Burning oil problem

[Robbyd]

I recently bought a 98 gst and it ran kinda low on oil enough for the light to flash on. So I put more in it and then it started burning a decent amount of oil only when I'm engine breaking, decelerating. But not when I'm in boost or anything. Just curious what would cause this, if it will be serious or what. Hopping its not bottom end, and can't be the turbo cause its not burning when accelerating. Smoke is whitish blue.

Any help would be awesome thank you

 

[weep87]

check the turbo for shaft play...

 

[DSM1G90]

You might have scorched the cylinder walls when oil pressure was too low to now allow oil to go past by the rings and being burnt off due to the massive increased vacuum in the intake manifold when you let off the gas and the throttle plate is closed-which you see when you engine brake or de-accelerate.

A bottom end rebuild is in order to eliminate this burning.

Turbo has nothing to do with this condition.

 

[Robbyd]

Can I tell if that's it by doing a compressions test?

 

[luv2rallye]

A leak down test would be more beneficial.

 

[Robbyd]

What's that?

 

[needbooost]

I know this isnt what you wanna hear but in my experience this is caused by failing ring lands. Do a compression test dry and then try it with just a little oil to determin bad rings. All cylinders should be within 25% range of each other.

 

[dsmcurse]

those symptoms sound like leaky valve guide seals to me. thats where i would start. at least the valve seals arent super expensive or major surgery to change out.

 

[needbooost]

Does your car let out a little smoke or does a cloud follow you?

 

[Robbyd]

That's what came to mind for me, bad valve seals. Which in the end I'm hoping its something with the head. If not I have to make the decision to sell it or swap a 6bolt in. And if I am just coming out of boost its a little more smoke but usually it's just a small cloud not to thick.

 

[luv2rallye]

Here's an excellent article on compression vs leak down tests - what they are and do, step by step proceedure on how to do each, and results interpretation: http://www.dsmtuners.com/forums/articles-engine-fuel/338152-compression-leak-down-testing.html.

 

[luv2rallye]

Do a compression test dry and then try it with just a little oil to determin bad rings.

For first timers, dry does not mean a cold engine. It means a warm engine without adding oil. Compression tests (and leak down tests) are done on a warmed up engine.

 

[Robbyd]

Also the longer I de-accelerate the thicker the smoke gets. Just put my exhaust back together and it's not as bad now, I was running just straight downpipe. But ill get to both the tests this weekend, if I can find that tool. Do you think most likely it's the valves?

 

[dsmcurse]

on decell when your totally coasting like in third or second gear and the revs are up but there is no load on the engine and your maintaining speed like down a hill, then at the bottom of the hill and you step on the gas and poof! blue oil smoke burns out. from my own experience that has always been valve guide seals.

on a in-line four cylinder changing valve seals aint to tricky. if you turn the number one piston to its very top of stroke it makes it safe to work on 8 of the 16 valves. the four valve directly above piston one and four can all be worked on. after changing those 8 valve guide seals you can then turn piston one to its very bottom of stroke which in turns brings piston two and three up to their very most top of stroke. with cylinders two and three at its up most you can now change those 8 valve seals.

the reason piston has to be at top of course is because if they were at the bottom of stroke and you dissconnected the retainer/keepers the valve would drop down into the bore and you'd be SOL. people make a spark plug replacement thingy that allows you to pump shop air into it and hold the valve up while you service its seal. I DO NOT TRUST THAT METHOD.

with the piston at the top of its stroke the valve will come down (not very much at all) and rest on top of the piston, change the valve guide seal, then re-install the retainer/keepers. (yes you will have to push the valve spring in another mm or to to compensate for the valve being a tiny bit lower.

some people say "i dont want metal to metal contact in there and have my bottom of valve pushin hard aginst my piston top as i try to reconnect the keeper"
for this its possible to take 3/16" nylon rope/string and carefully coil it down the spark plug hole (plug removed of course...duh) then as the piston is brought up to top of stroke it has nylon string in between the piston and valve. the string provides cushion for the valve and also makes it so it wont drop down that extra mm or two. putting the keepers back on are a breeze when you dont have to muscle down a crower titanium spring another mm.

it sounds whacky but it works damn good like that method. change valve seals with head on a car, not head on a work bench.

dont over look your valve seals, and dont be affraid to change 'em

 

[Robbyd]

But that's not what's happening, see if I was in full vaccume engine breaking down the hill I would be burning oil and the long I kept it there the more I'd burn. If I kept it at no load I would burn none that's noticeable, same with when I'm in boost.