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post #1 of 12 (permalink) Old 03-07-2008, 11:33 AM Thread Starter
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Default Definitive Answer: oil change frequency with synthetic

Hi:

I have read through many of the postings on this topic, but I have not been able to find a definitive answer. I do know, after having spoken with my dealer, that not changing the oil every 5,000 only voids the warranty insofar as the problem is directly attributable to not having the oil changed. Presumably, if there is no need to change the oil every 5k miles with synthetic, then a problem (e.g. seized engine) won't arise by not doing so.

SO, here's the question: if I am using Mobil 1 synthetic oil, how often is it recommended that I change the oil? Still every 5k miles or can I go a longer interval (e.g. 10k, 15k)? If the answer is I should still change every 5k miles, why then spend the extra money on synthetic?

Thanks in advance for any help.
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post #2 of 12 (permalink) Old 03-07-2008, 12:09 PM
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Default Re: Definitive Answer: oil change frequency with synthetic

Quote:
Originally Posted by Jonnyprius
Hi:

I have read through many of the postings on this topic, but I have not been able to find a definitive answer. I do know, after having spoken with my dealer, that not changing the oil every 5,000 only voids the warranty insofar as the problem is directly attributable to not having the oil changed. Presumably, if there is no need to change the oil every 5k miles with synthetic, then a problem (e.g. seized engine) won't arise by not doing so.

SO, here's the question: if I am using Mobil 1 synthetic oil, how often is it recommended that I change the oil? Still every 5k miles or can I go a longer interval (e.g. 10k, 15k)? If the answer is I should still change every 5k miles, why then spend the extra money on synthetic?

Thanks in advance for any help.
My last change at 70k miles on the Prius and 10k miles on the Mobil 1 Synthetic (no filter change during that 10k miles) I sent for UOA. It was in good shape and could have gone at least another 2500 miles or more. See attached file.
Attached Files
File Type: pdf OilReports10k.pdf (55.1 KB, 284 views)

Evan Fusco, MD
'04 BC/Seaside
Nixa, MO http://greenhybrid.com/compare/milea.../signature.png
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post #3 of 12 (permalink) Old 03-07-2008, 12:14 PM
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Default Re: Definitive Answer: oil change frequency with synthetic

First of all, if you follow the OEM recommendations for oil changes at 5K miles, there is no need for using synthetic oil. I'm sure that you can run 10K easily using synthetic but you do leave a loophole for the dealer to not honor the warranty. Call Toyota at (800) 331-4331 and ask them. If they say you can go longer intervals using synthetic, ask for it in writing.
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post #4 of 12 (permalink) Old 03-07-2008, 01:18 PM
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Default Re: Definitive Answer: oil change frequency with synthetic

History points to oil selection as a personal choice. Toyota says in manual a slight increase in fuel milage figures should be evident with synthetic but still requires 5,000 mile changes. A lot of folks continue with 3,000 mile changes from years of habit. No harm done by any of the choices. I always feel good and that my car runs a little better after every oil change. Talk to 100 differant owners and get 100 differant answers. Oil choice is still a personal matter. If you want to go "the cheepo" route go for standard oil at 5,000 mile intervals. Absolutely, no harm done.
(As one of the hundred, I change my standard oil and filters between 3 to 5,000 miles and accept the criticism that I am "wasting oil.")
I own a Cadillac classic convertible that gets driven probably 2,000 miles a year. I change my oil and filter in this car "annually" and with Mobil 1 only. So circumstances should warrant your decision, especially when your car goes out of warranty. (5,000 mile changes with synthetic is silly)
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post #5 of 12 (permalink) Old 05-08-2008, 04:13 AM
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Default Re: Definitive Answer: oil change frequency with synthetic

I can't see changing it more often than 10k using a quality synthetic. I'll go 20k in a year on Amsoil and Amsoil filter. Never had a problem doing this in any other car, and the prius should be no different considering the ICE runs less.
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post #6 of 12 (permalink) Old 06-28-2008, 05:03 PM
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Default Re: Definitive Answer: oil change frequency with synthetic

I believe that the EEC mandated a 10000 mile oil change interval or you can't sell the vehicle in Europe. Why does the USA not follow suit? Toyota follows this guideline in Europe and the cars are the same as sold here. Is the 5000 mile interval a scam to get you in the door more often and waste our time? I believe the use of synthetic oil should pay for itself in the slight mileage boost with todays crazy gas prices.

What is synthetic oil and why is it better for the engine?
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post #7 of 12 (permalink) Old 06-28-2008, 11:46 PM
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Default Re: Definitive Answer: oil change frequency with synthetic

European engine oil is held to higher standards than American, but some of the latter also qualify for the ACEA ratings. I think this is the key to their longer specified oil change intervals.

Two things are legally soil as synthetic oil in the US. One is polyalphaolefin, made from ethylene gas. The other is 'hydrocracked' mineral oil, which is similar to mineral (dino-oil) except that it does not thermally degrade (as fast) in the engine operating environment. Both are ultimately derived from petroleum. Theoretically both could be made from any hydrocarbon starting material, but so far it has been cheaper to make them from petroleum.

With 5000 mile Prius oil change intervals, you can probably do fine with dino oil. It will leave varnish deposits on non-contact surfaces (the thermal degradation mentioned above), but would arguably do no harm over the life of the engine.

With quality synthetic oils, longer change intervals make more sense. Evan posted above a used oil analysis, and getting these is a very good idea especially for those who experiment with long change intervals. It may be that synthetic oil won't wear out in the sense of failing to provide proper lubrication. But one of its additives absorbs acid produced in fuel consumption, and becomes depleted over time. This and the accumulation of insolubles probably dictates the maximum safe synthetic oil change intervals in Prius. To discover that for *your* car, there is no good alternative to getting the analyses.

An individual driver can certainly make the case that extending his oil change intervals would only reduce waste oil generation by a few gallons over the life of his car. However if a million drivers produce less waste oil, the savings would be noticeable.

Prius seems unusually amenable to long oil change intervals because of high quality manufacturing (not unique these days), and lower duty cycle for the engine (still pretty unique).

DAS
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post #8 of 12 (permalink) Old 06-30-2008, 08:44 PM
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Default Re: Definitive Answer: oil change frequency with synthetic

Hyperion,
You state that "5,000 mile changes with synthetic is silly" but you change your oil and filter at 2000 miles in your Cadillac, "with Mobil 1 only." Your Cadillac probably came with a book suggesting oil and filter changes every 3 months or 3000 miles. I'm wondering whether synthetic oils were even recommended by Cadillac when that car was built? Can you please explain your logic for your maintenance schedule? I have a '91 Miata on which I put about 2K miles a year, and I'm wondering if I should be using synthetic oil as well. I've heard that regular oils can gum up the engine in cars that don't get driven a lot or if the oil isn't changed often enough. Do synthetics not act the same over extended periods of sitting?
Thank you.
Roger
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post #9 of 12 (permalink) Old 07-01-2008, 06:44 PM
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Default Re: Definitive Answer: oil change frequency with synthetic

I guess I can't help why people make such a big deal about NOT changing the oil every 5,000 miles. In the end, over the life of the car you might be saving what?- perhaps $500?

I've always changed conventional oil A 3,000, synthetic @ 5,000. There are several reasons why you should do this. For one thing, crankcase gases will make the oil acidic, which in due time can cause slight corrosion to internal surfaces. It also causes the effect of excessive carbon to buildup.lastly, if you don't change the oil at a regular interval, sludge eventually builds up in the pan, which creates its own set of problems. I have a 96' Tacoma with over 200,000 miles. With oil changes every 3,000 miles, I can take the oil cap off and shine a flashlight into the valve cover. There is zero carbon buildup. The engine has perfect compression. Basically, its is in near-new condition despite the miles and usage.

On the other hand, my Brother seldom changes his except every 10k. The car has about the same mileage as mine ( 98 Avalon) but it burns through the oil, has a nasty sludgy buildup under the oil cap, and has started losing fuel economy.

If you want to save money, change it yourself. I do it on our older Prius and its easy.
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post #10 of 12 (permalink) Old 07-16-2008, 01:08 AM
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Default Re: Definitive Answer: oil change frequency with synthetic

my accord hybrid allows 10,000 mile oil changes, i recently ran my prius up to 15,000 miles before oil change visually the oil didnt look too bad, although i noticed a sludge buildup of some sort.

My toyota fleet, 01 prius,05 prius, 06 tacoma, 04 scion xa
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