oil mixing

[Badcow]

Is it wise to refill the engine oil (10w40 inside) with some 20w50 (I have a large amout of this one). they are both semi-synthesis but I have no idea about mixing/compatibility...

[Gerry Attrick]

There should be no problem if they are both reputable brands. Oil companies carry out compatibility checks to ensure the chemicals don't drop out.

[jchase]

Says to use 10W50 in my handbook. - Do you notice the oil pressure is a little low with 10W40 when up to temperature ?

-Jim

[opieoilman]

Why not just put a 10w-50 in it?

Cheers
Guy

[Badcow]

On the engine plate, it is written "20W50", but when the engine is cold (and the weather too), the pressure can rise pretty high (3.5-4 bar : 50-55 psi) and when the engine was hot, the pressure droped to very low level (less than 1 bar, 14 psi)...

When I talked to my mechanic he said that he was using 10W40 from a particular brand in all of his race and collection cars (he owns 17 of them), that's why he filled my engine with this 10W40...

With this oil, the "hot" pressure never drops below 1.5 bar (21 psi), the "cold" pressure never exceed 2.5 bar (35 psi), so it seems better than my "brand X" 20W50.

And I didn't use 10W50 because I didn't find semi-synthesis one...

Thanks for the answers.