is it ok to use synthetic motor oil on a highter mileage engine that has used regular oil?

Question

I was told by a mechaninic that the smallest amount of regular oil in the crankcase could harm the engine if synthetic is put in.

Answer 1

Synthetic oil was originally developed for high performance racing engines. Mobil tried to popularize synthetic oil for passenger vehicles back in the early 1970's. At the time, Mobil was promoting 20K or 25K oil changes with synthetic, but they soon backed down from this. Synthetic oil is a good choice if you have a vehicle with a high performance engine (in fact synthetic is required for many of these engines). It is also a good choice if your vehicle is operated in extremely cold climates. It has higher resistance to breakdown caused by heat and it flows better in extreme cold. Unfortunately for the synthetic oil industry there is virtually no advantage to using synthetic oil in a non-high performance engine that is operated in moderate climates. You probably could go a bit longer between oil changes with a synthetic, i.e. following the normal service schedule even if you fall into the severe service category, but I wouldn't advise this. In short, synthetic may give you the peace of mind of knowing that you are using an oil that is far better than necessary for your vehicle, but it won't reduce wear or extend the life of the engine. The mistake some people make it to wrongly extrapolate these benefits onto normal engines operated in mild climates, with the ultimate lack of any knowledge being manifested with statements such as "synthetics provide 'Peace of Mind,' or 'Cheap Insurance,'" or other such nonsense.

Extended Change Intervals Extended Change Intervals
Most manufacturers of synthetic oil advise users to not exceed the manufacturer's recommended oil change interval. Part of this is self interest (they don't want to be liable for any damage) but the real reason is that synthetic oil, while it does have certain advantages, still becomes contaminated.

Be extremely wary of synthetic oil companies that offer to pay for your repairs if it is determined that their oil and their extended change interval recommendation caused the problem. Think for a moment of the incredible hassle you would have to go through to prove responsibility for an engine problem. Who would pay your legal bills? Who would pay for replacement transportation during the battle? The more bizarre the warranty the poorer the product is a good rule of thumb.

API Certification, Phosphorus & ZDDP
Never use a non-API certified synthetic oil (there are many of these on the market). The problem with the non-API certified synthetics is that they contain too much phosphorus (in the form of the additive ZDDP (Zinc Dialkyl Dithiophosphates)). The API has limited the amount of phosphorus because phosphorus shortens the life of the catalytic converter. These oils are fine for snowmobiles, motorcycles, and older cars that don't have a catalytic converter, and the extra ZDDP does provide additional wear protection. Unfortunately, the marketers of some the non-certified oils do not explicitly and honestly state the reason for the lack of API certification. You can check the status of API certification on the API web site. Be certain to go not just by the manufacturer name but by the actual product as well. This is because a manufacturer will sometimes have both certified and non-certified products. Suffice it to say that Mobil 1, Royal Purple, Castrol, & Havoline all make synthetic oils that are API certified and that can be purchased at auto parts stores and other retail outlets. Amsoil has one product line, XL-7500 that is API certified, but it's other lines contain too much ZDDP to be certified and should not be used in vehicles with catalytic converters.

Answer 2

The two oil types can be mixed, but is not always safe. Some synthetic oil with additive is known to break down the sludge build up in the engine and cause it to block the oil circulation holes in cylinder head. This is why you should NEVER get that engine clean/flush service. In most cases, going to synthetic oil is perfectly safe (if you have been changing oil every 3000, then there is no engine sludge to worry about)

Answer 3

Its fine to use synthetic oil in a high mileage engine.

You do want to make sure you drain as much of the old oil out as possible (and change the oil filter too).

If you're car is leaking oil, then definitely avoid synthetic oil since its too expensive to be refilling on a periodic basis.

Mobil 1 now makes a high mileage synthetic oil for cars (saw it in the auto parts section the other day) so you could use that as well.

Answer 4

There's no need to dump 30 or 40 weight synthetic engine oil in any car or truck. The oil pump has to work much harder to pump the oil upstairs in the moving parts robbing horsepower and causing excess heat.
If you presently have no oil leaks use the recommended viscosity that your handbook calls for.
Very few companies offer straight weight synthetic oil anyway. Redline is one but most likely would have to be ordered on line or a local speed shop may have it.
If you'd like it do a little investigation go on line to check out Joe Gibbs Racing oil to see exactly what weight and type oils they use to break in a fresh motor, qualifying, plate racing and when the open 850 Holley carburetors are used. Bare in mind, their motors are clearanced properly for the multi-viscosity oils they use. These oils are not to be used for street use.

Answer 5

Don't use synthetic oil in a high mileage engine. You will be wasting your money. Synthetic is thinner, and due to the wear you already have, your engine will start to "use" or "burn" oil. Mixing the two will cause no problems; your mechanic doesn't know what he is talking about.

To get the most out of synthetic oil, you need to start using it when the car is new/almost new.

Answer 6

Save the dollars friend.synth won't do any good .Stay with your brand choice and perform the regular changes.

Answer 7

that's bull, but use the blended types in older cars

Answer 8

it wont ruin your engine,but any small leaks you have in your seals will leak more .Just stick with sae30 or 40 weight.

Answer 9

well if you use synthetic you're going to have to stick with it