Temporary Engine Oil Viscosity Changes at High Temperatures

The work starts with the investigation of the temporary viscosity loss of engine oils (SAE Paper No. 740976) and extends to the evaluation of the temporary viscosity changes on multigrade engine oils at the crankshaft bearings of European gasoline engines.

In view of this, oil temperature is measured and a calculation is made of the distribution of shear rates and pressures acting on the lubricant film at the central crankshaft bearing of a European engine.

Then an experimental evaluation is made of the temporary viscosity changes at high temperature of a multigrade oil under the separate action of high shear rates and pressures.

A rolling-ball viscometer is used to measure the temporary viscosity of oil under pressure.

Finally, an attempt is made to draw up a balance of the temporary viscosity of a multigrade oil in the different points of the bearing under examination.