My Hemi is overheating when under load

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Princeton_Man

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Last week on my way home from the lake, I noticed my engine temperature starting to rise while pulling a hill with the boat in tow. I eased off the accelerator but, just as I crested the hill, the overheat warning light up. I took my foot off the gas, knocked her into neutral, and coasted down the hill. The temperature began to drop quickly. The warning message was only on for maybe 5 seconds before it went out. During all of this, it never occurred to me to bring up the actual temperature on the display, so I have no idea what the highest number actually was.

Since the temperature gauge was back at center quickly, there was no odor of coolant, and I was less than 5 miles from home, I decided to watch the temperature closely, drive gently, and if it stayed cool, limp the rest of the way home. During those few miles I discovered that anytime I started to pull a little harder, the temperature would start to climb, ease off, and it would drop. When I arrived home, the gauge was still showing normal.

I left the the engine idling while dropping the boat in the garage, everything stayed normal, so I took it up the road. As I accelerated, the temperature gauge climbed, pulled over and idled, it came back down. That told me it was likely the fan clutch. So I ran down to the autoparts store, picked up a new fan clutch, and installed it. Probably the easiest repair I've ever had to do. The problem though, it didn't correct the problem. Even the slightest load causes the temperature to climb. My thought was maybe a head gasket, but the coolant is perfectly clean (orange) and there no sign of oil in the coolant or coolant in the oil.

I hate having to take it to the dealer, but it looks like my last option.
 

G-Ride990

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Sounds like the thermostat is not opening all the way. It is probably letting enough coolant through it to cool the engine down at idle but not enough through at higher rpm.

For as cheap as a thermostat is I'd swap it out before going to a service center.
 
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Princeton_Man

Princeton_Man

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Since I have a spare, I'll give that a try. I did just replace the thermostat back in July, but it's worth a shot I guess.
 

crazykid1994

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Yup. I’d agree on tstat. Even a new one may be faulty. What brand was your new one? I like stant or oem. I’ve had stant for 2 years and 0 issues. Only reason I switched was to go to a cooler temp for tuning reasons. I run a 190°
 

RamRod37

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Actually to me it sound's more like the radiator is stopped up had this happen to several vehicle both mine and customers temps run fine unloaded but under load not enough coolant flow. easy test take rad hoses off and run a water hose in top wide open you should not have to force the water through from a 1/2 or 5/8 inch garden hose if water is forced past your hand at top hose its stopped up with that size water hose water should flow through radiator with no issues
oh and FYI A head gasket can blow and not show any signs of coolant in oil or vise versa a head gasket can blow and does blow out right into the cylinder burning the coolant. I even had one blow On a toyota 2.4 between cylinders so every time cylinder 3 tried to make a compression stroke the air fuel mix was going over into cylinder 4 and vise versa. if it blows between a coolant pathway and cylinder bore you will normally when the vehicle running and rad cap off see bubbling boiling type effect out of radiator
 
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G-Ride990

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Since I have a spare, I'll give that a try. I did just replace the thermostat back in July, but it's worth a shot I guess.
That makes me lean towards a bad thermostat even more. It's not unheard of to get a bad thermostat even when you buy new.

Let us know how it goes!
 

James OBrien

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Princeton_Man

Princeton_Man

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Thanks for everyone's input!

Well, after learning that the dealer get's about $600 to replace the waterpump, I decided to spend today in my garage. I have trust issues with all dealers anyway. The waterpump showed no signs of leaking but, it did have considerable play in the shaft once I removed the serpentine belt, so I replaced the waterpump and the thermostat and it eems to have solved my problem. The impeller on the old pump looks fine, so I'm guessing the thermostat was the problem. They are Stant thermostats, but very few are still made here in the US. I tried very hard to get a US made Stant and finally had to settle for Stants made in Isreal. I hope this second one lasts a lot longer than the first.
 
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Princeton_Man

Princeton_Man

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Yup. I’d agree on tstat. Even a new one may be faulty. What brand was your new one? I like stant or oem. I’ve had stant for 2 years and 0 issues. Only reason I switched was to go to a cooler temp for tuning reasons. I run a 190°

These are Stant. I switched to 180° back in May. From what I was told, Stant was sold to a private equity company back a couple years ago. Now they manufacture their thermostats in other parts of the world. :( Buying American gets harder every year.
 

2021warlockram

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My 2021 5.7 is doing same thing with 21,000 miles. Dealer says they have no clue. So I yours still good with the tstat?
 

2021warlockram

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Thanks for everyone's input!

Well, after learning that the dealer get's about $600 to replace the waterpump, I decided to spend today in my garage. I have trust issues with all dealers anyway. The waterpump showed no signs of leaking but, it did have considerable play in the shaft once I removed the serpentine belt, so I replaced the waterpump and the thermostat and it eems to have solved my problem. The impeller on the old pump looks fine, so I'm guessing the thermostat was the problem. They are Stant thermostats, but very few are still made here in the US. I tried very hard to get a US made Stant and finally had to settle for Stants made in Isreal. I hope this second one lasts a lot longer than the first.
 

grizzstang

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My 2021 5.7 is doing same thing with 21,000 miles. Dealer says they have no clue. So I yours still good with the tstat?
Your dealer is a lazy A hole. Your truck still has bumper to bumper warranty. Thermostat is a pretty easy job and they are not very expensive. If you don't want to try another dealer I would just replace it and see if that fixes your issue.
 

Bimmerguy406

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Last week on my way home from the lake, I noticed my engine temperature starting to rise while pulling a hill with the boat in tow. I eased off the accelerator but, just as I crested the hill, the overheat warning light up. I took my foot off the gas, knocked her into neutral, and coasted down the hill. The temperature began to drop quickly. The warning message was only on for maybe 5 seconds before it went out. During all of this, it never occurred to me to bring up the actual temperature on the display, so I have no idea what the highest number actually was.

Since the temperature gauge was back at center quickly, there was no odor of coolant, and I was less than 5 miles from home, I decided to watch the temperature closely, drive gently, and if it stayed cool, limp the rest of the way home. During those few miles I discovered that anytime I started to pull a little harder, the temperature would start to climb, ease off, and it would drop. When I arrived home, the gauge was still showing normal.

I left the the engine idling while dropping the boat in the garage, everything stayed normal, so I took it up the road. As I accelerated, the temperature gauge climbed, pulled over and idled, it came back down. That told me it was likely the fan clutch. So I ran down to the autoparts store, picked up a new fan clutch, and installed it. Probably the easiest repair I've ever had to do. The problem though, it didn't correct the problem. Even the slightest load causes the temperature to climb. My thought was maybe a head gasket, but the coolant is perfectly clean (orange) and there no sign of oil in the coolant or coolant in the oil.

I hate having to take it to the dealer, but it looks like my last option.
What ended up fixing your truck?
 

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