Engine friction data at low temperature

[Azmio]

Hello everyone,

I am looking for some information on the engine friction data at extremely cold temperature. It would also be helpful if there is also information about the friction difference using different oil viscosity grade.

Thank you in advance.

 

[Xtrema]

The different oil viscosity grades winter rating define how thick the oil is at a certain cold temperature. The oil can be no thicker than XXXX at YY temperature in this test, called the Brookfield viscosity test. So, you can be assured that the engine will turn over more slowly with a 15W than a 0W oil. The classic test for such effects is called the cold cranking test.

Most automobile manufacturers require that everything work at -40 C.

The engine will self-heat the oil to somewhat a normal oil temperature after a few minutes, given enough load on that engine.

 

[Azmio]

Xtrema

I am looking for engine friction data at cold temperature. I need to find out how different grade oils alter the engine friction at extreme low temperature.

The best way to gather such data is through engine motoring at extremely low temperature. Unfortunately, such facility is not easy to find.

Oil viscosity at different temperatures are extremely easy to get but not the friction.

 

[patprimmer]

Azmio

This does not answer you actual question, but obviously clearances will have a significant effect where dissimilar metals are involved, like aluminium piston in iron bore and steel rings.

This might be a lot harder to find data on than oil viscosity and sheer, as it will be very individual from motor to motor.

Also, satisfactory clearances for very cold starting might not be suitable for continuous high load operation, but I guess quantifying that is their reason for your question.

I know in the late 50s early 60s, VW built some special beetles for operation in Antarctica.

As far as I know from anecdotal evidence, they simply increased piston to bore and used some very light weight oil.

I would think Nikasil coated aluminium bores would be more compatible to the extreme temperature range, as would gap-less rings with extra end clearance built in.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Azmio]

Pat

Thanks for your input. Increasing the clearance has been proposed. This can be applied to the piston to bore, crank journal and conrod big end.

However, the production side is too strong and they can easily overpower the design group. By increasing the clearance, the acceptable tolerance band is tighter and many part can be easily described as 'defects' though they perform perfectly under normal temperature.

I understand that engine friction varies from engine to engine, but it is still possible to see the friction trend with different oils and viscosities provided that the engine used is the same.

Nikasil coated block may stand better chance due to closer thermal expansion and cold temperature shrinkage. However, at cold temperature, material with solid lubricant capabilities would help a lot.