Impact of towing on engine oil temperature.

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Q:
What heats up the engine oil while cursing with no load vs. towing?

Longer version of the above question based on my limited knowledge:

Given a fixed rpm, is it correct to assume that the only reason the oil temperature goes higher when towing is due to the increased combustion?

For example if towing at 3000 RPM, more fuel is burned and it dumps more heat into the crankcase.
if cursing at 3000 RPM (with less load) there is less combustion heat.

My question is, if the rpm is fixed for example at 3K and the engine parts are I assume under hydrodynamic lubrication or regime ... Then the only impact that towing (or more load) has on the engine oil is the additional heat from the combustion. Is that cotrect? Anything else inside the engine that is making any significant contact and producing additional heat (friction) from the extra load? How does flywheel come into this equation as far heating up the oil? Anything else?

Thanks!
 
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The primary cause of engine oil heating is friction from shear. Oil temperature goes up with RPMs.

When pulling a heavy load, gear selection will through necessity result in more rpms to maintain speed with the additional rolling And wind resistance that has to be overcome.

combustion has a very small less significant effect on engine oil temperatures.
 

ZeeOSix

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Q:
What heats up the engine oil while cursing with no load vs. towing?

Longer version of the above question based on my limited knowledge:

Given a fixed rpm, is it correct to assume that the only reason the oil temperature goes higher when towing is due to the increased combustion?

For example if towing at 3000 RPM, more fuel is burned and it dumps more heat into the crankcase.
if cursing at 3000 RPM (with less load) there is less combustion heat.

My question is, if the rpm is fixed for example at 3K and the engine parts are I assume under hydrodynamic lubrication or regime ... Then the only impact that towing (or more load) has on the engine oil is the additional heat from the combustion. Is that cotrect? Anything else inside the engine that is making any significant contact and producing additional heat (friction) from the extra load? How does flywheel come into this equation as far heating up the oil? Anything else?

Thanks!

The flywheel is outside the engine block and isn't in any oil - so no effect there, unless maybe you slip the clutch (manual transmission) and it gets so hot that some heat soaks into the crankshaft. If you were just cruising down the road in one gear forever there's probably heat flowing out of the back of the hot crankshaft to the flywheel, so in that instance it could act as a slight heat sink.

As mentioned, most of the heat source causing the oil to increase in temperature is from shearing and friction. There is heat absorbed into the oil from increased engine load (more friction and maybe some increased oil shearing), and increase combustion heat because oil does come into contact with the bottom of the pistons (especially if the engine has oil squirters) and the hot ring pack area.

If you could put an engine on a dyno and run it at exactly 3000 RPM, and incrementally loaded the engine from no load to a full load and let it thermally stabilize, the resulting oil temperature would increase as the engine load increased. Exactly to what degree of oil temperature increase would depend on many factors.
 
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OilUzer

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...
If you could put an engine on a dyno and run it at exactly 3000 RPM, and incrementally loaded the engine from no load to a full load and let it thermally stabilize, the resulting oil temperature would increase as the engine load increased. ...

That's basically my main question.
Given the exact same rpm (e.g. 3000) and towing 8000 lbs. vs. driving (lets say even in the same gear) under exact same conditions without towing a load. Let's also forget about the wind resistance due to trailer , etc. ...
Under these exact same conditions (e.g. dyno) with the exception of load, is the combustion (extra fuel burned) the only or the major contributing reason heating up the oil? Maybe originally more heat is transferred from combustion to the oil and hot oil shears more and produce some additional heat. Kind of like a side effect or a domino effect?
 

OilUzer

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The primary cause of engine oil heating is friction from shear. Oil temperature goes up with RPMs.

When pulling a heavy load, gear selection will through necessity result in more rpms to maintain speed with the additional rolling And wind resistance that has to be overcome.

combustion has a very small less significant effect on engine oil temperatures.

What about exact same rpm but load vs. no load like the dyno example above. Is the oil temp going to be relatively the same with load since combustion has "very small less significant effect on engine oil temperature"?
 
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Q:
What heats up the engine oil while cursing with no load vs. towing?

Longer version of the above question based on my limited knowledge:

Given a fixed rpm, is it correct to assume that the only reason the oil temperature goes higher when towing is due to the increased combustion?

For example if towing at 3000 RPM, more fuel is burned and it dumps more heat into the crankcase.
if cursing at 3000 RPM (with less load) there is less combustion heat.

My question is, if the rpm is fixed for example at 3K and the engine parts are I assume under hydrodynamic lubrication or regime ... Then the only impact that towing (or more load) has on the engine oil is the additional heat from the combustion. Is that cotrect? Anything else inside the engine that is making any significant contact and producing additional heat (friction) from the extra load? How does flywheel come into this equation as far heating up the oil? Anything else?

Thanks!

high level...

combustion heat is one part.

When you are making higher HP and torque the rod is pushing down against the upper bearing shell and SQUEEZING that oil out under tremendous pressure every RPM The oil that runs out of those crank journals and bearing shells under load is hoooooottt.

you can express horspower in terms of BTU and get a good idea what kind of heat you are putting into the oil.

When you pull apart a high HP engine one of the things that shows stress is the upper bearings.
 
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You are burning more fuel when loaded than unloaded at the same rpm. More heat comes from more fuel being burned in the cylinder.
 

OilUzer

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high level...

combustion heat is one part.

When you are making higher HP and torque the rod is pushing down against the upper bearing shell and SQUEEZING that oil out under tremendous pressure every RPM The oil that runs out of those crank journals and bearing shells under load is hoooooottt.

...

your part 1 about additional Combustion heat makes sense to me ...

Question about your second point:
You stated that higher torque, HP and pressure resulting in hot oil ... Is that load dependent if the rpm (e.g. 3000) is the same? I thought the parts are under hydrodynamic lubrication and not making contact. Maybe the layer of oil between parts is much thinner when under heavier load and would result in higher shear (temporary) and higher oil temperature.
So both combustion and shear contribute to additional heat. No?

Btw, I just studied hydrodynamic lubrication a little and they were talking about a layer or wedge of oil supporting between parts and made me think of the thickness of this layer. That may explain the higher pressure you mentioned.
 

ZeeOSix

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your part 1 about additional Combustion heat makes sense to me ...

Question about your second point:
You stated that higher torque, HP and pressure resulting in hot oil ... Is that load dependent if the rpm (e.g. 3000) is the same?

Yes, it's load dependent - but it's not the major heat source that heats up oil. As I explained, if you kept the engine at exactly 3000 RPM and increased the load (opend the throttle more) then more air/fuel is going into the engine and making more power and heat. The tops of the pistons (and heads) will run hotter, and all the oil that hits the bottom of the pistons and flows over the top of the heads will pick up more heat.

So both combustion and shear contribute to additional heat. No?

Correct as explained earlier, but oil shearing from the RPM is the main source of heat.

Btw, I just studied hydrodynamic lubrication a little and they were talking about a layer or wedge of oil supporting between parts and made me think of the thickness of this layer. That may explain the higher pressure you mentioned.

That "thickness of the layer" is know as the MOFT (minimum oil film thickness) in the bearing.

When the oil gets compressed down into the thin wedge of oil that carries the load in the journal bearing, it shears and heats up. BTW, bearings that have a smaller clearance will actually heat up the oil more than a bearing with more clearance.
 
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OilUzer

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@ZeeOSix
I am pretty sure this stuff has been discussed here before. I recall moft, etc. and that higher is better ... I read a lot of stuff but don't pay real attention till I am faced with an issue, question or a problem and then I really have to think about it and that's when it sinks in.
I was discussing towing with a friend earlier and bunch of stuff came up ...

I maybe oversimplifying things.
so basically the conclusion as far as load (e.g. towing) is concerned is:

The higher the load, the thinner the wedge/layer which results in more shear and heat and you hope that the wedge doesn't approach 0. lol

with no load, the parts are more balanced and centered and we have the highest amount of wedge or oil layers between them and the least amount of shear/heat.

Is that correct?
 
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I would say yes to the OP. Not that I'm an expert but given the rpm are the same as you stated, then the extra fuel will cause more heat.

I've owned a Mazda 3 years ago. It didn't seem to have a faulty thermostat as it reached operating temp fairly quick but down a massive hill in 4th gear, engine braking with zero load; it managed to actually drop a large amount on the temperature gauge. Not very scientific but I'm assuming that because it was freezing cold in winter going down a massive hill at 80kmph just engine braking and the cooling system may have been very good, that it indeed lost heat. That was about 2500-3000rpm or so if I recall correctly. If I was going uphill with my pedal to the metal at the same RPMs, I'm sure it would have added much more heat.

So yes for sure, burning more fuel should equate to more heat in almost all scenarios I can think of.
 

ZeeOSix

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I maybe oversimplifying things.
so basically the conclusion as far as load (e.g. towing) is concerned is:

The higher the load, the thinner the wedge/layer which results in more shear and heat and you hope that the wedge doesn't approach 0. lol

Yes, and also the engine RPM plays a role in the MOFT in journal bearings. At higher RPM the bearing creates a larger MOFT oil wedge which makes the bearing center itself more. But, as that happens, the oil is also being sheared more due to increased RPM, but the wedge isn't squished down as much, so there are multiple factors going on at the same time. Bottom line is you don't want to "lug" the engine too much under heavy loads at low RPM because that will make the MOFT go even smaller. You want to find a happy medium between lugging and over-revving. There is a reason why some manufactures say to bump the viscosity up if using the vehicle for heavy use like towing or extended high speed operation.

with no load, the parts are more balanced and centered and we have the highest amount of wedge or oil layers between them and the least amount of shear/heat.

With no load vs high load, the MOFT will be a bit larger with less load on the bearing. But as mentioned above the engine RPM (along with oil viscosity) also plays a big role in what the resulting MOFT is. Thicker oil and higher RPM gives increased MOFT. But higher viscosity oil will heat up a bit more from shearing, but overall it will give more bearing protection because it still gives more MOFT even though it heats up the oil a bit more.
 
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