Oil's part in cooling engine

[PWMDMD]

Transfer of heat is cooling
Originally Posted by BrocLuno
So oil's job is heat transfer more than cooling.



Transfer of heat away from one thing to another IS cooling.

Also, I'd argue the reduction in friction by oil is its main job - in the other words preventing heat from being generated in the first place.

 

[vw7674]

multi-weight oils transfer heat far better than mono grade like 30w.
it's why my air/oil cooled VW bus runs better on 10w-40 versus the ancient call-out for 30w.
It's also why the engine sump is heavily finned for heat transfer. On the outside & the inside.
The thinner grade circulates faster, carrying heat with it to the cooler & finned sump faster than a dedicated mono-grade.

 

[y_p_w]

Originally Posted by Virtus_Probi
Originally Posted by y_p_w

Most OEM oil coolers should be an oil to coolant heat exchanger. Most often right where the oil filter mounts. I've heard of some aftermarket kits that are more like an oil filter base extension if there's enough room. Then there needs to be a coolant line and I'm not sure about how to tap into it.

Both cars I've owned had oil coolers where the oil filter mounted right on the cooler. I could always see the coolant hoses running into the heat exchanger. First was a 1995 Acura Integra GS-R. I don't believe the non-VTEC Integra had one. Then my 2004 WRX.

There are some odd aftermarket oil coolers that are like little radiators. Not sure how one is supposed to plumb an oil line though.

You're right, the cooler is right under the filter mount...I spaced out in my earlier post. It is right NEXT to the fill port, at least!

Technically the oil cooler becomes the filter mount, and I guess this oil cooler even has the collection cup since it's top mounted. Your sig says a 2014 Forester XT. I found this photo. The filter of course sits higher because of the oil cooler.

Compared to a 2016 Forester 2.5 the mount/cup sits lower because there's no oil cooler.

This type of oil cooler is great. Not only does it keep the oil from getting way beyond 100ºC but it also warms up the oil faster when cold. I believe without an oil cooler it typically takes longer for oil to get up to regular operating temperature, even when the coolant has reached the thermostat temperature.

 

[Virtus_Probi]

Originally Posted by y_p_w
Originally Posted by Virtus_Probi
Originally Posted by y_p_w

Most OEM oil coolers should be an oil to coolant heat exchanger. Most often right where the oil filter mounts. I've heard of some aftermarket kits that are more like an oil filter base extension if there's enough room. Then there needs to be a coolant line and I'm not sure about how to tap into it.

Both cars I've owned had oil coolers where the oil filter mounted right on the cooler. I could always see the coolant hoses running into the heat exchanger. First was a 1995 Acura Integra GS-R. I don't believe the non-VTEC Integra had one. Then my 2004 WRX.

There are some odd aftermarket oil coolers that are like little radiators. Not sure how one is supposed to plumb an oil line though.

You're right, the cooler is right under the filter mount...I spaced out in my earlier post. It is right NEXT to the fill port, at least!

Technically the oil cooler becomes the filter mount, and I guess this oil cooler even has the collection cup since it's top mounted. Your sig says a 2014 Forester XT. I found this photo. The filter of course sits higher because of the oil cooler.

....

This type of oil cooler is great. Not only does it keep the oil from getting way beyond 100ºC but it also warms up the oil faster when cold. I believe without an oil cooler it typically takes longer for oil to get up to regular operating temperature, even when the coolant has reached the thermostat temperature.


Good pics...that filter mount in the 2.5l looks like the one in my daughter's Impreza (2.0l NA), more substantial but narrower than the sheet metallish one in my FXT.
I am able to use the wider/shorter Tokyo Roki oil filter for the new WRX because the FXT cup is so wide, but it didn't look like it would fit in the Impreza's cup. Ended up buying her some of the blue cans (Fram?) they use in the US even though I'm not crazy about them, used another Tokyo Roki that was Mazda branded and a Wix 57055 (or NAPA Gold 7055) before that. Put the Roki on the Impreza because my wife took it to a super cheap quickie change and they used a filter without an ADBV that made my daughter say the car was hard to start...I would guess the oil drained away while the car sat and it took a bit more cranking to get it going. This is what convinced my wife to have me change the oil in that car...she was convinced I was going to destroy it and it is actually in her name.

EDIT - my 2014 FXT looks different from the pic because I have a super cool STI fill cap!!
Was ordering a thicker rear sway bar for it and the price of the cap brought me up past the free shipping minimum price...the cap looks nice, not that anybody ever sees it, but it is less practical than the yellow plastic one because it gets darned hot. I made sure to get one that said 5W30 instead of 0W20...

 

[Shannow]

Originally Posted by BrocLuno
Look at air cooled engines. The oil's part is to move the heat to the surfaces (fins) that can shed it. Oil does not cool unless you have an oil cooler. There are engines (mostly industrial and marine) with massive oil coolers where the oil going into the system is well below sump temp. Some of these engines have spray jets to cool specific parts. And oil does carry excess heat from most turbos. So oil's job is heat transfer more than cooling.


I had a paper around here somewhere where a thermal analysis of a 6 cylinder air cooled ('copter ??? it was a mil paper) was carried out.

When they sealed the under piston area to prevent oil contact o the piston underside, IIRC, it only changed the oil temperature by less than 10F...again, the majority of oil heat being generated from within the shearing oil film.

 

[Virtus_Probi]

Originally Posted by Shannow

I had a paper around here somewhere where a thermal analysis of a 6 cylinder air cooled ('copter ??? it was a mil paper) was carried out.
When they sealed the under piston area to prevent oil contact o the piston underside, IIRC, it only changed the oil temperature by less than 10F...again, the majority of oil heat being generated from within the shearing oil film.


(Shannow's new sig is just plain wicked, but I laughed anyway)

 

[Shannow]

Bwahahahaha
http://naca.central.cranfield.ac.uk/reports/1940/naca-report-698.pdf

I found it...lucky search strike.

 

[IndyFan]

I would imagine that a thin oil cools more efficiently in an oil cooler than would a thicker oil, so in that setup an oil would function to some, even if limited, extent.

 

[y_p_w]

Originally Posted by Virtus_Probi
Good pics...that filter mount in the 2.5l looks like the one in my daughter's Impreza (2.0l NA), more substantial but narrower than the sheet metallish one in my FXT.
I am able to use the wider/shorter Tokyo Roki oil filter for the new WRX because the FXT cup is so wide, but it didn't look like it would fit in the Impreza's cup. Ended up buying her some of the blue cans (Fram?) they use in the US even though I'm not crazy about them, used another Tokyo Roki that was Mazda branded and a Wix 57055 (or NAPA Gold 7055) before that. Put the Roki on the Impreza because my wife took it to a super cheap quickie change and they used a filter without an ADBV that made my daughter say the car was hard to start...I would guess the oil drained away while the car sat and it took a bit more cranking to get it going. This is what convinced my wife to have me change the oil in that car...she was convinced I was going to destroy it and it is actually in her name.

EDIT - my 2014 FXT looks different from the pic because I have a super cool STI fill cap!!
Was ordering a thicker rear sway bar for it and the price of the cap brought me up past the free shipping minimum price...the cap looks nice, not that anybody ever sees it, but it is less practical than the yellow plastic one because it gets darned hot. I made sure to get one that said 5W30 instead of 0W20...

I can't take credit for photos I didn't take myself, but they seemed to show the difference with or without an oil cooler.

The other cars where I've changed oil (without a cooler) the mounting surface is actually on the aluminum engine block. Obviously not for a top mount since that's more or less a factory filter relocation.

Is the cap pink? I remember back when I got my WRX I was looking at various STi parts that basically dropped in for any Subaru. That included radiator caps which cost 3 times as much with a pink color scheme. There might have also been an STi air filter. Didn't seem any different other than it cost twice as much.

 

[ZeeOSix]

Found this section in one of my ICE books. Only part I don't agree with is them saying all the heat going into the oil eventually gets absorbed by the cooling system. We all know that hot oil also loses some heat through conduction through the oil pan, etc to the environment and of course through a dedicated oil cooler (if equipped) which they mention. This is addressing oil as a coolant, and not addressing exactly where all the heat comes from that increases the oil temperature (ie, oil shearing as mentioned earlier). Any time oil that is cooler than a hotter surface comes into contact with said hotter surface, then it will provide some cooling and gain heat - basic heat transfer.

 

[Linctex]

Originally Posted by Shannow

When they sealed the under piston area to prevent oil contact o the piston underside, IIRC, it only changed the oil temperature by less than 10F...again, the majority of oil heat being generated from within the shearing oil film.


I ruined all 8 pistons in a Ford V8 that was NOT designed as a "truck" engine, but I was using it as one!

I'd sometimes run this engine under heavy load for hours at W.O.T. (100% throttle)

Oil jets spraying under them would have saved them.

 

[OilUzer]

I think trucks are designed with better (more effictive) cooling system, also have oil coolers, larger sumps, etc. ... I doubt if 10°F diff could have saved your engine. most likely WOT (%100) and under heavy load for hours did the damage assuming your oil selection was right.

 

[stanlee]

Originally Posted by CT8
That is like saying coolant cools the engine.Coolant transfers the heat.


So your saying transferring heat away from something is not cooling? What exactly is your definition of cooling then (popcorn and notepad ready)?

 

[ZeeOSix]

Originally Posted by stanlee
Originally Posted by CT8
That is like saying coolant cools the engine.Coolant transfers the heat.


So your saying transferring heat away from something is not cooling? What exactly is your definition of cooling then (popcorn and notepad ready)?


Yep, anytime there is heat being transfeted from hot to cold, one side is being "cooled" and the other side is being "heated". The most basic concept of heat transfer.

 

[Shannow]

Originally Posted by ZeeOSix
Found this section in one of my ICE books. Only part I don't agree with is them saying all the heat going into the oil eventually gets absorbed by the cooling system. We all know that hot oil also loses some heat through conduction through the oil pan, etc to the environment and of course through a dedicated oil cooler (if equipped) which they mention. This is addressing oil as a coolant, and not addressing exactly where all the heat comes from that increases the oil temperature (ie, oil shearing as mentioned earlier). Any time oil that is cooler than a hotter surface comes into contact with said hotter surface, then it will provide some cooling and gain heat - basic heat transfer.


Yes...but the quote that you attached gets a lot of it wrong.

The shear between the piston and the walls generates a tremendous amount of heat...that per the literature is transferred directly to the nearby coolant. It's hard to find any measurements bar motored test friction losses, and most of the thermal balances don't include it.

Re the cooling of the rods and mains...again, the heat is GENERATED by the oil, and again dumps a significant portion of the heat into the coolant, through the main webbing...as per the pics below.

Yes, any time oil flows over metals that it's cooler than, it will carry away heat...but consider the oil flowing down the valley of a V-8...the drain back holes on an inline engine etc...it's running over metal that's got coolant temperature coolant on the other side...it's can't get above coolant temperature, and chances are it wasn't LESS than coolant temperature when it was sent on it's way, and certainly not after a journey through some working part.

More on heat balances after I restart this infernal device...

 

[Silk]

Oil has been used as a cooling medium in itself. The mid '90's BMW boxer twin has oil cooled cyl heads, it has a seperate oil pump that just circulates oil through the head and an air cooler. The idea has been used plenty of times.

 

[Shannow]

Take the big end "spray" on the LHS, 3.69cc/sec, and at a temperature of 188C.

Let's make one bookend assumption (grossly wrong, but illustrative) on the top side, ALL of the oil between 270 and 90 degrees of crankshaft rotation ALL moves vertically up and hits the underside of the piston crown...which is running at 250C...removing heat from the piston crown.

So:
* 1.85cc/sec
* delta T 61C
* Cp of engine oil 1.67KJ/KgC
* density of oil at 190C ~ 0.75

0.00185*61*1.67*0.75 = 140W...less than half of the heat contribution of the big end bearing...plus a bunch of unrealistic assumptions...generally half the slung oil WON'T go splashing on the piston underside, tha majority of it flung on the top side (at 180+C) will spray on the walls and heat the coolant.

 

[ZeeOSix]

No arguments here. It's pretty simple, the oil gets heat input from only two things: 1) Shearing of the oil in all parts that shear the oil, and 2) heat transferred into the oil from hotter parts that it comes into contact with. Item 2) is the cooling effect of the oil.

Every engine is different, and the amount of heat the oil picks up from hot parts (ie, oil providing cooling) depends a lot on how well the engine's cooling and oiling system are designed. If the cooling system is lacking efficiency in the head area for instance, oil can certainly pick up heat there and provide some cooling up and beyond what the cooling system provides. No cooling system is 100% efficient to allow oil from not acting as cooling medium to some extent - there will always be some level of added cooling from the oil. For instance around the valve ports (especially the exhaust valves) and spark plug areas where cooling jackets may not be very effective due to the physical location of water jackets to those areas. In hot areas on the heads, the contacting oil is most likely a bit cooler than those surfaces so it also helps cool the heads if the cooling jackets aren't doing a perfect job.

Obviously, the hottest areas that oil comes into contact with is on the piston crown underside, cylinder walls and ring area. The ring area runs pretty hot because they are very close to the combustion gases. Oil in those areas gets the most beating temperature wise. The cylinder walls, even though water cooled, will still have a surface temperature well above any oil splashing on them even if that oil is coming right out of the journal bearings and heated up some from shearing.

 

[ekpolk]

On both the FAA private and commercial pilot tests, depending upon your luck (or lack thereof...) you may get the question about the several functions of engine oil. Even realizing that they're obviously thinking mostly of the very dominant air-cooled designs, they expect you to regurgitate -- oh, I mean know -- these:

- Lubrication of the engine's moving parts.
- Providing a seal between the cylinder walls and pistons.
- Carrying away contaminants.
- Cooling/removing heat from the cylinders.

Some references actually split the "cooling" and "removing heat" functions and call it five functions.

In my opinion, the difference between "cooling" and "removing heat" is essentially little more than semantics. In any case, it's about taking excessive heat energy from one place where it may cause problems, and moving it to another where it may be dissipated directly, or perhaps transferred to another surface (with cooling fins on the other side) or to another system (liquid cooling jacket). It all boils down (sorry...) to the same thing -- taking heat energy from where it's undesirable and moving somewhere else -- no matter what we call it.

 

[Virtus_Probi]

Originally Posted by ZeeOSix
No arguments here. It's pretty simple, the oil gets heat input from only two things: 1) Shearing of the oil in all parts that shear the oil, and 2) heat transferred into the oil from hotter parts that it comes into contact with. Item 2) is the cooling effect of the oil.

Every engine is different, and the amount of heat the oil picks up from hot parts (ie, oil providing cooling) depends a lot on how well the engine's cooling and oiling system are designed. If the cooling system is lacking efficiency in the head area for instance, oil can certainly pick up heat there and provide some cooling up and beyond what the cooling system provides. No cooling system is 100% efficient to allow oil from not acting as cooling medium to some extent - there will always be some level of added cooling from the oil. For instance around the valve ports (especially the exhaust valves) and spark plug areas where cooling jackets may not be very effective due to the physical location of water jackets to those areas. In hot areas on the heads, the contacting oil is most likely a bit cooler than those surfaces so it also helps cool the heads if the cooling jackets aren't doing a perfect job.

Obviously, the hottest areas that oil comes into contact with is on the piston crown underside, cylinder walls and ring area. The ring area runs pretty hot because they are very close to the combustion gases. Oil in those areas gets the most beating temperature wise. The cylinder walls, even though water cooled, will still have a surface temperature well above any oil splashing on them even if that oil is coming right out of the journal bearings and heated up some from shearing.

Would you say this is still true for a typical turbocharged engine with oil and coolant circulated to the turbo?