synthetic oil

[shj]

Can anybody tell me whether it's harmfull to mix synthetic and non synthetic oils.
I want to topup my engine, I have synthic 5W 40,but I am not sure whats in the car.
Thanks
Simon

 

[bitonw]

Myth #4: Synthetic lubricants are not compatible with petroleum.

Untrue. The synthesized hydrocarbons, polyalphaolefins, diesters and other materials that form the base stocks of high quality name brand synthetics are fully compatible with petroleum oils. In the old days, some companies used untested ingredients that were not compatible, causing quality synlubes to suffer a bum rap. Fortunately, those days are long gone.

Compatibility is something to keep in mind, however, whether using petroleum oils or synthetics. It is usually best to use the same oil for topping off that you have been running in the engine. That is, it is preferable to not mix your oils, even if it is Valvoline or Quaker State you are using. The reason is this: the functions of additives blended for specific characteristics can be offset when oils with different additive packages are put together. For optimal performance, it is better to use the same oil throughout.

http://www.synthetic-oil-tech.com/d.cgi/1234055/articles/ten_myths_about_synthetic_lubrication.htm

 

[Big Brin]

Conventioonal wisdom states that you ought not to mix synthetic oils with mineral oils and so I don't! I'd suggest you follow exactly what the recommended manufacturers oil is.

Rgds, Brin