Porsche Enthusiasts Club Forum

Last year the head gasket went on my 93 968 Tip, so it went into my local indie to get fixed along with a boat load of other things that had been planned. When I got the car back it drove beautifully and I was very happy with its performance and pick-up. I had hoped that fuel consumption would have improved, but this seems to have changed little. The one thing that has changed is the oil consumption, that appears to have gone through the roof.

When the head gasket was done, the head was skimmed, the values ground and re-seated, but the guides left as were, as they hadn't worn. The car was filled with Mobil 1 fully synthetic 10w 60, but is now getting through oil like never before. Over the past 3 years I've probably only done 2-3000 miles a year, and although I occasionally had to top it up, I probably didn't put much more than 1/2 a litre in between services. Over the last 1450 miles the oil light has come on 3 times, forcing me to stop and top it up. As of today, I've added at least 1 1/2 litres, around 5-6 times the amount I used to add.

When accelerating from cold it's easy to see the oil being burnt off, as I can see whitish smoke behind me. Not a lot, but enough to be embarrassed that my car isn't as perfect as I'd like it to be. Once the engine has warmed up there is no sign of any oil being burnt (from drivers seat that is). At fast motorway speeds the oil pressure is at 5, around 60 it's 4 1/2 and at hot idle it's 3 1/2.

I'm trying to understand the logic of the increased oil consumption and am wondering if it's a side effect of fixing the head or something that was missed when the work was done. Something that was missed also includes the opportunity to fix something or replace something that would have been wise to do when everything was apart.

I use a reputable indie and will take it back to them to resolve, but would appreciate some input before speaking with them.

Thanks in advance,

RDO

I've booked the car in, for early June, but if anyone has any ideas I'd be interested in hearing your feedback/theories.

All the best,

RDO

Have you just started using Mobil 1 since the rebuild it may be too viscous, i use a good quality 10/40 semi, another point is that when the engine is cold it is not a good idea to accelerate hard as this is the point at when all your engine wear is occurring.
Cheers Jim

Hi Jim,

I appreciate that I'm not supposed to drive it hard when cold , and that certainly does account for some of the oil, but it's getting through a lot on long journeys too. Having said that I didn't get the white smoke before the head gasket was replaced and the head fixed.

Another thing I thought of afterwards is that the car used to run on Mobil 1 fully synthetic 15w/50, so that's another change/factor, just not sure the two together can account for the oil consumption.

All the best,

RDO

If your car still has a cat, which I assume it has, this will explain the oil not being visible when it has warmed up, as the catalytic converter will be working overtime converting the hydrocarbons of the excess oil into water vapour among other things.

If you had said the oil smoke was on accelloration just after engine braking I would be tempted to blame the valve guides, however you did not mention this, so I suspect it is not the guides.

I would recommend the indi puts a borescope or endoscope down the spark plug holes and inspect the bores, as well as a compression AND leakdown test... I hate to say this, but I predict scored bores.

If when your head gasket blew, it got hot, then it is possible that the pistons expanded faster than the bores, which they can do when the coolant goes above 100 degrees, and they have picked up on the bores causing scores, which trap oil which is not wiped by the oil control ring, causing heavy oil consumption.

However these same scores, in this scenario, would have been visible while the head was off, which knowing your specialist, would be odd for them to miss...

Are you sure the valve guides and valve stems were still within spec when they had the head off? That is really unusual, as then tend to be outside of Porsche tolerances within 20k miles no matter how the car is driven.

The only other worry, is most engineering shops do not strip down and clean the head completely (including the oil one way valve) during or following a skim, which can lead to some swarf still being present during assembly, which can eat into bores very quickly. if not via the combusion chamber, but as they drain back into the oil pan and remain trapped in the sump, being thrown into the underside of the bores and therefore causing havock between the piston skirts and bore.

Good luck, let us know if you need more help

Hi Jon,

Thanks for the feedback. I was hoping you'd respond, but I guess I was hoping for something that
wasn't going to result in another remortgage.

I'll let you know the outcome, in early June, when my local indie has had a chance to look at it.

I don't know if this is relevant, but when I start the car from cold the oil pressure gauge pauses a bit
before shooting up. I don't recall it being like that before the work was done.

All the best,

RDO

You don't mention if you had the valve stem oil seals changed when the valves were lapped in if not then maybe your oil usage is linked to this.

But he wrote "The car was filled with Mobil 1 fully synthetic 10w 60" which is thicker than 10W/40!!!!

I have seen this after rebuilds when the carbon is scraped from the tops of pistons, where previously it formed a seal. Also the carbon can score the bores & increase oil consumtion that way.
As Jon says a compression test/borescope would be a good idea to see what is going on. What state are the plugs in, oiled?

Hi David,

I've checked the invoice, but don't see anything on the parts list that sounds like a valve stem oil seal.

I know this is a little unrelated and possibly out of the park, but the crankshaft rear main oil seal was replaced. I only mention this because it was the last of the oil leaks to be fixed, so the engine is now oil tight so to speak. Maybe there is a pressure build up somewhere and oil is being forced past the pistons instead of being able to escape the old way. Having said that it never got through much oil before.

Thanks to everyone for your interest.

All the best,

RDO

I would have hoped if the head was skimmed and valves lapped then the valve stem seals should have been changed, it is recommended to be done and could be a source of how the oil is getting into the pistons, you could also check the crank breather hose to see if that is blocked as that could cause a back pressure and oil to pass back through the seals.

Thanks David.

I'll give the garage a few pointers when I drop the car off in 3 weeks time. They may even think I know what I'm talking about.

only just read this post, how did you get on ?

Whilst scored bores would increase oil consumption, they should not increase it to those levels IMO. My old S2 for instance is not the heaviest oil consuming engine and the bores on that were definitely shot (it would even rattle upon being revved would the pistons).

A leakdown test should be able to narrow down any other areas of wear present in the engine, although a wet compression test should be doable by most people. TR7V8 does have a point with carbon buildup. It may be worth checking the breather hoses just in case. I would be tempted to go iffy valve guides or breather issues (either due to them being blocked or an issue when the head was apart (an oilway for instance).

What were the results of the outcome though?

Hi Jase & Chas,

Since my last post there hasn't been much progress in terms of getting the problem resolved. The car went back in and the oil stem seals were replaced as the garage wasn't 100% happy with how they looked. They had been replaced as part of the head refurbishment, by the engineering company that my local indie uses, so they should have been good.

I was then asked to drive the car for 500 miles and report back. After 600 miles there was no noticeable improvement and by my calculations the car is now using approximately 3 litres of oil per 1000 miles.

The car went back in again and a leak down test showed that air is now escaping past the cylinders and it can be heard if you listen through the oil filler cap. When it originally went back in after 1450 the leak down test was good, so over the past 600 miles is sounds like the situation has got worse. When they put a boroscope through the spark plug holes they saw a difference in colours on the cylinder bores, that wasn't apparent when they last had the head off, and this is where the fun starts.

Until the head comes back off (for the third time) we're not going to know exactly what the problem is. On the two previous occasions that the head was off the garage never noticed any problems with the bores, but it is possible that when the head gasket went, the coolant washed the lubricant from the bores which allowed the pistons to remove the silicon coating that protects them and further use of the car damaged the bores, but to be honest this is all guess work at this point.

The garage has checked the oil breather and everything appears to be fine there so that sort of leaves:
1. The piston rings.
2. The bores.

Of the two replacing the piston rings seems to be the cheaper option by a long way as replacing the crank case or re-coating the bores is both time consuming and very expensive (engine out job).

I've decided to go ahead with the work, but due to the cost I have to find some money first. Once I've got say 50% of the worst case scenario that's been quoted to me I'll book it in.

If I'm lucky I'll get it in before the end of the month.

The car is quite driveable, performs very well, but drinks way too much oil.

All the best,

RDO