Improving fuel economy

[2000StreetRod]

electric fan temp setting?

Al Franklin (aldive) promoted the use of an electric motor driven radiator cooling fan to improve fuel economy and performance. According to his thread he adjusted the temperature control to maintain an engine coolant temperature of 192 deg F with an installed 195 degree thermostat. I think the fan was wired to be on whenever the A/C compressor clutch was engaged. He stated that the fan seemed to run continuously probably because in Florida the A/C is normally running. He had no way to monitor the radiator temperature but could monitor the ECT. I noticed that his transmission (5R55E) temperature would sometimes reach 200 deg F.

It occurred to me that there is a trade off between fuel economy/performance gains with an electric fan and higher transmission temperatures. Available documentation states that the 5R55E external cooling loop opens when the ATF in the torque converter reaches 150 deg F. I assume some engineering was performed to decide that 150 deg is the optimum operating temperature. If the electric fan does not keep the temperature in the radiator internal ATF cooler less than 150 degrees then the ATF will be heated rather than cooled when passing thru the radiator. There will be some cooling provided by the auxiliary ATF cooler but air to air coolers are much less efficient than fluid to air coolers.

When installing custom radiator cooling, consideration should be given to the radiator coolant temperature (RCT) and its impact on ATF temperature. I may search for a way to monitor RCT while driving.

 

[masospaghetti]

A clutch driven fan will also be somewhat of a compromise for the same reasons as the electric fan will.

Has anyone experimented with grill covers to improve aerodynamics? My reasoning: A V6 motor requires less cooling air than the V8 and thus needs less grill area to keep cool. I was thinking of a simple plate to block off the lower grill in the bumper.

 

[FIND]

Yes... but his radiator is going to reach the same temp whether he is using a clutch driven fan or an electric fan...

The clutch only fully engages when there is sufficient temperature to expand the bi-metal springs, which, keeps the engine coolant to the same temperature as Aldive was trying to keep his coolant with his electric fan. I mean, it's not like there exists anything else in the system with a clutch driven fan that would keep the radiator cooler while still keeping the same temperature in the engine. There is a direct relationship between radiator temp and engine temperature, regardless of the system you are using to cool the engine.

However, if you are worried about tranny temps, might I suggest a second fan controller set to turn on at a far lower temperature, running very small fans on the tranny cooler? This would not only keep your tranny fluid temps down, but it would also draw much less of the engine's energy than the full size radiator fan, clutch driven or electric.

Also, it isn't so much that 150 is the optimum operating temperature, it is that you want to raise the temperature of the tranny fluid up to at least this point so it is operating in the temperature range that its viscosity drops enough for better performance. You'll want your tranny fluid between 150 and 180 degrees, so once it hits that 150 mark, it diverts to the aux cooler to keep it a little under the operating temperature of the engine. They are trying to more precisely control the temperature of the fluid so they work within a more narrow range of viscosity and additive performance.

 

[2000StreetRod]

Interesting comments

. . . There is a direct relationship between radiator temp and engine temperature, regardless of the system you are using to cool the engine.

I think it would be accurate to state that the larger the cooling capacity of the radiator (core thickness, air flow, etc.) and the lower the temperature of the radiator the less time the thermostat will be open to cool the engine.

However, if you are worried about tranny temps, might I suggest a second fan controller set to turn on at a far lower temperature, running very small fans on the tranny cooler? This would not only keep your tranny fluid temps down, but it would also draw much less of the engine's energy than the full size radiator fan, clutch driven or electric.

Excellent idea since the desired engine coolant temperature (195) is considerably greater than the desired ATF temperature (150).

Also, it isn't so much that 150 is the optimum operating temperature, it is that you want to raise the temperature of the tranny fluid up to at least this point so it is operating in the temperature range that its viscosity drops enough for better performance. You'll want your tranny fluid between 150 and 180 degrees, so once it hits that 150 mark, it diverts to the aux cooler to keep it a little under the operating temperature of the engine. They are trying to more precisely control the temperature of the fluid so they work within a more narrow range of viscosity and additive performance.

When the ATF temp is below a value I haven't been able to determine the PCM uses the cold start shift schedule. The PCM can also inhibit torque converter clutch operation and correct EPC pressures based on ATF temp.

 

[onecansay]

Fuel Mileage

Mine is a 1999 3.0L 4 Speed Auto.

Nothing special. Regular cab.

160,000 miles, trany needs freshening!

Getting consistently 24 Miles per US Gallon or 29 Imperial.

No mods like all of you here. Like most of them though!

70/30 country/city.

I pre-heat my fuel.

That is it.

Thank you all.