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Thinking of Going from a 15W 50 to 5W 50 on a HiCam to Lower Cold Oil Pressure Any Opinions/Advice

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So here is some rough oil pressure data I currently have running the bike on Motul 300V 15W 50 with the Griso spring in the PRV on the HiCam

20C  1200RPM 83psi

30C 1200RPM 81psi

40C 1200RPM 80psi

50C 1200RPM 79psi

58C 1200RPM 76psi

64C 1200RPM 63psi

64C 3000RPM 80psi

82C 1200RPM 40psi

82C 3000RPM 74psi

82C 4000RPM 76psi

90C 1200RPM 32psi

90C 3000RPM 72psi

I reckon that bike will normally run at least a 90C oil temp under normal running and in order to get the pressure down a little at the colder oil temps I was wondering if it would be worth changing grades to a 5W 50, Motul have a fully synthetic car engine oil in this grade and as there are no wet clutch issues with the Guzzi, I wouldn't have thought that there would be any harm running an oil specified for car use.

I'm pretty relaxed about any pressure below 80psi and the differences between the idle and 3kRPM pressures seem to be less when the oil is thicker (generally after 3k there isn't much change in pressure no matter the RPM). The problem being I daren't start it and ride it as I dread to think of the pressures I'd see below 65C when the RPM rises. The pressure pretty much plateaus at 2k more RPM just tends to raise the pressure perhaps around 4-5psi

I wouldn't do this right away as I need to get the bike out for a decent run to get an idea of where the oil temperature stabilizes and that would determine if I change to a 5W-50/10W-60 or not and/or adjust the PRV by removing the 1.5mm shim, which I think would drop the pressure around 15psi. I'd be a bit loathed to do that though as at the higher temps the pressure is pretty well where I'd like it to be

Just sorta throwing this out there for some experienced heads to comment and see what some of you thought.


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There is no downside to running the lowest W number you can in your climate John as long as it's a full group4 synthetic. The lower the W figure the better, that's why just about everything I own runs on Mobi1 0W-40. Heavier W grades are only a factor in mineral based oils that suffer from shear down.


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