Why change oil once a year? - PeachParts Mercedes-Benz Forum

shertex · #1 11-21-2009, 08:35 AM

I'm a big believer in long drain intervals using a good synthetic. But one of my cars, the 300SDL, just won't get driven that much. When I use it, I will get it out on the highway and up to operating temp, but this will only be a few times a month.

So everyone seems to say "X number of miles or once year, whichever comes first," and people engage in endless debates about how many miles. But could someone explain to me the rationale behind the one year (which seems to be universally assumed but not explained)? If I use Mobil Delvac 1 5w40 and drive, say, 1500 miles in a year and regularly get it up to operating temp, why should I change the oil at the one year mark?

So I guess I'm perfectly happy to change the oil annually if I really need to...just want to know why.

(And, yes, I did some searches...but there are so many oil threads that nothing obvious popped up.)

pawoSD · #2 11-21-2009, 08:51 AM

It may prevent things like moisture and such from contaminating the oil, or prevent oil filters from falling apart in the housing from being in there too long (as we've seen happen here on the forum).....and so on.

nhdoc · #3 11-21-2009, 08:52 AM

I would say if you routinely get the car up to operating temperature and occasionally drive it for a nice long trip there is NO reason to use any time period as a basis for changing oil and if you only put 1500 miles a year on the car then you can stretch it out to a few years. After all, oil does not "expire" in the bottle on the shelf.

The periodic change recommendations are based upon the fact that most people who drive a car very little don't fully warm it up or drive long enough trips to "dry it out" and therefore the oil tends to become contaminated with water from condensation and that is bad. The worst thing you can do to a car is drive it a mile or two and shut it down. It takes a good 20 minutes or more of driving in warm weather to fully warm everything up. In winter I would say 30 minutes minimum.

If you do warm it up frequently then I'd say you still want to change it more frequently than 10K miles but 5K miles is probably fine which would probably be about every 3 years based upon your 1500 miles per year.

I'm sure others will contradict me but that's what I'd probably do.

Brian Carlton · #4 11-21-2009, 09:17 AM

Quote:

Originally Posted by nhdoc

The periodic change recommendations are based upon the fact that most people who drive a car very little don't fully warm it up or drive long enough trips to "dry it out" and therefore the oil tends to become contaminated with water from condensation and that is bad. The worst thing you can do to a car is drive it a mile or two and shut it down. It takes a good 20 minutes or more of driving in warm weather to fully warm everything up. In winter I would say 30 minutes minimum.

Agreed.

If you drive it 1500 miles per year and average more than 20 miles each time you start it, a synthetic oil will easily go four years. The "one year" criteria is not applicable.

MTUpower · #5 11-21-2009, 09:39 AM

Quote:

Originally Posted by shertex

I'm a big believer in long drain intervals using a good synthetic... If I use Mobil Delvac 1 5w40 ....

Mobil Delvac engine oil is not a synthetic IIRC.

shertex · #6 11-21-2009, 09:47 AM

Quote:

Originally Posted by MTUpower

Mobil Delvac engine oil is not a synthetic IIRC.

You're thinking of regular Delvac. I use Delvac 1, which is full synthetic.

rocky raccoon · #7 11-21-2009, 09:58 AM

Question can be put to bed if you have an oil analysis done before you change. Analysis results are the only truth.

#8 11-21-2009, 10:03 AM

I don't know the answer but I might be concerened about the oil breaking down over time due to the contaminates reacting with the oil. I don't understand the chemistry well enough to know if that's a real concern.

Diesel911 · #9 11-21-2009, 10:05 AM

This is old time stuff and may not apply anymore. But, back around 1975 my Tradschool Instructor (Diesel Mechanics) siad that if you changed the Oil and parked the Vehicle and did not use the vehicle the additives in the Oil wouold still deplete in 6 months to a year.
I don't know if for praticle purposes it means much even back at that time.

With regular Diesel Dino Oil and the Car doing almost all short trip city driving I end up changing my Oil about aver 6-8 months or when I feel it is Black enough that I want to change.
Most likly I am wasting a little money by changing it earlier than is needed.
Here in S CA unless you live in the Moutains there is no cold starting issues that synthetic would help with.

Brian Carlton · #10 11-21-2009, 10:28 AM

Quote:

Originally Posted by MTUpower

Mobil Delvac engine oil is not a synthetic IIRC.

"Delvac" is a confusing term. Mobil uses it on many products.

You're thinking of "Delvac 1300" and need to refer to it as such.

HughO · #11 11-21-2009, 11:10 AM

LIke you I have too many cars, 3 MB diesels and 2 cummins, a Camry and a suburban. The solution is easy. Do an oil analysis. I go 2 years on my cars and my suburban still tests OK at 3 years. I don't go over 10000 miles on cars without by pass filters out of habit. On my 240D with a very tight motor I have seen good oil at 12000 miles. It depends to some extent on your engine. This is what fleet operators do to minimize unnecessary and expensive oil changes. The cost is usually around $10-15

leathermang · #12 11-21-2009, 02:13 PM

Medical labs make mistakes on a regular basis on stuff mailed to them...

I really do not think being extra frugal with engine oil compared to what a mistake in theory and practice might do to an engine is worth the gamble...

Do you people who are doing the stretching actually know what it costs to rebuild an engine ?

Not a good bet in my opinion. Cost savings / Benefit ratio not great enough to take the chance.

Do you people understand the much higher pressures on the rod bearings which a 21 to 1 engine works with ?

I will not be back to this thread... I have said everything I have to say. It is all based on my conservative mechanical philosophy .

shertex · #13 11-21-2009, 02:35 PM

Quote:

Originally Posted by leathermang

Medical labs make mistakes on a regular basis on stuff mailed to them...

I really do not think being extra frugal with engine oil compared to what a mistake in theory and practice might do to an engine is worth the gamble...

Do you people who are doing the stretching actually know what it costs to rebuild an engine ?

Not a good bet in my opinion. Cost savings / Benefit ratio not great enough to take the chance.

Do you people understand the much higher pressures on the rod bearings which a 21 to 1 engine works with ?

I will not be back to this thread... I have said everything I have to say. It is all based on my conservative mechanical philosophy .

All reasonable points...but begs the question. Even with a "conservative mechanical philosophy," what would be the reason to change oil that's been used only 1500 miles or so but has been in there, say, 18 months, especially IF the car is regularly driven so it gets up to operating temperature for a reasonable length of time?

I have no desire the scrimp in a way that may damage my engine. But I want someone to give me a reason to change the oil based purely on a time interval.

leathermang · #14 11-21-2009, 03:29 PM

Ok, I am back..
because just normal day to day life/weather causes the insides of engines to acquire condensation..
which can affect some oil additives in a negative way...

shertex · #15 11-21-2009, 03:36 PM

Quote:

Originally Posted by leathermang

Ok, I am back..
because just normal day to day life/weather causes the insides of engines to acquire condensation..
which can affect some oil additives in a negative way...

So maybe bottom line what I'm looking for (and some have already given their view) is this: how frequently and long do you need to drive a car to eliminate condensation? Because your point is certainly well taken.