Oil Weight
can you explain why not to use a single grade oil please .
single weight only if you pre heat your oil for a race
Exactly. Short explanation is:
Oil viscosity is very temperature dependent.
The colder the oil, the thicker it gets. The warmer the oil, the more easily it flows.
A multi-weight oil and a single grade oil will have about the same viscosity at operating temperature.
For example, at 212* F, a straight 30 and a 10w-30 will both have viscosity around 10.5 - 11.5 CentiStokes.
A multi-weight oil will flow better at lower temperatures than the equivalent straight weight.
Using spec sheet for Havoline's oils at 140* F
for example;
30 wt has a viscosity of 40 centistokes
10W-30 has a viscosity of 32 centistokes.
As rpm increases, more volume is needed to support the bearings. When the oil is thicker than design viscosity, less volume will flow through the engine itself. The working viscosity range depends on bearing clearances and so forth. A worn engine or one built 'loose' may need a higher viscosity at the same temperature compared with the same engine blueprinted to factory spec. on the tight side.
If the links to Wyrmrider posted to Widman's website aren't working right, this one should take you directly to the pdf.
Selecting Oil for Flat Tappet Engines, Widman pdf.
