Mark944na86

I was getting ready to do a 3000 mile oil change, when I noticed an article in latest issue of "Panorama" (August 2001, p71) that said 944 engines were designed to go 15,000 miles between oil changes. Any comments?

-Mark 86 944 NA

Tabor

I change my oil every 3,000-3,500 miles.

If you want your lifters to last, I suggest you change your oil every 3,000-3,500 miles.

Bob S. 1984 Silver

Twice a year, but then I only drive it about 4 to 6k a year at the most.....

Macabre

I change every 5k and am quite confident that I'm throwing away perfectly good oil when I do so, but it's piece of mind. I can't possibly imagine why you would need to do it every 3k (assuming you're using synthetic) in a street car. If the oil hasn't broken down, there's no reason to change it, and a good synthetic should not break down for long after 5000 miles (Mobil1 claims 10-15,000 miles. AMSOIL claims 25-30,000 miles). However, you really can't change it too often. If the car is to see track time, I would probably change it right before race day. If you aren't comfortable, send some 3000 mile old oil out to be independantly tested. They will tell you what if any additives have broken down, what the viscosity is, etc. Cost was around $50 last time I looked into it.

Black_951

I was just thinking about this today.. my car burns a quart every 1000 miles (the other 951's I have owned did too so I assume this is normal). So thats five new quarts every five thousand miles or almost an entire oil change.

Under the above scenario would it not make sense to just change the filter instead of all the oil?

Tabor

I use Dino oil. I have oil leaks, and I don't want to make it worse with synthetic.

TimC

I change every 4000 miles. This is simply because I live in apartment, so I can't convenviently do it myself - I normally rotate tires every 5000, so I split the difference betw 3000/oil, 5000/tires and get both done at the same time. Modern oil really can go quite a bit longer, even if non-synthetic.

On the subject of synthetic oil, I'm sure everyone has an opinion on this, but my shop (Stuttgart SW in Tempe, AZ) recommends against synthetic oil as the wipers on the pistons don't fully wipe it. I haven't asked what they recommend on newer cars that come w/Mobil 1 from the factory. At any rate, my car burns some oil (much less in summer, curiously enough)(presumably this is due to worn valve guide seals - I think), so that would also be made worse by synthetic.

T

"His world is under anaesthetic
Subdivided and synthetic"

- yup, Rush again, Digital Man (Signals, 1982)

Mark944na86

Except you'd still expect to have just over 32% of the original oil still left in the car, even after you added 5 new quarts.

0.8^5 = 0.32768

-Mark 86 944 NA

Ahmet

Black:

Everytime you add a quart, you're adding one quart to whatever is still in the crankcase, in otherwords to used, or 'conatminated' oil. It's not like all the dirty oil comes out one quart after the other, and doesn't mix with the new...
Ahmet

Thaddeus

Yes, and consider this: that oil is being burned off in the cylinders, it's getting past the rings or valve guide seals. Which means something's going the other way too! Doubtless, combustion vapors and gasoline vapors and water vapors are making it into your crankcase, there to stew and simmer.
Corrosion, acidity, etc in your crankcase. Sound like fun?

Change the oil.

Thaddeus

Dave

Once a year weather it needs it or not, around 3500 mi. Mobil1 10-30

Brent 89 - GT

I just love commenting on this subject. Opinions vary wildly, so here is mine. I use Blackstone, an oil analysis company to test oil in my semi trucks and diesel pick-ups. A big rig can safely run 20,000 miles on dino, some are going 35-50k on synthetics. These engines easily accumulate 750-1 million miles before a rebuild. Of course I error on the safe side and change at 15k(with dino). My pickups I change at 5k(dino), easy to remember and the oil is broken down in these by 8k anyway. I use the computer on my wifes BMW to determine its intervals, normally 10-12k on synthetic. On that one they pay to 50k and it is warrantied to 100k, not much incentive to do more. I go 5k(dino) on my MB, had it analyzed, still was OK, thats the way I like it. But to change every 3k seems like more waste than I need to contribute. I have never heard of oil being broken down that quickly. The Porsche gets an oil change a couple days before each track event. I only drive it summers and do 4-6 events a summer. I run Mobil 1 because of the turbo, I want it to last. I should test the oil after track time someday. I wonder how hard that really is on the oil? On one hand it is subject to more extreme pressure and temp, on the other it runs hot enough to burn off most of the bad stuff. I also think the synthetics increasing oil leaks is false. I know lots of people that have switched late in the vehicles life with no problems. So for a 944NA that doesn't see the track I would go every 5k on dino. If it is a stored car in winter, change it before you store it and at least once during the summer regardless of miles.

TimC, Ask that shop how they KNOW the rings don't swipe the oil off? That is the craziest thing I have heard in a while. The major difference between dino and synthetic is the lack of impurities in the synthetic. Do they know syn flows better? This would lead me to believe it would be easier to wipe clean, and isn't oil left there for a reason?, like lubricating the cylinder walls. I don't understand why some people fight this syn oil, it is better in every way except price.

Greg Hammond

Oil analysis is really the only way to determine if your oil is "good" or "bad". What DOES need to be replaced more often, and hasn't been mentioned in an earlier post, is your OIL FILTER. Oil filters make use of cellulose-based paper filter media, and this breaks down faster than the oil itself does. The result of of a deteriorated oil filter is that little pieces of cellulose flow through the engine, sometimes big enough to get caught in the bearing journals or piston cooling oil squirters (if your car had them).

Most big-rigs that do run 35-50K miles on synthetic replace their oil filter at 12.5K-15K intervals, AND many more use a "bypass filter" that in essense is a two-filter system whereby some oil is fed at substantially higher pressure to a secondary filter with finer filter media, to catch the abrasives that would fit through a standard 25 micron oil filter.


The long and short of it? Your oil filter should be good for 7500 miles. Your oil should be good for at least 10K miles. When to change? 5000 miles seems reasonable in a high-revving turbocharged gas engine. 3000 miles intervals were devised back in the 1940-1950's when engines AND oil technology were vastly inferior. The only people who recommend that short of an interval now are the *iffy *ubes out there.


Greg

jim968

(Advance warning: long & boring)

One of the major reasons for the old 3K recommended interval was the choke on the carb. Being a very imprecise device, it often supplied a too-rich mixture to a cold engine; a lot of the unburned gas got past the rings to contaminate / dilute the oil.

With modern manufacturing, cylinder bores are more perfectly round & straight, and rings seal better; less combustion gas gets under the piston.

Also, our cars have almost twice the oil capacity of a lot of 4's, so the same actual amount of contamination is diluted down more.

_But_ there's still one other issue, and that's condensation; every time you run the engine, you heat up the air in the crankcase; it expands, and some gets out. Then when the engine cools off, it draws in outside air to replace the volume that escaped. This air contains humidity, which may eventually condense on the inside walls of the block. vibration on the next run cycle makes it trickle down into the oil. If you do a lot of short trip driving, it may not get evaporated out of the oil, and can accumulate. Then it interacts with combustion by-products to form nasty acids & sludge. the more short-trip driving you do in damp weather, the worse it is. I've actually seen as much as 1/2 cup of "water' come out of an engine that was 'way overdue for an oil change.

Me? I now use full synthetic in the 968 & change every 5K. My Toyota pick-up, dino at 5K or every 6 months (it sits a lot).

Jim, "Where's my filter wrench?"

Manning

My odo doesn't work most of the time, so I usually change it every 4 to 6 months with Mobil 1.

We used to have a sales rep visit the bike shop who never changed his oil. Ever. He would just add when he needed to. No filter change, no oil change. And he was a traveling sales rep for a couple of the lines we sold. He had over 100K on his car, a VW Jetta, when he replaced it with a Volvo wagon. And it ran great to boot.