Viscosity comparison - is it important?

[paulswagelock]

So here is my question:

If you look at oil comparisons there is a viscosity at 40 and 100 listed in the specs. There are several calculators around that will extrapolate that out for any operating temperature. The combination of the 40 and 100 can make a large difference in viscosity at operating temp if it is not 100. So here is my question - how important is the viscosity at operating temps (affect performance?), and what would be the normal operating temps for cars (100?), boats (80?), air cooled engined (no guess?).

Should I plot out the OEM recommended oil for temps, and verify my new selection maps closely at the operating range?

 

[Steve S]

For what exact reason?

 

[paulswagelock]

The OEM designed an oil with some purpose in mind. I am asking, first - does this measurement of viscosity really matter at op temps, second - if it does should I try to match it as closely as possible?

 

[Quattro Pete]

Originally Posted By: paulswagelock

Should I plot out the OEM recommended oil for temps, and verify my new selection maps closely at the operating range?

What for? The normal operating temp for your engine is known by its manufacturer, and the manufacturer suggested some some specific oil grades that would work best in this application. That work has already been done, hopefully by someone with a PhD.

Why second guess it?

 

[paulswagelock]

Agree with everything you say so far, but what about when you are thinking of switching grades (which many on here suggest (as well as the Manufacturers like Mobil1), for instance 5w30 to 0w30, 15w40 to 5w40 in diesels.

 

[Ken2]

What IS important is the viscosity of the used oil. The new oil specs do not tell the whole story.

Engine oil is normally warm when it is somewhere over 180°F and under about 240°F. For example, the Perma-Cool thermostatic valve for their oil coolers begins to open at 180°F.

 

[Quattro Pete]

Originally Posted By: paulswagelock
Agree with everything you say so far, but what about when you are thinking of switching grades (which many on here suggest (as well as the Manufacturers like Mobil1), for instance 5w30 to 0w30, 15w40 to 5w40 in diesels.

I wouldn't think that the difference in viscosity at operating temp between 5w30 and 0w30 would be big enough to worry about. Most mfgs actually allow a whole range of viscosity grades, depending on how cold it gets in your area, and typically the 0w-XX grades are good across the entire temperature spectrum.

 

[Steve S]

Just use the recommended Viscosity. The numbers aren't important . Thick enough to protect in the hardest use the engine will see but not to thick as to cost you power and gas mileage. It is all a compromise because usually the oil could be considered too thick when the engine is warming up to too thin when driving the autobahn at 150 mph for hours on end. Probably the biggest killer is using too thick of an oil when for the starting temps are freezing cold or below it takes a long time for too thick oil to reach the pump. Boats are always going up hill with the brakes on. The marine engine is loaded constantly and running at a higher specfic HP at cruise than an auto engine so when I has a boat I would run a 15w40. the 15w40 gives a bit better actual viscosity than a straight 30.

 

[CATERHAM]

Originally Posted By: paulswagelock
So here is my question - how important is the viscosity at operating temps (affect performance?), and what would be the normal operating temps for cars (100?), boats (80?), air cooled engined (no guess?).

Should I plot out the OEM recommended oil for temps, and verify my new selection maps closely at the operating range?


Use the lightest oil (lowest HTHS vis) recommended by the manufacturer for the ambient temps you expect. Then choose an oil with a 0W rating if you want the lowest start-up viscosity.

OR, if you're really adventurous, install an oil pressure gauge an run the lightest oil that still provides the minimum oil pressure as specified by the manufacturer when the oil is at it's hottest (you may want to install an oil temp gauge as well).

If you do the later, you'll likely find that even a 0W-20 grade
is heavier than you need, as in most applications, bulk oil temps don't get above 95C and in a Pennsylvania winter above 85C.

 

[HangerHarley]

Originally Posted By: CATERHAM
Originally Posted By: paulswagelock
So here is my question - how important is the viscosity at operating temps (affect performance?), and what would be the normal operating temps for cars (100?), boats (80?), air cooled engined (no guess?).

Should I plot out the OEM recommended oil for temps, and verify my new selection maps closely at the operating range?


Use the lightest oil (lowest HTHS vis) recommended by the manufacturer for the ambient temps you expect. Then choose an oil with a 0W rating if you want the lowest start-up viscosity.

OR, if you're really adventurous, install an oil pressure gauge an run the lightest oil that still provides the minimum oil pressure as specified by the manufacturer when the oil is at it's hottest (you may want to install an oil temp gauge as well).

If you do the later, you'll likely find that even a 0W-20 grade
is heavier than you need, as in most applications, bulk oil temps don't get above 95C and in a Pennsylvania winter above 85C.


+1 the latter of the two examples is how I know that 10W-40 gives perfect, though not as high, but not blowing by-[censored] open, pressure in my car, and right around 20 to 30 psi hot (no higher than 40 with this one grade, more like 20 hot idle), even when its 100 degrees outside and im idling in traffic then go 80mph on the highway with the AC on blast.

I can only conclude this lower pressure, with Supertech, is lubricating and cooling the engine perhaps even better than a 50 would, and therefore even if it is about 115 out this IS Florida, the engine is lubricated, not blocked or starved for oil with a Thick one, and fine. This IS the correlation, as to "Flow" not Pressure, right?
Im really stunned i dont need a 50 in that example, except that cruising the highway IS easy on the engine, and then my OP is at 60Psi with a certain 10W-40. Even other 10w-40S,its at 75psi, which is past Bypass.

CATERHAM you rock!!!!

 

[mechtech2]

Engine oil runs at outside ambient temps when you start it dead cold.
On full warm up, it normally goes to about 200 F. Up to 225 or so is very normal.
In cold weather, it does run cooler, even though the water temp stays pretty constant [thermostat]. At least it takes much longer to get up to 200+.