Thermostat temp affecting fuel mileage??

[drdolittlerwc]

I was talking with a friend today and I started mentioning all the things I've done to my rig, and when the the thermostat came up (I changed mine to a 170* as we are moving to Belize in a couple weeks). He mentioned that this could affect my fuel mileage, as the higher temp allows for the fuel to better atomize.

I never thought about it before, but it does seem feasible. Could it affect it that much? Does anyone have any thoughts on that?

I changed it to a lower temp, since the heat in Belize is pretty constant @ about mid 70's and up (mostly, mid 80's and up, 70's are a cool day)

 

[98OzarksRunner]

170* is not that much cooler, but it might make a difference. In theory, the thermostat sets the minimum temperature, which is the temp the engineers determined is required for best performance, mileage, wear, etc. The electronics (ECM) are programmed for things to work best at that temp. Putting in a cooler thermostat won't keep the car from overheating or running hot (contrary to how it might seem); but it can keep it from reaching optimum operating temperature, costing mileage, wear, etc. It's probably not so much the fuel atomization - would have more impact on a carbureted engine - but that the computer is assuming that normal operating temp is around 200 and will adjust things based on that. But, the ECM will compensate for the effects of the lower temp on the fuel mixture using feedback from the O2 sensors, so it shouldn't affect mileage much, if any. I would be more concerned about wear on the engine components.

In high-performance applications (like the 65 Mustang I built - http://www.cardomain.com/ride/3838887/1965-ford-mustang/) you usually run cooler thermostats to ward off detonation when using superchargers or turbochargers, and there is a small power gain possible, even with normally-aspirated engines (when you are looking for every last HP). But the downside is usually increased engine wear (in the long term), and sometimes poorer mileage.

If you are concerned about the heat in Belize, a cooler thermostat won't help keep it cool. I don't think these 4Runners have problems with overheating. I have had mine crawling through the woods on 95 deg days in low range with no change in temp - it stays at 200* (+/- 2* or 3*) in any weather. Unless you are doing serious rock crawling in Death Valley, I think the factory cooling system is more than adequate. But, do make sure that your clutch fan is working, your radiator is clean, and your fan shroud is intact and in place.

 

[t4r4life]

I was talking with a friend today and I started mentioning all the things I've done to my rig, and when the the thermostat came up (I changed mine to a 170* as we are moving to Belize in a couple weeks). He mentioned that this could affect my fuel mileage, as the higher temp allows for the fuel to better atomize.

I never thought about it before, but it does seem feasible. Could it affect it that much? Does anyone have any thoughts on that?

I changed it to a lower temp, since the heat in Belize is pretty constant @ about mid 70's and up (mostly, mid 80's and up, 70's are a cool day)

it does affect the MPG but not much, 1-2 mpg at most. (i run 170 too)

 

[vipergrhd]

My 2 pennies

170* is not that much cooler, but it might make a difference. In theory, the thermostat sets the minimum temperature, which is the temp the engineers determined is required for best performance, mileage, wear, etc. The electronics (ECM) are programmed for things to work best at that temp. Putting in a cooler thermostat won't keep the car from overheating or running hot (contrary to how it might seem); but it can keep it from reaching optimum operating temperature, costing mileage, wear, etc. It's probably not so much the fuel atomization - would have more impact on a carbureted engine - but that the computer is assuming that normal operating temp is around 200 and will adjust things based on that. But, the ECM will compensate for the effects of the lower temp on the fuel mixture using feedback from the O2 sensors, so it shouldn't affect mileage much, if any. I would be more concerned about wear on the engine components.

In high-performance applications (like the 65 Mustang I built - http://www.cardomain.com/ride/3838887/1965-ford-mustang/) you usually run cooler thermostats to ward off detonation when using superchargers or turbochargers, and there is a small power gain possible, even with normally-aspirated engines (when you are looking for every last HP). But the downside is usually increased engine wear (in the long term), and sometimes poorer mileage.

If you are concerned about the heat in Belize, a cooler thermostat won't help keep it cool. I don't think these 4Runners have problems with overheating. I have had mine crawling through the woods on 95 deg days in low range with no change in temp - it stays at 200* (+/- 2* or 3*) in any weather. Unless you are doing serious rock crawling in Death Valley, I think the factory cooling system is more than adequate. But, do make sure that your clutch fan is working, your radiator is clean, and your fan shroud is intact and in place.

Very good point,i still don't understand why you would swap a stock thermostat to a lower temp to compensate for ambient temp.the only time that i would do that is when a particular engine runs at a constant high temp.due to high horse power and high compression engine.i would suggest you stick with a factory thermostat with the correct concentration of coolant and distilled water.

 

[drdolittlerwc]

170* is not that much cooler, but it might make a difference.
Putting in a cooler thermostat won't keep the car from overheating or running hot (contrary to how it might seem); but it can keep it from reaching optimum operating temperature, costing mileage, wear, etc. It's probably not so much the fuel atomization - would have more impact on a carbureted engine - but that the computer is assuming that normal operating temp is around 200 and will adjust things based on that. But, the ECM will compensate for the effects of the lower temp on the fuel mixture using feedback from the O2 sensors, so it shouldn't affect mileage much, if any. I would be more concerned about wear on the engine components.

The downside is usually increased engine wear (in the long term), and sometimes poorer mileage.

If you are concerned about the heat in Belize, a cooler thermostat won't help keep it cool. I don't think these 4Runners have problems with overheating. I have had mine crawling through the woods on 95 deg days in low range with no change in temp - it stays at 200* (+/- 2* or 3*) in any weather. Unless you are doing serious rock crawling in Death Valley, I think the factory cooling system is more than adequate. But, do make sure that your clutch fan is working, your radiator is clean, and your fan shroud is intact and in place.

Thanks! These are some good points to think about. I changed it thinking it would help keep the temp lower, and it does, temp does NOT go above 170*, my thought is that it would be better to run at a lower temp in a constantly hot climate. Not true??

As far as increased wear is concerned, what would be involved with that (what sort of wear are you talking about)?

 

[98OzarksRunner]

Thanks! These are some good points to think about. I changed it thinking it would help keep the temp lower, and it does, temp does NOT go above 170*, my thought is that it would be better to run at a lower temp in a constantly hot climate. Not true??

As far as increased wear is concerned, what would be involved with that (what sort of wear are you talking about)?

I know that putting in a lower temp thermostat sounds like it will keep the engine from overheating but it really doesn't. The lower temp thermostat will keep the engine at 170* IF (and only if) the rest of the cooling system (radiator, fan, shroud) are able to dissipate enough engine heat to keep it at 170*. The thermostat has nothing to do with the maximum temperature the engine will reach (unless it is stuck shut) but only the minimum temperature the engine will operate at once it's warmed up. To verify this, cut out a piece of cardboard the size of the radiator and put it between the radiator and the A/C condensor (so no air flows through the radiator - just kidding, don't really do this!). The temperature will go well above 170* very quickly since the radiator can't dissipate the heat with no airflow, even with the 170* thermostat. So, if the cooling system is working correctly to keep it at 170* it will keep it at 200* (or 195* - whatever the factory thermostat is) just fine. If it won't keep it at 200*, there's no chance it will keep it at 170*, no matter what thermostat you put in there. Thus, the temp of the thermostat has no bearing on the maximum temperature of the engine, only the minimum operating temp.

There is no real advantage to running the engine at a lower temp, unless you need to, and the only real 'need to' is to avoid detonation on high-compression engines, or with superchargers or turbochargers. It might make a slight bit more power (usually measured in the single-digits, even on race cars) but the tradeoff in wear, and possibly poor mileage, will more than outweigh this, unless you are building an all-out race car engine where every HP counts.

The engine is designed to run at a certain temperature, both for economy and wear. The engine is designed to have specific clearances between the parts (piston to cylinder wall mainly, but also bearing clearances on rods, main bearings, cam bearings, etc.) at the designated operating temperature. When the engine is cold(er) the pistons are not expanded enough to achieve the design clearances, thus will (typically) have too much of a gap between the piston and cylinder wall (causes noise called 'piston slap'). (Engines designed for superchargers or turbochargers have extra clearance built in and usually make a heck of a racket when cold, since under boost the cylinder temps quickly go WAY above temps for normally-aspirated engines, and make more noise than most cars even when warmed up.) This piston slap can cause excessive wear to the sides of the piston, as well as scar the cylinder walls (and can even break the piston skirts in extreme cases). That is why most of the wear on an engine occurs during warmup (especially in cold climates). (The bearing clearances are also tighter when cold, which is why oil is rated as 5W-30 [for example] - it's actually thinner at cold temperatures since the bearing clearances are tighter and the heavier weight oil can't flow through them well enough to fully lubricate them.) It isn't likely that running at 170* will cause much extra wear, but there is really no reason to risk any extra wear for no gain in cooling ability or power increase. Hope this helps.

 

[t4r4life]

Thanks! These are some good points to think about. I changed it thinking it would help keep the temp lower, and it does, temp does NOT go above 170*, my thought is that it would be better to run at a lower temp in a constantly hot climate. Not true??

As far as increased wear is concerned, what would be involved with that (what sort of wear are you talking about)?

little tip for running cooler, if your area never freeze, run 2 part distilled water 1 part toyota red coolant. the water will help it cool better. complete opposite if your area freezes a lot.

Engine will run rich when cooler, running at 170 is a bit low, idea range is 185-190. you can try to do a cold air intake to lean out a bit to bring up temp.

 

[drdolittlerwc]

Ok, not sure how to start this, BUT....

On our 3.6k trip I noticed a couple things.

1. We got about 17-18mpg on state-side gas

2. We got about 19-20mpg on MX gas

3. One benefit of using a lower temp thermostat was that we didn't have to wait long to open the radiator to check for coolant.... This has led me to think that the engine will ultimately run cooler and will cool faster once it's shut down, which I know is better for a shut down engine after running.

One thing I was taught is that an engine will continue to rise in temp after shutdown till it balances out. Which, of course, will be sooner if the temp is lower....

Not so sure about the higher mileage in MX, so many say gas is better in the states... still not sure about that.... We used cruise control the WHOLE way...

And don't talk to me about the difference in SAFETY... We felt safer in MX!

 

[nevada]

I was talking with a friend today and I started mentioning all the things I've done to my rig, and when the the thermostat came up (I changed mine to a 170* as we are moving to Belize in a couple weeks). He mentioned that this could affect my fuel mileage, as the higher temp allows for the fuel to better atomize.

I never thought about it before, but it does seem feasible. Could it affect it that much? Does anyone have any thoughts on that?

I changed it to a lower temp, since the heat in Belize is pretty constant @ about mid 70's and up (mostly, mid 80's and up, 70's are a cool day)

its not only feasible, its true. engines are most efficient just over 200*.
its best to run the stat it was designed for. running the engine too cool can cause it to add fuel, since its trying to get UP to temp.