Oil change conundrum 3

[RossABQ]

I recently took my '86 Porsche 944 on a 3500-mile cross-country trip. Before the trip, I changed the oil & filter (Castrol GTX 20w50 "conventional" with a NAPA Gold filter made by Wix).

I made the trip up and back in 2.5 days each way, approx. 1500 miles each way, and drove about 500 miles at my destination over a period of a week. This was in August, temps were pretty moderate, under 90 F. the whole time, above 70 at night. This car has a water-to-oil cooler.

Basically, each day of travel I had one "cold" start, and several warm starts. I was cruising at 2,500 RPM (60 mph).

So... "conventional wisdom" would say I have 3,500 miles on my oil, it's time for a change, right? I don't think so, but I can see things both ways.

Compared to driving around town (suburban cycle) for 3,500 miles, I had perhaps 1/100th the number of cold starts; and I have about 30 hours driving time on the oil, vs. 125 - 150 hours. In terms of time, this mileage occured in 10 days vs. 6 months that it would normally take me to accumulate that many miles.

The other side of the coin is, I have 3,500 miles on the oil. I suppose there are going to be a certain number of wear particles generated whenever an engine is running, but again, the amount generated at a relatively constant 2,500 RPM vs. constant cycling in traffic is bound to be much less.

I think it would be a waste to drain this oil. What say you?

 

[drwebb]

When introduced the trade mags reported Valvoline was going to position NextGen at price parity to virgin oil. But they don't control the retail price, so the markup may be going to the retailer's tils rather than the Ashland folks.

 

[RossABQ]

Isn't the owner's manual recommendation for that vintage Porsche 5000 miles for a non-turbo? And that was the days back when maintenance schedules may have had a dealer service agenda, before folks accuse manufacturers of just wanting to survive the free maintenance lease period?

My face is red on this one. I hadn't ever found the interval in any of the manuals, I relied on what I read in the many debates on oil quality and change intervals on Rennlist and elsewhere. The Owner's Manual doesn't give an interval, just the viscosity, API Service, etc. I dug thru all the paperwork some more and finally found the interval in the Warranty booklet.

After the first 7,500 miles (i.e., break-in) the recommended interval is 15,000 miles or one year! No mention of synthetics to achieve this, either. There are the usual caveats about racing or severe service. I'm honestly shocked.

 

[patprimmer]

It does have a big oil capacity though.

Regards
Pat
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[Tmoose]

various Moparz and Toyotae have had some sludge related horror stories that seem to indicate the factory may misjudge the change interval sometimes, but when Volvo embraced 5000 mile plus oil changes pretty early on it was easy for me to start stretching them out.

 

[dicer]

Some years back when the price of mineral oil(no such thing as dino)went up, I stopped doing the 3000 mile change deal. Switched to synthetic and don't worry about it. It maybe 6k to 10k for a change now sometimes more. Except for the wifes subaru, just mineral oil there, hasn't had an oil change in years. But has clean oil all the time. What can I say its a good old subaru.

 

[LionelHutz]

It's always ~interesting" reading options when this topic comes up. You can basically do one of 3 things. Follow your own "best guess", follow the manufacturer's recommendations or do the analysis tests like ivymike has suggested. Of course, the analysis tests will give you real data while the other 2 will either have you changing the oil too soon or too late.

 

[drwebb]

I'll bet if you showed the data to a room full of 'experts', half would still tell you it's too soon and half would say too late.

 

[KevinK2]

Why are you running 20W50?

 

[RossABQ]

Kevin, there are many reasons (you can Google it and find dozens of threads specific to 944's), but the primary one is that that is what Porsche says to use. The Castrol 20w50 also has a healthy amount of ZDDP etc.

 

[evelrod]

I was once totally anal about oil change/service intervals. As I have gotten too old to worry as much, I now simply devote the month of June (once a year) to change oil....in everything except the race cars which they have their Wix racing (51515R) filters and ten quarts of Red Line oil changer every two events. The rest, vintage, trucks, motor home and, cars get Castrol 20W-50 GTX. The wife makes me take her Lincoln to the dealer which is fine by me. Changing oil in seven cars is a PITA, and taking 15 gal of used oil to be recycled is no fun, either.

Rod

 

[patprimmer]

Rod

Don't you use your old race oil in a beater that burns oil anyway.

Regards
Pat
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[evelrod]

Yeah, Pat. I did that for a while. Not now, no beaters left, gave them all away. I've even cut back on most of my vintage car stuff. I sold my '39 Buick, '59 Nash and '48 Norton. Still have my two pre war Fords and my race Mini. Just cutting back a bit 'cause I'm just getting too old to keep it all up and running. Now the used oil gets dumped at several parts houses since they, individually, will only accept five gallons at a time. I have about twenty gallons out there right now. Gotta get off my arse and do something about that...

Rod

 

[dgallup]

Why do they limit it? I think they are making money selling it to the recycler.

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[evelrod]

Good question. Trust that I have asked. The only place that took all that I had (15 gal. at that time) was the Lube and Tune place. Parts stores are just closer and if I would just dump it when a five gallon can was filled there would be no problem...I'm the problem in this scenario.

Rod

 

[RossABQ]

The local AutoZone told me it was a zoning thing; 5 gallon limit ensures it is a convenience for residential/consumer customers, which keeps it within their zoning classification. Larger amounts put it in a class of commercial work that triggers some different zoning requirements, different fire prevention, etc.

 

[PEW]

I read some long time ago that BMW's original service indicator system for their fuel injected engines cars took all sorts of inputs to calculate the oil change interval, quite a complicated process.

Then someone realised that just keeping tabs on the amount of fuel run through the engine amounted to just about the same thing.

My year 2000 BMW 325's oil changes were supposed to be about 15,000 miles but the service indicator on mine calculated about 18,000 miles, due to my style of driving, i.e. mainly 70 mph cruising on the motorways. Engine still in top condition after 12 years and 126,000 miles, Emissions test came out perfect on it's original engine, exhaust system, cat etc. The oil never got black, only became darker brown in colour. OE filters always used.

Just part-ex'd that car in yesterday(!) for a Volvo S40 D5 turbodiesel. Very torquey engine for a 2.4 litre but I don't think this one will be so benign, albeit the service intervals are also supposed to be 18K miles.

 

[rmw]

Rod,

I always find that the oil seems to go down the storm drain better after midnight ;-)

rmw

 

[evelrod]

Yeah, we probably would be put in jail today for the stuff we did.
We moved around a lot in the 60's and 70's so we rented a lot of homes in various parts of the southwest. First thing I did was to dig a pit under the trash can...that's where all the drain oil went.
With our first home in Long Beach there was a storm drain at the junction of two alleys behind my house...coming back from a race weekend the motor home dump accidentally coincided with that particular storm drain.
I'm mister goody two shoes these days. I'm very conscious about recycling and environmental issues. Gettin' old, I guess.

Rod

 

[Tmoose]

plus a lot of places will take (back) drained oil and some other fluids for free. Walmart, in walmart containers, no questions asked. Autozone and Advanced auto. Probably lots of others

 

[evelrod]

I asked the 'lubentune' guy and all he said was "It's very profitable"...When they are not too busy, he will take all that I have...

I did manage to get three of my five gallon jugs emptied before I lost interest. I'll probably procrastinate until all five cans are full again...Why do today what you can put off 'till tomorrow?

Rod