The curious case of the vanishing oil...

espresso

Some more ideas here.

pulliptears

Other half just emailed me this, a little more detail hopefully!

Car runs fine, no misfire, no knocking, and no lack of power – he says 4th gear is a bit sluggish but it picks up well in 5th - and no smoking from exhaust. There is no oil in the water or vice-versa. There is no soapy residue on the filler cap but the top to the expansion tank does smell a little of burnt petrol – I know petrol won't be in here but that's the best description I can think of – but not the normal head gasket failure smell.

The main issue he's got is that he has to fill up between half a litre and a litre of oil every 2-3 days after travelling no more than 100 miles in that time; otherwise the oil level low light comes on. It's not a faulty oil switch as the oil is at the bottom of the dipstick or not there at all. Curiously the oil is a shiny silver colour – rather than dirty black or clear yellowy-orange - on the bottom of the dipstick but with it being filled so regularly I don't think it's unusual as the new oil mixes with the older oil still in the sump. He's using the recommended 5w30 fully synthetic to top up.

We've tried removing the oil filler cap with the engine running and the revs drop to almost stalling, put cap back on and revs return to normal tick-over.

He first noticed the problem when he had a large amount of white smoke pulling off at a roundabout, there was that much smoke he thought he'd used the wrong fuel at first but checked his receipt and it was correct. It cleared after little more than a second, and only returns on start-up and when the engine is first started. The car had stood for a month prior to this journey so may be something or nothing.

I'd think if it was valve seals or piston rings that the oil would have to be free-flowing past and down the exhaust to lose the amount he is but the exhaust fumes are quite clear and there's no liquid, either water or oil, coming out of the exhaust.

espresso

pulliptears wrote: »

We've tried removing the oil filler cap with the engine running and the revs drop to almost stalling, put cap back on and revs return to normal tick-over.

He first noticed the problem when he had a large amount of white smoke pulling off at a roundabout, there was that much smoke he thought he'd used the wrong fuel at first but checked his receipt and it was correct. It cleared after little more than a second, and only returns on start-up and when the engine is first started.

Check the crankcase breather pipes etc.

pulliptears

espresso wrote: »

Some more ideas here.

Interesting, and seems to describe the problem! Also interesting is the comment about the servicing being scrimped on, I do get the feeling the car has probably been a little neglected before DS bought it, it had stood for a month as well.

Will try the cardboard box trick tonight, hopefully it will fit in the garage and Ill park my car on the road. Will give us more clues before it goes in on Thursday.

gilbert_and_sullivan

Assume we have no signs in the water of oil staining?

If the oil was being blown out there should be oil strewn up the underside of the car as it gets blown back, has he looked?

My own suspicion is valve stem seals and valve guide wear, a good way to check this is to let the car overrun..no throttle...for a time such as down a long hill, this will suck oil down through the valve guides if it can.

Then don't actually come to a stop but boot the throttle and watch out the back, if valve guides there should a fair plume of smoke as any excess oil is burnt off.

If general engine wear/piston rings the thing should be smoking all the time especially under power and taking the oil filler cap off whilst the engine is ticking over should reveal smoke and excess pressure in the crankcase.

pulliptears

gilbert_and_sullivan wrote: »

Assume we have no signs in the water of oil staining?

No, not at all.

If the oil was being blown out there should be oil strewn up the underside of the car as it gets blown back, has he looked?

Couldn't see any, but to be honest we didn't suspect a leak at the time with their being no obvious oil patches under the car, now we know that they arent necessarily visible we need to get the car up on the jack again and have a good look.


My own suspicion is valve stem seals and valve guide wear, a good way to check this is to let the car overrun..no throttle...for a time such as down a long hill, this will suck oil down through the valve guides if it can.

Then don't actually come to a stop but boot the throttle and watch out the back, if valve guides there should a fair plume of smoke as any excess oil is burnt off.

If general engine wear/piston rings the thing should be smoking all the time especially under power and taking the oil filler cap off whilst the engine is ticking over should reveal smoke and excess pressure in the crankcase.

Valve seals were my first thought, I'll send the OH out tonight to try your test. Certainly not smoking all the time, and to be honest its not always smoking on startup.

We'd budgeted for Valve seals as a worse case scenario with it anyway so anything simpler would be nice now

Strider590

pulliptears wrote: »

Checked the plugs yesterday, OH said they were the worst looking plugs he'd ever seen in his life, but by the time he'd discovered this it was too late to do anything other than clean them up. DS should be picking up a new set on his way home from work. OH didn't see any oil, but will double check when the new plugs go in later.

Plugs are one of those things that rarely get changed with servicing, mechanics quite often don't bother, not worth the risk of snapping one off. Plus on most cars they're hard to get to....

pulliptears

Strider590 wrote: »

Plugs are one of those things that rarely get changed with servicing, mechanics quite often don't bother, not worth the risk of snapping one off. Plus on most cars they're hard to get to....

Really? Is it just me that enjoys stripping plugs out and cleaning them of a Sunday afternoon? lol
I think I must be weird.

That said, I've got a cross threaded one on the TR7 thats been the bane of my life for 2 years

New plugs going on later anyway so thats one less thing to consider.

s_b

a compression test is the only way forward

pulliptears

Currently working on the theory that the sump is either cracked or the seal has gone. As soon as the boy gets home from work we are going to get it jacked and have a look...