Colder thermostat and fuel economy

[Falcon_LS]

I'm replacing the thermostat on my '01 Grand Marquis, and decided to opt for the 180 F thermostat for the F-150 Lightening (as opposed to 192 F that came with the car). Seeing how it's now 48 C/118 F at 7 PM (55+ C/131+ F at noon), AC is always on full blast and I'm driving at higher speeds (140+ km/h/90+ MPH) constantly, I thought I'd give it a try.

I was just wondering if I should expect a slight drop in fuel economy as a result. Will 12 F make any difference? Fuel type is 98 RON with 500:1 ratio of TC-W3. I realise it's higher octane than recommended (91 RON), but this particular grade has a better detergent ratio and that is why I use it. Thanks.

 

[Jimmy9190]

My MPG actually improved a little when I installed a 180 degree thermostat. This is on a Dodge Dakota with a V6 engine.

 

[Brons2]

131 degrees! Wow. Highest I have experienced is around 110. I can't imagine adding another 21 degrees on top of that.

I think the 180F thermostat is a good idea and probably won't affect fuel economy, in that sort of an environment!

 

[Eddie]

I may very well affect emissions & cylinder bore wear.

 

[Chris142]

The stat only controls the opening temp. If your system is capable of holding the temp @ near the opening point you can expect increased bore wear and fuel contamination.

Most systems will still run 210 or so with a cooler stat. Just takes longer to get there.

 

[OVERKILL]

I know on EEC-IV, the 180 was the coldest you could get away with before affecting OL/CL operation; the ECM wouldn't go into closed loop until the ECT read north of 170F.

I've run a 180 in the Mustang (now Capri) for YEARS with an E-fan that comes on at 188F. I also have one in the Lincoln. I have been tempted to put one in the Expedition given that Ford put one in the Lightning. I also heard something about the new 3V trucks getting a 180 as well..... So there must be something to it.

 

[Trav]

Good point about the E-fan.Unless the sensor is recalibrated for the lower temp thermostat it still wont come on until the original temp setting is achieved.

I wonder what the piston piston/piston ring and ring/bore clearances are on the supercharged Lightning compared to the normal 5.4,maybe this has something to do with the lower temp thermostat.

 

[mechtech2]

Cooler thermostats are for tuning for power.
But for cruising fuel efficiency, you want stock, or even warmer.
Why? Because less heat will be given off from the burning mixture to the surrounding surfaces, and more is left to be used as piston push down force. With a colder thermostat, more energy will be used to constantly try and heat the surrounding surfaces - they are constantly trying to reach reach equiilibrium -homstasis.

 

[Trav]

I'm not sure about being for power as much as it is about octane requirements.
This is interesting.

A quote from the article.
"Contrary to the old tale of cooler is better for power; the higher temperature thermostats will actually help power. The oil will stay cleaner and burn off condensation easier. Friction is also reduced. Formula one cars typically run engine temperatures of 120-130 Celsius. If lower temperatures were better, they would run them. The only drawback is that for every 10 degrees F raise in temperature, there is a 1 point increase in the octane requirement of the engine. As sensitive as the XKE’s are to gas, this makes premium a must."

http://georgiajag.com/Documents/Thermostats.html

 

[OVERKILL]

Drag cars run cold. They slow down as they get hotter.

I wonder what temps NASCAR runs?

 

[SteveSRT8]

The quotes above are for specific cars.

EVERYTHING is dependent on the tune, and the type of engine control setup that manufacturer uses. Even the software. None of it is really general enough to apply to ALL cars.

Many modern engines pull timing at the slightest hint of knock and thus make more power running colder stats.

But too cold is just as bad. My car will quickly throw a code if not up to at least 180 in ten minutes for three cycles. But it is different from mfgr. to mfgr.

 

[demarpaint]

Originally Posted By: Eddie
I may very well affect emissions & cylinder bore wear.



I'd stick with the Thermostat the engine calls for. Just make sure the radiator fins are clean, and everything is operating properly. The engine was designed to run with the 192*F Thermostat, and unless you are experiencing problems I'd leave it alone. Just be sure to use a OEM Thermostat.

 

[OVERKILL]

Originally Posted By: SteveSRT8
The quotes above are for specific cars.

EVERYTHING is dependent on the tune, and the type of engine control setup that manufacturer uses. Even the software. None of it is really general enough to apply to ALL cars.

Many modern engines pull timing at the slightest hint of knock and thus make more power running colder stats.

But too cold is just as bad. My car will quickly throw a code if not up to at least 180 in ten minutes for three cycles. But it is different from mfgr. to mfgr.



EEC-IV started pulling timing when the ECT indicated a temp above 189F IIRC. With the stock 192F 'stat, you were guaranteed to be losing timing fully warmed up. A 180 cured that.

But as you stated, these are very specific to particular situations; though as far as EEC-IV goes, they had no knock sensors and I believe the temperature parameter for timing retard was across the board for all equipped.

 

[antonmnster]

My BMW stat is spec'd at 206. It has a little heater in it that raises the opening temp higher than that when the ECU determines that the load is light. They figured that one temp doesn't fit all, I guess. Only downside is that it costs $70.

 

[Colt45ws]

Originally Posted By: antonmnster
My BMW stat is spec'd at 206. It has a little heater in it that raises the opening temp higher than that when the ECU determines that the load is light. They figured that one temp doesn't fit all, I guess. Only downside is that it costs $70.

Thats nuts. Seems it would be simpler to directly control it with a solenoid or something. I actually surprised that has not happened yet.

 

[mechtech2]

Colder thermostats indirectly allow slightly more dense air into the CCs. This is indirect and is from ambient conditions, but it is a slight factor.
They allow more ignition advance - a sure power increaser for today's ignition advance starved engines. If you never knock now, there will be no gain - this allows tuning.

Ford tried a dual temp thermostat. Something like 215 cruising, and 195 when you step on the gas.
This is exactly the direction that you would expect for optimum results.

 

[rslifkin]

Not all factory engines are advance-starved. In my Jeep, the timing advance is aggressive enough (91 octane spec-ed) that if the engine starts to carbon up even a little, it'll ping on 93 under moderate throttle.

 

[mechtech2]

rslifkin - that is VERY unusual, to say the least.
That means the factory required 93, which it did not.
Something is wrong. You are too hot [coolant or intake air], carbon deposits, or an over advanced with regards to the intake side of the cam.
Or plain old poor design.

 

[SteveSRT8]

most modern engines will NEVER make audible knock no matter how [censored] the fuel.

No offense intended, but a 360 Mopar is a dinosaur.

They just pull timing like crazy, and performance/economy suffers.