I have a Case IH 7120 tractor with a 8.3L diesel engine in it that uses quite a bit of oil. I can't say exactly how much as I don't usually operate it but seems like every time I check it, its low a couple quarts. It starts great, runs great, doesn't smoke, doesn't seem to have any visible blowby out the draft tube, generally never misses a beat. I did a compression check on it and all six cylinders have 425 psi compression which is right where they should be. It built compression fast too. With those good of compression numbers, could it still be letting oil past the rings? I can't really tell how well it holds compression because my gauge leaks a little bit past the button to let the pressure off it.
Can I have high blow-by with good compression #s?
- Thread starter sdan27
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Not sure about diesel or your particular engine, on a gas engine oil can leak pass valve stem seal or other external gaskets.
gathermewool
Site Donor 2023
Blowby and oil consumption aren't necessarily exclusive to one another. With all but the oil control ring operating properly, you can most certainly experience oil consumption through vacuum dragging the oil on the suction stroke, while still having good compression.
It could also be leaking past a seal or gasket, as PandaBear stated.
It could also be leaking past a seal or gasket, as PandaBear stated.
right, i assume you looked all over under it for oil leaks?
It is possible the turbo seal could be leaking. There was a little bit of oil around one of the boots connecting the turbo and intake right on outlet of the turbo but there really wasn't much. Then it could be leaking past on the exhaust side of the turbo but might be getting burned away by the exhaust heat. If it were a problem with the oil control ring, would it generate much blueish smoke out of the exhaust necessarily? I do have an oil leak around were the front cover and block meet up but its much smaller than to account for the oil it is using. I think I'm probably going to take the turbo off and get that gone through before I go any further with anything else. The tractor does have a lot of hours on it, a little over 10,000 but I figure if that were in a vehicle and your average speed was 30 even that'd be like 300,000 miles which doesn't really seem like a lot now days.
Yes to the OPs question.
Where the oil is going is another matter.
Oil control rings are suspect, as are many other places.
Cranking compression is not an absolute test for any ring/bore problems.
Where the oil is going is another matter.
Oil control rings are suspect, as are many other places.
Cranking compression is not an absolute test for any ring/bore problems.
Originally Posted By: mechtech2
Yes to the OPs question.
Where the oil is going is another matter.
Oil control rings are suspect, as are many other places.
Cranking compression is not an absolute test for any ring/bore problems.
Agreed, weak oil ring seal has nothing to do with compression and in fact may increase it due to the cylinders having more oil than normal... Still good compression usually means all is well with the cylinder bore, rings & piston....
Opposite can be true as well... Years back I had a '64 Ford with a 289 that had excessive blow by from the road draft tube(so much vapor, looked as if may be on fire)due to weak compression... That engine used almost zero oil, never needed to add in 3K mi change...
Yes to the OPs question.
Where the oil is going is another matter.
Oil control rings are suspect, as are many other places.
Cranking compression is not an absolute test for any ring/bore problems.
Agreed, weak oil ring seal has nothing to do with compression and in fact may increase it due to the cylinders having more oil than normal... Still good compression usually means all is well with the cylinder bore, rings & piston....
Opposite can be true as well... Years back I had a '64 Ford with a 289 that had excessive blow by from the road draft tube(so much vapor, looked as if may be on fire)due to weak compression... That engine used almost zero oil, never needed to add in 3K mi change...
Hook a watermonometer up to the draft tube and put it under load. That is the only real way to check for excessive blowby. I have had it where the readings at idle and WOT are in spec, the second you put it under load it blows the water right out of the meter. As far as the turbo is concerned, it should be easily seen if oil is passing. Remove the turbo pipe and inlet to check for oil, check lateral and radial play, it will be evident if there are any issues. Turbochargers on tractors will pass a small amount of oil due to idle and no load conditions, this is why sometimes oil is seen leaking at the CAC pipes, especially if they aren't sealed properly. At 10,000 hrs it would be safe to assume that the valve guides are showing wear, this could also be an entry point for oil to be consumed. I have seen a large amount of "dusted" engines in tractors due to air filter failure/neglect.
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