What are the consequences of mixing regular oil with synthetics? Is it beneficial or harmful, and why? If I do mix, should I keep viscocity consistant? I'm planning a cross country trip (coast to coast) & anticipate that my 460 will burn some oil along the way. Since I am using synthetic oil now, I was thinking I might add a good quality regular oil when necessary. What do you say? Thank you.

 

I use Quaker State synthetic and on the container it says it is ok to blend with regular oil. In fact they make a blend.

 

There are several "Synthetic Blends" on the market. According to API, the manufacturer must add 10% synthetic to a hydrocarbon based lubricant to be called a "Blend". This means that there must be 3.2 oz. of synthetic in a quart of oil.
Take a look at the "Amsoil" thread. The rules have changed on Synthetic lubes. Now API has decided that any lube can be called Synthetic if it has undergone a chemical change. Post your e-mail address and I will e-mail the article from Car & Driver. Seems as though things are not necessarily what they are called anymore.
Danny

 

I've been mixing my own oil for years (syn with dino) with no apparent ill effects. Been using Castrol lately. I haven't had a valve cover off, so can't say how clean (or dirty) engine is from doing this. I've heard that synthetic helps protect on first start-up, that's why I use it. That's interesting about some "synthetics" not really being true synthetic. Anyone know about Castrol, or can recommend a good brand of syn?

"Nothing lasts forever except natural stone and old Ford trucks." (Willie Nelson)

 

Loneranger, Castrol syntec is not a true synthetic it is a hydrcracked group II or III oil. It has a pour point of -38F, while Mobil 1 is -54F and the oil I use Chevron syn -62F. All of these are 5W30. They are all good oils but the true syn will flow faster at startup.