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Steve, relay for the radiator fan is in the top left corner in the diagram at post #16 in this thread. Power for the fan comes from the 50 amp fuse 15 in the Power Distribution Center (same diagram). There is no fuse for the radiator fan in the junction block at the left end of the dash. According to the FSM, the radiator fan should run any time the a/c is selected, or if coolant temperature exceeds 217° or 230° (FSM shows two different values in different places). Wire carrying power to the fan is light green.
 

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Just a couple of thoughts Steve. You should try to artificially power and ground the fan to see it it works before jumping to buy a new one.
And a FYI on my own Dakota I tried an experiment about 2 years ago now. I removed the mechanical fan completely and ran my truck. To my surprise it didn't overheat! The electric fan was able to handle any cooling situation that I encountered. As I say I have been running the truck this way for over two years now with no issue. This was good for about a 1 mpg increase on the average. YMMV
 

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Discussion Starter · #23 ·
Thanks, turning the cover over I found the ledger and relay location. A new relay is cheap and they hardly ever fail. I will check the fan motor before changing it. I now wonder if the electric fan has ever worked since we have had the truck one year. The mechanical fan is always spinning and this heating issue began with the long drive though lines with mid to high 90s temps. Turning off the AC and switching to full temp heat and fan does bring engine temp down but no help for the driver.
I also like the idea of improved MPG and know the mechanical fan draws power. Of course where would I be now with a failed electric fan? One thing I have noticed since this began is I'm not sure what temp 1/8 inch above the left hash mark indicates. The reason I ask is for the last year 13,000 miles more less that is where the gauge stopped regardless of speed, load, AC or outside temp. Since flushing the system twice it takes longer to reach normal ( for us ) temp and sometimes with low outside temp will run lower than what I have come to know as normal. I have the new thermostat and water outlet for when I remove and clean the intake. Plan is a compression test and leak down to decide if heads will support another 25,000 miles. Steve
 

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The FSM states that the lower mark on the temp gage is about 130°, and the upper mark is about 250°. The needle movement is evenly graduated between the marks, so half way on the gauge is about 190°. Our systems use a 20psi radiator cap, where the boiling point of 50/50 coolant mix is about 275°, so even at the high mark on the gauge, the system should still not be boiling. But you wouldn't want to go much higher. According to the FSM, the "check gauges" light will be illuminated at 251°.

My gauge rarely goes above a third of the way up, even on hottest days (about 175°). But I have a manual transmission (no load on the cooling system to cool the transmission), and I don't pull any loads.
 

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One thing I have noticed since this began is I'm not sure what temp 1/8 inch above the left hash mark indicates.
Pick up an ELM327 Bluetooth/OBDII adapter, and install Torque Free on your Android phone (or there's similar products for iDevice owners).

See what the ECU THINKS the temp is.

RwP
 

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Discussion Starter · #26 ·
The truck continues to throw codes. Random misfire most recently. I have noticed with the cooler temps the engine temp is closer to the first hash mark. Also my high speed running issues have stopped and the idle has returned to normal. The last code was P0300 on the last very hot day. Steve
 

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Discussion Starter · #27 ·
What a difference a month makes. Weather here is now in the mid to high 70s. My / our 03 Dakota 3.9 could not be happier. It has not thrown a code since the temp dropped. It starts right up, for the most part the high idle is gone, has great power and does not miss at speed any longer. Since we have had it the temp gauge has always run 1/8 inch above the left hash mark. With the weather change it now lays right over that hash mark. I have purchased everything for the cooling system, something over $400. delivered. Based on my research that's going to be 10 percent of the total engine rebuild. That's based on a improved camshaft, bore and balance, modified TB, 12 inch clutch assembly.

Along the way someone it appears tried to jack the truck under the oil pan. I'm concerned about the water jackets and freeze plugs. Other wise I'd install the complete cooling system and drive on. If I pull this engine it will get a full rebuild. Steve
 

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Discussion Starter · #28 ·
Alright now I have some newly acquired info that may help or confuse. Here is where we are. I recently had to make a 1000 mile round trip in one day. The thought that ambient temp may have something to do with running issue I started at 1 am driving roughly 9 hours getting 7 MPG with very rough running. Maybe one hour of talking, unloading and looking around and I was back on the road. Going down I was pulling a 600 lb trailer and 1200 lb load. Coming back the empty trailer was it. As I pulled onto the highway it was clear the truck was happy. Pulled to 3500 RPM in each gear settled into 5th gear and settled down for a 237 mile run at 75/85 mph and that tank gave back 20.6 MPG. Now the fun part, I was so excited things were going so well I left it running while I filled up with gas. Going down the ramp I could tell we were back to 7 MPG. I nursed it home by 10:30 that evening.
Strange but it gets better. This past weekend I need to do a 450 mile trip in one day again. Running up to PA. to pickup a 3.9 V6 core engine. Going up in the morning empty I topped off the oil and checked evey thing for a day run. Right out of the box it was clear another 7 MPG day. Fought to maintain speed on the hills and just get there. Perfect timing I arrived at one end of the Fair Grounds while the guys I was meeting entered the other end. It took an hour or more to unload their 20 ft enclosed and get to my core engine. Once I was loaded and secured I got back on the road. Surprise the truck was as good as it ever is. I worked up though the gears to 4th and took off. Again running 75/85 MPH and it took me all the way home without stopping and gave 19.5 MPG. There you go Ralph chew on that. Steve
 

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Hi Steve,

Let me start by saying it was a pleasure meeting you in PA this past weekend. I'm confident that the 3.9 core will live up to it's provanence., and wish you the best of luck with it. Now will this be a 3.9 build or more like a 4.? build? I guess only time will tell. But I digress.
Now back to the issue at hand. I really have to agree with Ralphs suggestions of getting a ELM327 OBD2 adapter and downloading a copy of the Torque App. for your smart phone. Doing this will open you up to a whole new world of real time data that exists right there in your truck already. I have been using this set up on many vehicles for years and it has proved to be a very useful tool for diagnosis. The best part about this is the cost. Now read my suggestion about that from my own experiences.

To further Ralphs suggestion I will tell you not to waste time with the cheapest eBay ELM327s. Sure they can be had for $3 shipping included. I tried that and found unreliable connection issues and down right failures to comunicate. The brand adapter I reccomend is the BAFX Products brand. They cost about $20 and feature a spotless reliability record for me. Another thing about the BAFX adaptor is ofter it is sold with a copy of the Torque app on a mini disc.

Also, I know that you can download the Torque App for free, but life time ownership of the real deal only costs @ $5.95,
or at least it did when I bought in some 10 years ago. I have never regretted this purchase, and you can use it on any OBD2 vehicle ever made.

Best wishes,
David, alias Dynamo
 
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