Engine worries 3lt 16v

[colin944]

I have a strange issue with my engine. Its a bit smoky..... mostly at high revs but also a bit on start up. Ive just changed the seals on the AOS and checked the breather. I even fitted another aos from a car that didn't smoke.
When the car was off the road getting its rebuild, I replaced the head gasket and re ground the valves. I also replaced the valve stem oil seals while I was there. I checked the bores at the time and there was no evidence of bore score.
The car used to give a wee puff at high revs before I put it off the road but not anywhere near what I get now. ( its not like James bond but you can see the puff in the mirror when your accelerating hard.
I've done a compression test and the results were good and consistent across the four cylinders.
Another piece of important information is that I inadvertently over filled it with oil by about a liter-ish. I then took it for a bast round the industrial estate where my garage was and got a huge cloud of white smoke.I instantly dipped the clutch and the car idled normally. I drove it back to the garage slowly ( only about half a mile ) and switched it off. I drained some of the oil after realizing what had happened. ( I said I needed to add oil and my mate did it with out telling me, I then added more without checking and over filled it. ) The car then wouldn't run until I changed the plugs. I think the oil killed them. Ever since then it has smoked a bit.I also put some Wynns lifter treatment in it as I had a noisy tappet ( now quietened down ). so i wonder if the thinning effect of the treatment could be making it worse or is there another reason. Could I have blown a seal some where? eg Valve stem oil seals. The car runs really well apart from this issue and to be honest its more annoying than serious but I would be grateful for a bit of advice before I pull the engine out and send it for a rebuild or stick another in.

Thoughts ?

I know some of you on here really know these engines well.

 

[vitesse]

Before doing anything drastic, I would drain the oil ,into a clean container-then check that the dipstick is locating properly & that the dipstick tube itself is also correctly located & then refill the engine using a calibrated jug /whatever with 1/2 litre less oil than the correct capacity.
Check with the dipstick & if the level is over the bottom mark,try the engine & if ok,top up but slightly below the top mark.

 

[colin944]

I'll try that. But it was over a year ago that I over filled it and its been down below the max mark a few times since then.I did however replace the dipstick tube as I lost it during the cars rebuild.

 

[bmnelsc]

I wonder if this is not similar to the oil overfill problems with 911s where overfill results in oil in the intake tract and eventually building up in the exhaust produces lots of smoke. If your overfill overpowered the OAS then I assume it is possible. Your description of fouled spark plugs leads me to this train of thought. The remedy for 911s is to correct the oil level and then you have to drive it to burn off the excess oil in the intake and exhaust sides which eventually clears up the problem.

I don't see how overfilling could cause a problem with valve seals, etc as they are not exposed to pressurized oil, etc. If you still have a cat. converter installed, the excess oil in the intake side could ruin your converter - the oil interfering with the exhaust gas reaction. Oil build up in the muffler will eventually burn off.

Hopefully its as simple as that - let us know how you get on.

 

[colin944]

No more answers ?

 

[George Elliott]

Colin,

"I dont know is not much use as an answer", but it may be true........

Not sure how well I know the engines. They are fundamentally different to a dry sump 911 though

The valve stem oil seals could cause it, but you have sorted them

The compression test tells us the piston rings and bores are good

AOS breathing correctly, thats important and you have sorted it

I follow your logic all the way........

My thoughts are what happened when the overfill caused the white smoke cloud. The white smoke came from the combustion chamber, it wrecked the plugs on the way through, it would not burn like fuel, and so you had the smoke cloud, so how'd it get in there.......

Answer: "at high revs" gives a clue...

My guess is the higher oil level, plus the high RPM, combined to create a situation where the AOS was dealing with both excessive oil splash and maximum crankcase breathing, and maximum intake vacuum (air can come thru the air-filter or from the crankcase blow-by) and this worst case scenario created the perfect storm, and you got maybe a cup full of oil into the intake and thru the engine.....

In my mind that could all happen, but should cause no lasting harm given your response.

But, its not that simple as you have an outstanding problem.....

So, what else could have happened that would leave a small irritating oil burn from the engine under load....

Could the situation where the engine took a gulp of oil thru the AOS have coincided with a momentary crankcase pressure peak which damaged a Piston Ring Oil Seal? or displaced a valve stem oil seal? or displaced an AOS seal....maybe you saw weep-age from these? that would suggest pressure in the crank case where there should only be negative pressure. The seals are only designed for minimal and usually negative pressures.

Could the valve stem seals move easily with a pressure spike from inside the cam housing??

Is there an intake manifold "oil trap" which is holding some of that overfill gulp of oil?

As I said, I don't know really

If all else fails, stick a turbo on it

good luck
George
944t

 

[GPF]

ORIGINAL: colin944

I'll try that. But it was over a year ago that I over filled it and its been down below the max mark a few times since then.I did however replace the dipstick tube as I lost it during the cars rebuild.

I wonder if the overfill is a bit of a red herring.

If it has "been down below the max mark a few times since then" it is clearly been getting through some oil in the last year , and given it's not a turbo, could it be that it's just burning it now?

What exactly was the rebuild you refer to and how long ago? The compression test is useful but not conclusive - a proper leak down test done by someone who really understands them would be a good idea I think.

Also, you say you replaced the valve stem oil seals as a matter of course when you did the head gasket, but what about the valve guides themselves? If they are overly worn you will be burning oil.

Finally, you say that you lost the dipstick tube and fitted a new one. I don't know these engines but is it possible there is more than one dipstick/tube combination and you have a tube that sits a bit too high for the dipstick so the levels are out? Long shot, but have come across that on other engines.

 

[colin944]

I'm going to change the oil in it tomorrow and treat it to a set of plugs ( bosch 4 pin) and see if that makes any difference. I'll keep you posted.

 

[colin944]

A quick update from yesterday.Last weekend I did the AOS oil seals and the seal on the filler cap this weekend I changed the oil and the plugs. When I drained the oil it came out like water, I think the Wynn's cylinder head treatment I put in has really thinned the oil down. I replaced the oil and filter and fitted a set of Bosch 4 oin plugs. The car still smokes at very high revs but no where near as much. It may just be clearing oil from the breather etc that's lying in there.So overall a big improvement. I'll keep you posted.