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Oil temp study

tigeo

Autocross Champion
Oil temps. I read things all the time online that will state things like “XYZ oil dropped my oil temps 10 degrees” etc. I’ve never bought it. Here are my data. From my testing, it’s all based on ambient temp, RPM, and incline/decline of the road. I also believe elevation has an impact b/c it will impact engine cooling efficiency with our heat exchanger oil cooler – would need to test that but based on some info gleaned from a popular oil discussion forum (bobistheoilguy), this seems to be true. I have collected these data over a period of time (nearly a year) on the same commute (all highway) at the same speed (70mph), at the same time (driving time since start to collect reading), and going the same direction (to handle the slope as it’s downhill to work and uphill home…a 150’ elevation difference and I do note higher temps on my return trip at the same ambient). Elevations are in the 100-250’ msl range. I’ve controlled the variables to the extent that I can. I think folks just don’t understand how the oil temp varies and just flick their dash to oil temp and see what they see but don’t take into account the temp/speed/rpm portion of the equation. These are data from 3 different oils and there is no real difference under these conditions w/r to oil temp – all 3 trend lines are close.

Oils used:
LM Molygen 5W40
Mobil 1 5W40
Quaker State Ultimate Durability European Full Synthetic 5W40
I’ve also used LM Leichtlauf High Tech 5W40, added Ceratec and MoS2, and Mobil 1 0W40 but didn’t actually record any data for those. All of my memories are that these 2 would also fall on the same trend line based on the same conditions for this test. Of course you would need a v. long data collection period to get each oil across all the seasonal temp variations....but this is good enough for government work!

Bottom line – at 70 mpg/2500 rpm sustained for about 30 minutes, you get ~0.3 degrees change in oil temp for every 1 degree of ambient temp change regardless of xW40 oil brand. If you changed the speed/RPM you would just shift the line down or up but the slope should stay the same. I suspect if you changed to a xW30 you would also see an overall shift down.

Enjoy.


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-DK-

Go Kart Champion
Location
Bay Area
Car(s)
2017 GTI SE
This is great work! thanks for the diligence and sharing.
 

avenali312

Autocross Champion
Location
Mableton, GA
Car(s)
2015 VW GTI
Nice work. I wish my numbers were this low, but my daily commute barely gets over 45 mph. DSG supposedly also adds some degrees over manual. I'm usually floating around 235-237 in the summer and 225 in the winter (Georgia winter haha). Moving speed does seem to make a big difference here as I'm probably stopped more than I'm moving (9 mile commute takes about 35 minutes in the morning and 45-50 minutes in the afternoon.
 

tigeo

Autocross Champion
so, what's the best oil then?
That wasn't the purpose of this test. I've done UOAs on all of them - they all are basically....the same. And this is what you should expect if they all have the same approval. However, I have heard enough folks say "I changed to XYZ oil and my oil temps dropped 10 degrees" which if keeping the same approval/viscosity - is bullshit and related to folks not understanding how the variables work w/r to this.
 

tigeo

Autocross Champion
Nice work. I wish my numbers were this low, but my daily commute barely gets over 45 mph. DSG supposedly also adds some degrees over manual. I'm usually floating around 235-237 in the summer and 225 in the winter (Georgia winter haha). Moving speed does seem to make a big difference here as I'm probably stopped more than I'm moving (9 mile commute takes about 35 minutes in the morning and 45-50 minutes in the afternoon.
Oil temps drop with speed - that is one of things my data show. So slower = lower oil temps b/c you are generally at lower RPMs. When are you stopped your oil temps should drop way down.
 
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