Engine Temp vs oil weight

[bwco]

I'm curious as if your engine require 5W20 from the factory, and you put 5W40 or 5W50 or even 10W60 oil in it. Will the engine temp gets cooler/hotter/stays the same?

*don't ask me why I would wanna do that, but this is purely a theoretical question that got stuck in my mind for so long.

any inputs ?

 

[opposite_locker]

If anything, the engine will run a bit hotter on thicker oil. Generally speaking, thin oil cools better, thick oil holds up to higher temps better.

 

[hate2work]

Engine temp is regulated by the cooling system. In theory, thicker oil will not make your engine run hotter. It might make it run sluggish, but that doesn't translate to hotter temps.

 

[XS650]

Originally Posted By: hate2work

Engine temp is regulated by the cooling system. In theory, thicker oil will not make your engine run hotter. It might make it run sluggish, but that doesn't translate to hotter temps.


That's an abuse of the word "theory".

On most engines, coolant temperature is regulated, not oil temperature.

The primary reason higher viscosity oil runs hotter is that it takes more work to move the engine parts through and past the oil and that work heats the oil.

 

[Jaymus]

The cooling system does little to nothing for the oil temps. It may help regulate them slightly, BUT you could have 210F coolant temps and 180F oil temps, then go to the track and have 210F coolant temps and 280F oil temps.

The question is HOW MUCH do oil temps rise when using a thicker oil? Everyone says they go up, but is it by 5 degrees, 10? 30??

 

[21Rouge]

So should one compare two oils based upon oil temperature? That is, is there a correlation between engine wear and oil temp...even for oil temps in an acceptable range?

 

[Bluestream]

Thicker oil = more friction = higher oil temps

Same as in real axel...

 

[fito]

How about do syn oils run cooler then dino oils? All I can say is they do in my classic cars.

 

[bepperb]

"Thicker oil = more friction = higher oil temps"

Agreed.

Sure, the cooling system will keep it somewhat in check (without it, obviously the oil would continue to rise in temp to the point of failure) and it probably depends if you have an oil to water or air heat exchanger and other unit-specifics.

Even if your cooling system is so amazing that it can keep the oil temp the same, now the cooling system is working harder and your margin of safety is that much smaller.

 

[StevieC]

Doesn't the Cooling system only do 60% of the cooling and the oil does the remaining 40%?

 

[tomcat27]

Originally Posted By: StevieC
Doesn't the Cooling system only do 60% of the cooling and the oil does the remaining 40%?


In the absence of an oil cooler, much/some of the cooling effect of oil is by the oil transferring heat from one part of the engine to another: say from the piston to the cylinder walls.

 

[oilyriser]

Temp of oil in the sump means nothing. Bearing temps are important.

 

[Ken2]

bwco,

The point is to use the viscosity of oil that correctly lubricates the bearings at the normal, max, and minimum service temperatures. The oil at the hottest spot in the lubrication system needs to be thick enough at that temperature in that spot to prevent metal-to-metal contact.

In most cases the manufacturer's recommendation is just right. In a few extreme cases you'd want to go one viscosity grade higher for very hot & heavy work, or one grade lower for frigid winter temperatures, IF the new oil meets all other requirements for that engine.

 

[FastSUV]

Originally Posted By: Bluestream
Thicker oil = more friction = higher oil temps

Same as in real axel...


Not sure about more friction...maybe more resistance but not more friction I do not think?

 

[Gary Allan]

Originally Posted By: FastSUV
Originally Posted By: Bluestream
Thicker oil = more friction = higher oil temps

Same as in real axel...


Not sure about more friction...maybe more resistance but not more friction I do not think?


Not friction between moving parts ..friction of the oil with itself. This won't be correct for details ..but the difference in mass of one weight over another is virtually none. The difference is how much it drags on the surface it comes in contact with ..and how easily is shears (layers). In a pipe the flow looks like a telescopic antenna...the center moving the fastest since it sees the least cascading inward friction from the outer lay(ers) dragging on the outer circumference of conduit. The harder it is to shear the fluid, the more turbulence/friction ..the more self generated heat.

 

[FastSUV]

well that makes sense....but on the flip side; let's say in a resr diff...you'd think that a thinner oil would cause more heat because the metal-to-metal contact would be more intense and hence heat up the gears more & then heat up the oil itself more....sounds like that is totally untrue I guess

 

[mechtech2]

My empirical evidence is with oil temp gauges on cars.
Going from 20-50 to 15-40 showed a drop in highway temps of about 8 deg C.
Going from 10-40 to 10-30 was similar.
This makes logical sense to me because of the internal shearing and friction of the thicker oils, and the boundary layer that the thicker oils have which inhibits heat transfer.

 

[Gary Allan]

Well, you're switching horses in midstream there. You wanted to know how heavier fluids generate more heat due to friction. Now you want to compare it to how fluid subjected to enough heat allows friction of moving parts.

 

[elwaylite]

I always see the argument for 5w-30 vs 5w-20 in a car that calls for 5w-20, and they mention hot weather. Is your internal engine temp really that diff between a 90 degree summer day and 40 degree winter day, where 5w-30 matters over 5w-20?

 

[BuickGN]

Originally Posted By: elwaylite
I always see the argument for 5w-30 vs 5w-20 in a car that calls for 5w-20, and they mention hot weather. Is your internal engine temp really that diff between a 90 degree summer day and 40 degree winter day, where 5w-30 matters over 5w-20?


It is. I have a temp guage on one of my cars. There's a solid 30 degree difference from winter to summer and the temps tend to rise much quicker during the summer with hard driving.