Flash point?

[spanky]

Does a higher flash point temp. mean an oil can withstand higher operating temperatures and is therefore less likely to degrade or sludge? Would an oil with a higher flash point be better in engines that are known to run hotter than others (i.e. Toyota)?

 

[haley10]

I think your on the right track, but I have found comparing manufacturer's data sheets on flashpoint somewhat less than useful in making real world comparisons and there are different test methods.

Lab derived flashpoints and data sheet flashpoints look very different.

I know certain oils like Mobil Drive Clean @ 392 and Castrol GTX @ 415 (iirc) from data sheets were overly conservative, when the oil if far better than that.

NOACK volatility would be the best # to judge by, but it often not available as an actual #, just the
Just too much leeway for me to compare oils on flashpoints.

 

[TallPaul]

Definitely NOACK is the number to judge by, but alas, like haley10 says, it is often not available. Therefore, all else equal, I will go for the oil of the higher flash point.

 

[Blue99]

As both Haley & TallPaul have noted, some caveats are in order when viewing flash points.

Flash point is actually the ignition temperature for the most volatile component in the formulation.

So while the base oils may be high VI index with very good high temperature stability, a volatile component, such as a pour point depressant or viscosity modifier, may create an artifically low flash point.

And my example of this is the Clean 5000 & 7500 lineups that all have the same low 392F flash points, regardless of viscosity grade.

The other issue is in regards to method. Cleveland Open Cup(COC),ASTM D-92 is very common, but also seen is the Pensky-Martens Closed Cup(PMCC), ASTM D-93 in which the sample is stirred in a covered cup to contain the vapors.

Here's a Link that gives a brief description of both methods, not very in-depth, but at least conveys the general concepts of the 2 test methods.