Hi legends,

Whats the consensus on good quality thick oil, 40w 70, going into a clapped out 602cc that blows some smoke and leaks a bit, I want to get one long last run out of it. Preferably at full throttle.
Or is a full synthetic 10w 60 better?

Thanks!

Harley

If you really are going to do this......

10w60 fully synth, as it has a 10w rating so it will be thin enough to start when cold but as it's hot grade will be SAE 60 it will be almost twice as thick as an SAE40 grade.

SAE40 thickness (kinematic c/St) = 12.5
SAE60 thickness (kinematic c/St) = 21.9

There is always a downside however...better hope your oil pump can work at the kind of pressures that will be generated and it will take quite a bit of energy to push it around. You could end up with enough pressure to open the bypass valve and end up with no flow around the motor.

It will still leak just as much though as the molecule size will be almost the same.

Fix it

Great reply Dave, thank you.
That's what the supercharger is for Viking

Harley

Dave,
back in the days when Citroen credited owners of their cars with a certain amount of technical know-how, they recommended different grades of oil for different countries within Europe, dependent upon the maximum and minimum temperatures which would be experienced through the seasons.
The range spanned from 10W30 up to 20W50.

If you check the visocity indexes detailed on the site linked below, an SAE 50 multigrade could have a viscosity as high as 21.9, so using an SAE 60 on an engine which has rather generous clearances on its bearings may not be such a giant step as suggested, especially if Harley's planning to plough through any hot spots in Australia with the pedal firmly planted...

SAE grade Min. > Max. Viscosity mm2/s (cSt)
40 — — 12.5 > 16.3
50 — — 16.3 > 21.9
60 — — 21.9 > 26.1

From http://www.roymech.co.uk/Useful_Tables/ ... osity.html

There is a bypass valve as well as a pressure relief valve on engines built after 1970, btw.
In sub-zero conditions, the latter can sometimes be heard bouncing off its seat for a minute or so after startup, so I'd doubt that there's any danger of oil starvation.

Ken.