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Question on Deep Sump Cooling 1

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xpehbam

Automotive
Oct 28, 2006
5
The question has to do with a stock 2 cylinder, horizontally oppossed 40 h.p. (max rpm 5600) air-cooled motorcycle engine that will not be used for racing.

The engine has a stock oil capacity of 2 quarts. If a deep sump and extended pick-up are installed allowing an additional 1 quart of oil (total 3 qts.)...will the engine run significantly "cooler"? By cooler, I do not mean a degree or 5...but more in the range of 20 degrees cooler. Will the additional oil "cool" the cylinder heads?

I am looking for some good scientific data that will explain why or why not. Hoping I could find some smart guys in here that could shed some light on this subject or send me in the right direction.

Thanks,

Bill G.

 
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No and No

To get a significant drop in oil temperature you need a significant increase in surface area of the heat transfer surfaces. On a deep sump, the only increase in surface area is the extra length of the sides.

For oil to effectively cool, it need to impact the surface or drain across it so as to wash away the insulating layer of relatively cold oil that will tend to cling to the relatively cold surface.

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Thanks PP,

I should have added that the engine is "splash" lub'ed by the crank with a very low volume pump which trickles oil to the cam, push rods and timing gears. No forced lubrication. No HV oil pump, no oil cooler (outside of a OEM or deep oil sump) and the galley ways have not been modified.

I am in the camp that says the additional qt. of oil WILL NOT significately decrease the engine temp's. I figure you could plumb a 50 gallon barrel of oil to the engine and it would not make a difference. There are a few folks on another forum (motorcycle) who have stated "25 degree" temp. drops (measured at the cylinder heads) once a deep sump was installed. I can't see a quart of oil pulling that off. I'm just an uneducated bumkin looking for some technical data to prove this one way or the other. I realize it is not a simple subject with many variables and dynamics going on...and again appreciate any information tossed my way.
 
Extra oil will slow the rate of oil temperature increase AND decrease. It will not change the steady state.

Your example of the 50 gallon barrel is not all that good, as the 50 gallons would take a very long time to heat up and a 50 gallon drum has a lot of surface area vs your sump, but the general point is correct even if it falls down on detail.

I ran hot rodded air cooled VWs for years. You could substantially improve the cooling by running a big external oil cooler. This then allowed substantial power gains without overheating problems.

If you can install fins or pipes to carry cooling air through the sump, preferably above the normal oil level it could help a little.

If it is splash and drip feed, it must be very old and I guess you wish to retain some originality to the external appearance.

A full synthetic oil that will withstand higher temperatures might help.

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Perhaps you might consider a small external pump and cooler arrangement? Even a vey small OEM cooler from a car or motorcycle will halp much more than 1 more quart of oil in the sump.
 
What temperature does the oil normally run at? If it isn't excessively hot already then dropping the temperature significantly will make the service more severe on the oil due to contamination buildup. A short-trip service typical of vintage hardware will make this even worse. Air cooled motorcycles typically take 15-30 minutes of service to reach operating temperature.

Some folks figure cooler = better. But there's reasons the engineers designed the motor that way, and to improve on it you must understand what factors don't apply to your case that you are trying to fix. Only if the bike will be used for competition or longer trips than was originally anticipated, (or the engineers didn't do a very good job designing it, in which case there's probably other issues that oil won't fix and one wonders about its historical significance) will cooler oil automatically help.
 
I appreciate all the responses to my querey, but some of you are missing my original point. I am looking for data/explantions as to whether adding a deep sump and extended pick-up to a stock engine WILL or WILL NOT lower engine/cylinder head temps.

I am not having trouble with engine temps. I am not attempting to cool an engine. In a discussion in an outside motorcycle forum, folks have said adding a deep sump with an additional quart of oil has SIGNIFICANTLY reduce engine temps. Some say by 20 to 25 degrees. They all say more oil equals a cooler engine. No of this was done via any scientific means. I think this is B.S.

I'm not smart enough to come up with reasons why this would not be so. I do not believe a deep sump will do more than give you more oil to change at service time. Again, I speak of a stock engine as discribed above NOT BEING USED FOR RACING. I understand why a deep sump is used in high rpm/high lateral load racing to prevent oil starvation. I do not believe a deep sumps purpose is to "cool" and engine. I am just looking for reasons to prove my line of thinking is right or wrong.
 
Where is the oil temperature sensor mounted & is it's position changed by the instalation of the higher capacity sump?
 
I had one of those deep sump add on's on a VW 1200CC engine when I was much younger and in school. I felt real good about it. I just knew it was doing what the advertising said and cooling my engine and saving the cylinders.

Then I got my engineering degree and spent lots of years in heat transfer. If it cooled my engine at all, I doubt I could have afforded the instruments that would have been necessary to measure it.

rmw
 
I ran the deep sumps on my VWs, as well as large external coolers and full flow filters.

They did increase surface area by a reasonable degree as they left the top of the deep sump and the bottom of the original sump exposed to some airflow, and they were finned top and bottom and they had some internal posts that increased heat transfer area in an area of high oil flow.

They certainly fixed my oil surge problems and associated bearing problems.

They also gave a measurable power increase by allowing the oil level to be dropped by about an inch, while still allowing an increase in oil capacity and increased depth over the pickup.

Only downside was the moderate cost and weight and the considerable loss of ground clearance.




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Pat, what do you mean about he power increase with the level being lower? I don't remember lowering the level any, just adding the extra oil.

When the VW with that engine died, I was entering Gonzales, Louisiana, and slowing down from 87 MPH where I had been cruising passing through 70 MPH to get down to what ever the posted speed was. This was a 1200cc engine and was rated to do 72 MPH and that was all it would do until I put the big jugs, tuned exhaust, full flow cooler, and what ever else I did to that poor machine. It had dropped valves on me before and I didn't fix that one. When I told the lead engineer on the turbine overhaul that I was engaged in that I was going to have to go pull the engine, etc., L(no big deal-I dropped the engine to change the spark plugs, easier I thought) and might have to make a long weekend of it he looked at me and said "son you have a real job now and a salary. You aren't a poor college kid (I was less than 3 months out of school) and you can afford a real car if you want one." I said it'll be a long weekend because I am going to buy a car.

Never owned a VW since. At one time I had 5. The sedan, a impster body dune buggy, a kombi, a PU truck and a spare sedan. I don't think I had but 4 engines among the 5 vehicles, however.

Anyway, I recognize now that notwithstanding the additional surface area and finning that the deep sump had, there was no flow velocity inside the pan to get any good reynolds numbers for heat transfer.

rmw
 
Lower oil level means the moving parts like the crank don't have to swim through the thick oil any more a spin around easier allowing for more rpm's/power. Like the difference between you walking through air vs. water.

O.k. you thermal engineering types...why wouldn't adding a deep sump and an additional quart of oil (as stated previously above) make the engine run cooler? I get surface area, I understand the bit about the layer of cooler oil between the sump wall and "hot" oil. What else? How about the cooler oil at the bottom of the sump vs. the hotter oil at the top? How much cooler would the oil be at the bottom of a...say 5" deep sump holding a total of 3 quarts of oil? Remember...no coolers, no tubes running through. Just a plain aluminum sump with fins at bottom.
 
The operative word used above by Pat is "steady state". Once all the oil is heated up, it is at essentially the same temperature. Even thought that oil in contact with the wall is at a lower temperature, there isn't enough velocity or agitation to get good heat transfer.

A simplistic approach to heat transfer is TTT. Time, Temperature and Turbulence. The cooler wall exposed to the ambient aided by finning is the Temperature part, and the time that the oil on the skin of the inner wall of the cooler is probably not determinable, but the zone is very low flow and if the Reynolds number were to be calculated it would be well below the threshold of the point at which heat exchange is said to occur. I think I remember that threshold Reynolds Number is 2000. The oil in the sump being discussed is nowhere near 2000 Reynolds number.

Now, I wasn't aware that the crank was 'swimming' through engine oil. I thought that caused foaming and priming and was to be avoided at all costs vis-a-vis all the warnings about not over filling the sump.

rmw
 
It was to long ago to be sound on details, but say the deep sump increased capacity by 3 quarts, I only added an extra 2.

Like xpehbam says, less drag from splashing about in oil.

Mine where a 1962 model "40 HP Beetle then a 1972 "type 3" station waggon.

First really hot roded engine started out with 55 HP at the wheels with 1600 engine built on beetle crankcase from scrap yard bits. Lots of bearing problems until I fixed the oil system with work on OEM pump, full flow filter, external oil cooler and deep sump.

The last engine ended up with 2100 cc with 94 mm bore forged pistons, thick wall cylinders, big valves, welded up and ported heads, cam out of a speedway midget, 78 mm stroke fully counterweighted forged crank and twin Webbers. It made 130 hp at the rear wheels. It was quite a surprise to many unsuspecting V8 drivers.


Regards

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Pat,

I'm like you. I am having to clear away lots of cobwebs to remember some of this stuff, but now that your mention oil pumps, I remember that I also had an after market oil pump, or maybe an oil pump from a larger engine (1300 cc or whatever) that had wider lobes than the stock pump.

I am trying to remember doing something with the pressure relief spring line shimming it or stretching it. Supposedly all this got more oil flow to the bearings. I never was sure I believed it.

But I am flabbergasted to find out that the crank was in contact with the surface of the oil. If that was for splash purposes, didn't lowering the level penalize the lubrication of the engine? I am off into new territory here.

rmw
 
There is still plenty of oil thrown off the crank splashing around and lubricating cam and followers.

Oil pumps up the push rods via the cam followers and this oils the overhead valve train.

The standard oil level was above the windage tray, but with the lower oil level it was well below that and also less inclined to flood the rocker box.

I think we are somewhat off topic here and I apologise to xpehbam for hijacking his thread.

The oil level was a lot higher than a dry sump system.

I ran the oil pumps from the late model 1600 motor as they had longer gears. I hard anodised the housing as it reduced wear and also reduced clearance. I( ported the inlet port on the pump to reduce cavitation. I also sanded the face of the housing with the gears installed to give a good smooth flat surface and zero end clearance. The thin paper gasket is then installed to give correct clearance.

I shimmed the oil pressure relief valve so that pressure would continue to build at well above design level rpm.

I used a solid spacer to replace the spring in the second relief valve This valve served to bypass the stock cooler when the oil was cold, and as I had a remote cooler, it served no function.

I eventually installed an oil thermostat in the line to the external cooler.

I blocked the outlet of the pump, drilled the end plate and installed a fitting on it to divert 100% of the oil to a remote filter, then the thermostat then either to the cooler then main gallery or directly to the gallery. I fed into the gallery by drilling and tapping the crankcase at the end of the main gallery. I learnt the hard way, not to use Teflon tape and tapered pipe fittings into a cast magnesium allow crankcase. Loctite 515 became my friend for sealing the cylinders to the crankcase, sealing the crankcase halves and sealing all oil pipe threads.





Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
 
Y'all have convinced me that I made the correct decision when I bought my first car some odd 50 years ago...I have NEVER owned or driven a VW...only rode in one once. Fancy that.

Cheers

Rod
 
No elaborate data is necessary to answer your query. Will the added sump capacity that you identify cool the oil 20 degrees, and, additionally, cool the cylinder heads. The answer is no.

The oil will run cooler, to an insignificant degree, because the fifty percent increase in oil volume will wet a larger surface of the sump. Since oil transmits heat better than air, and the sump has a greater external surface exposed to the air, a lab tech could measure lower oil temperature, though not even close to the 20 degree drop that you stipulated.

I infer that this is the BMW roller bearing engine that you are discussing. The roller engine had no pressure oiling system, though it did have an oil pump. That engine had no oil lines to the rocker arm area, if I recall my old BMW shop manual correctly, and no oil jets to the underside of the piston heads. Most cylinder head cooling came from heat transfer to the cylinder head fins. Again, a lab tech might measure an unimportant marginal difference attributable to higher oil capacity, but it would be insignificant.

If data is needed to resolve an argument, I suggest doing actual measurements, or setting up equations to incorporate heat flow data on the computed differences on internal oil wetted surfaces and external air cooled surfaces. Other variables would include estimated oil movement over the sump interior, splashing effects, air velocity over the exterior, and still more, depending on the extremities of accuracy that are desired. Still, the simple answer to your question is no.
 
In a running engine, you have oil sprayed onto and running off all the surface area of the sump.

Oil running over the surface cools better than oil stagnated on the surface. Oil becomes more viscous when cooled and tends to stick to the surface rather than mix when below the oil level, but when above the oil level it has more tendency to run off due to gravity, so in fact the sump is a better heat exchanger with less oil in it.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
 
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