I posted this a while back in *ahem* another forum, before I was a member here, but it seems useful so I'm bringing it here.
In 2018, I had recently installed a winch and was seeing my 4.0 run warm. On a hot day, it was getting to 235. Even in 60 degree weather, it was getting into 220 territory. At the time I lived at 6000' in south Colorado Springs and commuted 40 miles to 4700' in Pueblo. The climb back up in 95°F heat was where I had the most trouble.
Note that the important thing is, regardless of my elevation, outdoor temp, or the presence of a winch, a properly operating factory cooling system will handle this stuff just fine.
My radiator looked pretty fresh. The coolant was brown enough that I couldn't tell whether it was supposed to be green or gold. So I did a flush with ThermoCure by Evapo-Rust and replaced with 50/50 distilled water and the all makes/models green coolant. I also replaced the thermostat, flushed the heater core, and put on a new fan clutch. Still overheated.
Following the helpful advice of some forum members, I checked the radiator. It was NOT a Mopar. So I ordered a Mopar radiator and swapped them out.
You can tell a Mopar by the embosed logo on the back side of the lower tank, above the drain valve.
The first thing you'll notice is that the new Mopar unit is black and the aftermarket is bare aluminum. If it's the common black coating used in the air heat exchanger industry, it's usually referred to as "e-coat", which most simply might be described as underwater powder coating. It has negligible effect on heat transfer but it does extend the life of the heat exchanger by preventing corrosion.
The top shows that the upper tank/header is similarly shaped but definitely a different mold as the joint lines are in different places and the radii of the curves are different. I'm curious what the feature is next to the inlet connection that appears to be a stiffening rib or something?
NOW FOR THE IMPORTANT PARTS
The FIN. This is tedious to show in a photo so I'm just going to explain it. This is the thin metal wavy strips that goes between the thin vertical tubes. The mopar has 17 fins per inch while the aftermarket unit has 16. Doesn't seem like a big deal, but it is a 6% reduction in secondary heat transfer surface area.
The TUBES:
If it seems in the photo like the tubes might be a little closer together in the new Mopar radiator, it's because they are. What this amounts to is a total of 44 tubes in the aftermarket radiator, and 55 in the Mopar. Since the tubes are similarly sized (both have a 1" deep core), that means the aftermarket radiator has a ~20% reduction in primary heat transfer surface area on top of the 6% reduction in secondary.
So it appears that the aftermarket company quantified how much margin was present in the factory setup and eliminated that margin, resulting in overheating when stressed with things like high temps, elevation, and a winch blocking airflow.
I repeated the flush (no Thermocure this time, just hose water, then distilled) and sprung for the Zerex G-05 HOAT coolant this time around. I'm happy to report that in the same conditions I was hitting 235, I now don't even get to 210.
So the moral of the story is, if you need a radiator, buy Mopar. And if you're running warm and you've eliminated the other possibilities, then your aftermarket radiator is a likely culprit.
In 2018, I had recently installed a winch and was seeing my 4.0 run warm. On a hot day, it was getting to 235. Even in 60 degree weather, it was getting into 220 territory. At the time I lived at 6000' in south Colorado Springs and commuted 40 miles to 4700' in Pueblo. The climb back up in 95°F heat was where I had the most trouble.
Note that the important thing is, regardless of my elevation, outdoor temp, or the presence of a winch, a properly operating factory cooling system will handle this stuff just fine.
My radiator looked pretty fresh. The coolant was brown enough that I couldn't tell whether it was supposed to be green or gold. So I did a flush with ThermoCure by Evapo-Rust and replaced with 50/50 distilled water and the all makes/models green coolant. I also replaced the thermostat, flushed the heater core, and put on a new fan clutch. Still overheated.
Following the helpful advice of some forum members, I checked the radiator. It was NOT a Mopar. So I ordered a Mopar radiator and swapped them out.
You can tell a Mopar by the embosed logo on the back side of the lower tank, above the drain valve.
The first thing you'll notice is that the new Mopar unit is black and the aftermarket is bare aluminum. If it's the common black coating used in the air heat exchanger industry, it's usually referred to as "e-coat", which most simply might be described as underwater powder coating. It has negligible effect on heat transfer but it does extend the life of the heat exchanger by preventing corrosion.
The top shows that the upper tank/header is similarly shaped but definitely a different mold as the joint lines are in different places and the radii of the curves are different. I'm curious what the feature is next to the inlet connection that appears to be a stiffening rib or something?
NOW FOR THE IMPORTANT PARTS
The FIN. This is tedious to show in a photo so I'm just going to explain it. This is the thin metal wavy strips that goes between the thin vertical tubes. The mopar has 17 fins per inch while the aftermarket unit has 16. Doesn't seem like a big deal, but it is a 6% reduction in secondary heat transfer surface area.
The TUBES:
If it seems in the photo like the tubes might be a little closer together in the new Mopar radiator, it's because they are. What this amounts to is a total of 44 tubes in the aftermarket radiator, and 55 in the Mopar. Since the tubes are similarly sized (both have a 1" deep core), that means the aftermarket radiator has a ~20% reduction in primary heat transfer surface area on top of the 6% reduction in secondary.
So it appears that the aftermarket company quantified how much margin was present in the factory setup and eliminated that margin, resulting in overheating when stressed with things like high temps, elevation, and a winch blocking airflow.
I repeated the flush (no Thermocure this time, just hose water, then distilled) and sprung for the Zerex G-05 HOAT coolant this time around. I'm happy to report that in the same conditions I was hitting 235, I now don't even get to 210.
So the moral of the story is, if you need a radiator, buy Mopar. And if you're running warm and you've eliminated the other possibilities, then your aftermarket radiator is a likely culprit.
