Thicker oil = lower temps? temp gauge owners only.

[zaibatsu]

I've seen people post that they've got lower oil temp readings on thicker oils on multiple occasions. This obviously contradicts BITOG understanding that thicker oil has more viscous drag and will cause an increase in temps unless the thinner oil has insufficient film strength and the resultant metal contact is causing frictional losses and resultant heat.

I'm not looking for a theory lesson here, but I am curious what owners of oil-temp gauges in their cars have experienced.

It'd be great to see which oils you are comparing, and what difference in temps were - assuming similar driving and outside conditions.

 

[BISCUT]

I've not gone with thicker than 5-20 in my F150 5.4 3V but have run PYB dino and M1 and MC blend....all showed the same operating temps on my gauge. THere was no temp difference between dino, syn blend, and syn. Not at least at the normal operating temps.

 

[JAG]

I used to have a BMW 135i (~310 hp; turbocharged) that had an oil temp. gauge. Comparing temps. using Redline 5W-40 to Mobil 1 5W-30 showed that in normal driving, temps. were slightly lower, but spiked higher after using full throttle for significant amounts of time. I don't know how much Refline's significantly higher density played a role in that but I suspect it did. Of course there is a large difference in HTHS viscosity in the oils which likely played a role as well. Additives may have played a role as well.

 

[SteveSRT8]

The car in my sig has run oil temps of up to 300 degrees at HPDE's.

I have run everything from 0w-30 to 15w-50 and have never seen much difference at all, nothing I could attribute conclusively to viscosity.

 

[Jim Allen]

zaibatsu: I suspect anyone who report lower oil temps with higher viscosity oil are mistaken or there is something more to the story. I can monitor Engine Oil Temperature (EOT) in my F150 (5.4L V8) and have kept records of it for years and in all types of climates. I pretty much know what my stabilized oil temp will be according to ambient temps, load and driving conditions. As an experiment, I installed 10W30 HDEO oil in it rather than the spec'ed 5W20. Stabilized oil temp rose by about 5 degrees. Granted that isn't much but the heavier oil flows less (increase in oil pressure too) and there is more fluid friction generated and those things contribute to higher temps. I just switch back to 5W20 and guess what... oil temps dropped back down to what I had experienced previously. Again, it isn't a huge difference but it's there.

 

[demarpaint]

Originally Posted By: Jim Allen
zaibatsu: I suspect anyone who report lower oil temps with higher viscosity oil are mistaken or there is something more to the story. I can monitor Engine Oil Temperature (EOT) in my F150 (5.4L V8) and have kept records of it for years and in all types of climates. I pretty much know what my stabilized oil temp will be according to ambient temps, load and driving conditions. As an experiment, I installed 10W30 HDEO oil in it rather than the spec'ed 5W20. Stabilized oil temp rose by about 5 degrees. Granted that isn't much but the heavier oil flows less (increase in oil pressure too) and there is more fluid friction generated and those things contribute to higher temps. I just switch back to 5W20 and guess what... oil temps dropped back down to what I had experienced previously. Again, it isn't a huge difference but it's there.


You're right JIm 5° isn't as much as I would have thought, at least from reading here. You'd almost think going from 5W20 to 10W30 would raise the temps by 50° or more the way some people talk.

LOL

 

[Jim Allen]

Well, it is what it is on my engine. And I'm not a proponent of thicker than spec'ed oil (generally speaking). I learned a lot from running the 10W30. Biggest lesson is that one grade thicker doesn't do much of anything... pro or con... under normal operating conditions. Biggest problem I saw was monumentally high oil pressure when cold.

 

[demarpaint]

Originally Posted By: Jim Allen
Well, it is what it is on my engine. And I'm not a proponent of thicker than spec'ed oil (generally speaking). I learned a lot from running the 10W30. Biggest lesson is that one grade thicker doesn't do much of anything... pro or con... under normal operating conditions. Biggest problem I saw was monumentally high oil pressure when cold.


I wonder if a 0W30 or a 5W30 would make a difference? Not in theory but in your actual application.

 

[CATERHAM]

Originally Posted By: zaibatsu
I've seen people post that they've got lower oil temp readings on thicker oils on multiple occasions.

I've never experienced it and quite frankly most people claim the opposite; namely, lighter oil equals greater flow therefore cooler oil temp's.
One thing of which there is no doubt, if the oil is so thick that the oil pump is in by-pass thereby reducing the oil flow through the engine, oil temp's can spike.

 

[aquariuscsm]

I have no scientific proof,but in my layman`s experience,using 20W50 after a long high speed run,my car`s engine bay was definitely cooler (less heat radiating) than with a 10W30. My theory,and with other Z32 owners,the thicker oil is keeping the bottom end cooler. Oil temps and radiator temps (where oem temp guages read) are two different things. This info comes from Z32 engine builders. Of course all engines are different,thus why some call for thick and some call for thin oils.

 

[SS1970chrysler]

In my experience (all with pre-1980's vehicles), my temps rose faster to normal with thinner oils. Using thicker oils, my temps rose slower, but got hotter.
In ultra simple terms, I got better heat from SAE40 oils than SAE30 in the same cars.

 

[zaibatsu]

All interesting posts, thanks for sharing,
I was mostly looking to debunk the posts I'd read from people claiming lower temps with thicker oils (often questionable - large drops). Most of you seem to agree that the scenario would be unrealistic, but there are a couple of opinions claiming the opposite as well.

I personally feel my engine is running a little hotter on thicker oil, just judging by heat radiation, however I don't have an OT gauge to confirm.

 

[Nederlander75]

In my RX8 I run about 6-10 F lower temps 20w50 versus 5w20 and 5w30 once ambient gets above 90F daily driving or 80F on the track. 40wt is about the same as 50 but over a larger temp span. I also only see maybe 6-12 psi difference 40 or 50wt versus 20 and 30wt with the heavier oil being higher.

 

[aquariuscsm]

Originally Posted By: Nederlander75
In my RX8 I run about 6-10 F lower temps 20w50 versus 5w20 and 5w30 once ambient gets above 90F daily driving or 80F on the track. 40wt is about the same as 50 but over a larger temp span. I also only see maybe 6-12 psi difference 40 or 50wt versus 20 and 30wt with the heavier oil being higher.


Which 20W50 do you run in your RX8? I`ve always wanted to drive one of those. Mazda RX`s are one of my fave cars!

 

[Nederlander75]

I've run Valvoline, Castrol, Redline, Valvoline Synpower, and RLI in all those flavors. Saw about 3-5 deg drop with the synthetic.

The 8 is a very easy car to drive fast and quite a pleasure if you are ok with getting blown by on the straights. In return you can catch the V8s and flat sixes in the tighter sections.

 

[Gasbuggy]

My CTS-V oil temps increased after going to 5w40 from 5w30. In my experience towards the end of oil life temps become higher. So if you compare the temps of old thinner oil to new thicker oil there could be some overlap.

 

[RobertISaar]

so, no mention of anyone checking the surface temperatures of the metals that the oil comes into contact with?

thermal coefficient could explain why what has been seen may not jive with current knowledge.

 

[Nederlander75]

Good point except in my case my water temps go down in synch and my fans run less with heavier oil too.

 

[Cujet]

In my old Turbo Miata with 385RWHP, oil temperature and oil pressure were constant problems here in South Florida. I did try to use M1 0W-20AFE oils and ended up with 250PPM lead in the oil. Mostly due to lack of film strength at temperature. That resulted in an overhaul. By the way, oil pressure and oil temperature were horrible with 0W-20. Temps would spike within minutes.

Even the Mightly Mobil 1 15W-50 would drop in viscosity at the oil temps this thing achieved on the track (about 260f)

I ended up choosing even more viscous synthetics. 20W-50 M1, V-Twin and Amsoil products. That worked better.

 

[alcyon]

I just got both oil temp and pressure gauges profesionally installed and just made a few observations. The oil temp rises very very slowly from "cold" startup. The pressure is almost 90psi . Engine is mitsubishi 4g13 from the 1980s which has been rebuilt 10 years ago. Oil is shell helux ultrs group3 5w40 which has 8000kms on it.
fter amsoil. Ambient temps is nearly 40c.
in heavy traffic..which means radiator airflow only depends on the fans..oil temp rise to 96c. The pressure drops to 18psi. At 85c the oil pressure is 25psi.
i also notice when driving on the highway..the stock coolant gauge reads a lower temp but the oil pressure almost does not drop from 96c. It did drop to 92c but thats after some 30min highway drive with lots of cooling airflow.so my conclusion the heat rises in the oil very slowly..and also loses heat very slowly.
When i rev to 3000rpm the pressure reads 60psi at temp of 94c.