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 10w30 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 10w30 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 10w30?

BTW, I went to 10W-40 for the summer heat (90+ degrees here). I plan on just going back to 10w30. 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 10w30 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 10w30 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 10w30?

BTW, I went to 10W-40 for the summer heat (90+ degrees here). I plan on just going back to 10w30. 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!