I think at least part of the problem at low speeds is, the fan isn't drawing air across much of the radiator..... which is only aggravated by running the a/c. The shroud really should cover the entire core area of the rad, so it's drawing air across more fins.

 

It's an old-school trick to drill 1 or 2 1/8" holes through the diaphragm of the thermostat to aid with bleeding - especially because of how the top hose on these is designed (it was worse before they moved the radiator cap), as you fill the system with coolant, there's a huge air bubble in the bridge across the intake manifold because it only has 2 ways out - out the thermostat (which is closed) or out the bypass hose (which goes through the water pump back to the block galleys or the lower hose). IOW, the air has nowhere to go. Drilling a hole or 2 in the stat allows that air bubble to come up the upper hose - on the 00+ it vents out the radiator cap. On the 99-, it gets stuck in that same highest point of the hose, but there is no radiator cap - the air bubble once again gets water-locked.

The holes also help get a little bit of water pre-circulating, which can help slow down initial thermal creep. But once you hit the point of heat soak, there is little you can do to cool the engine back down. The radiator is the only way to shed heat, and it needs to shed the heat faster than the engine can make it.

At which point I have to ask, what radiator did you put in? Accounting for 20 years of gunk, the stock brass-and-plastic dual-row (I think each row is 3/8 or 1/2 inch) is hardly even marginal. Unfortunately there do not exist any direct-fit all aluminum radiators. There are some options out there for an HD radiator.

 

The basic carquest radiator, seemed to do OK with the clutch fan, guessing that moved more air though.

Attached are the pics I took of samples of the coolant color through my process of around 20 flushes. I did it until I got clear coolant back after 1hr+ long runs. Used some cleaners to assist in getting crap outta the system too. This was done with the old rad still in place to make sure I didnt jam up the new one. After getting all clear & clean fluids I pulled the rad, installed new one and did one last flush which all looked good and clean.

I had an issue before with air in the coolant system due to a bad reservoir tank leaking which is what started this whole endeavor.

Also, likely unrelated, but I also replaced the intake manifold with the edelbrock hughes gap manifold, the result of a snapped bolt in my old keg manifold when doing a tstat replacement. :/ lol

Some info that may help, I did have an overheating issue one day when going to look at a boat, the hose running to the heater core split which inevitably led to overheating. Boiling coolant and what have you. Could I have some additional damage deeper into the motor that could be causing this? I still don't see signs of a bad head gasket though.

 

That fan isn't pulling enough air across the radiator the way it is, you need a larger single or dual fan setup with a fan shroud that covers the whole radiator, or just put the stock setup back in.

 

Do you have any other cars? Feel the airflow from those fans, and compare it to the Dakota one. If the Dakota one is weak compared to the other ones, then airflow could be an issue.

That shroud is pretty close to the radiator. No reason for it either, since there's obviously a ton of room between the engine and radiator that they could have built a 2 inch deep shroud.With 2 inches, they could also have covered the whole thing, and airflow at speed would not have been an issue.

On the AC, do you have overheating problems when you don't run it? Turning off the AC should cause the truck's temp to cool down quickly if the AC is the problem. When fixing an AC problem that opens the freon lines, it's a requirement to replace the dryer and vacuum the system down. If this wasn't done, then your AC is likely the problem here. An AC can work without doing this, but not without a lot of problems, and it won't cool well.

When you changed the radiator, did you use a water hose to clean out the AC condenser? Does the condenser look like it might be clogged up? You can put a droplight between the engine and radiator and see how much light comes out to get an idea on whether this might be an issue.

 

I did not clean out condenser, I did however replace it with a new one from orielys as my oem had a leak from a small accident. I had a friend suggest changing the dryer when I did condenser but did not do this. I'm probably going to take it for a quick wheeling session today with the air off since it's overcast and see if it has the same troubles with the air off to at least try and isolate the potential cause of this.

I know the rad also has the transmission cooling connections and there is a factory trans cooler in front of the condenser. This also needs replaced as just from a hand temp test I can tell that's not flowing properly. I don't think this is part of the issue as it never feels that hot but thought I'd mention it as it's up there with all the cooling stuff.

And ya. I was concerned about the shroud, FF Dynamics assured me itll work, and they seemed thorough on getting the right one for the application I told them. (Florida weather, towing, off roading and probably afew drag runs once I'm done upgrading to around 400rwhp). The shroud itself is probably only 3/4" off the rad but the fan is set back on it putting the fan about 2" from the rad. I'm not about to continue upgrading the engine until I can solve this overheating issue as more power will likely exacerbate the problem.

 

Here is the response I got from FF Dynamics, leading me to further believe there may be something else going on. I understand their response is biased as it's their fan I'm questioning but some of what they've said here makes sense and correlates with some of the answers on this forum as well...

What do ya'll think would be my next thing to attack to try and get this under control or should I accelerate my engine rebuild timeline and go through it all that way (and do my cam while I'm at it)?

"After reading all your detailed statements the one thing that stands out that is making us believe that this is going to be an engine problem is you state when the truck got to 245 off roading you had to cut the motor and stop for 15 minutes for it to cool back down. With our electric fan system if you reach 245 while wheeling, you should have been able to just put the truck in park and idle and the fan should have been able to bring that temperature down to around 200 within a matter of 2-3 minutes with the truck idling with no load on the motor. Because you could not get the engine temperatures down and you had to shut the truck off it is definitely pointing to a problem with the engine itself. Then you stated that when you got back onto the roadway driving over 30 mph the engine temp would not go under 210 until you got to the car was and sprayed it with water. If you were driving on the roadway and had a 30 mph wind speed through your radiator that would certainly be enough to cool your engine right down to your thermostat temperature opening, which should be right around 195 degrees. This is definitely going to have something to do with your engine, where when you are loading up with your engine something is happening. This could be anything from a cracked cylinder head, a bad head gasket, an intake manifold leak, a blocked passage in one of the water jackets...any of these items that we just mentioned would make the truck drive normal everywhere and then when under load, run hot and be very hard to bring the temperature back down. Keep in mind that this is the most powerful electric fan system on the market for the Dakota trucks.

Another area you might want to look at that can cause this same type on and off type problem is your radiator core, at how thick it is. A lot of times when people replace radiators, they will go to a cheap unit off of the internet that is a thinned core radiator and some of the companies that sell these radiators will tell you that they are for all engines and they will be less than 1" thick. This would cause your overheating also. Measure your core and see how thick it is, if you have a radiator core that is under 1" thick, that would be what they use on a 3.9L 6 Cyl Dakota. Our advise if you have core under 1" thick is to look for a 1.5" radiator core or thicker. This would more than double your cooling capacity and would help prevent heat soak.

Check these areas out and let us know how you make out.

Thanks!
FFD"

 

Get the test kit from the parts store, to see if you are getting combustion gases into the coolant. (head gasket issue.) Also, measure the radiator as they suggest, and let us know what ya find. (might do that first..... if it's just too small, that would explain a lot.)

 

Image shows rad specs, appears to be 1.25" thick core.

Any particular product you recommend for that test? Head gasket is on my list of things to replace but wanted to hold off on that obviously until I have the funds/time to do my rebuild with cams and some other upgrades while it's torn down.

Took it for a drive around town today, 40 miles city and highway driving. Temps stayed right around 180-190 whole time, air on or air off didn't change it much. Temps today in the low 80s though due to tropical storm elsa. Lol gonna take it in some mud once afrw inches get on the ground with air off to see if the air is playing any sort of large factor.

 

Parts store should be able to recommend a test kit. Probably only have one flavor on the shelf.

If you are going to move to a higher performance engine, think I would be looking for a better radiator as well..... Especially if you plan on towing with it. Which one though? No clue. Gonna have to check and see what's out there.