In this case, we are talking about an used car inspection so the benefit of watching the oil level over the course of weeks etc.. isn't an option.

We are actually looking at an early 2003 M45 which seemed to have the same problem.

What have you guys determined as a good way to determine if a particular car is an oil burner within the limitations of an inspection?

Do oil burners show low compression accross the board? Or would a leak down test be able to detect an oil burner motor?

Thanks

 

There are few ways for oil to get inside the combustion camber. One primary problem is rings: they do not seal against the cylinder walls. A compression check will find this leak.

 

What type of compression reading does an oil burner exhibit? Is it typically 1-2 cylinders way down or all of them lower than normal? Let's say 40-50 psi down?

 

I think very few people will knowingly let you take their Z to your mechanic to do a compression test on their engine during a pre-buy inspection. There's just too much disassembly involved to let anyone other than their own trusted mechanic do the job.

 

It's just a matter of taking the plugs off, not major surgery here.

 

you obviously havent seen where the 350z plugs are located!

 

I would guess I have since I own a G35. But how about let's actually start with HOW to determine if an engine is an oil burner or not. Then concentrate on how to convince the owner to submit to whatever test there is to determine this problem

 

No telling. One bad cylinder or 6. On a car with 10,000 miles something is broken. On a car with 150,000 miles the motor is just tired.

 

Doesn't an oil consumption motor exhibit ANYTHING different than a non-oil consumption motor during a compression test or leak down test?

 

I don't know where the "oil-burning" engines get their oil. It might be coming past the rings at some specific part of the stroke, throughout the stroke, or through the valve guides.

If it's coming past the rings, it might show up on a running compression test where the pressure is measured at the spark plug as the engine is turned over. It might not show up on a static compression test where each piston is cranked to TDC, and a differential pressure gauge is used to measure leakage past the rings and valves.

If it's coming past the valve guides, a compression test wouldn't show it.

 

I think you may have to remove the plenum to get access to all of the plugs.

 

If a car is consuming excessive oil, you might be able to visually see some signs, depending on the blow by. Look at the valve covers (but distinguish b/w condensation and leak), take out the plugs, see if oil is pooled and if the plugs are fouled/soaked in oil. Take off the upper plenum and see if there is a lot of oil pooled in the plenum. These are just some suggestions, I am by no means an expert, there may be other/better ways to determine excessive oil consumption.

But, I think, according to Infiniti/Nissan dealers, the only approved way to determine oil consumption is through testing oil levels over a period of time.

 

Try searching "revup" ( late '05-06 ) some of them had oil consumption issues. Read a thread on the other site in the OZ section. Nissan Australia did a test ( sealed up the engine ) found it was using and replaced the long motor.

 

easy way to tell is to test drive it and get on it... If it blows black smoke guess what, oil is being leaked somewhere... If it doesn't and you buy it, then you broke and let the tear down begin.

 

Black smoke usually just means an overly rich mixture. Grey / blue smoke is oil.

On the compression test, you really don't want to see any more than a 15psi spread across the cylinders. But leakage from a number of places could cause a bad compression test ( bad valves, rings etc. ) best to do a cylinder leak down test if your compression test reveals sub-par results.