Mixing oil weights?

I got an older car-1989 Toyota with 263,000+, I’ld like to use a high mileage 15W-40 but they don’t make one! Can i mix 2 qts of hi mileage 10W-40 and 2 qts of regular 20W-50 to get a mix of 15W-45?? Or do I now have 4 layers of different weight oils in my oil pan that don’t know how to get along??? thanks…

Your plan is a good one. The oils will readily mix to give you a single oil with an intermediate viscosity.

The 15W40 weight is widely available. Go to any truck stop and you will find a gasoline/diesel mixed fleet oil that meets your needs. EXXON, BP, Shell, Etc. all have these grades. Just do not use this oil in very cold weather, unless you have a block heater on your engine, or park inside. Also expect slightly lower gas mileage, but that should not be your concern. Mixing different grades is OK, as per SteveF. My friends with pickup trucks who tow trailers use the 15W40 since it has superior load carrying capacity. It is also the standard oil for most truck fleets.

You can mix them or you can use some 30 weight. If you are consuming oil, it will slow down. There really is no such thing as high mileage oil. Who the heck knows what’s in it? Is it better or is it just something the same as regular oil? We all know what 30 weight is. Higher viscosity oil.

There is very little difference between 10W-40 amd 15W-40   The 15W-40 is the same oil except it will be a little thicker when it is cold out and no difference once the engine warms up.

thanks for the feeback. i’m hoping the extra 5w (10w VS 15w) will keep more oil from blowing by the rings and seals till the engine warms up and the oil thickens to 40weight

Not sure what you mean by “There really is no such thing as high mileage oil.” It is currently being sold in most stores. I know Valvoline has a version.

Now if you are talking about “just” the oil itself, I suppose you are right. But the oil we put in our vehicles isn’t straight oil. It isn’t pumped out of the ground and put straight into our crankcases. The oils we us are a concoction comprising of many “secret” additives and detergents and refined oil.

So technically, there is a high mileage oil. Whether or not they actually do what is claimed. . .

Oil NEVER thickens as it warms up. It just thins out less.

Agreed, 10W40 acts like cold 10W when it’s cold, and acts like hot 40W when its hot. Cold 10W is still significantly thicker than hot 40W.

Just use the 10W40 and don’t bother with mixing them.

Where “cold” is defined as 0 degrees C, and “hot” is defined as 100 degrees C.
Those are the temps the weight ratings are measured at.