Excessive Oil usage 2006 QX56

[Janene]

Has anyone experienced their vehicle using too much oil? I got an oil change then a month later (1500) I was about 1 1/2 qts low. Took it to the dealership where the oil change was done at and they said bring it back in 1000 miles to see if it goes real low again. Took it back in 1800 miles and it was 2 qts low. Now they are saying it needs a new engine but when they tested the engine last month all was fine. I see no evidence of oil leaking.

What should I do?

[RED_DET]

Infiniti engines have been known to burn oil here of lately, especially in the VQ series. I'm not quite familiar with the QX, but no engine should burn oil, period. I'm sure it is still under warranty, so let them replace the motor.

[Janene]

I bought it used and the warranty has expired. They want to do a JB Sludge test. Do you think that is a good idea?

[C-Kwik]

A general battery of tests to see where the oil would be advisable. Typically a leakdown test is ideal, but a compression test might be able to reveal the problem as well. At the very least, if it turns up nothing, you will likely have ruled out most of the potential causes. Once the cause is determined, then you can determine the best course of action ro remedy it.

[SteveTheTech]

Hey there,

This is interesting.

Although one model of VQ had an issue over a limited production run. Others are much much more varied.

You may have found a simple coverall diagnosis and if your car is out of warranty that is the best that the basic diagnosis might cover. In modern shops we do very little internal engine work and the amount of diagnostic tools required are becoming more and more scarce as the majority of techs no longer purchase the a cylinder leak down tester, or a borescope. The profitability just isn't there for the majority of us to buy them. However that has to be someone there that has them or they can point you in a direction of someone who would know. This does not have an issue at many dealers as the engines that are under warranty usually get visual inspections and tare downs but entire replacement. If you are out of warrantable range, are not the original owner, or have no service history the chance of getting any good will from Infiniti is pretty slim.

However with something like this you have a very unique issue and diagnosing the route cause over the internet will not be possible the best we can give you is a guess and an honest second opinion.

[SteveTheTech]

A general battery of tests to see where the oil would be advisable. Typically a leakdown test is ideal, but a compression test might be able to reveal the problem as well. At the very least, if it turns up nothing, you will likely have ruled out most of the potential causes. Once the cause is determined, then you can determine the best course of action ro remedy it.

I agree whole heartedly but the amount of people out there who know how to correctly perform these tests and give an honest answer as to the results are continuely decreasing. The new breed of guys are not really outside the box thinkers. Oil consumption is one of those things that you think would be obvious but they can be pretty tricky.

If this were mine, I would start by pulling the plenum before doing much else, if nothing else it makes getting to the plugs easier and you would able to clean and thoroughly assess the pcv system. Pull the plugs, loosing that much oil has to leave a sign somewhere. A compression test would be the best/cheapest test to diy if that is the chosen route. But to pay for these tests is going to be pricey.

[C-Kwik]

I agree whole heartedly but the amount of people out there who know how to correctly perform these tests and give an honest answer as to the results are continuely decreasing. The new breed of guys are not really outside the box thinkers. Oil consumption is one of those things that you think would be obvious but they can be pretty tricky.

If this were mine, I would start by pulling the plenum before doing much else, if nothing else it makes getting to the plugs easier and you would able to clean and thoroughly assess the pcv system. Pull the plugs, loosing that much oil has to leave a sign somewhere. A compression test would be the best/cheapest test to diy if that is the chosen route. But to pay for these tests is going to be pricey.

I have one. It was like $100. But you are right that modern techs are a somewhat less into this type of detail. Which is why I do my own work when I can. For anything else not specific to Nissan, I go to an independent shop.

As for removing the plenum, I didn't even need to remove the cover over the plenum to get to the plugs on the Titan. Can't imagine it would be that much better for access to the plug holes.

I agree the sompression test would be cheaper. I think the only thing you really lose out on is measuring leakdown while moving the piston through its motion. For detecting where the air ends up, most compression testers have the same quick release that a leak down tester has so you can plug it straight onto the end of a compressor hose and regulate the pressure through the compressor (perhaps not as easy for shop air though).

[SteveTheTech]

The test equipment is not in my cost/benefit range...meaning I don't actually have one and I have only used 1 one time in 10 years. Compression and visual inspection can be done for enough of margin of savings that it just makes sense. Plus you need shop air to measure the active drop, a home compressor might not supply constant enough pressure to complete this test accurately.

I think a properly performed compression check along with several of the other basic inspections would lead to an appropriate diagnosis. However the willingness and ability of the person who holds the keys.

[C-Kwik]

The test equipment is not in my cost/benefit range...meaning I don't actually have one and I have only used 1 one time in 10 years. Compression and visual inspection can be done for enough of margin of savings that it just makes sense. Plus you need shop air to measure the active drop, a home compressor might not supply constant enough pressure to complete this test accurately.

I think a properly performed compression check along with several of the other basic inspections would lead to an appropriate diagnosis. However the willingness and ability of the person who holds the keys.

A home compressor does fine. Unless the leakdown is huge, the compressor won't need to cycle much. One could further extend cycle times using lower pressures as well. Say 50 psi instead of 100.

Not saying a compression check isn't useful or that one couldn't use it to diagnose. But a leakdown test (even without the guages), can make it easier to find a leak. If air starts coming out of the radiator cap, you have air entering the cooling system. If its coming out of the crankcase (breather or oil fill), its poor piston sealing or head gasket. Of it comes out the intake, its a problem with the intake valve seal. Out of the exhaust is an exhaust valve problem. You can also turn the crank while performing the test and if the leakdown increases halfway through the stroke, you can pretty much tell its a cylinder wall problem. Its a pretty versatile way of testing several things at once. Are there other ways? Sure. But leakdowns are quite beneficial.