Thin Oils and Lower Operating Temperatures

Shel_B

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I recall reading somewhere that some/many/all engines designed to run thinner oils (0W-16/20) operate at lower oil temps in order to maintain greater film thickness and provide better protection. Is my memory accurate, at least to some degree?
 

ZeeOSix

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If the oil was cooled to raise the operating viscosity in order to give more film thickness, then it would essentially be like running thicker oil at "normal" oil temperature (200 to 220F), and therefore no real gain in fuel mileage would be realized. So I don't see why they would run the thinner oil at lower temperature to protect better when they could simply specify a grade thicker oil. Besides, it's bad for oil to run it too cool all the time.

Engines (if designed well) that use thinner oil should have an effective oil cooling system to ensure the thinner oils don't get too hot and thin to the point where MOFT can essentially go to zero. Especially when used in conditions that can get the oil temperatures above that normal 200 - 220F operating range.
 
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There is a oil/coolant temperature exchange device, but since the coolant increases temperature before the oil the exchange is to warm the oil. It is as simple as to follow that device on the coolant side and see what the coolant thermostat is set for.
 

ZeeOSix

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There is a oil/coolant temperature exchange device, but since the coolant increases temperature before the oil the exchange is to warm the oil. It is as simple as to follow that device on the coolant side and see what the coolant thermostat is set for.
The coolant to oil heat exchanges are dual purpose. They help warm the oil up faster, and they also help keep the oil cool when at full operating temperature. The coolant that feeds the oil cooler is coming basically from the cold side of the radiator, which will be cooler than what the coolant temperature is in the engine that's controlled by the thermostat.

Some vehicles only have an air to oil cooler, and no coolant to air cooler.
 
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Another factor in this is that lower viscosity typically means less hydrodynamic friction (everything else equal). Lower viscosity also typically has a lower specific heat capacity, allowing it to get up to temperature faster but also cool down faster.
 
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More or less it is what it is. I always thought newer engines not necessarily run hotter but produce more heat to scavenge the most from the combustion cycle. At least that's mazdas thoughts and those that use an Atkinson cycle engine

Essentially I believe these 0w20 and 0w16 viscosities work in harmony with the newer engines for maximum efficiency and power
 
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I recall reading somewhere that some/many/all engines designed to run thinner oils (0W-16/20) operate at lower oil temps in order to maintain greater film thickness and provide better protection. Is my memory accurate, at least to some degree?
Hi @Shel_B , in order to facilitate a reasonable discussion, can you please cite your source(s) for the claim above?
 

OVERKILL

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It has been mentioned on here (by me) that along with the implementation of thinner oils, we've seen a very broad adoption of coolant/oil heat exchangers. As @ZeeOSix noted, these are dual purpose:

1. To warm the oil faster. Coolant comes up to the temp MUCH faster than the oil does, so this rapidly reduces viscosity by bringing the oil up to operating temperature alongside the coolant. This reduces frictional losses and improves fuel economy.

2. The prevent the oil from getting too hot. Thinner oil of course means a reduced margin, so, preventing the oil temperature from greatly exceeding the coolant temperature serves as a method of essentially capping oil temperature and thus preventing the oil from getting too thin.
 
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I recall reading somewhere that some/many/all engines designed to run thinner oils (0W-16/20) operate at lower oil temps in order to maintain greater film thickness and provide better protection. Is my memory accurate, at least to some degree?
Operating at lower temperatures goes against lowering emissions, not very popular these days.
 
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I can tell you on my VWs the 1.4 with 0w20 runs no cooler than my 3.6 with 5w40 did. The 0w20 oil is slower to hit full temp though. When I beat on it a bit and push temps up the 0w20 seems to cool back down faster than 5w40.

I have no idea if that's due to the different oils or changes VW made to other engine components. Its well known VW made some modifications to run 0w20.
 
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