Burning oil but good compression?

[adventureboss]

So my 06 TJ with the 4.0 has 227k miles on the clock. Runs great, no noises, overheating, etc. I did a compression test today and got between 176-184 psi on all cylinders (seems a tad high?). I also checked oil pressure and have 18 psi at idle with 10w-30 oil. My concern is it burns a quart every 3500 miles or so, and I know these motors aren't supposed to be oil burners, right?

I replaced my rear main seal so no leaks from there, did notice a bit of seepage around the PCV tube thing. Is my oil burn most likely just age and wear related or is there something obvious I'm missing? How much oil do you guys burn?

 

[Chris]

So my 06 TJ with the 4.0 has 227k miles on the clock. Runs great, no noises, overheating, etc. I did a compression test today and got between 176-184 psi on all cylinders (seems a tad high?). I also checked oil pressure and have 18 psi at idle with 10w-30 oil. My concern is it burns a quart every 3500 miles or so, and I know these motors aren't supposed to be oil burners, right?

I replaced my rear main seal so no leaks from there, did notice a bit of seepage around the PCV tube thing. Is my oil burn most likely just age and wear related or is there something obvious I'm missing? How much oil do you guys burn?

Normally I'd say that's not normal to burn that much oil at all. However, given that it is a higher mileage engine I'm not as alarmed as I normally would be.

The seepage around the PCV tube could indicate that the PCV system isn't working optimally, which might lead to increased pressure in the crankcase and oil consumption. That's probably the first place I'd be looking.

Again, you've got higher miles but that still seems like a bit much to be burning IMHO.

 

[adventureboss]

Normally I'd say that's not normal to burn that much oil at all. However, given that it is a higher mileage engine I'm not as alarmed as I normally would be.

The seepage around the PCV tube could indicate that the PCV system isn't working optimally, which might lead to increased pressure in the crankcase and oil consumption. That's probably the first place I'd be looking.

Again, you've got higher miles but that still seems like a bit much to be burning IMHO.

I'm wondering if maybe a clog in that tube could cause it? Maybe I should start with replacing it and that grommet its seeping oil from. But what is there to fail in the PCV system since there is no real valve?

 

[Zorba]

Back in the day, it was considered completely normal to burn a quart every 1,000 miles!

 

[Zorba]

I'm wondering if maybe a clog in that tube could cause it? Maybe I should start with replacing it and that grommet its seeping oil from. But what is there to fail in the PCV system since there is no real valve?

The little orifice could be clogged.

 

[Chris]

I'm wondering if maybe a clog in that tube could cause it? Maybe I should start with replacing it and that grommet its seeping oil from. But what is there to fail in the PCV system since there is no real valve?

Yep, that could sure as heck cause it. Try replacing the PCV valve as well. Cheap and easy!

 

[Strizzo]

If its burning that much oil through the combustion chamber, you'll see it on the plugs and oily, sooty exhaust pipe. The high compression could be somewhat caused by oil in the combustion chamber. Oil helps the rings seal which bumps compression numbers. The oil pressure at idle is pretty low, but that could be due to bearing wear and not necessarily connected to the oil burning.

Has this engine had long oil change intervals in the past that could have gunked up the oil rings and/or the CCV orifice? the crankcase ventilation system creates vaccum in the crankcase and helps with ring sealing and oil burning.

 

[JKP]

Yep, that could sure as heck cause it. Try replacing the PCV valve as well. Cheap and easy!

Can you show us a 4.0 PCV valve?

 

[JKP]

If the CCV orifice is clogged, it will push oil back into what is normally the CCV fresh air intake hose.

 

[TJ4Jim]

One of the easier fixes are valve stem seals and with the youngest engines now being almost 20 years old they can eventually harden.

 

[Zorba]

One of the easier fixes are valve stem seals and with the youngest engines now being almost 20 years old they can eventually harden.

This. I was wondering about seals and/or valve guides.

 

[Moglocker]

So my 06 TJ with the 4.0 has 227k miles on the clock. Runs great, no noises, overheating, etc. I did a compression test today and got between 176-184 psi on all cylinders (seems a tad high?). I also checked oil pressure and have 18 psi at idle with 10w-30 oil. My concern is it burns a quart every 3500 miles or so, and I know these motors aren't supposed to be oil burners, right?

I replaced my rear main seal so no leaks from there, did notice a bit of seepage around the PCV tube thing. Is my oil burn most likely just age and wear related or is there something obvious I'm missing? How much oil do you guys burn?

Normally I'd say that's not normal to burn that much oil at all. However, given that it is a higher mileage engine I'm not as alarmed as I normally would be.

The seepage around the PCV tube could indicate that the PCV system isn't working optimally, which might lead to increased pressure in the crankcase and oil consumption. That's probably the first place I'd be looking.

Again, you've got higher miles but that still seems like a bit much to be burning IMHO.

Just do them all

 

[TheBoogieman]

The oil pressure at idle is pretty low, but that could be due to bearing wear and not necessarily connected to the oil burning.

13 psi at idle is normal. His is 18 psi.

 

[SkylinesSuck]

A qt every 3500 miles is certainly more then many, but not a big worry. That's not a crazy amount. Just something to keep an eye on. The compression numbers don't really indicate much either as they vary quite a bit between gauges and with conditions. Consistency across cylinders is more important. Mine is 204-208 across all 6 for example (higher compression stroker though).

 

[Gilaguy23]

Back in the day, it was considered completely normal to burn a quart every 1,000 miles!

No kidding. Granted 90% of my way to many vehicles were tired and if they only used a quart in 3500 miles id be thrilled.

 

[adventureboss]

Okay, will replace all of them and report back. Hopefully it reduces it but I guess a quart every 3500 miles for an engine this old isn't too horrible.

 

[JKP]

Also verify your valve cover gasket isn't leaking.

And stay away from energy conserving oil, it's always on the thin end of the grade.

 

[GoldenGorilla]

With cylinder pressures that high a leakdown might also provide some insight, but I think it would also show fine. If a cylinder or two are leaking down quickly, it could signal some blow by, which can increase the loss through the CCVs. Only way to resolve that would be addressing the piston rings. I'll second that this isn't bad oil consumption - but mine (~80k) has never consumed much oil. Maybe a 1/2qt every 5000 miles and I have always had a minor RMS leak from basically the day after the warranty expired. I've owned mine from day 1.

Assuming leakdown doesn't show an issue.

I agree that the CCVs and their gaskets are the place to start. You don't want to do everything at once. Do that and monitor the oil consumption over an oil change. If it drops, you've found your culprit.

Next thing I'd look at.

It's possible that the weep holes in the pistons oil control ring groove have clogged up. This could cause some oil build up on the cylinder walls that the 2 upper rings can't push out. Especially if an owner wasn't keeping up with oil changes and things got sludgy at some point. A good oil flush right before an oil change could serve you well. I run the one from Liquimoly in our twincharged V90 and have total confidence in their products on gasoline engines. With that one you run it on idle for 10 minutes without driving. Then drain. Do this for several oil changes and it may improve. You can also research some alternatives. An injector cleaner can be helpful on that last tank of gas before an oil change too.

This is also a case where running an oil change cycle with an oil with a higher detergent content (Calcium) like Rotella T5 10W30 might provide some benefit to just clean things up before going back to what's working for you. That oil is designed for the higher soot content in a diesel (not good for our motors), but also has a higher zddp content which is good for our motors. It has a slight propensity to encourage predetonation in gasoline motors, but the 4.0L is super low compression like a tractor.