Viscosity at 275 Degrees

[Jim]

What would be thicker at 275 degrees F, a 20W50 or a SAE 50?

 

[Al]

I would guess the 20W bc it has polymers which will unravel more and make oil thicker than the 50 wt. But this oil will not be shear stable like the straight 50 wt. and therefore after a while will (may) shear down and get thinner. Just a guess though These should be in the 8cSt Range (equal to a heavy 20 wt oil at 210 F ) [ November 03, 2003, 09:01 PM: Message edited by: Al ]

 

[Kompressor]

I would put my money on the SAE 50, if we're talking about 275F in the crankcase of a running engine. I have mentioned before how my jetboat punishes oil with heat, its been my experience that even SAE 40 holds up much better than 20w50 under extreme heat (much more consistent WOT pressure).

 

[unDummy]

It depends on the brand/type. As far as I know, SAE doesn't test the oil at 275f for the SAE50 or 20w50. So, there is no answer but your own personal experience and testing.

 

[Flimflam]

quote:

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Originally posted by Kompressor: I would put my money on the SAE 50, if we're talking about 275F in the crankcase of a running engine. I have mentioned before how my jetboat punishes oil with heat, its been my experience that even SAE 40 holds up much better than 20w50 under extreme heat (much more consistent WOT pressure).

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Kompressor, you are absolutely right. That straight 40-weight is one tough oil. Even running OHC 4-cylinder engines at 12,500 RPM in the racetrack, on 95 degree Summer days, straight 40-weight Dino held up. Even straight 30-weight Dino wasn't too shabby. Multi-grade oils, with all their squiggly V.I polymers: as one of the brothers said in here a few days ago, it is like certain chain Hot Dogs and Hamburgers: "if you knew what goes into them, you would not eat them."

 

[Patman]

One thing that needs to be addressed here is that if you're seeing 275 degrees on a regular basis, then an oil cooler is definitely in order.

 

[Dr. T]

Not knowing much about straight weights, since both are a 50, they should roughly be the same at that temperature...however, after many miles of use, then my money would be on the straight weight holding it's viscosity better than the multi-visc. oil (which starts off with a thinner molecular weight base oil) which depends on the polymers for thickening. Guess it will depend on the quality of polymers added...