Would larger oil hose size increase cooling?

I don't know how a larger oil hose would give better cooling. All it would do is lower the oil pressure somewhat which would not affect cooling. Oil flow rate would not increase because the pump has a fixed displacement and puts out the same flow independent of pressure. As long as the normally used 1/2" hoses keep oil pressure within acceptable limits, which they do, the only thing larger hoses would do is add weight. I would guess that the larger (#10) fittings which are on the oil pump suction side help reduce the pump inlet vacuum to avoid cavitation.

hi Mike

you can not compare the 912/914 systems to the 915 and 916.  The new bigger lines are needed first because these engines have piston oilers internally.  These supply oil spray to the bottom of the pistons to keep the dome cooler underneath.  The extra oil adds a lot of volume to the system circulation, more than the 912 iS.  All of the injected versions have a larger oil pump that is capable of about 20%more flow than the legacy pump on the 912/914.  The 915 and 916 also require double return lines to the oil tank, a single larger line is not suitable as flow is not the same in a very large hose compared with 2 smaller ones.  Naturally the larger fittings are to limit the times there is a "squeeze" point in the oil flow.  

Cheers

Rotax Wizard wrote:

hi Mike

you can not compare the 912/914 systems to the 915 and 916. 

Thanks for the reply Rotax Wizard!  Although I'm not sure where you get the idea that I'm comparing the 912/914 to the 915/916 systems.  Everything I discussed was pertaining to the 915/916.  

When you say "new bigger lines" what size are you referring to? 

I'm trying to figure out if I need to use 5/8" hose to/from the AN10 fittings instead of the 1/2" hose I've been using on my 915 and if it would improve cooling if I did.  And if so, why doesn't Rotax specify that in the Installation manual because 10mm (.39") ID hose is the minimum it specifies at least twice.  

It would seem larger is better but I'm trying to learn here if that's actually the case and why.  And if not, I would like to remain 1/2" hose which is what I currently have on the 915 and is over and above the minimum specified in the manual.  I'm about to replace the 915 with the 916 so oil cooling will be even greater concern.   If I'm going by AN fitting size, I should be using 5/8" hose from the tank to the pump, and then 1/2" return hoses.  Also the 916 parts catalog only shows AN10 fittings using the larger M22 threads for the large oil cooler vs the 915 which shows both M22 and M14 fittings so it would seem they want greater volume with the 916.  But again, this isn't reflected in the installation manual so I'm looking for clarity. 

Thank you!

Mike

Mike

The IM says 10mm (.39”) “minimum” internal diameter.  So I would think that after that size there would be no additional benefit.  The 1/2” hose likely already provides a bit of margin. Avoid sharp bends.