Switched to higher viscosity oil and getting higher temperatures

[rockyraccoon]

Previous owner was running Mobile 1 10w30 fully synthetic. I drove the car pretty hard with this oil and the temp never got above 200.

I had some minor issues taken care of last week and had my mechanic change the oil to Brad Penn 20w50. The first time I drove it the temp quickly went up to around 9'oclock (225?). As I drove it went between 200 and 225 depending on the traffic.

It seems counter intuitive to get higher temps with thicker oil. Is this normal? Anything I should watch out for?

[DaddyGlenn]

This should be interesting, so I'm subscribing. I'm thinking it may have less to do with the viscosity and more with the difference between a synthetic and dino oil.

[steve84]

Heat is transferred to the oil by contacted with higher temperature metal parts and heat is transferred from the oil to the atmosphere at the oil cooler. The amount of heat transferred at the oil cooler would be a function of the flow rate through the cooler. Your oil temperature may be higher because the thicker oil has a slower flow rate through the cooler.

[duncan1437]

i dont have any personal experience, but this post on bobtheoilguy is consistent with your experience.

'Heavy oils can for sure cause hotter running temps.
My empirical and vicarious experiences show thicker oils have more drag and cling, and can cause hotter oil!
Something like temps 10 deg F cooler on the highway with 10-40 vs.20-50. '

Higher viscosity in summer heat?? - Bob Is The Oil Guy

posts 2259028 and 2260060

you switched from 10-30 to 20-50 with a 25*F increase, and the other post switched from 10-40 to 20-50 with a 10*F increase. roughly, each 10 point increase in oil weight leads to a temperature increase of 10*F.

admittedly a limited sample size...

[tobluforu]

Not sure why, but when I went from valvoline 20-50 to brad penn 20-50, my car ran hotter and leaked like hell.

[Don Ivey]

I, too, noticed slightly higher temps when I switched to Brad Penn 20W50. I don't remember exactly what I switched from, but it was either Castrol 20W50 or Valvoline 20W50. Another data point.

[db_cooper]

Very interesting...thicker engine oils run hotter..just like Porsche thought in 2004....and recommended using synthetic 5w40, 0w40 and 5w50 engine oils retroactively to 1973 in all Porsche models.

[oliver88]

BP is a very thick 20w50 HTHS is over 6…Takes more energy to turn a thicker oil and also wicks away less heat than a thinner oil would. Volume and flow lead to lower heat. Your oil pump is working a little harder and that translates into more heat. That's the over simplified explanation.

[enzoducoing]

Originally Posted by steve84

The amount of heat transferred at the oil cooler would be a function of the flow rate through the cooler. Your oil temperature may be higher because the thicker oil has a slower flow rate through the cooler.

This is correct, in these air-cooled engines flow comes first and extra viscosity is not necessarily better as in water-cooled cars.

[rockyraccoon]

Thanks for the feedback. When I mentioned the previous owner ran 10w30 in another thread people screamed bloody murder. While 10w40 or 50 was probably a better choice, 10w30 isn't that far off and seemed to perform well.

So with the thicker dino oil you're getting better protection but at the cost of higher temps? Seems like they cancel each other out.

Is 240 about the temperature where you'd start to get concerned?

[M.D. Holloway]

Yup, stands to reason...Perhaps the single most important characteristic of a lubricating oil is the viscosity.

The viscosity of a fluid is a measure of its resistance, it corresponds to the informal notion of "thickness". For example, honey has a higher viscosity than water.

Viscosity is due to friction between molecules of the fluid that are moving at different velocities. When fluid is forced through a tube, the fluid generally moves faster near the center and very slowly near the walls. A liquid's viscosity depends on the size and shape of its molecules and the attractions between the particles.

The thicker the oil the greater the restriction and the increase in shear which translates to increased temperature...

[redridge]

Originally Posted by rockyraccoon

Previous owner was running Mobile 1 10w30 fully synthetic. I drove the car pretty hard with this oil and the temp never got above 200.

I had some minor issues taken care of last week and had my mechanic change the oil to Brad Penn 20w50. The first time I drove it the temp quickly went up to around 9'oclock (225?). As I drove it went between 200 and 225 depending on the traffic.

It seems counter intuitive to get higher temps with thicker oil. Is this normal? Anything I should watch out for?

did you also notice increase in pressure? this is why I like thicker oil...

[Reiver]

Originally Posted by redridge

did you also notice increase in pressure? this is why I like thicker oil...

Anything over 10 psi per 1 K rpm is wasted HP. I do run 20w50 in our summers @ 100 degrees plus but in most areas that's not required at al....just old habit.
OTOH the car ran very cool...normally 190-195 in 100 degree plus weather. Winter 10-40 am running 180- 190. Both BPenn.

[James Brown]

keep in mind the W measurement means WINTER or cold viscosity, the 2nd number is the viscosity at 100˚C. So you went from 30 weight to 50 weight at operating temperature. You want good cold flow (lower W number) but good or high hot oil viscosity that meets OEM requirements that the engine was designed to run with. I don't know what year engine/car we are dealing with but the oil either synthetic or dino should match the owners manual requirements. Also, what was changed/fixed by the mechanic. Might want to try the Brad Penn 10W30 oil and see what happens.

[Nick Triesch]

I know there have been a lot of threads on what is the best oil but it seems the factory would know best about what kind of oil should go in our cars. Why would Porsche say to use synthetic if it was bad for our cars? What would they have to gain?

[MrBonus]

I noticed the same thing going from 15w40 to 20w50.

[dcjones56]

Since Mr. Freeman switched Imogene to fully synthetic Motul 8100 X-cess 5w-40 I've also noticed the engine oil temperature does not rise as high as it did when running the Valvoline 20w-50.

[duncan1437]

not sure if this is old news, but both shell and exxon/mobil have webpages which suggest specific oils for specific cars.

The Shell global homepage - Shell Global

What's the right oil for my car?

FWIW, for my car (1981 911sc), shell recommends 5W-40 full synthetic, and exxon recommends 0W-40 full synthetic. (the shell website doesnt include the 1981sc, so i used the 1984 carrera instead.)

edit...castrol UK has a similar webpage and suggests a full synthetic, either 0W-40 or 10W-40

http://www.castrol.com/castrol/sectionbodycopy.do?categoryId=9024084&contentId=7073092

castrol US has a similar page which includes different suggestions for different climates, and suggests 20W-50 above 14*

http://www.castrol.com/castrol/LubesSelector.do?categoryId=3240

[Reiver]

Originally Posted by dcjones56

Since Mr. Freeman switched Imogene to fully synthetic Motul 8100 X-cess 5w-40 I've also noticed the engine oil temperature does not rise as high as it did when running the Valvoline 20w-50.

What is your oil change sequence?

[Dave Kost]

One of the traits of a lubricant is to act as a heat transfer medium. The better the flow the better the heat transfer. Thinner oils will flow better and reduce temperature up to a point. That point is if it thins out too much the film strength is lost and friction will increase and the operating temperature will increase.

Follow the engine manufacture's recommendation as to oil weight and climate.