I was told yesterday ( by a used car salesman :dubious: ) that the diesel truck I was considering purchasing only needed to have its oil changed every 5,000- 10,000 miles.
Is this true? How? Do diesel engines really “use” the oil within the engine block so much more efficiently that they don’t require the usual 3,000 mile oil changes?
Cartooniverse
If it’s like my neighbor’s big Dodge truck, it has 2 oil filters that cost $50 each and each oil change requires 21 quarts of oil. Sounds as if adding more capacity and filtering is a way to extend the oil change interval.
Note: the truck i referenced has had some modifications done so I don’t know if the oiling system is stock or custom. He just complains it costs him $150 every time he changes the oil.
I wouldn’t say this is so much a characteristic of diesels as just a general trend in all engines. I assume the truck uses synthetic oil?
New, high-end synthetic oils support very long service intervals. The factory recommendation for my BMW is every 15,000 miles. Mercedes, Audi and Porsche all have similarly high intervals. I would imagine that this trend is making its way to other manufacturers, too.
I initially didn’t buy into this, but studies have shown that it seems to have merit (and isn’t just as scam on the part of manufacturers to advertise lower maintenance costs). I still change the oil in my car every 7500 miles, but I’m anal about things like that.
Synthetic oil has been shown to actually reach peak lubrication at around 2500-3000 miles, and maintain lubrication very well until up to 18,000. It takes a while to “break-in”, and so people changing their synthetic oil every 3000 miles to be safe are actually doing damage (however slight) to their engine.
It seems that the reason manufacturers set 15,000 as the upper limit is the life of the oil filter, not the life of oil. The oil could go a bit longer, but the filters start to disintegrate.
My only experience is with gasoline engines, though. If anything, I would think that diesel engines are harder on oil, which would explain why the interval would be 5000-10,000 instead of 15,000.
3,000 mile intervals are still applicable for non-synthetic oil, at least in gas engines. If the truck doesn’t take synthetic, the guy might be BSing you. Check the manufacturer recommendations in the manual to be sure.
It sounds in line with what many manufacturers are recommending for cars these days. I don’t think you really need to change your oil every 3K miles and I have been changing mine every 6-8K miles for many many years and haven’t had any oil related problems. You could always check the owners manual. Perhaps if you drive primarily on undeveloped roads?
Diesel engines typically operate at half the RPM of your average petrol engine. This means less tear and wear. Also, diesel engines have a slightly lower operating temperature. Quite the opposite is true for high-revving motorcycle engines. So, in effect, a petrol car with 100K kilometers, a diesel truck with 200K kilometers and a motorcycle with 50K kilometers are aproximately in the same mechanical condition.
Ah, no. Using inferior grades of oil would require more frequent changes, synthetic or non-synthetic is not the issue, quality is.
My company is right now looking at changing our oil change intervals (currently 7,500 miles for our gas engine cars here in the US) One of the big concerns is what quality oil is being supplied by our dealers. Is it SM, SJ, or SF or even SA? Here is a list of API service classifications (PDF!)
I can tell you from long experience in the industry that if you follow the car makers recomondations regarding oil changes and you use the correct grade of oil, you engine will probably last way longer than you will want the car. (My previous 240 went 750,000 miles before it went to the junkyard. It averaged 6,000 miles between oil changes, never saw synthetic)
Three thousand mile change intervals were required back the oils and the metalurgy was not what it is now. Technology has come a long way since the 1970s when 3,000 mile oil changes were required.
Iffy lube has done a wonderful job of creating a need / desire for 3,000 mile oil changes where none exists. Lube or lose it my ass. Have your car serviced when the guy that designed the car says to, using the materials they recomond. The guys (and ladies) that designed your car / truck know a hell of a lot more about it that the 18 year old beer puke at iffy lube.
Looking around the net, you also have to take into account the fact that a deisel has a larger oil sump when compared to a gas engine. My car takes 6 quarts of oil, a Ford 6.0l Power Stroke takes 15 quarts.
I don’t find a 5K service interval for a diesel to be out of line.
I can post for hours about extended oil change intervals and synthetic motor oils, but in this post I’ll just comment about this particular vehicle.
Later I may come back with some citations on extended drains.
It is normal for a new gasoline-powered car today to have a reccomended drain interval anywhere between 3,000 and 7,500 miles.
Diesels aren’t really “easier” or “harder” on oil than gas engines. They DO contaminate their oils with different substances.
A gas engine exposes its oil to gasoline, sometimes water, heat/pressure and a little bit of soot.
A gas engine exposes its oil to a lot of soot, water, more heat/pressure and very little fuel contamination.
A gas engine’s oil will typically go south due to gas contamination or water contamination speeding up the oxidization of the motor oil, and be about to hit the “bad” point right when it gets changed. Either that, or the owner will change it out early while it’s still in more or less serviceable condition.
While I don’t advise doing it, if you don’t engage in extensive idling or highly-congested traffic driving, almost any gas-engined car will make it 10,000 miles before the oil really fails. At that point a cheap conventional oil will likely have travelled between 50% and 90% of the way from “new” levels to “sub-therapeutic” levels. While oxidization will not be at a critical or even remarkable level, once the additives drop below a “therapeutic” level, acid formation and oxidization will rapidly go into places you don’t want them to go. Incidentally, levels of wear metal in this motor oil will typically be at harmless levels. Some silicon contamination will occur, which is typically dirt dragged in past the air filter. If your air filter is good, this too will be at trivial levels.
In the case of a full-sized pickup truck diesel engine, oil capacities are frequently dramatically greater than those found in gas. My first sampling showed capacities ranging from 8-15 quarts. The bigger the capacity, the longer it will take to use up the additives and contaminate the oil.
Diesel engines don’t usually contaminate their oil with diesel fuel. When over-the-road semis experience oil failure, what you typically see is that chemically, the oil is in dandy shape. Not too oxidized, not too acidic, additives still working, but the soot levels hit 1.5%, and seeing as some soot can be as hard as diamonds, that’s just not something you want to have hanging out in your motor oil in a $20,000 engine. This soot contamination failure point is frequently between 20,000 and 30,000 miles. If soot contamination doesn’t kill the oil, the other thing that causes the oil to fail will tend to be the wear metals exceeding the threshhold of sanity, which is typically around 125 parts per million for a given metal.
While I’ll grant that semis have much greater oil capacities, they also run lighter throttle settings than small trucks do.
Most guys with a diesel-equipped F-350 have more engine than they need, which is not the case for semis.
As a result of these factors, a 5,000 to 10,000 mile oil change interval for a full-sized pickup with a diesel engine should be unsurprising.
[1] AM General Hummer’s 6.5L GM Diesel takes 8 qts.
http://www.amghummer.com/Diesel/GM99Diesel/6_5LV8TurboDieselFeatures.htm
[2] Dodge Ram’s 5.9L Diesel takes 11 qts.
http://dodgeram.org/tech/dsl/Facts/94specs.html
[3] Ford F-350’s 7.3L Powerstroke Diesel takes 15 qts.
http://www.thedieselstop.com/faq/1999faq/General-Specs.htm
[4] Wanna’ see a disgustingly big “pickup” ?
http://www.internationaldelivers.com/site_layout/XTFamily/cxt.asp
Actually, if you look at manufacturers specifications, those oil changes are not out of line for SI engines either. Consider the interests of those that recommend more frequent changes.
The PowerStroke engines utilize the lubrication oil to hydraulicly power the injectors. Foaming of the oil causes problems with this. They carry 15 qts. so as to extend the change intervals to near “normal”.
That said, gasoline does tend to wash down cylider walls and contamonate oil worse than diesel fuel.
Rick,
Are you saying that Volvo actually has legitimate concerns that its dealers would use something besides API SL or API SM oils in gas-engined vehicles that come in for service?
I knew that a lot of car dealers in general have a bad habit of using the cheapest bulk 10W30 they can find, but I’d always assumed it was bulk 10W30 that met an API grade no more than one API grade out of date.
PS… can I persuade you to give me an answer in this thread: http://boards.straightdope.com/sdmb/showthread.php?t=327479 ?
I don’t know if concern is actually the correct word. I saw a presentation where a comment was made that we don’t in fact know what oil comes out of a dealer’s tank. This got me curious, so I went label reading at a large chain auto parts store. You can still by SA oils in quarts, so I assume that they are available in bulk.
As to the other thread, I will be there in a minute.
I think there was a min-scandal last year when Mercedes got sued because they had an “oil change indicator” calibrated for European-style synthetic long-life oil and some of their dealers were putting in bulk conventional oils instead of the reccomended spec of synthetic. (The algorithm in the Mercedes cars in question would allow oil change intervals beyond 20,000 miles, hence the desire for specially-specced synthetic oils.)
Your employer may be afraid of its dealers making similar missteps.