oil

I have a quick question and was wondering if anyone knows the answer. I know that you cant put synthetic in a car with a fair amount of miles because of the seal and leak thing and all that. What about if you add a synthetic to conventional oil, in effect making your own synthetic blend? Are there any rules to this or anything that it can do to the engine? Thanks.

Actually that's a commonly held fallacy for the most part, you can easily put synthetic oil in any modern car engine regardless of mileage. If you have an oil leak it's because you have a bad seal, not because the synthetic is causing a problem, but this is a very rare occurance anyways. Try out full synth for awhile before jumping to the conclusion that it'll cause an oil leak.

Synthetic oil seems to cause or aggravate oil leaks because it is more slippery than a conventional oil of the same viscosity. Therefore it slides past seals more easily. Go ahead and replace your gaskets and then switch to synthetic. Blending is best left to the chemists; just try what's on the shelf until you find something that works for you. Just remember, synthetic oil can't start a leak, it can only indicate one that was already there.

most new cars come with a factory fill of synthetic, the engines are made to handle it. You can use it in any engine, if it's real old then I wouldn't unles you are sure you have no oil leaks. What type of car do you have, year?, Milage?. Yea, and don't blend your own oil, it's nt good, just like how you aren't supposed to mix viscosities.

I would never mix oil, not even oils of different brands with the same viscosities. I would try it unless you have a nasty oil leak. If you have a leak that bad I would suggest replacing the oil pan seal or which ever seal it may be leaking from. If it isn't leaking go ahead a use it.

Synthetic oil only makes sense to use in large diesel engines. There is no evidence that it makes your engine last longer; at least not at the price you pay for the oil. In large, diesel engines, synthetic oil improves fuel mileage enough to more than pay for the higher costs of the oil.

Originally posted by enginerd
Synthetic oil only makes sense to use in large diesel engines. There is no evidence that it makes your engine last longer; at least not at the price you pay for the oil. In large, diesel engines, synthetic oil improves fuel mileage enough to more than pay for the higher costs of the oil.

i think that just about any owner of a car with forced induction would disagree with you.

I would disagree, big time. Having stared in amazement at the block of a Dodge Aries with over 400k on it. It ran about 80k with conventional oil, and the rest of it on two or three fills of synthetic. I think it was rebuilt at 100k or so, but it ran a hell of a lot and looked about a year old at 400k. I was so impressed I offered to buy the car. I have since learned that a good synthetic (like Amsoil) will do that for ANY car. The proof on my daily driver was the crank journals. I run the engine pretty hard cruising on the weekends, and it shows. You should've it the last time I cracked it open. Now why did I order those oversize bearings??? Also, no metal on my magnetic drain plug. Wear has slowed to a crawl, and I couldn't be happier.

I suppose it does make more of a difference in a large engine with a lot of internal friction. My driveway is occupied by a 4-cylinder and a nicely polished V6, so I don't really know much about that. But I do know that it makes a big difference in my engines. I use conventional oil for break-in (which is usually about two or three VERY long drives...), and then go straight for the synthetic. I wouldn't do this much if I could only settle on one set of pistons...

Er... my point was, synthetic benefits all engines, not just diesels.

Originally posted by bluetwo


i think that just about any owner of a car with forced induction would disagree with you.
Modern diesel engines=forced induction (turbo)

Modern diesel engines=forced induction (turbo)
Yes, but there are non-diesel engines that also use forced induction, and I believe the point that bluetwo was trying to make is that synth oils help these vehicles too. Remember, the statement was made that Synthetic oil only makes sense to use in large diesel engines which is, I think, what bluetwo's example would tend to refute.

An article that some people may find interesting: http://mr2.com/TEXT/synth_oil.txt

I'm sorry, I didn't want to seem that I was saying that synthetic oils don't make an engine last longer. I agree synthetics are superior. My point is from an economic standpoint if you want to break even or spend less, using synthetic oils doesn't make sense unless you have a large diesel engine. The added fuel economy more that pays for the added costs of the oil.

assuming, of course, that running dead-dino oil doesn't result in catastrophic failure early in the engine's life... When it comes to cooling a turbo, some "natural" oils may not be up to the task.