When using a multi-viscosity oil, what's bad about

[MrCPU]

using say a 10-40 oil, over a 10-30?

I have a vague idea bout the lower weight, and cold start protection and such, but not so much of an idea how the high number affects things.

 

[widman]

It will cause a little more resistance/consumption, although probably not enough to matter. More resistance is more heat, which thins the oil back again. I stay away from 10W-40's unless they are synthetic, as I don't like that many polymers

 

[Jaymus]

I decided to go from my always chosen 10W-30 Castrol GTX to 10W-40. I really didn't need to. It takes forever for my oil pressure gauge (idiot gauge, as some say) to get to the normal spot at idle now after driving. The 10W-30 thinned down much faster. The 10W-40 will get there, too, just takes longer.. so I guess that lets me know my bearings are still fine with 10W-30?

BTW, I went to 10W-40 for the summer heat (90+ degrees here). I plan on just going back to 10W-30. I don't think my 302 has lost any life. It's an 86 model with 118k miles on it.

 

[OVERKILL]

Originally Posted By: Jaymus
I decided to go from my always chosen 10W-30 Castrol GTX to 10W-40. I really didn't need to. It takes forever for my oil pressure gauge (idiot gauge, as some say) to get to the normal spot at idle now after driving. The 10W-30 thinned down much faster. The 10W-40 will get there, too, just takes longer.. so I guess that lets me know my bearings are still fine with 10W-30?

BTW, I went to 10W-40 for the summer heat (90+ degrees here). I plan on just going back to 10W-30. I don't think my 302 has lost any life. It's an 86 model with 118k miles on it.


Pffffffft, it's a spring chicken! I LOVE 302's, I put an HO in my F-250 when I had it, I have one in my boat, one in the Lincoln (now HO) and the one in the Capri/Mustang. Great engines!