6.4 Hemi Overheated

[FlatbedHemi]

Was sitting in the trailer line waiting to unload at our local fair and I noticed the A/C wasn't cooling as well as it should. I figured it was because we were idling in a parking lot in 96 degree heat, so I turned on the recirculate and kept doing what I was doing. A few minutes later it dinged, popped a light, and said engine too hot on the screen. I went through the SOP for overheating; A/C off, heater on high, pop hood. We made it through the line and got loaded without getting the temps over 235-240 again, but I knew there was an issue somewhere. Long story short, I think I narrowed it to the fan clutch because it cools when parked and revved or in motion. Its just sitting still at idle that it gets hot. So, i ordered a new fan clutch.

Now Im wondering if I need to go ahead and change the coolant and do a flush or something. The truck has 131K miles and never had any coolant maintenance done. Is there a specific procedure for performing a flush on these trucks?

What about the T-stat? Is it likely that it likely that the minute or so that the truck hit 255 that it ruined the t-stat? I have noticed that when at speed and unloaded, temps run between 195-205. Honestly, I never paid much attention to the temp other than just where the needle is, so I dont really remember what temp it normally ran at.

 

[mtofell]

IIRC, the factory recommended flush is 150K so probably a good idea.... although, I doubt that's the issue. I think you're on the right track with the fan clutch and maybe the thermostat. Over the years I don't recall reading too many problems with the 6.4 Hemi overheating. My thermostat went out once but it was opening too soon and I was getting an error message about the engine not reaching temp quick enough.

 

[Choupique]

Our work trucks (ram 6.4's) will sometimes overheat in the dead of summer with the AC blasting and the sun beating down. RPMs is the short term answer. Get the engine up to about 1800 and the temps will nose dive.

Nothings wrong with those trucks other than the cooling system is just inadequate to handle all that heat.

 

[FlatbedHemi]

This may be a stupid question, but does the 6.4 have an electric fan under the machanical fan shroud? It doesnt make much sense to me that it would, but I was watching a couple of videos on changing the fan clutch (to make sure there werent any hidden boogers to work around I wasnt aware of) and I saw what looked like an electric fan mounted between the radiator and the mechanical fan. I havent torn into mine, so I thought I would ask.

 

[buckeyexx]

This may be a stupid question, but does the 6.4 have an electric fan under the machanical fan shroud? It doesnt make much sense to me that it would, but I was watching a couple of videos on changing the fan clutch (to make sure there werent any hidden boogers to work around I wasnt aware of) and I saw what looked like an electric fan mounted between the radiator and the mechanical fan. I havent torn into mine, so I thought I would ask.

Yes it does have both a mechanical and electric fan. Just had both of mine out when changed my radiator and water pump. If you have access to an air hammer it will make breaking loose the fan clutch a breeze.

 

[Travelin Ram]

Have you checked the electric fan? I’d expect that’s doing most of the cooling at idle.

 

[2003F350]

Have you checked the electric fan? I’d expect that’s doing most of the cooling at idle.

This. I never had an issue with mine, but then mine didn't sit and idle much, I was usually moving. But on the rare occasions when I was idling, I could hear the electric fan kick on and off and never saw high temps.

 

[FlatbedHemi]

Finally got around to this, and using the Alpha OBD program I was able to diagnose my fan was in fact bad. Since I had already ordered the mechanical fan clutch before I realized there was an electric fan, I opted to go ahead and replace it too rather than return it. Everything was incredibly smooth and easy to replace, which was surprising. Now that everything is replaced, the weather will be in the mid to low 70s for the foreseeable future. Guess I shoulda gotten to it sooner if that was all it took to drive the 105+ degree days away.

 

[marcdaves]

I have a 2017 2500 6.4l with the 6 speed. I've been towing a 5500lb travel trailer with no issues and running between 204 and 220 degrees under very hot, Florida, conditions. One my last tow temps got to 245 as we got underway. Ended up switching vehicles to tow and since then it's always between 204 and 220. Thoughts?

 

[Daw14]

What codes is it showing ? That is the place to start. Bad fan/s , sticking thermostat ? Hoses ? Belt ? Pulleys ? Any of the above may be the cause.

 

[2003F350]

I have a 2017 2500 6.4l with the 6 speed. I've been towing a 5500lb travel trailer with no issues and running between 204 and 220 degrees under very hot, Florida, conditions. One my last tow temps got to 245 as we got underway. Ended up switching vehicles to tow and since then it's always between 204 and 220. Thoughts?

If there's any codes, definitely check those out and see what they are.

If there's no codes, you need to know if it got hot because it was sitting still and idling, or if it happened while moving.

If it happened while sitting still and idling, I would suspect either the electric fan or the mechanical fan clutch. You should be able to hear the electric fan kicking on and off when the truck is running at idle and hot, if you don't it's probably bad.

If it happened while moving down the road, you likely have a different issue, could be a clogged radiator. Fins of the radiator could be clogged with dirt/gunk, causing airflow issues.

From the description you gave it sounds like it happened while moving, which would lead me to think it's a bigger problem than just a fan.

 

[theblackduck87]

My '12 Ram did that just sitting. Turned out my electric fan had broken. Replaced it and no further overheating issues.

 

[marcdaves]

I just put the code reader on it and nothing related to cooling. I'm going to get a coolant flush tomorrow and then let it run at idle and hot to see if the fan kicks on. This weekend im going to try to tow around town to see if the problem happens again. I've been driving around for the past two weeks since it happened with the temp gauges on to monitor and it sits between 204 and 220 in cool and hot conditions. Also it has a new tensioner pulley and belt about 3 months ago.

 

[2003F350]

Those temps are about what my '17 6.4 always ran. Seems hot but it's where they designed it to run for efficiency. It's also why it's recommended that the 6.4 be run on full synthetic oil only - it fights the thermal breakdown that semi-synthetic and regular oil suffer from.

 

[marcdaves]

I do run full synthetic changed regularly. But those temps are with all of the other times I've towed before except this last time that's when in spiked to the low 240's. Coolant is getting flushed thus weekend.

 

[Bturner1185]

Same year model and same exact issue, I don’t get it I’ve done all necessary maintenance and then this hit me at random.

I’ve changed water pump, thermostat, thermostat temp sensor and fan clutch and it’s still going on.

 

[JDunk]

Have similar issue going on. Live in Phoenix so its 100+ right now. Have 2018 6.4 Hemi. Just replaced thermostat, water pump and radiator. Temp stays good as long as moving. When sitting idle or in line to pick kids up from school it will climb up to 235. Bad electric fan or somewhere along those lines?

 

[62Blazer]

Have similar issue going on. Live in Phoenix so its 100+ right now. Have 2018 6.4 Hemi. Just replaced thermostat, water pump and radiator. Temp stays good as long as moving. When sitting idle or in line to pick kids up from school it will climb up to 235. Bad electric fan or somewhere along those lines?

Generally when an engine overheats when sitting still but is fine when moving that indicates an issue related to the cooling fans. Just sitting still idling with no load on the engine produces the lowest amount of heat, and thus requires the least amount of cooling capacity. However if sitting still and the fans are not working there is no air being pulled across the radiator to take away the heat. When you start driving the engine produces more heat, however you get a lot of airflow going across the radiator just from the speed.
For examples:
Do you get more worn out just standing up someplace, or running around a track?
Stick your head completely out the window going just 30 mph and think about the blast of air you get.

In any case, I would concentrate on the cooling fans.