Oil temps w/r to ambient temps - plotted for my VW Golf Sportwagen

The one on my 80s toyota is like this
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These types of coolant-to-oil coolers typically take coolant from the bottom of the radiator where the coolant is the lowest temperature. I could see in hotter weather where the coolant may not cool down as much depending on the size and efficiency of the radiator, and the ambient air temperature. This is probably why TiGeo still saw oil temperature increase proportionally with increase ambient air temperature.
 
This morning - 63 out and hit 214 on the way in - falls right on the line.
 
I don't have a fancy graph, but I am averaging about 5 degrees cooler overall with VW 504 0w30 over VW 502 5w40s. FWIW?
My comment is - unless you are monitoring it and control the variables, monitor outside air temps etc. - you don't really know that.
 
For fun & games, here's a 12 valve Cummins oil to coolant heat exchanger (later ones are very similar).

It's fun aligning the filter housing, outer gasket, cooler/plate, and inner gasket together - I've seen them where they were slightly misaligned, and the resulting oil/coolant milkshake blamed on the "boost likely caused the head gasket to blow" LOL.

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Collecting more data and it's plotting up as expected/clustering nicely. Also important to note - these have all been collected at 70mph/2500 RPM after oil temp plateaus which does take a bit of driving. AC was on for a few of the warmer ambient runs but I've not noticed any difference between having the AC on or off w/r to oil temps. This is all for the current fill/QSUD Euro 5W40/no other additives. The line will effectively shift up or down depending on the RPM/speed.
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Been collecting more data and broke out my chart/trend lines by oil. I need a few more data points for the Molygen now that it's getting cooler - only changed it a few weeks ago and don't have enough spread on the dataset for that one. They will all basically line up/be close.

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The oil cooler becomes more efficient when the temperature difference gets larger, and less when the difference becomes less. That means it's working hard to hide any differences between oil viscosities that should be there (but are small anyway).

As you know, the engine coolant temp isn't static either but will be somwhere between the opening temp of the thermostat and the fully open temp. That accounts for differences between summer and winter aswell.

Your cooling system works well during your commute
 
VW is really good in keeping temperatures under control. Their EA888 engines warm up fairly fast (also depending on transmission. My Tiguan has coolant at operating temperature within 3 miles). But ambient temperature is not really a problem, an altitude is.
Their oil/coolant exchanger is fairly small and it shows at altitude. Aggressive driving to top of the Pikes Peak will send coolant gauge in my Tiguan to 3/4 mark in no time once I pass 10,000ft regardless of ambient temperature. It happened when ambient temperature was in 40's.
In EA888 Gen3 I think oil sump is larger so that helps for sure, but you ain't gonna see those temperatures being so consistent here.
 
VW is really good in keeping temperatures under control. Their EA888 engines warm up fairly fast (also depending on transmission. My Tiguan has coolant at operating temperature within 3 miles). But ambient temperature is not really a problem, an altitude is.
Their oil/coolant exchanger is fairly small and it shows at altitude. Aggressive driving to top of the Pikes Peak will send coolant gauge in my Tiguan to 3/4 mark in no time once I pass 10,000ft regardless of ambient temperature. It happened when ambient temperature was in 40's.
In EA888 Gen3 I think oil sump is larger so that helps for sure, but you ain't gonna see those temperatures being so consistent here.
I've never thought about elevation at all b/c I'm near sea level and at most, when I go to the mountains here on the east coast, it's ~2K feet tops.
 
I've never thought about elevation at all b/c I'm near sea level and at most, when I go to the mountains here on the east coast, it's ~2K feet tops.
Yep. You are fine. That is why you don’t have issues on the track. Here, no VW can do track day without CEL if ambient temperatures are above 80 degrees and no upgrades in cooling system.
 
Here's my final wrap-up:

I have collected these data this 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. The impacts of the VWR oil cooler would be interesting to look at as well.

Enjoy.

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MOAR data! Here is an update adding the HPL Euro oil I am current running. Bottom line, no difference here. Any slight variation in the trend line slopes is related to simply not having a full range of ambient temperatures when I ran each oil which is seasonal. Info on the control variables here are listed above somewhere. It just de-bunks a common online comment I read that I tried XYZ oil (same viscosity!) and it lowered my temps 10 degrees - not happening in normal conditions.

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^^^ That graph right there is why manufacturers that don't have to bow down to CAFE have oil viscosity charts that show what viscosity to run depending on the ambient temperature. Even if it's a water cooled engine and has an oil cooler like yours. Hotter outside ... they say to use a thicker oil.

It would be interesting to see the same data plotted for a xW-20 and xW-30 oil to see how the viscosity changes the trends when used in the same engine.
 
Winter and summer here in mid-Florida my oil temp is around 175F around town. Interesting that on the highway at 75-80 MPH the temp drops to 165F. The water temperature is always around 185F regardless.

812 Superfast.

ali

PS: "It would be interesting to see the same data plotted for a xW-20 and xW-30 oil to see how the viscosity changes the trends when used in the same engine."
In my experience the oil temperature is always lower with thinner oils, and therefor it does not thin as much for the same load.
 
Winter and summer here in mid-Florida my oil temp is around 175F around town. Interesting that on the highway at 75-80 MPH the temp drops to 165F. The water temperature is always around 185F regardless.
Anytime you have more air flow through a cooler, it's going to decrease the outlet temperature of the fluid being cooled. This is also true with coolant radiators that feed coolant-to-oil coolers since those coolers feed off the cold side of the radiator. At highway speeds vs city speeds, the engine's coolant temperature coming out the cold side of the radiator will be cooler too.

PS: "It would be interesting to see the same data plotted for a xW-20 and xW-30 oil to see how the viscosity changes the trends when used in the same engine."
In my experience the oil temperature is always lower with thinner oils, and therefor it does not thin as much for the same load.
It won't be low enough to make much difference ... I'd like to see formal data of how much cooler, especially on a vehicle with an oil cooler. A thicker oil if a few degrees hotter will still provide better viscosity/MOFT protection between moving parts.

PS - wish you could use the quote function. Just hit the
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button. ;)
 
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