Sources of engine heat and effects of oil viscosity

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in general, what % of engine heat is generated by viscous shearing, combustion or friction? Anything else terminology wise? Is viscous shearing a component of friction which is causing the heat, and heating up the oil which is heating the block ...

I always thought that most of the engine heat is from combustion ... viscous shearing was mentioned in one the recent threads on this forum and made me wonder about the percentages.

my final question and as much as I enjoy it,
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it is not my intention to turn this into thick vs. thin discussion
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some will be assimilated eventually
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However, if you were NOT concerned about any other oil functions/qualities EXCEPT heat generation (viscous shearing? and friction) and heat transfer (e.g. away from the engine to oil cooler or the block), how does lower viscosity oil compare to higher viscosity oil? overall which oil will keep the engine cooler? I've read that thinner oil causes less heat but thicker oil will carry more heat (away) so I'm not sure about overall impact!
 
Ultimately every bit of energy in an engine comes from the fuel (yes, even the energy in the battery), so ALL heat comes from combustion.
 
Originally Posted by OilUzer
I've read that thinner oil causes less heat but thicker oil will carry more heat (away) so I'm not sure about overall impact!


Where have you read that thicker carries away more heat ?

Interested in sources...

Per heat transfer, a heavier oil should carry more heat per unit volume, but that's about it.
 
Dang Shannow ... your first post has all kinds of "scary" graphs and tables.
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Thank you! I will have to study the above charts and figure and see if I can come up with some numbers. I am assuming my questions may not have a simple yes/no or % answers.

Another question after seeing the above charts, assuming that less heat is generated with thinner oil at the beginning of the oil life cycle ... the engine may run cooler at first compared with thicker oil. However after several thousand miles, is it possible that thicker oil may "lubricate" better (friction wise) and produces less heat than a thinner oil of the same age? You see what I am getting at? Basically is it possible that thinner oil has advantage (heat generation wise) at the beginning and for a while (let's say few thousand miles) but when old(er), thicker oil will produce less heat? I am just trying to understand the science of it and this is not going to influence my choice of viscosity. Was trying to avoid thin vs. thick but looks like it's not possible
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Originally Posted by Shannow
Ultimately every bit of energy in an engine comes from the fuel (yes, even the energy in the battery), so ALL heat comes from combustion.


I meant the heat generated by moving parts and friction (where oil comes into play) vs. the heat generated by combustion.
 
Dunno...there's only one poster in the thread so far who has used the "thick/thin" verbiage and multiple times...you say that you are avoiding that, then reference it, then state that it's unavoidable...why ?

You can look at the Stribeck curve, with and without friction modifier effects, and that will add understanding.

I've posted around BITOG (can't be arsed finding it) of my experiments with a type K thermocouple in the dipstick hole of my Briggs mower..5W20, and 25W60 as book ends...the increase in temperature was 100% due to the increase in viscosity, and clearly measurable...just didn't make an horrific knock on cold start like the 5W20 did at 30C.
 
Originally Posted by Shannow
Originally Posted by OilUzer
I've read that thinner oil causes less heat but thicker oil will carry more heat (away) so I'm not sure about overall impact!


Where have you read that thicker carries away more heat ?

Interested in sources...

Per heat transfer, a heavier oil should carry more heat per unit volume, but that's about it.


I don't have a scientific source or any paper just the stuff I've read on bitog and wasn't sure what is true or not. Basically I would like to know (everything else aside), if an engine runs cooler with thinner oil or thicker oil or is it insignificant? I am talking about overall heat generation (friction and effects of oil viscosity) and heat transfer (from oil to oil cooler and engine block and effects of oil viscosity on that) .
 
Simplest example is my air cooled briggs...could be yours too.

Thermocouple down the filler/dipstick hole, and the thicker oil runs hotter...it has to, that's physics.
Thinner is cooler, until thinner to the point that something picks up, then temperature skyrockets on the way to failure (note to usual suspects, this is not saying that thin kills engines in every case, but thick can't kill until it can't pump on cold start).

Does that meet what you wanted ?
 
Originally Posted by Shannow
Simplest example is my air cooled briggs...could be yours too.

Thermocouple down the filler/dipstick hole, and the thicker oil runs hotter...it has to, that's physics.
Thinner is cooler, until thinner to the point that something picks up, then temperature skyrockets on the way to failure (note to usual suspects, this is not saying that thin kills engines in every case, but thick can't kill until it can't pump on cold start).

Does that meet what you wanted ?



Yes kind of, my question regarding overall engine heat was if heavier oil carries more heat per unit volume (as you have mentioned above), isn't that same as what I said that I've read on bitog that thicker oil will carry more heat away? I am assuming heavier oil is thicker!
 
OK, thickness and density...yes the are typically correlated.

I am not stating that what you offered in your original post is correct, as you aren't even providing that which you claimed that you read, while claiming that I'm now supporting it.

Per the scary pictures in my first post...heat in the bearings transfers INTO the block, and is generated BY the viscous shearing...so how is thicker oil "carrying away more heat" ?

trip-trap-trip-trap...is that what I'm hearing ?
 
Originally Posted by Shannow
OK, thickness and density...yes the are typically correlated.

I am not stating that what you offered in your original post is correct, as you aren't even providing that which you claimed that you read, while claiming that I'm now supporting it.

Per the scary pictures in my first post...heat in the bearings transfers INTO the block, and is generated BY the viscous shearing...so how is thicker oil "carrying away more heat" ?

trip-trap-trip-trap...is that what I'm hearing ?


I am not claiming that you are supporting everything i said ... It was just a question! It sounded to me that what I said (from my bitog reading) and what you said were the same thing as far as thicker oil being able to carry more heat. You called it more heat per unit volume .... I am no longer sure if we can agree on this or not! lol
However if we agree with the above (ability of heavier oil to carry more heat) then my main question was the overall impact. If the heavier oil which is causing extra heat is also taking some or most? of that extra heat (due to its ability to carry more heat vs. thinner oil) to the oil cooler or transfer more heat to engine block (contact surfaces) where the extra heat will dissipate in both cases ... So more heat is produced and more energy is lost (heat) but (again this is a question) not all that extra heat stays in the engine due to better efficiency of thicker oil (source of the problem/heat) in dissipating some (most?) of that extra heat. So your engine will run hotter but not as bad as you may think (relative to lighter oil) again based on my understanding of what I've read on bitog ... and I wanted to see how true that is hence my "overall impact" questiin.
 
Forgot to mention that one of my co-workers has a digital coolant,oil temp and trans oil temp readout. I asked him about engine temperatures after he switched from 0Wx20 to 5Wx30 ... and he said he hasn't noticed any differences and they are within the same range as before. His car has engine oil cooler and he has also added 2nd trans oil cooler and is into these kind of things and pays attention to gauges!

This is just one example and it is not a scientific test. I am sure his engine will run hotter with 5Wx30 but it hasn't been significant enough for him to notice. I guess it also depends on where the temperatures are taken...
 
According to oil charts, in Tennessee(Chattanooga) , we should be able to run straight 30 wgt oil year around if your car calls for 30 wgt oil...

30wgt oil should be able to flow at 23degrees F. or some use -5C. depending on what part of the world you use either F or C.

Our average temp here in January is mid 20s F.
 
Forget the concept of carrying away more heat since it's tripping you up and it's not what's important. What's important is that in normal circumstances, a thicker oil will be hotter because of more viscous heating occurring in it. Shannow's table 7 quantifies the heating power being generated in different viscosity oils in a connecting rod bearing. Thicker...more heat...higher temperature. If flow rate is lower, as it is in that table for the thicker oils, residence time is longer, further increasing how much heat is generated in the oil and what temperature it rises to.

RPM has a very large effect on viscous heating, as Shannow's 2nd to last (scary) graph shows.
 
Originally Posted by OilUzer

I don't have a scientific source or any paper just the stuff I've read on bitog and wasn't sure what is true or not. Basically I would like to know (everything else aside), if an engine runs cooler with thinner oil or thicker oil or is it insignificant? I am talking about overall heat generation (friction and effects of oil viscosity) and heat transfer (from oil to oil cooler and engine block and effects of oil viscosity on that) .


I can add a bit of anecdotal evidence here from the period when I used M1 5W30 ESP, which has a higher HTHS (~3.6 vs. 3.1) as well as a higher 100C viscosity (~12 vs. 11 cSt??) than the M1 5W30 I had been using for quite a while.
I always keep oil temp up on the small display in my car and I did notice very quickly that these were running higher with the ESP...I had a pretty good feel for where they were going to run for a particular kind of driving at different times of the year and I felt that the values I was seeing after warmup were 5F or more than what I was used to.
This actually freaked me out a little bit and I made a panicky post either here or on subaruforester.com and was informed about the effects Shannow is explaining in detail here.
I guess it might be questionable to assert that the engine as a whole is hotter because the oil temps are up, but it makes intuitive sense to me.
 
Originally Posted by JAG
Forget the concept of carrying away more heat since it's tripping you up and it's not what's important. What's important is that in normal circumstances, a thicker oil will be hotter because of more viscous heating occurring in it. Shannow's table 7 quantifies the heating power being generated in different viscosity oils in a connecting rod bearing. Thicker...more heat...higher temperature. If flow rate is lower, as it is in that table for the thicker oils, residence time is longer, further increasing how much heat is generated in the oil and what temperature it rises to.

RPM has a very large effect on viscous heating, as Shannow's 2nd to last (scary) graph shows.


I totally agree with you, "carrying away more heat" subject went off track by focusing only on one component (heat generated by viscous shearing).

Let's go back to my original question of what % of heat is generated by combustion and what % by moving parts and friction.

Doesn't oil also get hot from the effects of combustion and the heat generated in the cylinder head? What % is contributed by that. So if a heavier oil can carry more heat (e.g. to oil cooler or heat transfer with oil contact with the engine block), then even though a heavier oil is causing more frictional heat, isn't it carrying more of combustion heat (as opposed to lighter oil) away?
What is the overall impact of that? That's where I am somewhat confused. Maybe Shannow's chart explain that. I need to pay more attention
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See Shannow's 3rd to last figure for that. Don't think about carrying away more heat. A hotter liquid is carrying away more heat but when it's hotter because of more viscous heating, it still causes a net increase in temperature in the engine That heat is transferred to the later places that liquid goes.
 
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