Smokey when cold

[noneil]

After sitting for a few days last weekend my car was chucking out loads of bluish smoke out of the exhaust until the engine has warmed up; the oil pressure was also noticable higher than normal, again until warmed up.

It did this again this weekend after it had been sitting for a week but was fine on the way home on the same day.

Is oil leaking interally somwhere? It did use a bit of oil before, but this change seems to have come out of nowhere . . .

Cheers,

Neil

 

[delboy1974del]

This is a sign of worn piston rings


Basically what happens is when you start your engine from cold the rings are not sealing in the bore as they are worn .
As the crank turns the pistons move up and down heating up the metal and causing it to expand
When they expand they seal in the bore and dont allow oil to pass by them and get burnt thats why it stops smoking after a while and only smokes when cold

[]

 

[944Turbo]

unless its steam, has the car been outside more or shorter runs than before? Has the oil use gone up?
Tony

 

[delboy1974del]

Changing the rings is a big un btw

Either the rings are worn or the bore itself is worn

If the bore is worn you need a rebore and oversized pistons (which i'm not sure i ever supplied in my time as an engine reconditioner parts supplier so dont know id they were ever made)

If its rings you need to sort out why they wore down

Overfuelling is a major cause (the fuel washes the oil off the bore and starves it of lubrication)
Also letting the car idle for long periods of time (taxis on the rank suffer greatly from this ) this causes insufficiant oil pressure as the engine isnt under load and lack of oil wears down the rings

Youll need to change the big ends to cope with new rings . . . and thats just a start !!!

 

[Wardy 944]

Sounds more like valve stem oil seals to me.

Still not a easy job, head off, remove valves, replace seals (you'll need a head-set), and re-fit

A few car manufactures have cunning tools that allows you to change the seals with the head still fitted, I'm not sure if Porsche do one, worth a look.

 

[noneil]

OK, well it sounds like bad news or bad news . . .

Not that I'm ungrateful for the advice though []

In answer to your questions Tony the car lives outside more and has regularly been on longer runs than before; the oil usage doesn't seem to have changed.

Delboy and Darren - is there anyway to distinguish between worn piston rings, bore or valve stem seals short of taking the thing to bits?

I quite enjoy playing with oily bits, but the costs of new oily bits can be pretty scary, and this is my only car . . . !

Cheers,

Neil

 

[944Turbo]

Is it smelly? the exhausts can store huge amounts of water which will evaporate as steam as the engine warms from cold, especially noticeable if stored outside in damp conditions. Oil smoke is smelly, stream isn't.
Tony

 

[Wardy 944]

1. When the valve stem oil seals leak, oil drips onto the valves and makes its way into the combustion chamber, when you start the car it will smoke until the oil has been burnt away this could take a few seconds or a few minutes depending how bad they are.

2. With worn rings/bores the smoke will not clear no matter how long you wait, in fact as the engine gets hotter and the oil thinner it could actually get worse.

Which one best descibes the symptoms 1 or 2? *






*or it could be a combination of the two, or something entirely different []

 

[delboy1974del]

what makes you think valve seals ?

valve seals would fail under load would they not and rings when contracted when cold ??

 

[Suffolk944]

Sounds like it could well be the valve stems if it clears after a while rather than the piston rings. Still a considerable job but much less of a one than worn bores ! Just had mine done while having the new turbo fitted.

 

[vincematthews]

ORIGINAL: delboy1974del If the bore is worn you need a rebore and oversized pistons (which i'm not sure i ever supplied in my time as an engine reconditioner parts supplier so dont know id they were ever made)

PET lists only 1 oversize in 3 tolerance classes, either 'Porsche' or Mahle . . . . but don't know about availability

 

[noneil]

I ddn't notice it being particularly smelly but the smoke seemed too thick for steam; the weather last week wasn't particularly damp and the symptoms were link to the increase in oil pressure.

I took the car out briefly after my original post and it was all clear. I imagine both failing piston rings and valve stem seals will be smoking all the time, not after sitting for more than 2 days.

Incidentally Darren is sounds more like option 1, but both your description of that and Delboy's of piston ring failure seem to make sense . . . [&:]

Cheers,

Neil

 

[Indi9xx]

To test for worn valve guides or stem seals.. drive the car until its warm... ideally on a motorway... select a gear where your running it about 60mph and at 3000 rpm, accelerate up to 6000 rpm and completely lift off the throttle quickly... let the car engine brake down to 2000 rpm while checking your mirrors and then accelerate again.. if you get blue smoke during the engine braking or re-accelerating, its probably the valve guides or stem seals.

Ideally, get a leak-down and compression test performed on the car to be sure.

 

[Suffolk944]

ORIGINAL: Indi9xx

To test for worn valve guides or stem seals.. drive the car until its warm... ideally on a motorway... select a gear where your running it about 60mph and at 3000 rpm, accelerate up to 6000 rpm and completely lift off the throttle quickly... let the car engine brake down to 2000 rpm while checking your mirrors and then accelerate again.. if you get blue smoke during the engine braking or re-accelerating, its probably the valve guides or stem seals.

Yup thats what I had and it was indeed the valve stems, bores etc were fine.