If you drop to a 165 degree thermostat in a direct injection engine I think it will cause you grief. Direct injection needs hot cylinder walls. An ideal oil temperature is around 212 degrees.

 

That's quite a big change, you're taking about decreasing the steady state operating temperature of your motor. The clearances in the moving parts were designed for the proper operating temperature. Is there a motivation for doing this?

 

Modern engines are precisely designed for fuel efficiency and emissions. Messing with the operating temperature is a good way to screw it up. Have no fear, it won't overheat as long as the cooling system is operating as designed.

 

What's wrong with 194?

 

The engineers that designed it know more than what us mugs do (I hope). I would not stuff around with it.

 

I agree. No need to mess around with it.

 

I'm a bit paranoid about heat.

Why?

I'm contemplating switching to a 165 degree T-Stat. Anyone done this?

No, and for good reasons.

 

Here's the problem with trying to lower the operating temperature.

One, Subaru doesn't make a thermostat that low, for good reason, so that leaves an aftermarket that will be a gamble for actually causing the engine to overheat.

Two, the computer fueling and ignition map is programmed to heat the engine up fast and then it can run its most efficient. Older EJ turbo engine are happy around 190°F. Newer engines need 200°-215° for combustion efficiency and to ignite the fuel from the direct injection.

Three, while the engine is warming up to its normal temp, it's using more fuel and combustion rates are lowered which leaves higher carbon deposits which will affect the engine operation over time. As well as the turbo.

4, turbo operation depends on heat.

You think Subaru operating temps are high, Ford 4 cylinder turbo engines run at 230°F.

 

As said, bad idea. If you're concerned, just use one of the best oils, like Amsoil, and send a oil sample off to Blackstone Labs, to see how your oil is doing. Having a Fumoto oil drain valve helps to do oil samples and changes.

That 194F is pretty much what most cars trucks see, now days. I seem to recall, my 86 F150 has a 192F T'stat.

Yesterday, I changed the oil and filter in our 24XT after a 5000+ mile road trip over the past 2 weeks. The Castrol Edge 20,000 mile oil had just over 6000 miles on it, but oil is cheap. I normally do 10,000 mile oil/filter changes.

During the drive around the Yellowstone area climbing the hills I saw oil temps of 226F, Can't imagine doing that climb in summer time.

 

Yesterday, I changed the oil and filter in our 24XT after a 5000+ mile road trip over the past 2 weeks. The Castrol Edge 20,000 mile oil had just over 6000 miles on it, but oil is cheap. I normally do 10,000 mile oil/filter changes.

During the drive around the Yellowstone area climbing the hills I saw oil temps of 226F, Can't imagine doing that climb in summer time.

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On any of my cars using full synthetic oil, I do a 7500 mile change interval. I will shorten that mileage figure before or after a long journey. (6000 miles)

 

Dude you are a driver you are no engineer these cars normal operating temperature is 207°, you're not overheating and your fans are working I'm guessing you have a CVT transmission the temperatures need to be at a certain operating temperature for the transmission to work correctly don't touch your car

 

You're going to be fine don't use zero w20 oil especially in the summertime use 0w-40 in the summer 5W30 in the winter but in the summertime on longer trips I see 235 oil temperature haven't had any issues you might want to consider lowering your oil change intervals to 5000 miles you'd be surprised how much cleaner your engine will be.

 

I use factory recommended weights only. Again, like operating temperatures in the engine, the best performance curves of any modern engine are achieved with oil weights recommended by the manufacturer.

 

Most likely trigger a cel. Modern engines have very efficient heat transfer systems , some even use electric t stats to maintain stable engine temps.

 

Stop it. Find something else to mess with. Leave this alone.

 

Going to a lower temp thermostat will certainly trigger a CEL.

P0128 to be exact.

 

I would leave everything alone for the most part unless doing a full performance/tune kind of package.

1. This change will likely void your warranty.

2. The air fuel ratio and catalyst operating temperature could be problematic. If the engine temp is too cold, you could create a situation that would cause the car to run rich. Over time this could foul the spark plugs, cause poor fuel economy, foul the oxygen sensors and potentially harm the catalytic converter.

3. I can see some flexibility with the oil weights, but a premium oil and filter of the recommended weights and more frequent oil change intervals is probably a better approach. One thing to consider is that most newer engines use oil pressure driven timing chain tensioners and any variable cam timing stuff is often driven by oil pressure (not sure if your engine has variable timing). Drastic oil weight changes could result in significant oil pressure changes at these sensitive locations.

4.) I don’t know too much about direct injection but I can imagine it depends on certain temperature parameters for normal operation

5. As you mentioned in the original post this could also mess with cooling fan settings. There are probably multiple settings for high/low fan speed. A/c on and off, etc. if they aren’t all set up just right you could invite an overheat situation.

On a dedicated performance set up. Where fuel maps and fan settings, timing and etc are all adjusted to work together, lower temp thermostat may be a good addition. But as a stand alone option I would stay away for these reasons.

 

You're going to be fine don't use zero w20 oil especially in the summertime use 0w-40 in the summer 5W30 in the winter but in the summertime on longer trips I see 235 oil temperature haven't had any issues you might want to consider lowering your oil change intervals to 5000 miles you'd be surprised how much cleaner your engine will be.

In winter, you would be far better off with a 0W oil than anything else, that's the low temperature rating. The second number is the operating temperature viscosity.

Most likely trigger a cel. Modern engines have very efficient heat transfer systems , some even use electric t stats to maintain stable engine temps.

Which is what amused me about this thread - 6th Gen Outbacks have exactly that, an electronic thermostat, aka, TCV. You would probably need some advanced tuning skills to change anything.

 

In winter, you would be far better off with a 0W oil than anything else, that's the low temperature rating. The second number is the operating temperature viscosity.


Which is what amused me about this thread - 6th Gen Outbacks have exactly that, an electronic thermostat, aka, TCV. You would probably need some advanced tuning skills to change anything.

I was thinking the same thing--I'm no expert, but I got a not-a-recall extended warranty notice from Subaru for the TCV on my 2020 Limited. Being curious, I performed a bit of Google Fu to discover that this more-complex device controls engines temperature similarly to but more accurately than the old-school thermostat plug (I've changed my share of stuck thermostats as a youth).

So I was puzzled by this post and the responses acting like there is still a rated thermostat plug you could just "switch out." Did I miss something? I was about to start looking for a parts list when I scrolled down to your reply.

TL;DR / to summarize the replies so far: It would be a terrible idea to lower the engine operating temperature by replacing the thermostat with a lower-temp one, for a variety of tolerance and efficiency reasons, if there even was a thermostat to replace.

 

You will totally confuse your ECU, and your dashboard will look like a Christmas tree.

 

no, don't the car will NOT go into closed loop, it will stay in warmup mode and burn excess fuel ,all modern auto must reach 195 F. to enter closed loop for max fuel economy avg. temp on modern cars is 200-210 F.

 

Already mentioned by @cardoc dozens of posts ago.

 

Keep coolant temperatures and oil temperatures separate in one's mind. I agree with the comments about retaining the original coolant temperature set point. Everything works best when "normally" warm.

Normal conventional engine oil temperatures can reach 250°F for a practical maximum and damage to the oil may begin at 275F. Synthetics are OK up to 270° and briefly up to 300°F. If a separate oil cooler is fitted there is often a thermostatic valve to bypass the cooler until the set temperature is reached (the oil needs to be "normally" warm). 200°F is a common point where the thermostatic valve begins sending the oil through the cooler.

It is not just the maximum temperature as much as it is time-at-temperature. The longer the high temperature is held the more damage is done to engine oil, transmission fluid (a specialized hydraulic oil), differential gear oil, any oil product.

 

My 2022 outback runs at 195 - 205 oil temp during the summer but runs at 1765 in the winter around town. I have to drive highway speeds for 5-10 miles to get the oil temp up.

 

That's a downfall with short trips the oil doesn't get hot enough to burn off any condensation in the engine and it's not good for the transmission if it doesn't get up operating temperature the best thing you can do if your car does a lot of short trips is change the oil sooner around 4 5,000 miles don't believe the hype on extended oil change it just creates a very dirty engine