Zetec engine: oil weight question

[wemtd]

oh my! amazon first offered me a 'smile' popup. And then proceeds to list a 275Gal option for higher spec engines?

[oilteq]

Perhaps the difference in the test is in the additives put in by the oil mfg, not the weight?

 

There is not a lot of data on HP vs viscosity, but with government mandates, there is a lot of data for fuel economy vs viscosity. So, if fuel economy is a good proxy for HP…

 

The gains to be had by using a lower viscosity oil come from fluid efficiency, not mechanical efficiency. There is just less parasitic drag from pumping and churning. Although friction modifiers help, the big gains come from lower viscosity.

 

The biggest gains in fuel economy come at low loads, where the energy required to pump the oil through the engine is a greater percentage of the total energy consumed. At WOT, pumping and churning is a smaller portion of the total energy used, and therefore much less of an influence on fuel economy.

 

I think there is a trade-off between sealing the rings and lower viscosity. Too thick, and you waste energy circulating the oil through the engine. Too thin, and combustion gasses blow by the rings instead of converting that energy to the flywheel. The sweet spot would vary somewhat with oil formulation, but I am thinking primarily with the engine (tolerances, combustion pressure, rings, pump, and windage). If I am right, modified engines, especially those with higher compression or forced induction, would benefit from a thicker oil than the stock engines they are based on.

 

Blaine

[1turbofocus]

I run Mobile 20-50 full synthetic in all my Customers engines and on mine , I feel they will be run hard and I prefer the added protection over the very very minimal loss to pump it , In colder weather I tell them to drop to mobile 15-40 full synthetic

 

Tom