Actually, on Page 60 of the owners manual (2002 models, at least) they DO recommend running 10W-40 in applications where the lowest ambient temperature will be below 40 Deg. F. For a guy living in southern Wisconsin during early springtime this is not, perhaps, an unreasonable expectation. I have noticed that the CE light comes on momentarily when doing a cold start at these temperatures (while running 20W-50 Syn3) - I suspect that the motor is a little sluggish with the heavier oil, causing a fleeting voltage drop and triggering the engine light. The 10W-40 grade would provide superior cold-start protection. However, once the temperatures warm up, I would stick with the 20W-50.mjw930 said:There's a lot of oil discussions on the forums but no one has been running anything other than either 20/50 or 15/50 ...I suspect that Harley / Porsche had a few decent engineers come up with the spec
OKIE said:Is this the same recomendations as the big twins? I thought the diesel oil thing was for the higher temps of the air cool motors? Is it also better for the water cooled revolution or did they get lazy and take the same page out of their old manuals?
I'm going to go with the 10/40 synthetic. I sure don't like what I hear on a cold start with 20/50.zzzz said:That is the same thing I was wondering. I do use 10w-40 and have had no problems.
Probably true to a degree. But oil companies do spend millions in the R&D of their products in the support of ever increasing engine requirements. Also, I've got to believe that when HD/Porche engineers were disigning the motor, the extreme capability of available hi-tech lubricants was a defining factor.greenham said:Sorry,
I don't believe for a second that they (any MoCo) spends MILLIONS on R&D then consider a specific oil viscosity. At best I would think that the protection values of all oil are known to the MFG's. They pick the oils that fit in a range of usage and call it done.
If you live in an environment where you are unlikely to ever see cold temperatures, all the more reason to stick with the 20W50.ecuflasher said:I live in a tropical country where the ambient temp ranges between 30C to 34C so cold start is not a concern for me. ...<SNIP> seems like a good reason to choose the lower allowed viscosity to allow for cooler running temp and fuel efficiency.
vroddrew said:If you live in an environment where you are unlikely to ever see cold temperatures, all the more reason to stick with the 20W50.
The engine is designed to run with the coolant fluids (and I'm including the oil in this) running between 185-200F. You will gain nothing by running any cooler, and in fact are more likely to damage the engine by not having sufficient viscosity.
The oil's viscosity is what makes is stick to the metal surfaces inside the engine (think of how honey sticks to surfaces, where water would just run off). Viscosity is also dependent on temperature - as the oil gets hotter, it also gets less viscous. Running too low a viscosity oil would give you insufficient thickness of oil on the bearings and cam surfaces.
Its a reasonable question. But stick with the factory recommendations.