Oil consumption and when to overhaul

[Decolliber]

I have been monitoring my Carrera's oil consumption for over a year now, and have added a quart of oil, on average, about every 500-600 miles. I know this is on the high side, but the car runs well otherwise, and oil is cheaper than overhauls. I have several questions:
1. Is there danger that by putting off an overhaul, the eventual cost might be higher, because a component (valve stems?) will fail?
2. What would a typical top overhaul entail, other than new valve guides, in my case? Pistons & rings? Valves? What else?
3. What price to expect. I have called a few places in the Chicago area and been given quotes that range from about $2500 (Fischer) to over $6000 (Motor Werks in Barrington). Does this simply reflect different assumptions about what they would do?
4. Nominal mileage on my 88 Carrera is 68K, but I know that is not accurate; real mileage is probably closer to 100K. I recall that Anderson says in his book that once you get up to that mileage, it does not make sense to just do a top overhaul, and you should bite the bullet and have a full overhaul done.
5. What would normally be done in a full overhaul?
6. My clutch is not slipping, as far as I can tell, but since I have no prior service history on my car, I wonder if I should have the clutch changed while the engine is out, given that much of the cost is labour in removing the engine. Can a clutch be easily inspected for wear, with the engine out?

These are a lot of questions, and I am still at the musing stage, and in no hurry. In addition, if anyone has any particular recommendations for a mechanic to do this kind of work, in the Chicago area, I would be grateful for suggestions.

And if 993s are now in the mid $30Ks, perhaps I should just forget the overhaul and sell it for a 993! Or maybe a '93 or '94 964.

[Early_S_Man]

John,

I don't think a qt per 600 miles is HIGH ... it is just at the point where you need to take notice and start thinking about options! At twice that rate you need to take the engine down. The spec book allowable figure is 1.5-2 liters per 1000 km, or 620 miles.

You can't really make any assumptions about what any shop WOULD do ... get an itemized estimate, then you can compare with alternative shops, or doing the job yourself!

If you wait too long, then the expensive WHUMP you hear one day will be the destruction of your engine due to a dropped valve ... THAT does tend to get expensive!

[Jack Olsen]

You might also want to pinpoint where the oil is going. If it's all being burned, that's one thing. But if you've got a leak in the external cooler loop, you might be dripping the stuff out -- but never seeing drops on the garage floor.

[Rick Lee]

I second Jack Olsen. My '87 Carrera burns about 1qt per thousand miles, which is still high for my comfort level. But I've discovered several leaks, which certainly account for some of that lost oil. Top off you oil level to midway between the tick marks, write it down in a log book with the mileage, date and amount of oil added, get your undercarraige cleaned up real nice, take her for a long, hard, spirited spin and then put a large pizza box underneath her. Come back and check the pizza box in the morning and see how much oil is on it. A lot of times, oil leaks onto the heat exchangers and burns off. So many people do top ends prematurely, I'm afraid the reseller market may eventually expect all 911's above 60k miles to have had one. You've got a lot of homework to do before worrying about top end vs. the full job. Get a leakdown and compression check too. It's a pittance compared to the costs of an overhaul.

[Jim T]

I agree with most of the above, although I think if you were leaking 1 quart every 500 miles, you would probably not have much of a problem detecting a leak!

Bruce Anderson addresses high oil consumption in the Carreras in around every third Panorama.

I just randomly pulled one off the shelf, and there was one!

Sept 2001 Pano, some guy wrote in with 1 quart every 300 miles:

BA said 300 miles is "way too much."

"I really hate to see them consume more than 1 quart every 1000 miles."

"Your car cannot be leaking that much oil or your garage would look like the Exxon Valdez"

"A very small amount of oil will make a very large mess in your garage. A spill of six inches in diameter will probably not be detectable on your dipstick"

The spec book gives max allowable consumption as 1.58 quarts per 621 miles.

"For some reason, it seems if this problem (the Carrera premature valve guide problem) is going to happen, it will happen somewhere between 40,000 and 60,000 miles."

Your shop may have a slightly different definition of "top end" but on a most cars, incl. the 911, that would usually mean redoing the heads. New valves (if they are out of spec), valve job, etc. basically doing everything above the pistons.

BA in his response to the above reader says "With that kind of oil consumption you had better plan on doing some engine work. I suspect you are going to need a top end overhaul. You can figure about 30 hours labor plus the machine shop work and parts."

Yes, with the engine out, the clutch can easily be inspected. Although with 60-100K on it, given the relatively low cost of the clutch parts, I think it would make sense to simply replace it.

While 500 miles per quart is still technically within spec, that would be hard for me to live with. That is a lot of oil, and it means that something is getting very close to its wear limit.

Having just driven a friend's 97 Carrera 2S at Dunkel's a couple of weeks ago, if I had an 87 Carrera that was using a quart every 500, I'd be really tempted to sell and get the 993. It really is an awesome car!

[emcon5]

I have come to the conclusion that my car has a secret oil reservoir someplace where is is storing away Mobil 1 for the next energy crisis. I use about 1 quart every 500 miles, and I have no idea where it goes. When I had the engine out for a clutch job, there was 2 small leaks on top (oil press switch and therm O ring) which I fixed, without changing the consumption rate any measurable ammount. It does not drip on the garage floor. It rarely makes a puff of smoke on startup, but otherwise doesn't smoke. Compression is good, all 6 in measuring 180-195. I had a valve adjustment done and had my mechanic check the valve guides by trying to wiggle the exhaust stems. He said they felt fine.

The only thing I can think is there is a leak somewhere that only happens with a few bar of oil pressure, but even if this was the case, I would expect some residue hitting the garage floor.

I just keep a close eye on the level, and top it off when it gets low, and drive the piss out of it.

EDIT: After seeing Paul's post, It doesn't foul plugs either. (shrug)

Tom

[pbs911]

In an Excellence column, Bruce Anderson stated that oil consumption should not really be a problem until the plugs start fouling.

[APKhaos]

I've been very much in the same place with my 85 Carrera's 150K mile virgin [unopened] engine. Its totally dry [after replacing return & thermostat lines], does not smoke, but uses close to 1Qt in 300 miles. Compression and leakdown are fine, which put me in the 'keep driving it' frame of mind.

FWIW, I've seen quotes ranging from 30 hours to 45 hours, and rates vary as well. Most quotes are meaningless without a build sheet - you need to know what parts are covered. Some assume a full set of valves, some exhaust valves only, some treat valves as a $50 per shot surprise! Some include rod bearings, some don't. These difference in parts estimates make a giant difference, and make it nearly impoossible to compare apples with apples. An honest wrench will give your a build sheet and time - any surprises found wwhen the engine is opened are obviously going to add to this.

As DE season approaches, I've decided its time to bite the bullet. The peace of mind from new guides, valves in spec or replaced, good seating and sealing is worth the time and money, and a whole lot cheaper than grenading the engine with a dropped valve or two. So.......

Engine out today. The big plus was that I think I found the ugly rattling noise that I have always thought was 915 bearings. The throwout race is literally slopping around in the springs - a good 1/4 inch of play all round, and I'm convinced that's the noise I was hearing in neutral with the clutch out. Sure beats spendy bearings if so!

[czwbkx]

There is an article touching on this subject in the current issue of "911 & Porsche World" called "Trouble at the top" about top-end rebuilds and oil usage symptoms. Although not comprehensive, it provides perspective.

[82SC]

I am in the came boat...'82SC with 190K miles 1qt every 400-500 miles

and all the above posts are correct...

I have not done this but checking your plugs is a great way to start...

I have done most of the pre-emptive strikes like fixing common oil leaks...but still it is about 1qt every 400-500 miles.

No spots on the ground....some general leaking of the underside...but not enough to show that much consumption...

my friends following behind say if I step on it hard there is some smoke...but I never see it in the rear view...so I think from a driver's POV it is hard to see the burning that is going on during driving...

plus your car has a small medium-ly common problem with valve guide wear...

Some say drive it till it smokes..others say do the preventative maintence...I like the former philosphy...

but because I got bored and with all the board members flexing their DIY muscle...I decided to rebuild as a summer project...

But what you have to ask yourself is do you want to commit yourself to your car or move on...rationally moving on is probably the more prudent and financially sound move...but for me I have a special attachment to my car (like most of us) and even after weighed all the cons...I still would like to keep my POS p-car, pour money into it...and have they feeling that this is MY car...one that I know inside and out and that I enjoy...

Good luck at this crossroad of p-car ownership and keep us posted...

MJ

(but my heart still yearns for a 993 2S)

[CraigD]

I keep seeing "check the plugs" to access engine oil burning. If memory serves me right, it doesn't always, you can have bad valve guides causing oil consumption but not oil burning. I believe the oil runs along the guides and is then sucked out the exhaust by the exhaust gases. You can do a search, I think Early_S_Man was the one that wrote the response to a question about oil consumption or smoking.

One more thing, I believe Early_S_Man also tells how to access valve guides while driving. Run the car up a hill reaching around 6000 RPM at the peak, let off the accelerator on the way down and observe your exhaust. If after a few moments you start seeing a trail of smoke you have very suspect exhaust valve guide wear. See Early_S_Man post