porschemikeandnancy

I've been reading about all the "top end" rebuild issues with the 993 engine. My '95 is an OBD I car - so no CEL issues with clogged up secondary air passages. My car just passed its smog check with no problems (it was not even close on any of the measurements)

My question is if you don't get a CEL due to it not being an OBD II car, I assume I still have clogged up secondary air injection passages. I've asked my local independent Porsche shop should I have them "cleaned out". Their answer is: "no, cleaning out the secondary air injection passages does not solve the basic problem of weak valve guides. It is almost a certainty you will need a top end rebuild when you start (which you will) burning excessive oil".

So I'm a bit confused. If my secondary air injection passages are clogged up, does that lead to more oil consumption? I'm (68k miles) consuming about a quart/thousand miles. There is no visible blue smoke from the exhaust - even under heavy throttle or engine lugging. At the 60 k service, I asked them to check the old spark plugs for oil deposits. There were none. Also the compression was even in all cylinders - and the right numbers.

What further complicates my question is my mechanic said there is some oil weeping from a lower valve guide cover. He says "it drops on the muffler/exhaust and simply burns up" as I see no oil dripping on my garage floor.

So I guess I'll just drive the car until it consumes a quart - what? - every 500 miles? Any guess when that will be?

Thanks for your replies.

NC TRACKRAT

Inquiring mind wants to know: Are you sure you're using 1qt./1K mi.? Could you be overly sensitive to the situation and topping off more than you should? Are you using the dipstick or the gauge? If you really are using the 1 qt. and not blowing smoke on shifts, I'd say that $6/1K mi. is much cheaper than a top-end re-build. Drive it 'til you see evidence of where it's going and/or a drop in performance.

p.s.: Isn't Milford close to Brookline? I've got kids there.

Geoffrey

Not only does the 993 have soft valve guides that wear prematurely, they also have soft valves. The oil consumption occurs under high crankcase vacuum which happens mostly under deceleration and the oil is sucked through the worn valve guide and burned in the exhaust port. Since the secondary air injection ports are in the exhaust port, they get clogged with this oil residue.

If your car is burning 1qt / 1000mi, don't worry about it. Yea, the top end probably isn't as tight as it was when new, or would be if a top end was done, but so what? Continue to drive the car, add oil appropriately, and don't worry about it. When adding oil becomes a pain or too frequently, then address the top end.

Edward

Exactly ...on all counts.

The venerable air-cooled engines earned their reputation for longevity ...this is no folklore. Sure you'll eventually start consuming more, but that's just not likely to happen overnight. Worry about rebuilding the top end when you really need it ...which is 1 qt/600mi as per the factory, or when you are sufficiently annoyed. If it helps ease your mind any, I noticed that my car was consuming about 1qt/2500-3000 miles when I bought her with 50K miles; I just added a topper last week and I figure I am consuming maybe 1qt/2000-2500 miles ...and I am at 125K miles. You've got some time

As for the valve cover dribble, that's age + miles + hardened o-rings. That's an easy fix for your wrench, or one you can do yourself with little hassle. But if that's only a minor nuisance, then you can wait on that as well ...FWIW, when I knew a clutch replacement was in my near future, I made a "things to do while you're in there" list.

Bottom line is take care of the normal, common-sense preventative stuff, warm the car up properly, and drive it like it like the good Doctor meant it to be driven ...this is your prescription for enjoying your 993

Edward

tctung

No need for top-end job, definitely. You can try a different brand of oil. Some are consumed relatively slower than the others. My 993 is a 94/95 C2 with about 60K miles. It consumes about 1 qt every 3,000 miles if I use 0W-40 Mobile 1. Pretty good.

soltino

Can you extend the time and clogging by the way you drive?

e.g.: Coasting more, shiffting into neutral when coming to a prolonged stop etc?


tino

Ed Burdell

Make sure the car is warmed up, and then drive it hard to keep the revs up. Short jaunts around town running errands with a lot of engine stops and starts aren't the best for it, but again if you get the engine to operating temp first, you can get away with that sort of thing.

JPS

I was at 130k mi. No top end. I had a hard time determining oil consumption since for awhile I was using mostly only to/from/at the track, so I wasn't adding a quart without some track time in there. I did replace one of the lower valve cover gaskets.

soltino

Given proper warm-up is it a catch-22; drive it hard to clog less but wear out the valves/guides quicker?


tino

Edward

I seriously doubt (and personally disbelieve) that there is any driver "habit/procedure" that would mitigate the clogging SAI ports. If you've seen them, their small size and placement (combustion chamber) almost dictate that clogging will occur, the matter of when being the only variable. The only permanent fix is to either bypass SAI ports altogether (been done by a few here), or own a 95 (the clearly superior 993 ).

As for wearing out the valve seats/guides faster by driving hard? ...nah! One can make the argument that higher temps and combustion pressure (within spec, of course) that accompany spirited driving is the best preventative measure ...given good, clean oil, car is up to per temp, and all else is correct. Driving at low (or lower) revs theoretically yields less wear on all engine parts, but I have yet to see anyone prove such with hard data.

Paradoxically, the converse is more often the case (anecdotally, anyway): that "babying" the engine doesn't allow the necessary heat/pressure to build and will thus leave deposits which will eventually build, causing problems.

Edward

VNTGSPD

BTW, how are you checking your oil (gauge or dipstick when warm and level) and do you fill it completely. Your oil consumption may not be as bad as you think.

I began to get concerned when my oil consumption varied from 1500 - 1600 miles per quart. Then I learned on here not to fill it and instead keep the level at the middle of the dipstick. Since then, the consumption has been reduced to about 2500 miles per quart. I'm not sure WHY this matters but the numbers don't lie.

I have some weeping oil leaks but nothing serious. I have 118K miles on mine and it passed smog, even with one dead and 11 marginal spark plug wires!

Ed Burdell

That's true - my car does better with the dipstick in the middle of the range, althought that makes my oil gauge in the car useless.

Question for the group - with higher mileage engines (mine has 86K now), do I go with a thicker oil, say 15W-50, or do I go 0W-40?

BSL

Isn't that "getting broken-in" mileage? (I am pushing 98k now)

Sorry, don't have an answer to your question, but am interested in what others might opine...

Edward

If I fill so the dipstick is in the middle of the range, it "just" makes my gauge register around 1/4-1/2, depending on the engine temp. I'd say that's about right ...not to mention we're supposed to rely on the dipstick, anyway.

I have about 124K now and she feels tight and responsive as ever; and have been using M1 15w/50 since 50K miles. That said, I have been doing lots of reading (dangerous thing, mind you), and decided to decrease viscosity to the M1 5w40 (their truck/diesel oil). It purportedly has a very good additives package, good zddp content, and is about on par cost with the M1 15/50 as both come in big jugs at WalMart (where the 0w/40 comes only in qt bottles so cost is significantly more for 10 qts.).

You'll obviously get lots of opinions here. But given the reading I've done, I am confident in the choice I have made for my use and my change intervals. And frankly, if the 0w40 were cheaper, that would sway me as there are "good numbers" there, as well. But as with all things related to the topic of oil, YMMV

Edward

tctung

Ed, never go with a thicker oil. Keep going 0W-40.

Dan