Thick vs Thin Oil Qu

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Originally Posted By: MolaKule
It's on here somewhere but I did IR readings on an air cooled single cylinder engine during a hot summer day in Kansas.

As I recall, the thicker oil caused a head temperature of about 50F hotter than the thinner oil.


Wow! Might justify the thinner oil then.
 
Originally Posted By: FoxS
All things being equal except oil, which engine will reach operating temperature faster, the one with 20 weight oil or the one with 40 weight oil?

And why?


This thread has been rattling around in my head for a while, and I've found this chart in a paper.

warmup.jpg


Frictional losses due to the lubricant viscosity in the test engine are shown with time (warmup), and as I've mentioned regularly (and been pooohpooed by many), are significant.

In the test engine, you can see that just after start, 4KW of heating is provided just by the oil being sheared in the engine...naturally this drops off as the oil heats.

for a given load/RPM, this heating is dependent on viscosity (I've duplicated Molakule's tests on my mower with 5W20 up to 20W60).

So I'm confident that were the lubricant a ganuine SAE40 versus SAE20 test, the SAE40 WOULD reach temperature sooner.
 
I've noticed with my car that the fuel consumption just after a cold start is easily 3 times higher than when the engine is fully at operational temperature. This consumption quickly falls off to 2 times but after that it takes longer to decrease.

It's a diesel engine, and take a LOT longer than that spark ignition engine to get up to temp. I can drive 2-3 miles (typically 25-30 minutes of running) even when it's not yet freezing before the coolant even gets up to operational temperature. The oil and gearbox take longer as evidenced by the fuel consumption. I stick to the speed limit and accelerate slowly until the car is fully heated though. Also quite a bit of traffic congestion in the mornings so the 10Nm torque output is probably not too far off what my engine sees on average.
 
A manual choke and fast idle when cold make more of a difference to fuel use in the warmuphase than the KV, but at the same time every little helps.
 
yes, that's what interested me!

but maybe the 3.5 HTHS is an exaggeration? the kinematic viscosity is in range of an ilsac grade...

MSDS claims it's a groupIII basestock, do they exist with that viscosity index, without significant VI use?
 
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It doesn't expressly claim A3/B4, but suitable for...given what I've seen with some of the names out there in "recommended for", it's possibly false.
 
Originally Posted By: MolaKule
It's on here somewhere but I did IR readings on an air cooled single cylinder engine during a hot summer day in Kansas.

As I recall, the thicker oil caused a head temperature of about 50F hotter than the thinner oil.


That difference is a lot more than I'd expect.
 
http://www.bobistheoilguy.com/forums/ubbthreads.php/topics/3464122/Re:_Aviation's_Version_of_Mobi#Post3464122
 
Originally Posted By: MolaKule
It's on here somewhere but I did IR readings on an air cooled single cylinder engine during a hot summer day in Kansas.

As I recall, the thicker oil caused a head temperature of about 50F hotter than the thinner oil.


50F, as compared to what a 0w8 to a 25w60? What was the intial and final temperatures? Do cylinder temperature difference hs correlation to engine oil tempertures. I flew a Cessna that CHT was way high at 400+F, EGT at 1250F and the oil temperature remained in the green arc for the whole flight ... So you measure viscosities endo-friction heat at the head of the subjct engine?
I'm not impressed by that
grin.gif
 
Originally Posted By: Pontuual
Do cylinder temperature difference hs correlation to engine oil tempertures.


Do a search Ponty.

I was never impressed by your obfuscations or lack of tribology education.

Oil temp tracks cylinder head temps. Basic thermodynamics.

This informal test was done on an air cooled mower engine using an IR gun; ambient air temp was in the low 90's as I recall.

Oil used was a synthetic 15W50 at the high end of viscosity verses a synthetic 5W30 at the low end.

In between was a 10W30, 10W40, 15W40.

At every notch up in viscosity I saw an increase in head temp.

More energy is required to move a high viscosity oil than a low viscosity oil. Where does tha energy go, Ponty? Explain please.
 
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CHT and oil temp correlate rather poorly in most light aircraft. Oil coolers are almost universal, and there is also a thermostatic oil cooler bypass valve in most systems. Doesn't mean oil temps can't go way too high in the right circumstances, but in 'normal' conditions there is not a near-linear oil temp rise and fall in concert with CHTs as one might find in an air-cooled engine without an oil cooler (such as the typical lawn mower engine).
 
Originally Posted By: INDYMAC
I thought the question was about SAE 20 and SAE 40 grade oils. Where do you get multi-viscosity from in the discussion?
From the simple fact that in the real world multigrade is by far the most common oil, and differing flow rates was one of the motivations for creating multi viz oils. What's the point of hashing this out when multi grade oil changes the parameters. I'm not much interested in academic exercises. The time would be better spent in observations of multigrade oil behavior.
 
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Originally Posted By: HerrStig
INDYMAC said:
I'm not much interested in academic exercises.


Maybe in the wrong forum then?

Straight-weight oils are admittedly a minority interest, though they still have a following here in Taiwan and in the hotter areas of the US.

I'd guess straight-weight oil was used here as a simplifying case, since viscosity was the main interest.

Multigrades would complicate the interpretation, and its complicated enough.
Click to expand...
 
Originally Posted By: FoxS
All things being equal except oil, which engine will reach operating temperature faster, the one with 20 weight oil or the one with 40 weight oil?

And why?


That depends on which engine is being lubricated the best.
The engine with the least operating friction will run the coolest.
 
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