Thicker vs. Thinner and oil temps.

[chubbs1]

I would assume and also have read on here that the thinner the oil the faster it will transfer heat thus cooling quicker. I have just made an observation in my Charger SXT (3.6 pentastar), that when I am using a 5w30 (first was Castrol Edge FST so basically a thick 20grade, second G-Oil) the temperature of the oil runs about 10-12 degree F higher than when I used M1 0w40. Could anyone shed some light on why that may be? Oil pressure is a little lower at max temp idle with (27-30PSI w/ 5w30) and (29-32PSI w/ 0w40). Worth noting as well is the M1 0w40 was used during the peak of summer and still ran a 10degrees cooler at the highest temps.

Any ideas why maybe?

Thanks
Chubbs

 

[HTSS_TR]

I don't have oil temp/pressure gauges in my cars. I would think thinner oil should yield lower oil temp in the same engine with similar driving conditions.

I observed the coolant/engine temperature of my E430 is lower about 10-15F with xW20 than with M1 0W40 while we were on Vegas trips in summers. The speed was similar at 80-90 MPH and ambient temp was 115-125F.

 

[jorton]

I guess oil temp is measured after oil has cooled in the sump. Could it be the thin oil got hotter than the M1 did while moving through the oiling circut to the sump?

 

[JimPghPA]

Ideally, when the oil is up to temperature, at the maximum RPM's the engine normally sees, you want the oil to be at the viscosity that causes the oil pressure to be "just below the oil pressure that would cause the relief valve on the output of the oil pump to open". If this is the case you are getting the maximum flow rate of oil through the engine and therefore the parts that are cooled by the oil get the maximum amount of oil cooling. So if you have an oil pressure gauge you should see the oil pressure reach the maximum desired pressure just as maximum normal RPM's are reached. Be sure the oil is up to temperature before using this reading to chose a thicker or thinner viscosity.

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If you have a oil pressure gauge and you put too thick of an oil in the engine, with the oil up to temperature, at some RPM below the normal maximum RPM's, the relief valve of the output of the oil pump will open and limit the maximum pressure before the maximum RPM's are reached. This means that because the oil is too thick it can not achieve the maximum flow rate of oil through the engine, and therefore the parts that are being cooled by the oil do not get the maximum amount of oil cooling.

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If the oil is too thin, then when it is up to normal operating temperature it may flow too freely through the engine and not provide proper oil pressure to cause enough oil to flow into areas that require oil pressure to get the oil to flow to them properly. And hydraulic lifters (if the engine has them) may not operate properly if the oil pressure is too low.

 

[CATERHAM]

Originally Posted By: JimPghPA
Ideally, when the oil is up to temperature, at the maximum RPM's the engine normally sees, you want the oil to be at the viscosity that causes the oil pressure to be "just below the oil pressure that would cause the relief valve on the output of the oil pump to open". If this is the case you are getting the maximum flow rate of oil through the engine and therefore the parts that are cooled by the oil get the maximum amount of oil cooling.

The optimum oil pressure (representing the optimum operational viscosity) is usually well below the oil pump by-pass pressure capping point. For example the optimum oil pressure may be 60 psi at elevated rev's although the oil pump pressure release setting could be as high as 115 psi. So the lightest oil that
still provides 60 psi of OP at maximum oil temp's represents your optimum operational viscosity. If this is accomplished using a 2.6cP 20wt oil any oil heavier than this will provide higher oil back pressure and reduced oil flow up to the by-pass point. If the oil is so heavy that the by-pass valve is beginning to open oil flow will be further reduced as oil is starting to be diverted from flowing through the engine.


chubb1, the heavier M1 0W-40, as confirmed with the higher OP reading will in theory run a little hotter but not likely noticeably in my experience than the lighter 30wt oil. Since you've observed the opposite effect suggests something else other than the oils viscosity is the cause.
It could be any number of things.
Was the coolant temp's higher as well as the oil temp's? That could be the reason right there. Something could have reduced air flow through the rad' (some temporary debris) or over the sump of the engine. Again it could be anything.

 

[Shannow]

Originally Posted By: CATERHAM
So the lightest oil that
still provides 60 psi of OP at maximum oil temp's represents your optimum operational viscosity.


While I agree with your assertion that the oil backpressure demonstrates the bearing's operation as a functional viscometer, it does not, in any way correlate with the optimum viscosity for successful bearing operation...they are two different sets of parameters.


Originally Posted By: CATERHAM
If this is accomplished using a 2.6cP 20wt oil any oil heavier than this will provide higher oil back pressure and reduced oil flow up to the by-pass point.


Positive displacement pumps don't work that way...they shift stuff, and withing very broad parameters (and an engine oil is pretty narrow in the scheme of things), the same amount of stuff per revolution.

Increased backpressure doesn't materially affect flow.

 

[GMorg]

At fixed flow rates, the oil that removes more heat will be hotter.

 

[CATERHAM]

Originally Posted By: Shannow
Originally Posted By: CATERHAM
So the lightest oil that
still provides 60 psi of OP at maximum oil temp's represents your optimum operational viscosity.

While I agree with your assertion that the oil backpressure demonstrates the bearing's operation as a functional viscometer, it does not, in any way correlate with the optimum viscosity for successful bearing operation...they are two different sets of parameters.

Is that not a contradictory statement?
If a certain minimum oil back-pressure represents the minimum optimum viscosity for an engine how does that not "correlate with the optimum viscosity for sucessfull bearing operation"?

Originally Posted By: CATERHAM
If this is accomplished using a 2.6cP 20wt oil any oil heavier than this will provide higher oil back pressure and reduced oil flow up to the by-pass point.


Originally Posted By: Shannow
Positive displacement pumps don't work that way...they shift stuff, and withing very broad parameters (and an engine oil is pretty narrow in the scheme of things), the same amount of stuff per revolution.

Increased backpressure doesn't materially affect flow.

Yes that is how positive displacement oil pumps work in theory but in practice to put it simply, they leak. As the oil back-pressure increases so does the rate of oil pump leakage in the system. That is why heavier oil pumps more slowly through an engine than light oil. Of course if the oil so heavy that the oil pump by-pass valve is activated the oil flow through an engine will be decreased at an even faster rate.

This was discussed in detail in the following thread:

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2732602&page=2

 

[GMorg]

Take-home message from the thread above:

Post #2732953 - 09/02/12 08:51 PM

"Well, I took CATERHAM's advice. According to every pump manufacturer (and a few educational sites) that I can find that offers web-accessible info, as oil viscosity increases, slippage decreases, the pump efficiency increases and pump output increases (when on test rigs). In practice, when mounted, the pick-up screen and pick-up tube diameter can become limiting as viscosity increases and a vacuum is created. As a result, the vapor pressure of the oil and the differential in pressure between the pump and the sump determines if cavitation occurs. If cavitation begins to occur, pump output can decrease due to cavitation. So, in practice, output decreases as viscosity increases when the oil's vapor pressure allows cavitation.

Other sources of flow loss due to increased viscosity are mated surfaces on the pump. Since most pumps do not use gaskets and mounting surfaces aren't perfect, the pumps simply leak. As a result, as pressure builds, oil can leak from mated sufaces.

All pump literature that I could find attributed increases in oil temps with increase viscosity to be due to the increased energy that it takes to pump the fluid. Some also noted that when flow rate decreases, primarily due to high bearing velocity, the oil has higher resident time in bearings and can come closer to equilibrium with the metal surfaces. The oil exits the bearing hotter, but due to lower flow, actually removes less heat.

I need to apologize for stealing the thread. Thanks for tolerating the distraction. I learned something."

 

[TFB1]

All of the above may well be true with cold oils, but you'll never convince me there is a measurable difference from say 8 to 15 cSt when hot, flow will be 99.9% equal...

 

[Shannow]

Originally Posted By: CATERHAM
Originally Posted By: Shannow
Originally Posted By: CATERHAM
So the lightest oil that
still provides 60 psi of OP at maximum oil temp's represents your optimum operational viscosity.

While I agree with your assertion that the oil backpressure demonstrates the bearing's operation as a functional viscometer, it does not, in any way correlate with the optimum viscosity for successful bearing operation...they are two different sets of parameters.

Is that not a contradictory statement?
If a certain minimum oil back-pressure represents the minimum optimum viscosity for an engine how does that not "correlate with the optimum viscosity for sucessfull bearing operation"?



Contradictory ?

How ?

The bearing is protected by it's design, which includes size, load, and operating viscosity.The oil backpressure has nothing to do with any of those parameters.

I agree with your assertion that providing a pressurised feed to a rotating bearing and measuring the resistance to oil passage through the bearing as an indicator of viscosity, I do.

But it does not correlate, infer, imply or otherwise that is the optimum viscosity for that bearing.

Heck, some bearings even suck oil into them...

Originally Posted By: CATERHAM

Originally Posted By: Shannow
Positive displacement pumps don't work that way...they shift stuff, and withing very broad parameters (and an engine oil is pretty narrow in the scheme of things), the same amount of stuff per revolution.

Increased backpressure doesn't materially affect flow.

Yes that is how positive displacement oil pumps work in theory but in practice to put it simply, they leak. As the oil back-pressure increases so does the rate of oil pump leakage in the system. That is why heavier oil pumps more slowly through an engine than light oil. Of course if the oil so heavy that the oil pump by-pass valve is activated the oil flow through an engine will be decreased at an even faster rate.


Come on, leakage, in any sort of designed system that we are talking about in an engine lubrication system isn't going to change markedly between a 15 cst oil and a 9 cst oil...and a difference in operating pressure on a typical gear pump of 200bar (from 50 to 250 bar) results in approximately 10% internal leakage...here we are talking about 4 bar +/- 1...there is simply no meaningful change in pump output, due either to backpressure or viscosity...(and they work such as to cancel each other out, as the higher viscosity oil has less internal leakage for a givern pressure rise)

Flow loss due to cavitation isn't going to play a part in this discussion either, just like we're not talking bypass valve in this case, just normal operation.

 

[virginoil]

So then you debate the "thick v thin" in a 5w50 multi grade what part of the 5w50 grade is in question.

The 5w at start up or 50 when at operating temperature ?

 

[virginoil]

BTW I will be using the Penrite 5w60 in my next oil change.
Vis at 40degC=146 cSt and at 100degC=23.8.cSt
CCV at -30degC=5696 HTHS=4.4 VI=196 See link PDF below

http://www.penriteoil.com.au/pis_pdfs/10 TENTHS PREMIUM 5 AUG 2012.pdf

Will this be a problem ?

 

[GMorg]

As far as I can tell, different oils are observed to have different flow rates in the same engine, at the same RPM. However, the range appears to be less than 10% variation across 4 SAE grades and is NOT always predicted by viscosity. The trend is HIGHER flow rate with increased viscosity with pumps on test rigs and LOWER flow rate with increased viscosity with pumps mounted on engines. The pickup tube/screen appears to be the limiting factor for reduced flow.

 

[Brit33]

Originally Posted By: virginoil
BTW I will be using the Penrite 5w60 in my next oil change.
Vis at 40degC=146 cSt and at 100degC=23.8.cSt
CCV at -30degC=5696 HTHS=4.4 VI=196 See link PDF below

http://www.penriteoil.com.au/pis_pdfs/10 TENTHS PREMIUM 5 AUG 2012.pdf

Will this be a problem ?


Nice specs, zddp levels etc. but the HTHS is pretty low for a 60wt oil.
I use Castrol 10W60 and the HTHS is 5.3 which is a thin 60wt oil.

 

[virginoil]

Originally Posted By: Brit33
Originally Posted By: virginoil
BTW I will be using the Penrite 5w60 in my next oil change.
Vis at 40degC=146 cSt and at 100degC=23.8.cSt
CCV at -30degC=5696 HTHS=4.4 VI=196 See link PDF below

http://www.penriteoil.com.au/pis_pdfs/10 TENTHS PREMIUM 5 AUG 2012.pdf

Will this be a problem ?


Nice specs, zddp levels etc. but the HTHS is pretty low for a 60wt oil.
I use Castrol 10W60 and the HTHS is 5.3 which is a thin 60wt oil.


You are right the HTHS value is approx 5.6 see old PDF below

http://www.penriteoil.com.au/pis_pdfs/SIN Engine Oil 5 JAN 2010.pdf

 

[Brit33]

Originally Posted By: virginoil
Originally Posted By: Brit33
Originally Posted By: virginoil
BTW I will be using the Penrite 5w60 in my next oil change.
Vis at 40degC=146 cSt and at 100degC=23.8.cSt
CCV at -30degC=5696 HTHS=4.4 VI=196 See link PDF below

http://www.penriteoil.com.au/pis_pdfs/10 TENTHS PREMIUM 5 AUG 2012.pdf

Will this be a problem ?


Nice specs, zddp levels etc. but the HTHS is pretty low for a 60wt oil.
I use Castrol 10W60 and the HTHS is 5.3 which is a thin 60wt oil.


You are right the HTHS value is approx 5.6 see old PDF below

http://www.penriteoil.com.au/pis_pdfs/SIN Engine Oil 5 JAN 2010.pdf


Very nice oil indeed. Would be perfect for my old alfa. Better than the Castrol TWS.
Shame they don't import it.

Good HTHS.
Excellent zddp level.
Excellent low W grade for cold start ups and a nice 60wt for my large bearings clearances to keep the pressure at the right specs.

 

[CATERHAM]

Originally Posted By: Shannow
Originally Posted By: CATERHAM
Originally Posted By: Shannow
Originally Posted By: CATERHAM
So the lightest oil that
still provides 60 psi of OP at maximum oil temp's represents your optimum operational viscosity.

While I agree with your assertion that the oil backpressure demonstrates the bearing's operation as a functional viscometer, it does not, in any way correlate with the optimum viscosity for successful bearing operation...they are two different sets of parameters.

Is that not a contradictory statement?
If a certain minimum oil back-pressure represents the minimum optimum viscosity for an engine how does that not "correlate with the optimum viscosity for sucessfull bearing operation"?



Contradictory ?

How ?

The bearing is protected by it's design, which includes size, load, and operating viscosity.The oil backpressure has nothing to do with any of those parameters.

I agree with your assertion that providing a pressurised feed to a rotating bearing and measuring the resistance to oil passage through the bearing as an indicator of viscosity, I do.

But it does not correlate, infer, imply or otherwise that is the optimum viscosity for that bearing.

If you're implying that an OP gauge can't tell you what the optimum minimum viscosity is, in and of itself, I would have thought that goes without saying. One needs to know the OP spec' that coincides with the optimum viscosity.

 

[CATERHAM]

Originally Posted By: GMorg
As far as I can tell, different oils are observed to have different flow rates in the same engine, at the same RPM. However, the range appears to be less than 10% variation across 4 SAE grades and is NOT always predicted by viscosity.

In the CarCraft magazine article on oil pumps I referenced in that other thread the difference in oil flow between a 20W-50 and a 0W-20 race oil was 14%. I would think that the flow rates between the two viscosity extremes; that would be an oil that almost triggers by-pass and a very light sub 20wt oil like Motul 0W-15 (HTHSV 2.0cP) at high oil temp's, would be considerable higher than that.
Additionally the variation in flow rates should coincide with oil back-pressure which relates to the HTHSV rating of an oil and not necessarily the oil's SAE grade.

Of course this is an academic discussion.
If there is a practical take away, it's to never run an oil that is so thick that you cannot use maximum power, with the oil at normal operating temp's, without the oil pump going into by-pass mode.
If one has an OP gauge equipped vehicle it is good practice to use the gauge as a variable red-line.
When the engine is cold do not rev' the engine any higher than the OP by-pass point. As the oil heats up and thins out more rev's can be used before the by-pass activation point is reached. Even with a light 0W-20 oil grade you'll likely need oil temp's of around 70C before maximum rev's can be used without going into by-pass. A light 30wt oil about 80C and a light 40wt 90C or so.
If you find that the way you operate your vehicle you can't avoid going into by-pass 90% of the time, then a lighter viscosity oil may be a better choice.

 

[Jim Allen]

Is there any way to tell when or if the bypass has opened by observing the OP gauge? In my case, I have conflicting data on the bypass setting (and yes, I am very annoyed by not knowing for sure).