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  #1  
Old 08-19-2006, 05:01 AM
ctandc ctandc is offline
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Cooling fan, thermostat, PCM controlled???

Maybe I'm just lost since this is my first Dodge I've owned that was made since computers and sensor were used in vehicles. However...I have been around late model GM and other makes and unless I'm out in left field..here's something I don't quite understand.

First off..my truck is a 01 Dakota 4x4 3.9 5 speed. It's a TRUCK...it's used as a TRUCK. So I'm not looking to make a bunch of mods and try to make the 3.9 into something it's not.

However...on the majority of the last project vehicles I've owned / wrenched on, I've consistently replaced clutch driven fans with electric fans. Usually pirating fans from junkyards ( some Lincoln / Mercs come with some nice dual fan setups )...in the process the cooling systems normally operated more efficiently, and it frees up some of the parasitic drag ( HP loss in essence ) that thermal clutch driven fans cause.

I've seen COUNTLESS threads on Dakota ( and other Dodge ) owners removing the clutch driven fan, and relying simply on the factory electric auxillary fan.

I've got some reservations about this. First off, the factory aux cooling fan is only cut on two ways that I'm aware of...( without mods )...

- engine temp reaches 210 degrees
- AC system is engaged

Me personally, 210 is a bit warm for my taste. Plus, I don't think the fan would be strong enough to take the abuse of the constant cycling it would go through in this setup. Not to mention the additional strain on the cooling system when in traffic, AC on etc.

On this same topic..I see MANY Dakota owners replace the factory thermostat ( I'm assuming it's a 195 ) with a 180 degree unit.

Now I see how many people would equate running cooler with better power...but I've got to go with my gut, and my experience with stock / non-tuned PCM controlled engines. The PCM wants to see a certain temperature. Hotter temps lean the air/fuel mixture out....cooler temps, the PCM normally richens the mixture. While this is normally seen to "increase power"...in actuality it's the result of the 'butt dyno' which in my experience with tuning and dyno's and using wideband O2 sensor setups....the butt dyno is rarely correct. Think about it...you just spent time and $$$ installing a part..of course you're expecting a power increase....so of course you 'feel an increase'...but I digress...

Is there some evidence from Mopar die hards that these engines ( 3.9 Magnum in my case ) run better overall, more efficiently, at slightly lower temps...using the 180 thermostat?

I know how harmful 160 thermostats can be on engines....I've seen the sludge and garbage build ups on many motors that ran these low temp thermostats on otherwise stock tuning. 180 thermostats work well in several GM EFI applications...but what about the Dakota?

I'm more concerned with overall efficiency ( such as increase MPG ) than "power gains".

And maybe this is a REALLY dumb question....but I see many Dakota owners mention "The truck never runs over 190 now" or "The e fan kicks on at 210 or so, I'm watching the gauge"...

Did Dakota's come with different temp gauge options or is everyone installing aftermarket temp gauges, which read in degrees and not C to H????

I may try removing the clutch fan and see how the temps range....and check the mileage, since I don't get stopped in traffic a lot.....it's made me curious now. However installing aftermarket or complete fan kits ( like the Viper kit ) don't appeal to me because of the cost outlay vs. gain received.

Also...for those using just the stock E fan....are any of you wiring up a manual switch so that the fan can be cut on when needed / wanted?

Any tips or wiring diagram to splice this into the factory wiring / relay system?

Sorry for the long-winded post, just wanted to get input from all different sides here.

I'm thinking I might try just changing to a 180 thermostat first and track the mileage.


The truck only has 37k on it....and in an almost dead split of 50/50 city / highway driving with the 5 speed, the truck knocked down a respectable 18.3 mpg on the first tank I ran through it.

That's not babying it either.....averages probaly 15-20 miles a day, if not more at 70-75mph...

Thanks for any input here.


Chris

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  #2  
Old 08-19-2006, 01:06 PM
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Nicely written so I'll give you my take on the whole experience plus a few facts as well. Fisrtst everything you said is correct; however, the fan is not set to come on at 210 deg. That # is purely a coincidence. The fan is set to come on when the ac system reaches a certain pressure. More ambient heat increases the pressure. That is why some peoples fans will turn on at 190 and others at 210. Also, why some people think you can turn the ac system on and the fan will come on automatically. It doesn't. The truth is if you are turning the ac on to engage the fan then the system is already pressurized enough to do it on its own. I've let mine idle for 30 min. in the driveway on a 70 deg. day and the fan didn't come on till about 220. In around town driving we had some 97 deg. days here. The truck will get up around 190 quickly under these conditions. would flip the ac on at stop lights and bring it right back down. The only reason it was coming on though was because it ws so hot out.

One thing I didn't know was that after out trucks hit 192 deg. the pcm automatically retards the timing. This may be the loss of hp that people are feeling. I was told this by B&G Chrysler.

You can wire in an auxillary temp. caontrolled fan switch that will kick on sooner. I plan on doing this, but I'm not very electrically inclined. I have seen a switch that you can set the temp on at Advanced Auto for $30. It doesn't need to be screwed into the block to read as it has an auxilary thermostat for the radiator. There are many threads and part #'s here about the correct way of installing these though.

In the winter my truck is perfect without the fan. I warms up quicker and stop and go trafic is no problem. Once it hits 80 out though it will warm up quickly to around 190-195 in stop and go traffic. Highway driving has never been a problem. I have driven the truck 60 miles straight with the tamp. gauge right in the middle on the highway. Once, I got off the freeway though it warmed up quickly at stop lights.

In my opinion, especially on the V6 removing the fan was a good move. It really made a noticeable difference in the performance and the sound too.
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Old 08-20-2006, 06:39 AM
HemiDak HemiDak is offline
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Quote:
Originally Posted by moore_716
Nicely written so I'll give you my take on the whole experience plus a few facts as well. Fisrtst everything you said is correct; however, the fan is not set to come on at 210 deg. That # is purely a coincidence. The fan is set to come on when the ac system reaches a certain pressure. More ambient heat increases the pressure. That is why some peoples fans will turn on at 190 and others at 210. Also, why some people think you can turn the ac system on and the fan will come on automatically. It doesn't. The truth is if you are turning the ac on to engage the fan then the system is already pressurized enough to do it on its own.
Your idea is a nice theory, but is completely inaccurate. In reality, the engagement of the electric fan has NOTHING to do with the pressure of the A/C system. According to your theory, this would mean that trucks NOT equipped with A/C would not be able to have an electric fan. Also, trucks that lose 100% A/C pressure will lose the electric fan ability. This would be a very bad idea for any company to do, as many vehicles lose A/C pressure and quit working over time. That would also mean the failure of the electric cooling fans, and enormus amount of overheating trucks possibly resulting in fires. This would cause a massive recall and luckily, is not how the electric fan is setup to operate.

The PCM is set for the electric fan to come on at 220 degrees and shut off at 216 degrees. This is via the coolant temperature sensor at the block. The reason why people typically see it come on at 210 degrees, is because that's the only close number around it. The temperature gauge on the dash is vaguely accurate, at best. The PCM knows the exact temperature, but displays it poorly to the driver, as the gauge is at fault.

The fan will also come on when the A/C is engaged, regardless of engine temperature. Turn the knob to A/C, defrost, or mix (vents and feet) and the A/C will also be engaged, thus turning on the electric fan.
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Old 08-20-2006, 06:46 AM
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If your worried bout overheating i have a 5.9 liter and am in birmingham alabama, very humid recently, 103 sometimes, never overheated the highest it got was dead center of gauge, im thinking bought going with a lower temp thermostat
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Old 08-20-2006, 01:04 PM
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Originally Posted by YellowKota2k
Your idea is a nice theory, but is completely inaccurate. In reality, the engagement of the electric fan has NOTHING to do with the pressure of the A/C system. According to your theory, this would mean that trucks NOT equipped with A/C would not be able to have an electric fan. Also, trucks that lose 100% A/C pressure will lose the electric fan ability. This would be a very bad idea for any company to do, as many vehicles lose A/C pressure and quit working over time. That would also mean the failure of the electric cooling fans, and enormus amount of overheating trucks possibly resulting in fires. This would cause a massive recall and luckily, is not how the electric fan is setup to operate.

The PCM is set for the electric fan to come on at 220 degrees and shut off at 216 degrees. This is via the coolant temperature sensor at the block. The reason why people typically see it come on at 210 degrees, is because that's the only close number around it. The temperature gauge on the dash is vaguely accurate, at best. The PCM knows the exact temperature, but displays it poorly to the driver, as the gauge is at fault.

The fan will also come on when the A/C is engaged, regardless of engine temperature. Turn the knob to A/C, defrost, or mix (vents and feet) and the A/C will also be engaged, thus turning on the electric fan.

I'll admit you know a hell of alot more about our trucks than I do, but I'm still gonna have to disagree. If you get a refrigerant chart you will see exactly what I'm talking about. The only reason that elec. fan is there to begin with is for the AC. When the AC/ press goes up the refrigerant turns into a gass. Then it's condensed back down into a liquid by cooling. That's where the fan comes into play. I can go out right now and turn my truck and AC both on and the fan will not come on because the system isn't so warm that the refrigerant is turning to a gas yet. I'll also bet that if you find a good chryser machanic they will tell you the same thing. Personally I happen to know a thing or 2 about refrigeration myself. I'm not arguing just stating what I believe are the facts. BTW how was the dream cruise?
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Old 08-20-2006, 04:02 PM
cloknem cloknem is offline
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just tried right after cold startup, the fan will come on as soon as the a/c is turned on. however, a/c pressure has something to do with it; the pcm surely has alot to do;

Quote:
Description and Operation

The fan is electrically controlled by the Powertrain Control Module (PCM) through the fan control relay. This relay is located in the Power Distribution Center (PDC) . For the location of the relay within the PDC, refer to label on PDC cover.

OPERATION
The PCM regulates fan operation based on input from the engine coolant temperature sensor and vehicle speed.
The fan is not energized during engine cranking regardless of the electrical input from the engine coolant temperature sensor. However, if engine operating conditions warrant fan engagement, the fan will run once engine starts.
The fan is energized whenever the engine is running and engine coolant or transmission oil sump temperature is greater than 104C (220F) or air conditioning head pressure is greater than 32 kPa (220 psi) .
The fan will turn off when engine coolant or transmission oil sump temperature drops below 102C (216F) , or air conditioning head pressure drops to 24.6 kPa (170 psi) .
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Old 08-20-2006, 05:03 PM
HemiDak HemiDak is offline
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Quote:
Originally Posted by moore_716
I'll admit you know a hell of alot more about our trucks than I do, but I'm still gonna have to disagree. If you get a refrigerant chart you will see exactly what I'm talking about. The only reason that elec. fan is there to begin with is for the AC. When the AC/ press goes up the refrigerant turns into a gass. Then it's condensed back down into a liquid by cooling. That's where the fan comes into play. I can go out right now and turn my truck and AC both on and the fan will not come on because the system isn't so warm that the refrigerant is turning to a gas yet. I'll also bet that if you find a good chryser machanic they will tell you the same thing. Personally I happen to know a thing or 2 about refrigeration myself. I'm not arguing just stating what I believe are the facts. BTW how was the dream cruise?

All the information I got was from my factory Service Manual, so I know it's 100% correct. The post just above mine states exactly what I read in mine.

The Dream Cruise was okay, but not as good as previous years. The weather was just like last year which sucked. Turned out to be a decent day later on.
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Old 08-20-2006, 05:12 PM
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Alright you guys are starting to make me wonder if my local Dodge guru has lead me astray. My fan does not come on with the AC unless the temp is around 210. When I pulled my clutch fan I read that it would that's why I contacted him. He's a Chrysler legend around here. I mean the guy built a 57 chevy pickup and put a 440 in it just to piss everyone off at a local chevy show. :biggthump Anyway he's the one that told me there is a pressure fan switch in the AC lines. I also pulled my refrigerant chart out and the #'s verified the 210 thing. I'm not afraid to admit I'm wrong, but I aint givin up yet. Sorry about all the typos, it looks like a 5 yr. old typed it.heheheh
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Old 08-20-2006, 05:46 PM
HemiDak HemiDak is offline
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Now that I re-read my Service Manual, it doesn't mention anything about A/C pressure. The post above mine is almost exactly like what my Service Manual says, but has the addition of the A/C pressure written in there.

What I think may be possible, is there were a few changes after 2000. Since 2000 was the first year of the electric fan, they may have added the addition of the A/C pressure later. Just something interesting I thought I'd add...
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Old 08-20-2006, 06:06 PM
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Well, right or wrong I'd like to find out. B&G Chrysler are the ones that told me about the timing thing at 192 deg. I also want to change the switch so that the fan comes on sooner. I would really like a manual switch, but one that would still come on when the AC wants it to. Is this possible. I don't use the AC much, but I wouldn't want to screw it up because I made the fan purely manual and forgot to turn it on. Atleast with th 3.9 there's shit loads of room between the radiator and the motor.
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Old 08-20-2006, 06:52 PM
HemiDak HemiDak is offline
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Yes, it's very possible. The flex-a-lite controller I have for my fan has an A/C relay that will turn the fan on. I just decided not to use it.
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Old 08-20-2006, 07:39 PM
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I'm not too inclined to get rid of the factory fan shroud. I may try the electric fan only route with the addition of a 180 degree thermostat..BUT..I need a factory service manual for my 01 so I can get the wiring diagrams. Because there's no way I'd get rid of the clutch fan w/o having a way to manually cut the fan on.

Does anyone do any custom programming for these trucks? I'm not talking a 'full tune' or HP gains...I'm talking about adjusting the temp that the PCM kicks the electric fan on. I've been able to do this on several of the GM EFI cars I've worked on in the past.

As for the fan control...like I said, I've never messed with Dodge / Chrysler much, but I know that every other PCM controlled car I have worked with, they ALL used a preset temp to cut the fan on via the PCM.

From the factory, these cars are tuned to run at peak performance for emissions requirements...so they tend to run a bit warmer that what is optimal for efficiency and true performance...

In the past, depending on the engine / tranny combo, I've normally started with 190 degrees for a starting point to cut the fan(s) on. This seems to be a pretty good compromise for performance and warm enough to keep alot of buildup accumulating in the engine.
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Old 08-20-2006, 09:08 PM
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Quote:
Originally Posted by cloknem
The fan will turn off when engine coolant or transmission oil sump temperature drops below 102C (216F), or air conditioning head pressure drops to 24.6 kPa (170 psi).
So that explains why the fan continues to run a while after the A/C is turned off. Thanks!
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Old 08-21-2006, 03:27 AM
HemiDak HemiDak is offline
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Quote:
Originally Posted by ctandc
Does anyone do any custom programming for these trucks? I'm not talking a 'full tune' or HP gains...I'm talking about adjusting the temp that the PCM kicks the electric fan on. I've been able to do this on several of the GM EFI cars I've worked on in the past.
You could have it adjusted through the PCM, but that will still require a custom PCM flash; which isn't cheap for our trucks. Best way IMO is to cut the factory wires and wire up your own controller.
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Old 08-21-2006, 03:48 PM
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Quote:
Originally Posted by ctandc
Does anyone do any custom programming for these trucks? I'm not talking a 'full tune' or HP gains...I'm talking about adjusting the temp that the PCM kicks the electric fan on. I've been able to do this on several of the GM EFI cars I've worked on in the past.

As for the fan control...like I said, I've never messed with Dodge / Chrysler much, but I know that every other PCM controlled car I have worked with, they ALL used a preset temp to cut the fan on via the PCM.
I'm wondering why no one has try to use GM PCM in a Dodge. I believe they have been used in other applications. All the sensors would have to be compatable and I think many of the are. You would have to switch to MAF instead of the MAP. Most likely you would have to run two computers to keep your dash happy.

I dunno, anyone have any thoughts on it?
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