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DH
Dodge Dakota
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5/22/2003
09:30:53
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 Subject: Fans and Overheating
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Can someone clarify for me what fan or fans serve to reduce coolant temperature and just exactly how they operate? Does one operate all the time and the other only at times when needed?
I have a 2000 Quad Cab, 4.7 engine, 3.92 gears, Heavy Duty Service group including larger radiator and transmission cooler. Occasionally I tow a small hybrid trailer / rv. I'm interested in knowing what exactly will happen when and if engine temperature rises.
Does one of the radiator fans only come on when temperature rises to a certain level? If so, what temperature?
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gps_jetskier
Dodge Dakota
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5/22/2003
12:12:25
| RE: Fans and Overheating
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Clutch fan comes on when the truck is started. Runs a bit till it warms up slightly. Then slows down to almost nothing. Then at some point...not exactly sure..but I'd guess around 190 or so it goes on full tilt. The electric fan kicks on either when the AC is running or when it gets past 210 (kicker/helper fan).
GPS_JETSKIER
01' Quad, 3"PA Body Lift, 285/75R16 BFG AT
SS Nerfs
Line-X
Custom Safari Rack
Custom Prerruner Bar
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ScojoDak
Dodge Dakota
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5/22/2003
15:52:15
| RE: Fans and Overheating
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Let's not forget that another important element to a cooling system is the thermostat. The thermostat will stop the flow of coolant at a set temp. That lets the coolant stay in the radiator for an amount of time where the fan (clutch or electric) cools down the coolant in the radiator. When the thermostat opens, the cooled down coolant flows throughout the system. Then the cycle continues. A lower temp thermostat increases the cooling cycle, hence the cooler running temp. Hope that helps.
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HotRodSRJ
Dodge Dakota
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5/22/2003
17:19:55
|  RE: Fans and Overheating
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The last poster has it wrong sorry to say, no disrespect meant. This is a common held position for alot of folk so don't feel bad. Holding water/coolant in the radiator with the theory to cool it and somehow maximizing cooling is a MYTH. I will tell you why!
Your cooling system is a closed loop system. If you hold water/coolant in the radiator you are also holding water in the engine. Chemistry fact: Water loses it's ability to absorb heat as it approaches it's corrected vapor point (boiling point...meaning that water/coolant will aborb and carry more heat per unit at 180 degrees that the very same amount at 210 degrees) Also what this means is that it leaves more heat behind the hotter the water gets being held up in the engine. The heat in the engine eventually get's left behind to overrun the engine. This makes the whole system very inefficient as well as the radiator. In simple thermodynamic physics, the more flow the more capable the system is of transporting heat. Therefore, stopping and/or holding water for any reason reduces cooling ability,.... period.
This same fact shows why you can literally support more hp on a given system of yesteryear (like in muscle cars) with a higher flowing water pump. Same thing on different.
For more articles on cooling (tis the season) check out my cooling forum at http://www.inccn.net/jscooling.htm and for another good tech site and product support http://www.stewartcomponents.com/html/tech_support/advanced_cooling_system_basics.asp
Enjoy.
By the way. I have a Dakota Quad 4.7 and do some light towing and upgraded the electric fan to a larger CFM. I don't know if it really needed it tho....but we have long grades going north to the mountains of GA and Tenn...so I overkilled it. The fan is computer controlled. It will run all the time with the air going.
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steve789
Dodge Dakota
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5/22/2003
19:12:32
| RE: Fans and Overheating
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Good information. I just replaced my clutch fan with an electric, and installed an underdrive crank pulley. I've been watching the temp carefully for the last couple weeks and haven't seen it go above 195. I have a '99 5.2L, with a 180 Tstat. I live in SoCal, and I'm a little worried about towing a trailer in 90+ heat. But I can definately tell difference in HP!
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Shank
Dodge Dakota
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5/22/2003
19:51:01
| RE: Fans and Overheating
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I'm with Hotrod up there. Thermostats are great for winter time. I live in So TX and as soon as a vehicle shows signs it's starting to overheat the 1st thing i've done is pull the thermostat out completely, flush the system and then add the proper water/antifreeze.
The thermostat closes at set temperature ie. 190Deg. The thermostat won't open to allow water flow until the water in the Engine reaches 190. Prior to reaching 190 the system is "Closed" and the water flows from the water pump thru the engine and the heater coil only. This causes the engine to warm up faster to normal operating temp and makes your heater/defrost work faster.
Without a thermostat it takes longer for your engine to warm up and because you now created a full time "Open" system which water flows continiously thru all components of the water system including the radiator which is cooling the fluid like it is supposed too.
The thermostat creates a flow restriction point and when they become worn out they do not open far enough to let enough water flow thru the "Open" system. That's why they recommend if your engine is overheating to turn your heater on & roll down the windows. In this scenario the water flow to your Radiator is being restricted by the malfunctioning thermostat but you still have full flow thru the heater coil, Your heater Coil is acting as a mini-Radiator and your Fan motor is now the Fan.
I know It's a Pain in all Dodge engines where they located the Thermostat and usually requires removing the Alternator. If your vehicle is running 10-15 deg hotter than usual either replace the thermostat and flush the system or just leave the thermostat out until fall comes around and you need the heater again.
Hope this helps & Good Luck
Shank
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HotRodSRJ
Dodge Dakota
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5/22/2003
20:27:05
|  RE: Fans and Overheating
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Steve789......be forewarned....underdrive pulleys reduce flow and pressure. NOT GOOD under any circumstance on the street, except MAYBE pure drag racing.
FWIW, Underdrive pulleys do not significantly improve power at the rpms you are working on the street. Heck, a full blown Stewarts high performance/flowing racing water pump (they deliver over 120 gpm) only takes a total of 2.2 hp at 8,000rpms (this is tested...not vaporware)! The problems with running underdrives is that you may be reducing the friendly pressure in the block that can cause vunerability to hotspots! A reduction of 5 psi due to slower impeller speeds will reduce your boiling temperature about 15*! Also, as I stated before.....flow is king and reducing the rotation of the water pump is doing just the opposite..reducing the flow. Do not believe the claims by these morons that tell you that you will have stratospheric gains with THEIR high performance underdrive pulleys. Under drive pulleys were really invented to keep stock water pumps from cavitating at high rpms when used in racing applications. I put OVERDRIVE......yes I said OVERDRIVE pulleys at 17% on all my performance muscle cars, hotrods and trucks. NO appreciable hp losses on the chassis dyno at all..trust me. Why do I know so much about this.....because I help to design, manufacturer and market high performance pulleys (www.conceptonepulleys.com), so alot of experience and design info here for you to absorb...no charge.
Another note for Shank. I do not recommend running without a thermostat either. The reason is that it could set up laminar flow in the radiator (in other words reduces the turbulence) and lower the efficiency of the system. Always use a thermostat...they have NO function for cooling capability at all, simply determine range of operation..that's all. If you are looking for a high quality, high flowing and accurate "balanced thermostat" then try the Robert Shaw models from Summit Racing. These are accurrate withing 2 degrees and do not slam shut on pressure changes and are higher flowing stats. They actually induce turbulence to the radiator as well. Just a recommendation and check this site out for more on "balanced thermostats". Go to http://performanceunlimited.com/illustrations/thermostats.html
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gps_jetskier
Dodge Dakota
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5/23/2003
07:55:37
| RE: Fans and Overheating
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HotRodSRJ,
Your right on the money. I did'nt read the post well enough. Should have answered that better. As for the "laminar flow in the radiator"...I seriously doubt that is going to happen. Not that I would recommend taking it out, it's just that it still has to take several turns entering the radiator. It'll stop being laminar soon after all that. I still agree with you though on the rest.
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ScojoDak
Dodge Dakota
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5/23/2003
08:40:35
| RE: Fans and Overheating
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HotRodSRJ, none given, none taken. Just goes to show, you can teach an old dog new tricks. I've just been edumacated.
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Daksmack
Dodge Dakota
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5/24/2003
09:42:56
| RE: Fans and Overheating
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Great read fellas. Applause to all. Gotta admit I learned a couple of things.
I doubt our 4.7's would be as effected by it much (seems quite efficient), but I definately agree about not removing or gutting the T-stat.
Just to put it in laymans terms, the flow may be so fast that the radiator may not get the coolant temp dropped enough before re-entering the engine.
Ive had experience with this. Of course it was on a high compression engine with a radiator that we found soon enough that was too small.
Hope my lil tid bit adds to this plethora of info.
BTW, Im in the market for a RS 180 stat. And havent found them anywhere. Is it listed in Summit cat. or must I call them?
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Lab Rat
GenIII
5/24/2003
12:09:12
| RE: Fans and Overheating
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'Smack,
Stop by your favorite Autozone in Allen or Plano. Bypass the counter zombies, go straight to the cooling system section. Look for part number GT755-180. When you're swapping it, file a notch in the edge like the factory one has and reuse the seal. Can't find the stat?? It's in the housing where the lower hose attaches to the engine (coolant return).
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jjj
Dodge Dakota
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5/24/2003
15:29:39
| RE: Fans and Overheating
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Message:
Water pumps do not produce pressure, the pressure in a cooling system is due to fluid expansion... plain and simple period. And the only reason to leave the pressure there is to raise the boiling point.. period.
Thermostats do have a cooling function, their job is to restrict flow so the fluid has the time to absorb heat. Too much flow will cause hot spots since heat absorbtion is not instantaneous. The fluid also has to remain in the rad. to disappate the heat. Heat transfer takes time among other things..
Jeff
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steve789
Dodge Dakota
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5/24/2003
18:17:14
| RE: Fans and Overheating
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I didn't know the underdrive pulley would harm any cooling. That sucks. Well now I'm working on where to connect the electric fan so that it doesn't turn on when the ignition is off. Is it the alternator B+ terminal (output) or Field terminals? I made the mistake of asking the shop to wire it to the battery, which has been a nuisance.
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Shank
Dodge Dakota
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5/25/2003
01:33:51
| RE: Fans and Overheating
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Thx for the "Other side" of the Story, Nobody has ever tried to explain it that way. I've had too many thermo's go bad at the wrong time and it's been easier to yank the thing out while burning myself multiple times and throwing it as far as possible than trying to replace it.
Thx Hotrod butcha lost me on "Laminar" ?? what the heck is that?
I do notice a higher flow rate thru the radiator without the Thermo and It's worked well for me soo far.
Now I'm reconsidering the whole thermostat theory and maybe I'll give it another try if the dang thing wasn't so freakin Impossible to reach.
Laterz,
Shank
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benigas
Dodge Dakota
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7/24/2010
18:16:34
| RE: Fans and Overheating
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need a straight answer I have a 2000 Dakota with a 4.7l motor.what is the normal operating temp of the vehicle. My gauge goes above 210 to maybe 225. I have a manual that says the electric fan comes on at 230. I live in las vegas and it is pretty hot here now. It take awhile about 45 minutes but the gauge seem to start reading about 220 and never gets back down to 210. took it to the dealer and thay say everthing is OK
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daddio
Dodge Dakota
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7/25/2010
09:13:29
| RE: Fans and Overheating
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I guess the 4.7's temp settings are set different than the 3.9's because my '00 3.9 electric comes on right @ the 210 mark. There are aftermarket temp switches you could use to operate the fan.
My 3.9's normal temp range is 195. Without the mechanical fan it will get to 210 idling in traffic but takes about 20-30 minutes to do that then the electric fan kicks in and it comes right back down.
What shape is your cooling system in? Have you changed coolant or tstat lately?
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