts in the lower manifold. They are good too. Is 150 lbs. of compression sufficient? I have no leaks and no smoke, just annoying oil consumption.

 

[bigcrunch]

On compression numbers, check a repair manual.

Have you looked at the spark plugs on coloration and deposits on porcelain and electrode?

 

[IAmTodd]

I'd be more inclined to do a leak down test rather than a compression test.

Coming from an OHV that uses a lot of oil I have no idea where it all goes. My rear main drips but not enough to justify the quart every 750 miles or so. It's much worse on the highway than it is around town.

 

[1998Exp]

Modern engines do not have absolute compression specs, because there is too much variation due to starter speed, temperature, etc. If all cylinders are within 20 psi or so of your 150, the compression is just fine. However, compression reading is not an indicator of oil consumption. That's because there are separate 'compression' and 'oil control' rings on the pistons. Some years ago the 3.8L V6 on my LTD was burning oil to the tune of 1qt per 100 miles, and still reading perfect compression with no decrease in gas mileage and no suspicious noises.
If your engine is burning oil significantly, for any reason, it will be obvious by looking at the plugs. It could be worse in one or two cylinders, so check them all.
Also, it's not all that easy to see blue smoke out of the tailpipe when you are driving. Warm the engine up, have someone standing behind the car, and hit the accelerator wide open.

Mileage = 140,000. The PVC valve was in good shape. I also checked the tightness of the bolts in the lower manifold. They are good too. Is 150 lbs. of compression sufficient? I have no leaks and no smoke, just annoying oil consumption.

 

[admsvcs]

Thank you for all the great comments. I replaced the plugs about 1000 miles ago. The old plugs did not look bad at all. All plugs seem show evidence of clean burning with no oil residue. I will pull them again. I am also inclined to a leak down test.

 

[Flash]

I would have thought that that sort of oil consumption would leave evidence somewhere, either with a smoking tail pipe or drowned spark plugs and probably even a haze of oil on your tail gate.

If it's not dripping out of the engine then it must be burning, eh?

There's 2 ways excessive oil can enter the combustion chamber, through the oil control rings as previously mentioned or through the valve guides/seals.

If the oil control rings are stuck a Seafoam or similar treatment can unstick them but nothing can fix valve guides or seals other than replacement.

I'd say that pretty soon your cat is going to be a solid block of coke and muck which will cause its own problems and if the muck starts to burn then you'll have a slagged cat.