Join Date: Aug 2006
Vehicle: 01 Dakota Sport 4x4 Club Cab 5spd 3.9
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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.
01 Dakota Sport 4x4 Club Cab
5 speed, 3.9