How many ways can oil get burned off?

[jtsarnak]

Hey guys. I have a '95 240sx SE with auto trans. I have a problem where my car is eating a quart of oil about every 150 miles or so. The engine was just recently rebuilt and I know there's some break-in time, but I've put over 2000 miles on it now and it still consumes a lot of oil.

I get a brownish smoke coming from the exhaust when I push it above 4k or so, but most of the time I see no visibile smoke. I also can't find any place where I am leaking oil.

So my question is, could I be burning a little oil at a time so that I don't see visible smoke when there's no real load on the engine and still be losing oil that quickly? What are all the possible scenarios that oil can get into the cylinders or otherwise be burned off? I am now questioning whether this engine was rebuilt properly. Please help!

[:: orion ::]

Sounds like the rings are not sealing...

Do a compression test, see what that turns up.

If it looks normal (+179psi per cylinder, max difference of 14psi), then perform a leakdown and see if the valves are to blame.

- Brian

[jtsarnak]

Yeah, I need to get on that compression test. What is a leak down test? Is it expensive to have done? I don't have these kinds of tools handy so someone would have to do it for me.

Also, any other guesses if it's not a ring or valve seal?

[InsanityInc]

if oil smoke is coming out your tailpipe, then those are probably the only reasonable causes if the engine otherwise runs fine.

[jtsarnak]

I guess that's my problem. I have always been told that oil smoke is blue in color or white/blue. This looks like brown smoke, almost like I am running rich (which could very well be).

The reason I think it's oil smoke is because the oil is disappearing. Is there anywhere else for it to go?

[Darius]

You're not leaking it are you?

[:: orion ::]

Compression test take a $20 gauge you can get at any car part store.

To do a compression test, you:

1) pull all the plugs

2) Pull the fuel pump fuse and distributor main wire.

3) Test each cylinder, while holding the throttle wide open.

Report the results to us.

- Brian

[jtsarnak]

So I finally had time to get the car checked out and had my mechanic do a compression and leak down test.

Compression checked out, 175-180 across the board.

Leak down showed 8% leakdown in cylinders 2-4 but 20% in cylinder 1.

So something is up in cylinder 1, any ideas?

[:: orion ::]

You could check the shim clearance for the valves...use a feeler gauge between the cam base lobe and the shim...should be between .013-.016".

Any tighter and it could be holding the valve open ever so slightly and allowing air out there...

BUT...

That DOES NOT explain burning oil, and with a valve like that, compression will usually be lower.

Still sounds like ring sealing to me...

??? - Brian

[250sx]

valve seals maybe? that leakdown test sounds like it too

[InsanityInc]

if the rings weren't seating, he would have bad compression as well.

The only thing I can figure is that somehow oil is getting into your intake air because of some problem.

[toptechracing]

PCV system?

[gumby]

either that or out the valve cover, which would get sucked into #1, but how could that be? would that mess up the ring seating?

(im guessing)

[jtsarnak]

Several things:

I opened up the throttle plate and took a little look around and nothing out of the ordinary showed up. It was dirty, but not oily wet looking. If it was coming in through the intake, it could be further downstream, but I don't know.

My mechanic indicated that I could still have good compression with a ring problem because the compression ring could be fine and doing its job but the other rings may not be.

My mechanic also said that he looked down the spark plug holes and could see oil residue heavier in the first cylinder (the one with more leakdown) but that there was residue in all cylinders. This doesn't necessarily mean I'm burning in all cylinders. I could be burning in 1 and then recirculating oily exhaust gases into the other cylinders through the EGR system. It could also be build up from when the timing chain was off 2 links and it was smoking like a chimney.

Finally, I have a slightly shaky idle after the car has been run about 20 minutes.

I'm going to get in contact with the machine shop that did the block/head work this week and figure out a plan of recourse, but any further insight would be appreciated.

(or if you want a really nice chassis/body for an SR swap, I'll sell it to ya )