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Hey guys,
I need some advice. Here is what I've done and what I need.
I have replaced my thermostat with a 195 fahrenheit (180 is stock), replaced my radiator cap with a 16 psi (13 is stock), redirected my air filter housing to draw air from behind the radiator and blocked my air dam/grill with cardboard all to increase engine temperature and draw hotter air into the intake manifold.
In theory and practice a warmer engine runs more efficient, albeit less performance.
My question is how do I control my fan from turning on at it's normal regulated temperature setting? What controls this and can I use something to adjust it to turn on at a higher temperature?
Lets say the thermostat opens at 195 and the fan turns on at 210, I want to run operating temperature at 260 and have the fan on at 261-265. I know I can wire a switch to manually turn the fan on and off, I have done this before on another car but it wouldn't be a safe solution because I would always have to be completely aware of my engine temperature gauge or I could overheat the engine and blow a head gasket or worse.
I believe a reostat (I'm no electrician and will make up stuff that sounds close) regulates the flow of electricity and it could be wired into the fan wiring and be dialed to turn on the fan at what ever impedance limit it is set at.
Does anyone have any ideas on how to accomplish this? - Dale

Hi Drimportracing:

___It is doubtful 260 degree coolant will increase your FE over 190 and you could be raising hell with your block and its mating surfaces to everything else.

___My reasoning on the 260 degree coolant temp is you are losing the driving temp differential on the Carnot cycle from Intake temp after the cylinder is sealed up through the expansion phase let alone a higher propensity to pre-detonation. The intake charge will not be 260 degrees of course but it will be higher than design. 160 degrees is usually the area that the CAT light off is inferred so we definitely want to get to that as quickly as possible including closed loop ops at slightly lower temps and hold but I am not so sure running hot is going to offer much in the way of better FE and may in fact harm your FE?

___Good Luck

___Wayne

Wayne,
The Carnot cycle is a little difficult for me to comprehend. I looked it up in wikipedia and I'm not sure if I grasp it's meaning as well as you understand it.
Also the "Cat light on" is not a term I'm familiar with. I'm only GUESSING that it and the closed loop ops is refering to the O2 sensors signal to maintain a 14.7:1 air/fuel mixture (lambda) while the engine is not warmed up and during other conditions such as decelerating, accelerating, under heavy loads and wide open throttle .
Here is a way I would like to explain what I'm trying to do. Let's say I have a Geo Metro in Yuma, Arizona during the summer and the outside temperature is 110 degrees and I'm cruising on the interstate doing 55mph and I'm getting a theoretical 48mpg and I take this same car to say Concord, NC and the outside temperature is 60 degrees and I'm cruising on the interstate doing 55mph and I'm getting 40mpg or less.....
How would I be able to recover that lost 8mpg? I think I would want to increase the intake temperature and the engines operating temperature to compensate for the colder outside temperature. How could I do this?
Also if my car didn't overheat in Yuma could I not improve my FE by increasing my engine temp by a FEW percentage points above the Yuma operating temperature?
Or as you mentioned would that lead me to an unknown point where too much heat would increase metal expansion and/or lubricant breakdown within the engine and cause power loss, friction and eventually mechanical failure either immediately or eventually?
Where is that point of highest efficiency and how far is it from mechanical failure?
Each of these questions are important to me. - Dale

Hi Dale:

___There is a loss in overall fuel economy as temperatures drop but the loss in efficiency has more to do with increasing tire RRc’s, higher drag by rotating components open to ambient air and increased air drag due to increased air density with decreasing air temperatures. All three of these effects reduce overall efficiency in a negative linear fashion (at a given constant speed) vs. ambient temperature far more than the reduction in engine efficiency under a similar drop in temperature. Add to that a 3 + percent hit with winter RFG the Northern States are being transitioned too and we see upwards of a 30% fall-off in fuel economy from 80 degrees F ambient to 0 degrees F ambient and only a small portion of the overall reduction in fuel eocnomy can be attributed to a fall-off in engine efficiency.

http://www.cleanmpg.com/photos/data/522/RRc_vs_Temperature.gif

___A Radiator block can help to reduce the small loss in engine efficiency due to heat escaping to the atmosphere from anything under the hood. A WAI pushing IAT’s back into the 80 to 100 degree range is optimal as well but it really is the fuel and driveline losses (not drivetrain) that are killing us as temperatures fall unfortunately :(

___For the driveline losses, aero-mods at higher speeds can help but keeping the tires warm while driving on pavement that may be 50 degrees on a sunny day in 20 degree F temps let alone bearing housings that are exposed to twenty degree temps is just not enough.

___What I am trying to say is if you could completely seal your engine bay and control both the intake air temps and the entire block/engine components to a constant 100 degrees F as well as coolant temps to 190 degrees F, your fuel economy would still be down 25 + percent at 0 degrees ambient for all the other reasons not related to engine efficiency itself.

___If only we had the ability to separate all the individual variables and test everything in isolation to come up with an actual fall off due to ambient temperatures, we would have one heck of a document to rely upon when questions like this arose every fall and winter.

___Someone you may want to PM is Tim S. (Brick) as he has done quite a bit of theoretical work on ICE’s under a variety of fuels and I suspect he may have a great deal of experience with those same engines in temperature controlled test boxes leading to a wealth of data that we could all use.

___WRT optimal efficiency from a given coolant temp, I doubt it is much over 190 degrees F myself? Saying that, some Ford’s coolant temps read in the 240’s but that is not measured on the block return vs. off the radiator outlet IIRC.

___Good Luck

___Wayne

Thank you Wayne; for taking the time to explain the RRc to me and the effects of ambient temps. This helps me get closer to my goals. I will look into changing my fluids to a lower viscosity, I have already used full synthetic wheel bearing grease.
I'm still holding onto the idea of a warmer engine performs far more efficiently than a normal temperature operating engine.
Two words: TOM OGLE
Normal ICE with a gas cell under vacuum (cell is heated to prevent fuel from freezing under vacuum), carburetor is removed and replaced with a ??? (I think I know what and why) which allows gasoline vapors to enter combustion chamber rather than liquid gasoline.
To do this you need heat; hot fuel, hot intake, and warmer engine. Ignition temperature is 495 degrees F for gasoline. So warming the fuel cell is safe at say 300 - 375 degrees......I just realized how far off topic I have drifted.
Questions I need answered:
How do I control my fan from coming on at the standard parameters set by the Metro's engine temperature sensor? Could I use a Ford temperature sensor? (thanks for the lead, Wayne) Is there a hotter sensor available? Would a rheostat work or would I need a potentiometer to control the fan?

Thank you Wayne; for taking the time to explain the RRc to me and the effects of ambient temps.

...
I believe a reostat (I'm no electrician and will make up stuff that sounds close) regulates the flow of electricity and it could be wired into the fan wiring and be dialed to turn on the fan at what ever impedance limit it is set at. ...

A rheostat is just a manually variable resistor. It might help manually change fan speed, but it will not change fan speed according to temperature.

Variable speed fan drive circuits usually include a thermistor, which changes resistance according to temperature, but normally include numerous other electrical parts. A thermostat would turn the fan on and off according to temperature.

-- Dean (electrical engineer)

This is what I found: http://www.thehoffmangroup.com/zirgo/product.lasso?prodinc=tempswitches
It is exactly what I'm trying to do myself. I have found both the analog and digital model on ebay for $50 and $60 shipped respectively. I should be able to build something that will do the same thing for $30.
I believe a hotter reading temperature sensor, ie a 240Fahrenheit sensor from a different vehicle with the same national pipe thread (NPT) and a single blade to match my wiring will work.
In addition, wire a rheostat to slow down the fan after the higher temp sensor sends it's signal to turn the fan on. Thank you Dean for the heads up on the rheostat.
With these two component changes I should be able to use my temperature gauge inside my car to observe engine temperature and manually turn the rheostat knob to allow the fan to turn slower or faster to regulate my engine temp.
I know my car will run safe at 3/4 hot on my temperature gauge with the fan unplugged UNLESS I'm pulling up a hill in first below 5mph, because I did that and it was kinda sketchy. This should fix that.

Very nice explanation Wayne. That helped me understand the effects of cooler tempatures a lot.

Thanks,
Stan

Great tire data Wayne. A couple of questions. First, what does the legend mean? Second, what is the source and is there addition tire data there - like perhaps rolling resistance vs. tire pressure?

A much more complete way to conclude this experiment would be to manually activate your fan at various temps while using a scanguage or for carby cars an in fuel line glass pipette mounted on your dash.

Best FE may occur at a temperature different from what one thinks. Same for your intake temp.

Best FE vrs engine temp is a component of hypermiling, but careful you dont make a bomb and your fuel lines are sound.

How do I control my fan from coming on at the standard parameters set by the Metro's engine temperature sensor?
You could try putting a thin plastic washer under the temp sensor on the radiator. I agree, yours may be different but on my civic, the sensor was bolted to the top of the radiator by its heatsink. I figure if it was insulated slightly from the radiator, it would switch on the fan at a higher temp. Obviously this is fraught with risk as the fan may not come on until a dangerous temp but i'm sure it could be made work.
You could test it by putting the washer on a heated surface, measure the temp of the surface and measure the temp on top of the washer. Try it at different temps and you'll get an idea of how much temp difference is across the washer.
I haven't tried this but it works in my head!!:D

ollie