Sump Oil vs. Coolant Temperatures

MolaKule

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Tech Brief: Bulk Oil Temperatures in the Sump verses Coolant Temperatures; A summary. By Molecule Many times the heat transferred to the lubrication system from combustion, and the kinetic components of an engine, are overlooked until a problem arises during dynamometer or track testing. A study* was undertaken to develop a heat flow and heat transfer model of an engine's lubrication system to predict primarily sump oil temperatures, and secondarily, coolant temperatures. The temperature relationships between the oil and coolant were found to be most interesting. This technical brief is a summary of the referenced paper. A model was developed to account for numerous items in the engine /lubrication system: 1, Engine Speed and Load, 2. Head and Block Geometry 3. Bearing clearances 4. piston design 5. coolant and ambient temperatures 6. material properties. If the engine had an oil squirter system, this was included as well. Energy balance equations and heat input sources were incorporated into the Model, with heat sources and heat sinks within the engine accounted for. To verify the model, the model was plotted against full-up V8 engine data from a dynamometer. The model correlated quite well with the dynamometer data, with a slight under-estimation of oil sump temperature at high rpm. It was found that the piston undercrown contributed about 70 to 80% of the heat into the oil with bearings contributing 10 to 20% of the heat energy to the oil. Here is a breakdown of heat sources for 2,000 RPM WOT: Energy to Oil from Piston Undercrown - 76% Main and Big End Bearings - 13% Camshaft Bearings - 1% Energy to oil from Cylinder Wall - 0% Oil Deck in Head - 2% Oil Pump Energy - 8% At 4,000 RPM WOT, the only increase in heat energy came from the Main and Big End bearings at 19%, a 6% increase from 2,000 RPM WOT. The Piston Undercrown's energy contribution to oil temp was 4% less at 72% for the 4,000 RPM WOT case. The predicted sump (bulk) oil temperature versus the coolant temperature was shown to be about 18 to 20 degrees C higher for the oil than for the coolant at 2,000 RPM WOT. At 4,000 RPM WOT, the oil sump temperature was about 50 degrees C higher than the coolant temperature. The slope for both RPM ranges was about 0.7 C/C, which means that on the average, the Oil Sump temperature is always 1.2 to 1.43 times higher than the coolant temp. An interesting side-bar of the study was that the bulk oil temperature increased "only" 0.3 C for every 1.0 C increase in ambient (oustside) temperatures. · Zoz, Steve, et. al., Engine Lubrication Model for Sump Oil Temperature Prediction SAE Paper 2001-01-1073. [ July 07, 2003, 03:55 PM: Message edited by: MolaKule ]
 

LM

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Good stuff. An archival search wrt to oil vs coolant temp suggested that they are somewhere close to the same, or that oil temp runs ~20F higher than coolant temp I wonder how much lower the temps would be (were?) at steady-state non-WOT, and what the sump vs coolant temp ratio would be I'm currently running a slightly cooler than OE rad cooling fan switch and t-stat (82C), but have been considering changing back to OE (89C) Some feel that 88C/190F is the ideal oil sump temp? But others post temps in the 225 - 250F range (maybe measured at areas other than the sump?)? Was there something to go w/the "*" | "A study*". Thanks http://www.teaching-english-in-japan.net/conversion/celsius
 
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I think the results are interesting. I'd have thought that most of the heat gain for a V8 would have come from the oil flowing around in the head/valves. Engines that squirt oil on piston bottoms, like some Suzuki bikes, I'd expect the oil to pick up lots of heat there. hmm? Makes me wonder about other 'seat of the pants' ideas I have.
 

MolaKule

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quote:
Was there something to go w/the "*" | "A study*".
The "*" was a reference to the full technical paper referenced at the bottom. I prefer to generate a Tech Brief that summarizes the core data. This avoids copywrite problems and simply gives the pertinent data in which most of the Board memembers might be interested. [ July 13, 2003, 03:05 PM: Message edited by: MolaKule ]
 

LM

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Thanks for taking the time to do the summary, Molakule. Sometimes I think these less often mentioned topics are quite important/relevant
 
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agree with it 1000% for as long as I have been alive, the age old question of 'what if I put too large of an oil cooler on my engine' has been answered with: dont worry about it. what the old salts knew for generations, and what I had reinforced at gm tech, was that the temps of the pistons and in the crank bearings (be it main or big end) bring the oil up high enuf to ditch any water- regardless of thermostat, oil cooler etc. now people have a 'fer instance' to add to the handed down wisdom. good job. can I download a copy from somewhere?
 
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As a generalisation at what is the optimum temp range for a branded standard 20/50 oil and what sort of temp difference would an oil cooler have on sump temps. Oil themostats used with coolers tend to operate at 80degc similar to Water thermostats. The oil sump temp should therefore be in 100-110 range. If you can maintain the correct Water temp why bother with a cooler, added expense and potential for leaks
 
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I wonder how this would translate to an inboard boat motor with little air circulation to aid in cooling but runs a 160 F thermostat. The theory (really probably speculation) that most people have, including me, is while the coolant (usually fresh water) runs at 160 F, the oil temp is much, much higher.
 

Al

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Great information. I'm going over to that site (SAE.org) and order the paper. For those of you interested it costs $10 to get an instant download. Im curious as to how the time vs temperatures lookes in oil and coolant temps-we had several discussions on this [Roll Eyes]
 

Al

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I did buy the article $12 instead of the previous $10 [Mad] for really only 11 pages of information. Much of it was fluff. For most of us here its a big waste of money. But for me it gave some very insightful information especially about maximum oil temps in a SI V-8 engine at different loads. It showed Oil Pan temps in the range of 290F degrees with undercrown temps higher than this. It left little doubt that a 20 or maybe a 30 wt. oil in this engine under heavy loads is not a wise idea. It really confirms that heavy loads require heavier oils due to the magnitude of the temp increase (IMHO) I'll post some specifics later when I'm in the mood to think clearly [Smile]
 

Patman

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quote:
Originally posted by Al: I did buy the article $12 instead of the previous $10 [Mad] for really only 11 pages of information. Much of it was fluff. For most of us here its a big waste of money. But for me it gave some very insightful information especially about maximum oil temps in a SI V-8 engine at different loads. It showed Oil Pan temps in the range of 290F degrees with undercrown temps higher than this. It left little doubt that a 20 or maybe a 30 wt. oil in this engine under heavy loads is not a wise idea.
I believe this! Which is why I feel my LT1 350 engine needs a thick 30wt to low 40wt oil. Especially with the hot oil temps I see. I'm sure my oil temps were close to 300 yesterday when I melted that oil sample bottle taking the sample.
 

Al

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quote:
Originally posted by Patman:
quote:
Originally posted by Al: I did buy the article $12 instead of the previous $10 [Mad] for really only 11 pages of information. Much of it was fluff. For most of us here its a big waste of money. But for me it gave some very insightful information especially about maximum oil temps in a SI V-8 engine at different loads. It showed Oil Pan temps in the range of 290F degrees with undercrown temps higher than this. It left little doubt that a 20 or maybe a 30 wt. oil in this engine under heavy loads is not a wise idea.
I believe this! Which is why I feel my LT1 350 engine needs a thick 30wt to low 40wt oil. Especially with the hot oil temps I see. I'm sure my oil temps were close to 300 yesterday when I melted that oil sample bottle taking the sample.

Well Patman that was all out WOT at 4000 RPM. So 300 is about the very very max the sump would see-if the model that they used is right. Doing a little calculations from their model at 2000 RPM and WOT- with a coolant temp of 200F and a 100 F day (assuming say 150 air temp in engine compartment) Those conditions give you about 160 degree oil temperature. That's probably aan upper limit for highway miles at reasonable higher high speeds. If the graph that I have on a 40wt. oil is accurate in that region that means you are dealing with 4 cSt. oil [Eek!] [Eek!] [Eek!] Consider that a 30 wt oil is 10 cSt at 210F. Thats what tells me that in hot conditions a 40 wt. oil is hardly overkill. [Smile] This article totally convinces me that 40 wts in summer are not a bad thing.
 
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Just a few observations: This lists the cylinder wall pickup as 0%. I was under the impression that the cylinder walls were the major cooling source of the engine oil (negative number then). The pan can't do it all, or can it? I work on diesels and heavy trucks and what I notice is that their oil coolers (which they all invariably have) use hot engine water for cooling instead of cool like the transmissions do. Also at least the one Chevy P/U we have with a 350 has an oil cooler and its lines go into the hot tank of the radiator. We do have an old gas powered C-70 Chevy truck with an air to air oil cooler but that is common to all Chevy big blocks I think. Birken
 

MolaKule

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Using heat conduction theory, it says that heat energy will flow from the hotter object to the cooler object. Here, the cooler object would be the jacket around the liner which has the circulating coolant which would be at a lower temperature than the oil. So heat is flowing from the oil film to the jacket in fully warmed-up engine at operating temperature. [ September 12, 2003, 10:29 PM: Message edited by: MolaKule ]
 
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Hi, sump capacity plays a real role in controlling engine oil temperature Generally, the longer time the oil is in the sump the greater the amount of heat is dissipated from it This applies of course even if a heat exchanger or cooler is fitted too One reason why heavy trucks use a oil/water heat exchanger is that it is as much to heat the oil ( up to 40 litres )as to cool it. In my experience the variance between coolant and oil temperatures in my Detroit 60 Series diesels is that the oil averages about 10C-15C hotter than the coolant ( 90C coolant - 100/105C oil - D1) Regards
 
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What I am asking, is there a direct correlation between sump capacity and oil temps. Like for X additional quarts of oil, there is x temperature drop. I just wonder how much of a change in capacity, makes a significant change in oil temp.
 

MolaKule

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The greater the volume of oil, the larger the sump, so you have to have a larger surface area to contain the larger volumes. The greater the surface area of the sump, the greater the convective and conductive area for the heat to dissipate (not considering a heat exchanger for the oil). Now a heat exchanger (say water/oil cooler) simply increases the "effective" area for heat dissipation, which would lower the oil temp.
 
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Molakule.....So you are saying that the difference in temperature, is not from the additional oil, put from the increased surface area of the larger oil pan required to hold the additional oil. Correct?
 

MolaKule

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Correct. The larger the heat dissipating surface for the oil, the more heat that is going to be transferred from the oil to the outside (to the coolant or to the air). Now in large diesels, please remember that large sump capacities not only mean lower oil temperatures (compared to a smaller sump area), but also that the larger amount of oil also means a larger reserve of additives.
 
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