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Re: Higher viscosity = higher operating temps? [Re: CR94] #5209660 09/10/19 09:46 PM
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The preferred oil for new 2019 rav4 hybrid in USA is 0w16. Higher viscosities are allowed for high speed driving and extreme loads etc. The Australian rav4 hybrid allows upto 15w40 in warmer temps.

Re: Higher viscosity = higher operating temps? [Re: 2015_PSD] #5209671 09/10/19 09:59 PM
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Bryanccfshr Offline
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No difference in performance between 0w20 and 0w40 in my Tacoma or 4 runner.
As always mileage is impacted by short trips, while longer trips where the oil warms up to operating temps yield the best mileage.

Increased oil temperatures with higher viscosities are normally attributed to viscous friction. The engine isn’t working harder enough to notice but the higher viscosity oil film resist shearing and allowing moving parts to touch. The cost of this is heat.
Fortunately many vehicles have oil to coolant coolers and the oil temp is relatively stable in the sump.


2018 Trd Pro 4Runner
2018 Tacoma off-road

Dealer 0w20 to M1 0w40 FS -it depends
Re: Higher viscosity = higher operating temps? [Re: Bryanccfshr] #5209675 09/10/19 10:08 PM
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Originally Posted by Bryanccfshr
No difference in performance between 0w20 and 0w40 in my Tacoma or 4 runner.
As always mileage is impacted by short trips, while longer trips where the oil warms up to operating temps yield the best mileage.

Increased oil temperatures with higher viscosities are normally attributed to viscous friction. The engine isn’t working harder enough to notice but the higher viscosity oil film resist shearing and allowing moving parts to touch. The cost of this is heat.
Fortunately many vehicles have oil to coolant coolers and the oil temp is relatively stable in the sump.


+1 i personally would take a hit to fuel economy in lieu of a thicker oil film. Now there are limits on this, it is possible to run too thick of a lube where internal parts are not getting adequate lubrication and the lubricants ability to cool is reduced.

Last edited by Mad_Hatter; 09/10/19 10:09 PM.
Re: Higher viscosity = higher operating temps? [Re: 2015_PSD] #5209748 09/11/19 02:49 AM
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wemay Offline
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Thicker oils absolutely contribute to higher operating temperatures just like they also offer better protection. But both are as minuscule as the mpg gains a lower viscosity oil contributes. All of these are facts that make chosing between one grade up or down a wash under normal daily driving conditions. Hence the difference of spec'd viscosity for different countries in the same geographical regions with no discernible difference in operating lifespans of the vehicles.


2018 KIA Sportage LX 2.4 AWD:
PP 5w20, PH9688
Next: PEAK 5w30 Syn, L14459

2013 Hyundai Santa Fe Sport 2.0T:
M1HM 10w30, XG9688
Next: same
Re: Higher viscosity = higher operating temps? [Re: 2015_PSD] #5209780 09/11/19 05:26 AM
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yowps3 Offline
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Only reason for 20, 16, 8 wts is for sticker economy. In reality you'll get more lubricity and oil film in a 0w40 than 0w20.

Not to mention more resistance to fuel dilation, reduced shear rate and reduced chances of LSPI etc

Ever wonder why LSPI in unheard of in euro TGDI. Answer is xW40 oil!

Re: Higher viscosity = higher operating temps? [Re: 2015_PSD] #5209787 09/11/19 05:42 AM
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I'd rather have better protection of my engine, giving up a small amount of fuel economy and running a few degrees hotter at operating temperature. The fuel savings I'm not capable of measuring, and the temperature difference is so slight that I haven't noticed it. I'm not suggesting using a 50 grade oil in an engine recommended for a 20 grade oil, but I see zero downside to running a 30 grade oil in a 20 grade oil application.


God Bless Our Troops

Re: Higher viscosity = higher operating temps? [Re: 2015_PSD] #5209932 09/11/19 08:49 AM
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Originally Posted by 2015_PSD
Originally Posted by alarmguy
I have agreed for a long time on the bearing thing but here is why, just found this, "Too thick oil, wonderful oil pressure, yet parts inside the engine could actually be starved for oil due to lowered volume. Another downer, circulating oil accounts for nearly 50% of engine cooling, so reduced oil-flow reduces cooling causing lubricated parts to operate at higher temperatures. Higher parts temperatures, more wear."
I am not concerned with "oil starvation"; modern engines have positive displacement pumps and the oil pressure remained the same for both oils (about 31 PSI at highway speeds). At 210-225°F oil temperatures, I would have to believe the oil is "thin enough" to reach all of the critical places.


Oh I was just posting the article, you asked if higher viscosity could result higher oil temperatures. I posted the link to show why it can.

No way are you starving your engine for oil using a 30 weight. In fact I only use 5w30 in all my vehicles that call for 5/20 and 0/20 but also say 5/30 is ok.
Ill never use a 20, way more so in my hot climate.


Lets face it, 5/20 and 0/20 is ONLY for EPA meeting gas mileage and so slight a vehicle owner will NEVER see it but for manufacturers the tiny percent savings adds up.
Also, of course, if you live in an area where winter temps are below zero, it certainly cant hurt and would be my choice.



Last edited by alarmguy; 09/11/19 08:50 AM.

14 Road King (current)
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Re: Higher viscosity = higher operating temps? [Re: 2015_PSD] #5210426 09/11/19 07:38 PM
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Originally Posted by 2015_PSD
Has anyone seen an oil temperature increase by moving from say an xW-20 to an xW-40 (with everything remaining the same)?
Nope. But from 0W-40 to thicker sort of 5W-50 (on the "Nordschleife"). VCDS logs says on same weather: ~4-5°C hotter.

Change it to 5W-40 and all is fine.


On the arduous way...to learn...English.
Re: Higher viscosity = higher operating temps? [Re: rideahorse] #5210637 09/12/19 04:28 AM
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Originally Posted by rideahorse
Well let me tell you that just driving a car down the road is not working it at all. You are only using about 20% of it possible available hp. Now put that in a engine in Agriculture or the dirt working equipment that are running 100% of their hp and see how long your engine last. And I am talking about $80,000 engines vs your $2,000 engine. There is a reason you don't see thin oils in engines that have to work.


Also, there's no CAFE requirements for agricultural engine use. Auto makers go as thin as possible to get every sliver of added gas mileage and still maintain good enough engine longevity. Many technical SAE type papers have shown use of thinner oil does increase engine wear over the long run. It might not be noticable to the guy behind the wheel during ownership, but it does happen.

Re: Higher viscosity = higher operating temps? [Re: 2015_PSD] #5211492 09/13/19 07:52 AM
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With higher viscosity oil than the engine is clearanced / designed for, I'm more worried about bearing temperature than oil temperature.


"He who is without oil, shall throw the first rod." - Compressions 9:1
Re: Higher viscosity = higher operating temps? [Re: RDY4WAR] #5211662 09/13/19 11:18 AM
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2015_PSD Offline OP
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Originally Posted by RDY4WAR
With higher viscosity oil than the engine is clearanced / designed for, I'm more worried about bearing temperature than oil temperature.
One would reflect the other, would it not--I cannot see how the oil would not heat up in response to the bearings increasing their temperature? Also, what engine would be clearanced/designed for a single viscosity? Not being sarcastic--just learning...


2019 o)|||||(o Rubicon Wrangler Unlimited 3.6L V6 [Castrol Edge 0W-20 + FRAM Ultra]
2018 Mercedes Benz C300 2.0L Turbo [Pennzoil Platinum Euro 0W-40 & Mann filter]
Re: Higher viscosity = higher operating temps? [Re: 2015_PSD] #5211668 09/13/19 11:25 AM
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It's good to remember that higher operating temperatures are a fact when higher viscosity is chosen, but that's only at higher RPM. At the low RPM's we typically see in today's engines, there really is little difference.

For track days, the use of 5/10/15W-50 viscosity oil is still common in many newer vehicles. Including Ford and GM toys. In some engines, the increase in operating temps due to track use reduces the viscosity of thinner oils into risk territory. Where the same cannot be said about the higher viscosity oils.


People who count on their fingers should maintain a discreet silence.
Re: Higher viscosity = higher operating temps? [Re: 2015_PSD] #5211674 09/13/19 11:33 AM
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Originally Posted by 2015_PSD
Originally Posted by RDY4WAR
With higher viscosity oil than the engine is clearanced / designed for, I'm more worried about bearing temperature than oil temperature.
One would reflect the other, would it not--I cannot see how the oil would not heat up in response to the bearings increasing their temperature? Also, what engine would be clearanced/designed for a single viscosity? Not being sarcastic--just learning...


With higher viscosity, the temperature delta through the bearings will be higher. With sufficient surface area of the pan and coolant temperature through the block, the oil temp may not rise but 5*F but the bearings can be 20-30*F hotter.

There's an ideal flow vs viscosity through the rod and main bearings. Too much flow from too little viscosity risks cavitation. Too little flow from too much viscosity reduces cooling and increases hydrodynamic friction. More friction + less flow = more heat.

The ideal oil viscosity is dependent on the bearing clearances and operating oil temperature. Some hydraulic lifters are picky about viscosity as well (GM LS based engines, for example). Here's a chart of comparing bearing clearance to temperature for ideal oil grade / viscosity. The majority of modern OEM engines have between .0010-.0018" rod and main bearing clearance.


main and rob clearances to oil viscosity.jpg
Last edited by RDY4WAR; 09/13/19 11:35 AM.

"He who is without oil, shall throw the first rod." - Compressions 9:1
Re: Higher viscosity = higher operating temps? [Re: RDY4WAR] #5212023 09/13/19 07:33 PM
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Originally Posted by RDY4WAR
Originally Posted by 2015_PSD
Originally Posted by RDY4WAR
With higher viscosity oil than the engine is clearanced / designed for, I'm more worried about bearing temperature than oil temperature.
One would reflect the other, would it not--I cannot see how the oil would not heat up in response to the bearings increasing their temperature? Also, what engine would be clearanced/designed for a single viscosity? Not being sarcastic--just learning...


With higher viscosity, the temperature delta through the bearings will be higher. With sufficient surface area of the pan and coolant temperature through the block, the oil temp may not rise but 5*F but the bearings can be 20-30*F hotter.

There's an ideal flow vs viscosity through the rod and main bearings. Too much flow from too little viscosity risks cavitation. Too little flow from too much viscosity reduces cooling and increases hydrodynamic friction. More friction + less flow = more heat.

The ideal oil viscosity is dependent on the bearing clearances and operating oil temperature. Some hydraulic lifters are picky about viscosity as well (GM LS based engines, for example). Here's a chart of comparing bearing clearance to temperature for ideal oil grade / viscosity. The majority of modern OEM engines have between .0010-.0018" rod and main bearing clearance.


Nice find on the chart.👍.. I've read that 10cSt was the "ideal" viscosity for bearing clearances? "Much higher than this and drag results, much lower than this and boundary lubrication occurs" in link below 👇. (what I said in my previous post).. now the question for me, at what point does boundary lubrication become an issue? 8cst?..7 or 6?

KEW Engineering

Re: Higher viscosity = higher operating temps? [Re: 2015_PSD] #5212104 09/13/19 09:39 PM
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Interesting chart, RDY4WAR. Assuming the intermediate temperature range, it would've had put 0W-20 or 0W-10 in my 1981 Mazda, for which the service manual specified 0.0009" to 0.0017 clearance for mains.


2011 Toyota Prius now at 102K
1981 Mazda GLC (323) retired at 606K
1972 Subaru DL retired at 190K
1954 Chevrolet retired at 121K
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