What a Great Forum and More Oil Talk

[milehigreg]

I have been through the thread by British Bob ( Important Questions ) and am amazed at the willingness of the folks on this forum to get involved with these troubleshooting exercises. Nothing but positive suggestions and support and a desire to help solve the problem.

I posted a reply to the oil discussion in the " This One's for Hib" thread. Not about choice of oil but the relationship of viscosity to flow and pressure. I don't know this to be true but seems correct to my engineer's brain. Can anyone out there confirm my theory or expound upon it from a position of certainty? Take a look and see what you think. Also, if you know how to pull my reply there into this thread , please do so!

[Mart]

Just thought I would run this up the flag pole. I believe that the oil pump on engines is a positive displacement pump. This means that as long as there is fluid avaialble at the intake, that fluid will be moved through the pump and into the system. It follows then that with a thicker fluid ( higher visciosity ) the system oil pressure would be higher and vice versa with lower viscosity since the same flow through the system occurs from the pump with either. Therefore, low oil pressure with a thinner oil is to be expected and does not mean there is less oil flow through the system. Further, it seems to me that thinner oil which induces less pressure drop though the system and therefore less pressure would flow more easily to all parts of the system. I'll let someone else discuss how the oil actually behaves on the bearing surfaces thick vs thin, bearings vs rings, rings vs valve train.

There ya go
Mart

[silver98]

I think the above thermo-hydraulic discussion is correct, but I would like to add that although a higher oil flow rate would remove heat generated from friction at a higher heat rate, the viscosity is required to linger / coat the bearing and friction surfaces to reduce the friction and subsequent heat production. Without having all the calculations available with the proper values, I can not say at what point the trade off between heat removal rate, Q-dot, and mass flow rate, M-dot, crosses and affords the required protection for the bearing and friction surfaces.


Just my $0.02

Joe

[milehigreg]

Thermo-hydraulic. Q-dot. Man you're gettin' me excited! Anyone else want to weigh in? Remember, there are two parts to this. Flow, pressure and viscosity and behavior at the bearing surfaces. I heard a while back that the manufacturers all went to 5W 30 because they found it provided better protection in the bearings. Less viscous oils also should produce less frction drag. Come on oil gurus!

[G Winter]

I believe the real reason manufactures went to the lighter oil was for gas milage. Bearing clearence has a lot to do with the oil pressure. Another reason for the thiner oil I have notice in newer engines that everything is fit tighter then it was yrs ago. As for heat, I would think that the same principals would apply as with the cooling system. There has to be time for heat transfer. Not very technical but I think I got ro the point .