What are safe oil temperatures during spirited driving?

[ZeeOSix]

To avoid possible confusion before I comment fully, what specific "it" are you referring to?

The "It" I'm talking about refers to the subject of "thinner oil cool better". Specifically in the application of heat exhangers (oil coolers) since Post #9 specifically brought that up, and that's the main focus I was discussing.

But there's also the heat generation aspect of oil due to viscosity (ie, thinner oils don't heat up as much from shearing), which is a different factor than the basic heat transfer properties based on viscosity alone involved with just an oil cooler (fluid thermal properties dependent). As a couple of the links I posted shows, the formulation of the motor oil with the same viscosity rating can also change the Cp (maybe more so than just viscosity alone), so when you really start looking at it closely it's a bit more complicated than just saying "thinner oil cool better" because there are multiple factors going on when you consider all the thermal dynamics of an ICE oiling system going on.

I think people who see that the oil temperature might run slightly cooler in an engine that's pushed really hard are seeing more of the difference from the effect of the heat generated from shearing than from the difference in the oil's cooling performance. Even though a thicker oil might cool slightly better due to higher Cp (release more heat) , it is also heating up more due to shearing (compared to a thinner oil), which could still result in a net increase in oil temperature than a thinner oil. That would give the illusion that "thinner oil cool better".

 

[edyvw]

The "It" I'm talking about refers to the subject of "thinner oil cool better". Specifically in the application of heat exhangers (oil coolers) since Post #9 specifically brought that up, and that's the main focus I was discussing.

But there's also the heat generation aspect of oil due to viscosity (ie, thinner oils don't heat up as much from shearing), which is a different factor than the basic heat transfer properties based on viscosity alone involved with just an oil cooler (fluid thermal properties dependent). As a couple of the links I posted shows, the formulation of the motor oil with the same viscosity rating can also change the Cp (maybe more so than just viscosity alone), so when you really start looking at it closely it's a bit more complicated than just saying "thinner oil cool better" because there are multiple factors going on when you consider all the thermal dynamics of an ICE oiling system going on.

I think people who see that the oil temperature might run slightly cooler in an engine that's pushed really hard are seeing more of the difference from the effect of the heat generated from shearing than from the difference in the oil's cooling performance. Even though a thicker oil might cool slightly better due to higher Cp (release more heat) , it is also heating up more due to shearing (compared to a thinner oil), which could still result in a net increase in oil temperature than a thinner oil. That would give the illusion that "thinner oil cool better".

I think when there is argument like this, we should assume that people compare two oils of similar base stock properties, like Castrol Edge 0W40 and 0W30, which basically have same base stock.
All things being equal (as much as possible) thinner oil will dissipate heat faster.
However, again, I do not see any benefit running hypothetically Castrol 0W30 over 0W40 on track bcs. with thinner oils comes lower HTHS etc.

 

[ZeeOSix]

I think when there is argument like this, we should assume that people compare two oils of similar base stock properties, like Castrol Edge 0W40 and 0W30, which basically have same base stock.
All things being equal (as much as possible) thinner oil will dissipate heat faster.
However, again, I do not see any benefit running hypothetically Castrol 0W30 over 0W40 on track bcs. with thinner oils comes lower HTHS etc.

What are you basing the bolded statement on?

The word "dissipate" implies that thinner oil will transfer more heat (at a faster heat transfer rate). Not sure anyone can actually prove that except in a very controlled laboratory setting like some of the papers I linked earlier show. Even different oils with the same viscosity rating can vary in thermal properties that can effect their heating and cooling performance.

Agreed that thicker oils are better in hotter oil use conditions because of MOFT and HTHS retention ... otherwise car manufacturer's wouldn't say to run a thicker oil for track use. If someone uses a thinner oil for track use because they think it "cools better", they're probably going to have a big surprise when the MOFT goes to zero.

 

[edyvw]

What are you basing the bolded statement on?

The word "dissipate" implies that thinner oil will transfer more heat (at a faster heat transfer rate). Not sure anyone can actually prove that except in a very controlled laboratory setting like some of the papers I linked earlier show. Even different oils with the same viscosity rating can vary in thermal properties that can effect their heating and cooling performance.

Agreed that thicker oils are better in hotter oil use conditions because of MOFT and HTHS retention ... otherwise car manufacturer's wouldn't say to run a thicker oil for track use. If someone uses a thinner oil for track use because they think it "cools better", they're probably going to have a big surprise when the MOFT goes to zero.

Which transfers heat better, thick or thin oil?

I am somewhat confused on this topic. I have read, I think on this sight that the thicker the oil, the higher your oil temp will be. I have read elsewhere that thicker oil will will keep your engine cooler vs. a thinner oil. What is the truth?

www.bobistheoilguy.com

 

[ABN_CBT_ENGR]

The "It" I'm talking about refers to the subject of "thinner oil cool better". Specifically in the application of heat exhangers (oil coolers) since Post #9 specifically brought that up, and that's the main focus I was discussing.

But there's also the heat generation aspect of oil due to viscosity (ie, thinner oils don't heat up as much from shearing), which is a different factor than the basic heat transfer properties based on viscosity alone involved with just an oil cooler (fluid thermal properties dependent). As a couple of the links I posted shows, the formulation of the motor oil with the same viscosity rating can also change the Cp (maybe more so than just viscosity alone), so when you really start looking at it closely it's a bit more complicated than just saying "thinner oil cool better" because there are multiple factors going on when you consider all the thermal dynamics of an ICE oiling system going on.

I think people who see that the oil temperature might run slightly cooler in an engine that's pushed really hard are seeing more of the difference from the effect of the heat generated from shearing than from the difference in the oil's cooling performance. Even though a thicker oil might cool slightly better due to higher Cp (release more heat) , it is also heating up more due to shearing (compared to a thinner oil), which could still result in a net increase in oil temperature than a thinner oil. That would give the illusion that "thinner oil cool better".

OK, I'm tracking.

That's correctly stated in context.

 

[ABN_CBT_ENGR]

What we have here is a failure to communicate

 

[ZeeOSix]

Which transfers heat better, thick or thin oil?

I am somewhat confused on this topic. I have read, I think on this sight that the thicker the oil, the higher your oil temp will be. I have read elsewhere that thicker oil will will keep your engine cooler vs. a thinner oil. What is the truth?

www.bobistheoilguy.com

MolaKule said: "A thinner oil, while having a slightly lower heat capacity, actually transfers heat quicker because it moves faster."

But when oil volume in an ICE is being pushed through the oiling system by a PD oil pump, the flow rate (and velocity) through the force fed circuits and parts is the same regardless of viscosity - and that most likely holds true for an oil cooler. Therefore, if the flow volume is the same, and the oil's heat capacity is higher with a thicker oil, then more heat will be transferred. And when oil is at 200+ F I highly doubt you will see much if any "faster moving" oil to non-force fed areas (in the heads & valve train) between the different viscosities because they all flow so close to each other at that high temperature.

I think the biggest difference in the thermal dynamics as a whole is the amount of heat self generated by the oil due to shear heating and friction with parts that are not in full hydrodynamic lubrication. Thinner oils generate less self heating from shear, and if the overall oil temperature is a bit lower because of that, then it's perceived as the thinner oil "cooling better".

I've ran both 5W-20 and 5W-30 in a Coyote V8 and did not see any oil temperature difference at all. I wasn't in a track environment, so maybe if I was I would have seen slightly higher oil temperature with the 5W-30, but it would still depend on the increased heat input due to more shearing, and the performance of the coolant-to-oil heat exchanger. There are factors going on that are going in opposite directions (shear heating and oil cooler performance) at the same time, so it's not as simple as just concluding that "thinner oil cools better", especially when talking about the whole thermal dynamics of an ICE oiling system.

 

[ZeeOSix]

I would like to hear from someone here who tracks their car that has an accurate digital oil temperature readout, to say what is the oil temperature difference seen between two different oil viscosities (like 5W-20 vs 5W-30 in same brand/additives) ran on the same track in the same weather conditions for the same number of laps. Is it a 4~5 deg F difference, or is it a substantial increase like 40~50 deg F.

There's no doubt that the thicker oil would show a bit higher oil temperature, but the reason IMO is caused more by the increase shear heating from higher viscosity instead of the slightly thinner oil "cooling better".

 

[390pcode]

Agree. The C5/C6/C7 guys I talk to who track their cars see oil temps up to 300* with 0W40.
At that point, some guys add an oil cooler.
Seems like 300* is the (max) magic number for 0W40.

I know on 964 Porsches the “hot” marker of the gauge is 300F. Try and aim somewhere below that.

 

[ABN_CBT_ENGR]

Again, a large part of this is what I have to "get straight' ( all too often) with clients and trainees in various lubrication trainings because it is one of the foundational underpinnings of these sessions possibly going off the rails and ending up with more confusion.

I call it "definition swapping". Engineering ( like chemistry, physics, medicine, law and many other specialized fields) has specific definitions, conditions and qualifications that apply to words that have very defined limits.

Conversational English is a whole different animal where "cool" is actually "hot" and so forth.

In layman's terms

Viscosity = resistance to deformation ( which can be anything from pouring or general movement, not a measurement of "thickness" and does affect shear)

Density= ( by weight is the particles "weight" totaled in the compound, by "volume is particles by area and those 2 are different)

Thickness= A linear dimension measured between points (.125" of "water" is the same "thickness" as .125" of caramel)

Heat transfer is a cycle with lots of parts and conditions- no single entity really governs it and will crash it or often even significantly affect it.( within reason)

On the "shear generated heat"- yes every level of shear ( and in a recip journal there is generally 3 shear layers: the outer wall friction shear/inner wall friction and the shear line between the 2).

In modeling they can generate "heat" around 500 to 1000F ( yes) but that's at the molecular level and generated absorbed all in a fraction of a second leaving a net increase by volume of temp F of only a few degrees. ( lots of conditions and special cases in calculating that and there is no "general" number or percentage)

The basic calculation is the total area of the shears measured against the total volume by the velocity ( number of changes and speed of exchange because if the fluid didn't change out then it would quickly super heat then cause real problems)

That's a real contributor but not a significant one when compared to the bulk of the oil volume ( Just like a white hot piece of 1x1x1 keystock dropped in a 10 gallon drum- lot of localized heat even leading to steam but quickly absorbed by the volume and net temp increase from ambient is small)

Just a calibration of terms for the masses

 

[edyvw]

I would like to hear from someone here who tracks their car that has an accurate digital oil temperature readout, to say what is the oil temperature difference seen between two different oil viscosities (like 5W-20 vs 5W-30 in same brand/additives) ran on the same track in the same weather conditions for the same number of laps. Is it a 4~5 deg F difference, or is it a substantial increase like 40~50 deg F.

There's no doubt that the thicker oil would show a bit higher oil temperature, but the reason IMO is caused more by the increase shear heating from higher viscosity instead of the slightly thinner oil "cooling better".

Go to any BMW M3 forum and check topics involving Mobil1 0W40 compared to 10W60 on track. Redline 5W30 compared to Redline 15W50 (which is what BimmerWorld is pushing) etc.
I agree that thicker oil will generate more heat, I do not think there is any argument contrary to that, and I personally am not lover of thin oils like W20 or W30 ILSAC. But, also I do not think it is prudent running too thick of an oil. Next week I am going to track BMW and will run M1 0W40. Wills ee where oil temp is and eventually will run Motul Sport 5W40, so will see where is that too.

 

[ABN_CBT_ENGR]

One other thing on the "thick V. thin" discussion that's critical for those attempting to define this.

These "multi grade" oils (Xw-anything) are not like ISO grades and in and of themselves are a blended chemical compound of numerous lower viscosity oil bases with whatever additives and VII's to meet the thicker requirements at temp.

That's critical in discussing all thermal transfer because you are not using a 100% "oil" such as say ISO 320 which is like a straight weight in whatever class but a "Frankenbrew" of different chemistries.

All of which can and will affect every thermal property of the brew not just at the compound level but even varying with chemical changes as viscosity and other properties come into play.

So the claim of any "Xw-??" oil being able to do this and that ( in terms of heat exchange) is going to be radically different across manufacturers proprietary blends and then even in operating temperature bands.

That's going to make legitimate comparisons difficult

 

[CBR.worm]

So, on the original topic, I also have a VQ35DE REV-UP in a G35 6MT. I see oil temperatures in the 240's when doing a track day or deal's gap. I use M1 0w40. I don't believe high oil temps were an issue for these engines, but the later HR engines with VVEL did run into issues due to high oil temps, and they limited output power above a certain temp. Apparently, a lot of the heat was from the VVEL components at high RPM (which, of course, we don't have). It was common on those to add an oil cooler to prevent the power limit. I don't know if better oil coolers were added from the factory at some point. Ours have water to oil coolers, so with spirited driving, the oil is being 'cooled' by 200+ degree water.