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?

 

[MikeHalloran]

It's your oil, and your engine.

Many years ago, I changed oil religiously at 3000 miles or so, and got decent engine life even from cheap oil.

I started using extended drain intervals when I changed to synthetic oil, which seemed to work just fine for up to 15,000 miles. An engine that I ran to a 20,000 mile change, on synthetic oil, died about five years later because the pickup fell off, but I don't think that was the oil's fault.


In your case, good quality dino oil hardly used, I'd run it for a while longer, probably to the engine manufacturer's change interval. ... but you're already feeling guilty, aren't you?


Mike Halloran
Pembroke Pines, FL, USA

 

[RossABQ]

... but you're already feeling guilty, aren't you?

Yes! My inclination is to run it to 4 months or 6,000 miles; in other words, discount the trip mileage. By then it will be colder outside and I like to change more often based on (truly) cold starts (condensation potential).

I didn't state it, but the car has 96k miles and runs like new after a healthy infusion of greenbacks, mostly for normal wear parts. I averaged 29.9 mpg overall on the trip, too.

 

[FoMoCoMoFo]

I'd keep driving.
Your oil has 3,500 miles on it, in that it traveled 3,500 miles.
It likely has quite a bit fewer rpm/hours on it than you would typically have after 3,000 miles.
AND, as you noted. far fewer cold starts, and just fewer starts.
far less cold operation, idling etc.
That oil has had it easy ;-)

Yep, drive on!

 

[patprimmer]

I use Mobil 1 and leave it in there for 5 times that long or more and still get good engine life, and my cars get a hard life with all sorts of conditions from red lining it through the gears through winding hilly roads to stop start city driving.

Regards
Pat
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[Tmoose]

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?

 

[ivymike]

if you really want to know the answer, spend $30 for an oil analysis now, then run a while longer (if analysis allows) and repeat until you've seen enough.

If you wait long enough to do the first analysis, you can probably end the experiment conclusively after just two measurements ("almost there" and "just past").

 

[TheBlacksmith]

Isn't the street price for Castrol GTX and a Wix filter around $30? Waste or not, it seems like a small price to pay for peace of mind. Personally, I aim for 7500 miles with Mobil 1 and a Purolater Plus or Bosch Oil filter (whatever is on special for ~$30 at my local store). I say aim because it rained for the last two weekends so I'm close to 8,000 and hope to do it this weekend.

 

[RossABQ]

$30 is $30... I have 4 vehicles, if I applied the "better safe than worry" theory I'd be in a world of hurt. The 944 uses 6 liters, and a filter that's not in the bargain bins, so it does come out to about $30. (The filter is very thoughtfully mounted upside down, too, great engineering there).

Thanks for the confirmation, I feel safe ignoring the mileage and driving it further.

 

[MikeHalloran]

With a spin-on filter installed threaded side down, a prick punch will make it drain where you want it to. ... mostly.

I have switched over to Valvoline full synthetic since Mobil 1 was reformulated.




Mike Halloran
Pembroke Pines, FL, USA

 

[ivymike]

for what it's worth, my '03 Mini Cooper was good for 20k to 25k miles between oil changes using Mobil 1 synthetic. Oil analysis showed no parameters out of range, but TBN was getting close.

 

[RossABQ]

for what it's worth, my '03 Mini Cooper was good for 20k to 25k miles between oil changes using Mobil 1 synthetic. Oil analysis showed no parameters out of range, but TBN was getting close.

Unfortunately, that is more than 4 years of mileage on this car, because I just don't drive that much (not commuting, 4 vehicles to chose from, live where I can walk or ride my bicycle to almost everything). In normal use, my oil concerns are more due to short trips.

With a spin-on filter installed threaded side down, a prick punch will make it drain where you want it to. ... mostly.

That's the theory anyway, in practice these filters seem to hold their charge until you get it tipped to a 45-deg angle right over the belts and wiring bundles...

One of my other vehicles is a lowly Chev S-10 w/2.2L 4-banger. They very thoughtfully provided a plastic drain trough on the side of the engine that surrounds the filter base and drains off to a spot that is accessible.

 

[ivymike]

annual mileage on my two current vehicles, a scion xb and ford explorer, is 8k-10k. I change the oil annually (Mobil 1 5w30 synth), and according to oil analysis it's not "used up" at that point.

 

[RossABQ]

I change the oil annually (Mobil 1 5w30 synth), and according to oil analysis it's not "used up" at that point.

Why do you change it, then? Feeling guilty?!

 

[rmw]

If you are still on the fence, change the filter and add a quart and drive on for a while.

rmw

 

[ivymike]

no, it happens that I'm off of work for an extended period at the end of each year, so things like changing the oil in all of my engines seem less of a time drain.

 

[Tmoose]

I wonder how many Prius/miles it takes to offset the petro dollars consumed in all the premature oil changes.

 

[ivymike]

depending on what's done with the reclaimed oil, probably not many.

 

[RossABQ]

I'm at a loss to understand how Valvoline is going to get almost a buck a quart more for re-refined/recycled "NextGen" oil than "virgin" oil. Guilt?

 

[patprimmer]

Properly re-refined instead of just filtered and topped up with extra additive I imagine has the advantage of starting with a much better feedstock than raw crude oil.

Regards
Pat
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