Reiver

Guys,
On oil change intervals I've never seen discussed the oil consumption variable.
I've seen guys say they change at 3k to 5k etc. but what about consumption.
On my 83 high miles SC I use about 1 qt every 600 miles...so in a 3 k change point I've added about 5 qts of fresh oil to the system at regular intervals.
That's a lot of fresh oil and additives in that time frame......so shouldn't I be looking at a 4 to 5k change point or more?
Being new to the ac/oc crowd I've never experienced oil usage like these P's do.
What say you tribologists?

Steve Weiner-Rennsport Systems

At 600/miles per quart, your engine needs work.

Assuming that leakdown tests show good ring sealing, your motor needs valve guides in the worst way and that may arrest the high oil consumption.

Generally speaking, 3K-4K oil changes ensure a long and healthy engine life if one uses a good product.

Reiver

Thanks but that wasn't my question....I've a friend that has a new Cayenne getting 500 mile to a quart...my car does not smoke, has 3-6 psi ld across the board and runs very well. It has 217 k on it and never been opened.

Reiver

Steve,
Ok in a perfect world I'd get a top end rebuild but it does not make any sense at this time.
I got the car way/way under the 20 k everyone talks about.."Every Porsche is a 20K car" stuff.
That is only true if you put out that money.
This is a nice 28 year old car, orig paint, interior, etc...everything works except the clock... a nice 10 footer.
The motor is far from clapped out, pulls strong, and works really well from zip to redline.
So why do a top end? Why spend 6-whatever k and be upside down in the car unless I repaint/restore it and then hope for a buyer for my now 30+k invested car (maybe I'll break even or only lose a few thou?)
Why not drive it until it is clapped out/croaks?
Their are differing opinions out there. The P mechanic that took care of it for 25 years has the same year/model...he drove his for 348k miles before a top end and said "Yeah, it burned some oil but ran well and was fun" ....6-8 k dollars buys lots of quarts of oil.
I can get years of fun out of the car with just maint.

masterdave

The reason why many people do the top end and not the bottom is because Porsche made these engines a bit different than most other engines you may run in to, there are 8 main bearings, more than needed which makes them last much longer than most other engines. I also have always felt that the flat engines were more harmonic and symmetrical than other engines. In my mind take a normal flat engine, the bottom of the bearings are going to be worn far more than the top, with a flat engine they are worn on both sides and thus far more evenly. I dont know if that is a fact but it sure seems logical. The top end of course has smaller parts that move more and thus would wear faster.

But to answer the question, its all a personal thing. Im sure there are people out there who change there oil at 3K even if they put in a full quart the week before and im sure there are people who would use that as an excuse to run the car another 500 miles. I have had many cars that have burned all levels of oil, for me it is far more important that the car be checked often and maintained at the right level. In terms of change, because I'm a college student and am away in the winter I usual do a start of summer change, a mid summer change, and an end of summer/fall change. 2.5 months roughly. Of course that depends on miles but usually the time is what reminds me.

Regards
Dave

Reiver

I agree on the bottom end. This 217k car has great oil pressure when fully hot, amazing for the miles...
I'll go about 4k miles between changes I think. With the additional oil I'm putting in the 'wear' package is getting refreshed regularly.
I'd never heard anyone discuss this aspect and I know there are a lot of guys burning similar oil consumption that just won't fess up lol.
I'm sure my valve guides are worn some but so what? If I had other symptoms along with then I might be concerned. In 6 or 7 years then I'll rebuild if SC's are worth something then.

Ed Hughes

Not all 911's go past 300K.

Daniel Dudley

I'm going to go out on a limb here, and suggest that you try keeping the oil level closer to the bottom mark on the stick and see if that decreases your oil consumption at all. Do not keep it topped up to the top line at every opportunity. Keep it just above the lower mark.

Also, I am no Porsche Mechanic, but I would still do the shorter change intervals, especially in the summer, as the oil is being used to cool your cylinder heads, and it gets hot up there. Cooked oil VS fresh oil, HMM, fresh please.

Reiver

True, but I know the history of this car and it's always been maintained so I'm hopeful for the 300k.
I drive it hard kind of asking for an issue and it seems to enjoy the challenge.
OTOH, not all cars are worth rebuild expeditures that will commonly cost more than the final vehicle is worth. I've watched the prices of the SC's for awhile now before I bought one, dropping large money in them doesn't make any fiscal sense right now. If you do it for fun or whatever then that's a dif deal. I'm not that attached to it.
Dan, I'll try that but normally keep it about 1/2 way twixt the lines anyway. I've got a used oil cooler and fan assembly that I'll throw on the car soon to keep the oil temps down for the summer.

theiceman

the phrase " oil is cheaper than metal" applies here i guess. But most enthusiasts here want to keep there rides in top condition, not settle for an oil burner .. but to each his own is all. Eventually at that consumption rate you are going to start fouling plugs, you're already poluting the environment and i cant imagine it is all too pleasant to drve behind .. Looks like you have the 20 K car allright . you just went the pay me later route.

if i was you i wouldnt even change your oil .. you dont have to .. just keep adding

My car consumes about 1 quart in 5,000km . A little more if i drive it hard.

Reiver

Oil burner, a Porsche...you gotta be kiddin me. Let's see, the Porsche factory said 1 qt in 600 miles in the late 70's as normal consumption. An SC motor is basically a late 70's motor. So for the time of this build and the mileage.....

Ed Hughes

The numbers Porsche put out for oil consumption are ridiculous. They were really covering their butts by saying if you burned Xqts in Ymiles, the motor was in spec. 1 qt in 600 miles is pretty high oil consumption.

Reiver

True, they are all oil burners but those are Porsches figures. Honestly, except for a puff of smoke on the first start of the day the car does not smoke...I have driven behind it too see. No leaks either, one drip overnite is the norm.
I agree the consumption is high, if any one of my cars burned 1 qt in 3k miles I'd have an issue and P drivers brag about that level of consumption/pollution .
I do enjoy the car and if SC's get to be worth something in the near future (not talking making a profit but maybe close to breaking even) I may invest the money on a rebuild beause they do have personality to make up for the lack of ponies.

Chuck Harmon

what weight oil ? I had an 83 SC with 250,000 miles on untouched engine, got about 800 miles before I had to add oil, 20/50 weight.

Reiver

Using 20/50 Brad Penn, in truth tho I do drive it hard. I suspect some ring wear (had 4-6 psi bleed down across all 6 pots) and some valve guide wear that leads to very 'even' oil usage. I don't see any smoke when I drive, downshift etc and the plugs aren't 'wet'. Sometimes (not always) on first start of the day I get some smoke but not later when warmed up. Good oil pressure so bottom end is fine.
Still a fun drive.
I'll drive it as long as it remains at this level of performance and hope that lasts awhile.
Really nice car, original paint and interior, not a spec of rust anywhere (so cal/Az all 28 years) no wrecks and I've talked to the one mechanic that has maint. the car for 25 of those years. Very 'honest' car.