Straight Weight Oil

[outoforder]

Anyone running a straight weight in their bike? I don't, but have thought about it. I currently run 15w40 in my V-Star. When summer rolls around and temperatures are constantly over 70, why couldn't I run straight 30 or 40? Ambient air temperature would not require the use of 15 weight on start up and I wouldn't have to worry about oil shear. Is there a flaw in my logic? Is there any advantage to running straight vs multi-weight oil in the summer?

 

[Bandito440]

It might be a bit harder on the starter, but I see no real reason not to use SAE40 oil as long as it meets requirements for addative levels. Straight weight would be more resistant to shear, so that's a plus.

BMW's oil chart allows everything from SAE30 to 20w-50 in their air-cooled bikes depending on temperatures. I think I used SAE40 on my old R1100S once without problems.

 

[Roadkingnc]

I have run straight 50w in my twin cam Harley

 

[Sonataman]

I run a 50/50 mix of Delo 400 30 and 40 weights.

 

[Robenstein]

If you have a high volume and low pressure system like a Harley, you can get away with a straight weight. But thicker oils on startup take longer to get to all parts of the engine as well as creating drag on the starter. So you get more start up wear and you put more strain on the starter. I see no reason to do it in any modern bike.

 

[Shannow]

"Start-up" wear is the wear that takes place between starting, and additives being fully functional.

Sequence IV doesn't simulate the seconds between cranking and oil pressure, it simulates gold engines/oil being run (with oil pressure, flow and the like).

 

[sunruh]

in a plain saddle bearing, if you have lost the hydrodynamic oil wedge between parts (almost) no amount of additives will save you.

using a straight weight can be not only ok but good, just make darn sure you match the weight to the ambient startup temps