Oil Temps FAQ

[SGKent]

[WhirledTraveller]

[skills@eurocarsplus]

77 by GPS and yes, 100% reworked for my application.

steve, take the water out of your acura
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[SGKent]

[skills@eurocarsplus]

just bustin' ballz....

i just moved my worries from oil temp to speeding tickets
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[SGKent]

[SGKent]

I noticed one older post where someone was impressed SAE 30 worked better at 64F than 20W-50. Why the heck would someone run 20W-50 at 60 -70F ambient temps and then complain about oil temperatures? Those are winter and spring temps around here. 20W-50 is a summer oil where temps are expected to top 90F frequently.

Here is a tale of two buses. FYI - if you cheat by changing the temperature or speeds in the tale you'll get called out on it. In other words, this ONLY pertains to the conditions herein.

Tale of two buses. Conditions 80F leaving the garage. Sea level, long trip ahead. Daytime temps to top 100F.

Bus one is running SAE 30. At 3pm he has been running 65 mph with it 105 F outside. He starts up a long grade, and gears down to 3rd. His oil is 220F at the base of the grade. His oil pressure was 50 PSI at 4,000 RPM when he started out at 8am when it was 80F outside. As he climbs the grade his oil temperature goes to 245 F. He looks at the RPM – 4,000 RPM. He looks at the oil pressure – 30 PSI and falling. He pulls over and parks to let things cool.

Bus two is running 20W – 50. At 3pm he has been running 65 mph with it 105 F outside. He starts up a long grade, and gears down to 3rd. His oil is 230F at the base of the grade. His oil pressure was 70 PSI at 4,000 RPM when he started out at 8am when it was 80F outside. As he climbs the grade his oil temperature goes to 255 F. He looks at the RPM – 4,000 RPM. He looks at the oil pressure – 43 PSI and steady. He backs down 10 mph but continues.

Which bus do you want to be? Would you rather be in the bus that is 10F colder as to the oil but is slowly eating a rod bearing, or in the bus that is 10F hotter but very mechanically sound and proceeding up the hill?
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[raygreenwood]

A quick note on Ratwells oil viscosity/temp chart. Its correct...for temperature versus flow....and totally incorrect....for real world use. Its missing a lot of data. That correlation just assumes that this is the whole story with regard to flow.

Not to get too nerdy on you....

The problem with the advertised viscosity...is in how its "expressed".

Notice that is listed in "centistokes". Really they are more accurate if expressed in centipoise. The difference is that you have to take the "density" of the oil in the sample being tested into consideration......and...motor oil is a SHEAR THINNING product.

The oil is massively sheared in the oil pump and between the bearings and against any sliding surface......so even before you factor in heat thinning.....the oil is thinner. And....that makes a functional difference in the density of the oil.

The viscosity in centistokes is derived from dividing the centipoise number by the density. And...that density changes....its called recovery....if you wait any period of time to test the viscosity on a rheometer from when it comes out of the crankcase. So really...you need to have a bench engine running with a rheometer set up in a hole in the crankcase.

My point is....that the higher the viscosity and tack rate you start with with a liquid....say like 50wt versus 30wt.....the higher the shear stress is because the thicker oil is more resistant ...film strength and density wise...to what is working it.
What they do not show....is what the friction modifiers they add do to that flow characteristic and density...while the oil is under pressure and running....whether flow gets better or worse.

The method they use (ASTM D445) is just a dirt simple temperature and flow comparison...and has nothing to do with film strength or density under shear....which can totally change the flow correlation presented. Many engineered fluids can actually INCREASE tack rate and resistance to flow under shear and pressure.
....which can explain why sometimes going to a thicker oil...just to combat oil thinning...can actually cause relief valve bypass on some engines with some oils and not others.

Here is the D445 method. It has so many issues with shearable non-newtonian liquids that its not allowed for use in many environments that measure fluid flow at temperature.

https://my3.my.umbc.edu/system/shared/attachments/...1334853004

Just some things to ponder. Ray

[SGKent]

Hi Ray - all I know is that when oil pressures falls, or shear is inadequate rod bearings and piston skirts are the first to tank. That said, shear and pressure are like being 10 minutes late to a flight vs 2 hours late - the plane still leaves without you. One either has enough of both or one does not. Below is a link to some oil stats. My whole concern is whether there is adequate pressure and shear when the outside temps are like they are here in the SW in summer. It was 104F yesterday afternoon when we got home here in the Sacramento area. It was 108F the day before when we got home. Split and bay folks up to the dog house cooler found out back in the 1970's that rod bearings and hot pistons can ruin a day. Many a bus was orphaned crossing the deserts of Arizona, New Mexico and California. A good friend of mine spent a week in the Sahara waiting for help when they drove too late one day and the heat seized up a split motor. Then he spent a month in a typhoid clinic. The doctors and nurses at the first clinic they took him to ran the other way - literally. According to the charts, shear in 20W-50 is about 20 - 25% better than in SAE 30, so in my book if shear and pressure are both better when the air outside is really hot, that is what I want. 15 F degree cooler oil won't help me here. To me it is like watching two guys waiting for the next flight arguing and one says but "I was only 10 minutes late so I did better... ." They both missed the flight, and the winner is the person who was waiting on standby in the line when they didn't show up in time ~ even if the route to the airport was not as efficient.

https://www.farmoyl.com/resources/sae-viscosity-grades
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[Wildthings]

250K miles on the bearings and around 400K on the crank, this engine ran about half of its life on 30wt during the summer (10w30 winter) and half with 5w40 in the crankcase year around. The rods plastigage fine and the mains bearing journals are still on spec for new. Sorry for the poor pic of the rod bearings

The only real problems on the bottom end of the engine was the plating on the cam bearings was failing and the cam had lost noticeable material off of its nose.

If you have an engine that is making 70psi at 4000 at highway speeds you are going to have no oil going through the cooler so your oil temps are going to start out much higher than 230°F, so the oil of number 1 still likely isn't as hot at the top of the grade as number 2 is at the bottom.



.

[SGKent]

who makes 70 PSI at highway speeds when warm - that would be too thick an oil - like running the summer oil in winter. I might do it if I was making one trip a month for 10 miles but not on a long drive. On an average 400 mile run at 6 am headed to the store when it is 70F outside under the delta breeze in summer oil pressure might be 15 PSI per 1000. By the time if is 2pm and we are headed out to Yosemite it is now 105F and we have 8,000 to 9,000 feet to climb from sea level. By the time we get to 6,000' the oil pressure is 10 - 11 PSI per 1,000 RPM. If you think my engine would survive SAE 30 under those conditions I don't think so. Even 10W -40 is too light. I've tried it in my 1977 and my 1971. 20W- 50 is the only oil that will survive those summer temps. 20W-60 is too heavy and SAE 50 is too heavy. SAE 40 is too heavy for the morning start up even. Come live here a while Mike and you will stop arguing about it. If we just drove to the store and back we'd be fine with SAE 30.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[Wildthings]

[raygreenwood]

[SGKent]

40 wt gives too high an oil pressure when it is cold. It might be 90 when we go to bed in a place like Yosemite and then 28F when we get up some times of the year when there is snow at the higher elevations and the breeze is downslope. SAE 40 will peg the needle when it is like that. VW doesn't even want one using SAE 30 when it is 28F outside.

None of the air cooled pages I have seen mirror what you show. The 1979 Bay page shows only SAE 40 above 80F. At that time multi-grade oils were not as refined as they are today. I designed and built several cars/motors that won SCCA championships using oil that was 20W-50 in those motors, so whatever is in that "mud" it is really good stuff. And - looking at VW's opinion based on their chart for a 1979 Bay, 20W-50 was too thin for them in 1979.

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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[Wildthings]

One page that I show covered mid sixties 1300 and 1500 engines they being the first VW engines I dealt with much at all and the other show the late sixties Bays. As I said I am glad I started into VW with cars of this era as running a 30wt oil in the summer proved very successful and kept me from a lot of grief.

As I also said previously a modern 40wt oil acts more like a 15w40 or 20w40, but without requiring viscosity modifiers to achieve such, just improved refining over the last 40 years. You needn't worry about starting an engine much of anywhere in the states during the warmer months with 40wt in the crankcase.

[wcfvw69]

I run 10-30 Valvoline 1 in all my VW's year around, here in hot PHX. My engines are type 1's. All have less than 10k miles on them. I have no oil pressure issues, even on the hottest summer days that I drive them in.

With these engines still having tight bearing clearances, they hate 10-40w and run hotter oil temps with it.
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[Wildthings]

[outcaststudios]

what is the consensus on synthetics for ACVW's?
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[Wildthings]