Engine Temp vs oil weight

[BuickGN]

Originally Posted By: 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


Got a temp guage in the diff too. It barely runs 30 degrees above ambient when running it hard so it really makes no difference.

 

[elwaylite]

WOW, the oil temp is a 30 degree diff?

So I guess some prefer the 5w-30 on summer days because it has a higher HTHS?

 

[BuickGN]

Originally Posted By: elwaylite
WOW, the oil temp is a 30 degree diff?

So I guess some prefer the 5w-30 on summer days because it has a higher HTHS?


It obviously depends on the engine and just how much of a temp swing. Another important factor is whether or not it has an oil cooler. If there's a cooler, the temp swing will likely be less between summer and winter.

I see roughly 30 degrees change from a low 30s winter to a 105 degree summer day. Nearly a 2:1 ratio but I'm sure that varies by engine.

 

[Gary Allan]

YMMV. I never saw much over 220F regardless of if it was 70mph loaded ...or idling and watching it cycle with the coolant temp. That doesn't mean that it was a typical oil temp. It just meant that it was the temp at typical highest sustained load and at idle. You're cooling system may allow for a broader or narrower span of temps "depending" on lots of stuff.

For example, except for idling or high speed, oil temps of 200F were hard to attain.

Again, this was a 50-60hp/liter engine driven like you're not looking to refit it so you can make even more power.

 

[Captain_Klink]

the oil is the single most important fluid to cool the engine. the oil gets right into the really hot spots. the thinner the oil is, the more it can flow. more flow = better cooling, everyone knows that. at the very high temperatures of engine combustion, this makes the oil get thinner, so the molecules "adapt" chemically to the very high heat by becoming thinner and cooling better.
at that extreme heat, there is very little difference between 30 40 and 50 weight, the main difference is in the film strength. that is why racers choose their oil weight judiciously, and resort to frequent engine rebuild. Everything is a trade off. for you and i, we just want the one engine to last, so we would use a thicker grade with more film strength if we were racing it, or a thinner grade for normal use.

i basically use the thinnest oil allowed by the manual, since i don't use more than just brief WOT, and only at higher rpm. at those normal conditions, the oil is running cooler, and a thinner oil will flow better to keep the engine hot spots cooled the best.

in some cases, especially motorcycle engines, engine life is extended by using an oil cooler.

 

[Bluestream]

I don't have a temp guage, but in the summer 10W30 drains out with the viscosity of water, and will burn my hand if in get splashed. IN a winter oil change, 10W30 drains out "warm" and much thicker, no risk of burnt skin.

In my opinion 5W20 in winter is way thicker than 10W30 used in summer. Operating temps I am talking about here.

 

[BuickGN]

Originally Posted By: Bluestream
I don't have a temp guage, but in the summer 10W30 drains out with the viscosity of water, and will burn my hand if in get splashed. IN a winter oil change, 10W30 drains out "warm" and much thicker, no risk of burnt skin.

In my opinion 5W20 in winter is way thicker than 10W30 used in summer. Operating temps I am talking about here.


I completely agree with that.

 

[XS650]

+1 An oil temperature shift of about 15F changes actual oil viscosity about the same as one full SAE grade at operating temperatures.

When you consider xW-20s tend to be on the high viscosity end of the SAE grade and xW-30s tend to be mid range or lower, the temp difference to make an xW-20 act like an xW-30 at operating temperatures is probably even less than 15F.

Edit: I ran M1 5W-20 and 10W-30 through a vis calculator. If you drop their 5W-20 from 100C to 90C (an 18F drop) it is the same viscosity as M1 10W-30 at 100C.

That's more than 15F, but only 60% the 30F seasonal change that BuickGN observed. A 30F seasonal change, which is a reasonable number, means the actual viscosity of the oil changes the equivalent of nearly two SAE grades.

 

[Gary Allan]

Originally Posted By: Bluestream
I don't have a temp guage, but in the summer 10W30 drains out with the viscosity of water, and will burn my hand if in get splashed. IN a winter oil change, 10W30 drains out "warm" and much thicker, no risk of burnt skin.

In my opinion 5W20 in winter is way thicker than 10W30 used in summer. Operating temps I am talking about here.


But neither of those temps are peak temps under sustained load. You're dealing with either not cooling fast enough fluids or fluids that have enough time to shed heat due to ambient conditions.

You can also cite that you can't touch your pan in the summer ..but can in the winter. You can be up against the max throughput of heat that the pan material allows ..and whatever that is under those ambient conditions is tolerable.

 

[elwaylite]

I think, after do a LOT of reading the last few days, Im gonna go with a 0w-30 or 5w30 flavor, as opposed to the 0w-20 and 5w-20 recommended for the cars. Im starting to think this is mainly CAFE, and that the 30's have better protection on the hot days, and do just fine on the cold days. Especially the 0w-30.

 

[Gary Allan]

Your fuel economy difference will be mainly determined by your trip length. The oils are most alike at the peak temps and more dissimilar the colder you go. 25 mile one way commuter? Little, if any, difference. 5 mile commuter? You may be on the SAE chart when you turn off the key.

 

[jorton]

Originally Posted By: Bluestream
I don't have a temp guage, but in the summer 10W30 drains out with the viscosity of water, and will burn my hand if in get splashed. IN a winter oil change, 10W30 drains out "warm" and much thicker, no risk of burnt skin.

In my opinion 5W20 in winter is way thicker than 10W30 used in summer. Operating temps I am talking about here.


So the only area the cooling system regulates is the radiator.

The watery summer 10w-30 probably has viscosity in the 5w-30 range which is normal. Best year-round grades would be 5w-30, and 0w-30 synthetic.