What are the contributing factors to an engine burning oil?

[nnorton44]

I have an '01 QX4 with 159,000 miles with a lot of engine problems. I am trying to fix them one by one and havent gotten far. But anyways, I have noticed within the last few months that when my car idles it emits big clouds of black smoke. I can tell its burning oil. I do know that the previous owner did go 15,000 miles without an oil change. Is my engine on its last legs?

[SnowSurfLax]

Black smoke should mean too much fuel. Oil burns and emits blue-ish white smoke. Is the CEL light on? I'd assume your MAF to blame w/o knowing any other details.

Engine should be fine though, even a 15K oil change shouldn't affect it.

[Buzzman]

Burning oil usually creates blue smoke, not black.What is your oil consumption like? Are you using a lot?15K without an oil change, especially on an older engine, is definitely not good. What about the power? Have you lost any get up and go?What's your gas mileage like? Lots to think about here.I also presume it's the 3.5 engine?Also, do you have any service history on this truck? Like when was the last time the plugs were changed, that sort of thing.Good luck.

[nnorton44]

Horrible service history, previous owner destroyed it. Car is running P0300 random cylinder misfire and P1320. Spark plugs never changed. When car idles it dies. Thinking of replacing ignition coilts and MAF.

3.5 engine, loss of power and horrible drive.

[bmlawless]

Blue smoke = oil, black = fuel, white = water. As long as you don't have white, you can still drive it.

It's OK to use some oil. My wife's Rabbit has almost 300,000 miles and uses/leaks almost a quart between oil changes. The trick is that she has been changing the oil religiously since 1985. Although it isn't good to let the oil go 15,000 miles without a change, that won't kill an engine on it's own.

Your smoke, codes, and crummy idle are all related. Fix those and you should have a decent running rig. If you are still burning a little oil and it is not noticable, don't worry about it at 159,000 miles. Just change the oil at the proper intervals and keep an eye on the levels.

[SteveTheTech]

Blue smoke = oil, black = fuel, white = water. As long as you don't have white, you can still drive it.

15 grand between oil changes will severely damage a 3.5. IMO I would look into scrapping the motor and saving the money and just buying a new one.

Sludge builds up on neglected 3.5s inside the VTC passages and causes all type of drivability concern.

Sorry to be the bearer of bad news but it would be worse to dump money and just be postponing the enevidable.

[nnorton44]

Yeah when I changed the oil it was nasty black almost sludgy, but based on the fact that I got a good deal on the car, $500, its worth putting some money into.

Ignition coils are only $200 for a set of 6 and the MAF is $80, so I might as well invest in fixing it.

Ive been debating on whether to fix it and sell it, but I love SUVs and the Q is a great car.

I have a friend who works on BMWs all the time and is pretty good with cars so we are gonna try and replace the coils and MAF and plugs.

[SteveTheTech]

The things that you have mentioned there are pretty easy repairs and you can find threads here that tell you exactly how to do them.

The black sludgy crap is not a good sign, having an engine cleaner run through the motor may give you some time but the future is not so bright for your 3.5. If you are interested in keeping it as they are great vehicles. I would take it somewhere and get it professionally evaluated by someone who deals with Infinitis on a regular basis. Having the ability to connect a Consult to the vehicle will give the technician a good idea of the current condition of your truck.

[nnorton44]

Since purchasing it I have been changing the oil every 1,500 miles and it runs better every oil change. As far as what you said with the motor being replaced, how much is an estimate of cost and, should I rebuild or replace?

[SteveTheTech]

That is a good start. I do not want to say to any conclusion what your next action should be as I cannot judge the condition of your engine. There are many commercial products on the market to clean out engine deposits. Most of them use a kerosene smelling chemical to remove harmful engine deposits, now this is not a guarantee but it may be something to look into.

I would still recommend getting it professionally evaluated by an Infiniti dealer. If you are willing to pay for a good ours check out and have them give you a detailed estimate of what will be needed to get this truck up to peak performance you should be able to judge just how invested you want to get.

As for a motor replacement estimate I think there are far too many variables to give an acurate estimate over the internet. I do not know where you will have it serviced, and a what labor rate they will charge for however many hours it will take them. Also the cost of the engine needs to be taken into account depending on where you choose to get will will have a significant effect on cost. A junk yard engine will be cheaper, but used. Most of them do have a warranty and some even have warranties on parts and labor. Do some research and see what works for you.

Since your motor already has over 150,000 miles it is already past it's useful life and the life expectancy that it was manufactured achieve. Hopefully your engine will be able to be saved just keep in mind that it is already pretty used.