2021 1500 5.7 coolant temp went nuts

[HemiDude]

I have been watching my temps the last couple of days, and I haven't seen the numbers you are experiencing. Granted, it has been cool out this week, highs in the 50's and 60's. My coolant readout has not gone above 206, either in town or on the highway. Like yours, it does warm up to around 140-150 fairly quickly, but takes it's time between there and 200. Oil temp rises a little slower than coolant, and trans even more slowly. Disclaimer, I have the Pulsar installed, set to Perf/no MDS, and I don't know if that has any effect.

It's good that are noticing anything out of the ordinary regarding temp swings, though the highest temps you are seeing aren't abnormal. I would definitely agree with having the dealer take a look at it since it is still under warranty. Even if they tell you they can't find any problems, you have it on record in case something should happen later.

 

[Gravel Roads]

I have been watching my temps the last couple of days, and I haven't seen the numbers you are experiencing. Granted, it has been cool out this week, highs in the 50's and 60's. My coolant readout has not gone above 206, either in town or on the highway. Like yours, it does warm up to around 140-150 fairly quickly, but takes it's time between there and 200. Oil temp rises a little slower than coolant, and trans even more slowly. Disclaimer, I have the Pulsar installed, set to Perf/no MDS, and I don't know if that has any effect.

It's good that are noticing anything out of the ordinary regarding temp swings, though the highest temps you are seeing aren't abnormal. I would definitely agree with having the dealer take a look at it since it is still under warranty. Even if they tell you they can't find any problems, you have it on record in case something should happen later.

Thank you for the information HemiDude. I will keep this post updated as I find out more.

 

[007longbeach]

Things sure are different from back when you would panic if your coolant temp hit 220, but these newer engines seem to be designed to run a bit hotter, and I'm guessing it's only about EPA b.s. Our 2015 has some large temp swings, and it's got 200k miles on it, so I put a 180 thermostat in it just to see. Not entirely sure where the temp sender is, but it certainly acts like it's way before the thermostat and so peaks higher than you would expect with the 180 degree thermostat, maybe an engineered lack of flow. Wife's 2023 eTorque, which lost the small water pump belt at 13k (originally I thought it only had 10k when it happened), got really hot, so now when I drive it, I literally stare at the electronic temp readings. Tonight it's in the 40s and we went for a drive to look at Christmas lights, and while idling around it hit 224! I checked the overflow as I didn't want to open the pressure cap, and there was coolant in it, and not too high, so I guess it was a normal event? IDK, seems really stupid to me to run coolant temperatures that high, but I'm guessing an engineer somewhere figured it was okay to NOT flow the coolant in an attempt to save on engine drag and therefore save a tiny amount of fuel. Give the chance to buy the 2023 again, I'd pass on it and find a low mileage 3rd Gen or older. LOL

 

[SD Rebel]

Things sure are different from back when you would panic if your coolant temp hit 220, but these newer engines seem to be designed to run a bit hotter, and I'm guessing it's only about EPA b.s. Our 2015 has some large temp swings, and it's got 200k miles on it, so I put a 180 thermostat in it just to see. Not entirely sure where the temp sender is, but it certainly acts like it's way before the thermostat and so peaks higher than you would expect with the 180 degree thermostat, maybe an engineered lack of flow. Wife's 2023 eTorque, which lost the small water pump belt at 13k (originally I thought it only had 10k when it happened), got really hot, so now when I drive it, I literally stare at the electronic temp readings. Tonight it's in the 40s and we went for a drive to look at Christmas lights, and while idling around it hit 224! I checked the overflow as I didn't want to open the pressure cap, and there was coolant in it, and not too high, so I guess it was a normal event? IDK, seems really stupid to me to run coolant temperatures that high, but I'm guessing an engineer somewhere figured it was okay to NOT flow the coolant in an attempt to save on engine drag and therefore save a tiny amount of fuel. Give the chance to buy the 2023 again, I'd pass on it and find a low mileage 3rd Gen or older. LOL

The factory thermostat is 203F or so. I think if you install a 180F thermostat, the truck will try to adjust the other cooling elements to raise the temp unless you program those metric in the ECU.

I believe the electric fan turns on at around 220F, which is a temp I have seen personally at a long hot idle during a long slow trail off-roading. Typically, you should see 224 or below while moving slowly. The coolant warning doesn't come on until about 245F!

 

[Kiwiaudio]

Id be concerned about the stinky coolant if indeed it is abnormal. Feel like i might be opening a can of worms as there are so many opinions about coolant color, but unless it has been messed with, it should be purple OAT mopar coolant, often changing to pink after being in the vehicle for a while.
Even half competent service guys should recognize this being correct or not, or if the smell is normal or not.

 

[HSKR R/T]

The factory thermostat is 194F or so. I think if you install a 180F thermostat, the truck will try to adjust the other cooling elements to raise the temp unless you program those metric in the ECU.

I believe the electric fan turns on at around 230F, which is a temp I have seen personally at a long hot idle during a long slow trail off-roading. Typically, you should see 224 or below while moving slowly. The coolant warning doesn't come on until about 245F!

Factory thermostats are 203, not 194. Electric fans aren't programmed to come on until 220 degrees.

 

[HSKR R/T]

Id be concerned about the stinky coolant if indeed it is abnormal. Feel like i might be opening a can of worms as there are so many opinions about coolant color, but unless it has been messed with, it should be purple OAT mopar coolant, often changing to pink after being in the vehicle for a while.
Even half competent service guys should recognize this being correct or not, or if the smell is normal or not.

Mine was pink from the factory. And the new jug of Mopar coolant I bought as also pink.

 

[HSKR R/T]

Things sure are different from back when you would panic if your coolant temp hit 220, but these newer engines seem to be designed to run a bit hotter, and I'm guessing it's only about EPA b.s. Our 2015 has some large temp swings, and it's got 200k miles on it, so I put a 180 thermostat in it just to see. Not entirely sure where the temp sender is, but it certainly acts like it's way before the thermostat and so peaks higher than you would expect with the 180 degree thermostat, maybe an engineered lack of flow. Wife's 2023 eTorque, which lost the small water pump belt at 13k (originally I thought it only had 10k when it happened), got really hot, so now when I drive it, I literally stare at the electronic temp readings. Tonight it's in the 40s and we went for a drive to look at Christmas lights, and while idling around it hit 224! I checked the overflow as I didn't want to open the pressure cap, and there was coolant in it, and not too high, so I guess it was a normal event? IDK, seems really stupid to me to run coolant temperatures that high, but I'm guessing an engineer somewhere figured it was okay to NOT flow the coolant in an attempt to save on engine drag and therefore save a tiny amount of fuel. Give the chance to buy the 2023 again, I'd pass on it and find a low mileage 3rd Gen or older. LOL

The water pump is always turning and moving coolant. The thermostat being open or closed doesn't prevent coolant from flowing. There is a bypass hose and heter hoses/heater core that have coolant flowing constantly while engine is running. So has nothing to do with engine drag.

 

[SD Rebel]

Factory thermostats are 203, not 194. Electric fans aren't programmed to come on until 220 degrees.

I was kinda close

 

[scott511]

Not trying to derail this thread, but I purchased a 2020 Bighorn/Lonestar 5.7 a few months ago; quick question:
Does anyone know why someone would write "-250" with a sharpie on the coolant dipstick cap?

 

[Grape_Ape]

Mine was pink from the factory. And the new jug of Mopar coolant I bought as also pink.

So long as it's not orange I think it's good. Not doubting you just sharing what the alternative is. The orange was for the 4th gens iirc.

 

[kapinallinen2]

My 68163849AB (50/50 premix) that meets the MS.90032 is orange...

Cooling System *

Engine: 18.3 Quarts / 17.3 Liters

We recommend you use Mopar Antifreeze/Coolant 10 Year/150,000 Mile Formula OAT (Organic Additive Technology) or equivalent meeting the requirements of Material Standard MS.90032.

68163848AB

68163848GB

 

[Grape_Ape]

My 68163849AB (50/50 premix) that meets the MS.90032 is orange...

Cooling System *

Engine: 18.3 Quarts / 17.3 Liters

We recommend you use Mopar Antifreeze/Coolant 10 Year/150,000 Mile Formula OAT (Organic Additive Technology) or equivalent meeting the requirements of Material Standard MS.90032.

68163848AB

68163848GB

That's interesting..Did some more research and online seems to point to all rams since 2013 called for the purple. The purple turns a reddish hue after running for several thousand miles.

 

[munozjavier48]

Thank you for the information. Today when I drove it to work it got worse. It shot up to about normal operating temperature within a couple of minutes from an 86 degrees start. When I started my commute took a while for it to cool down from 215 down to about 203 where it will normally run in the morning for a couple of minutes.

Thank you for the reply. Believe it or not this is my first forum of belonged to so I'm still trying to get the hang of it. This morning the situation got worse the temperature rocketed up to almost 146 degrees from about 86 degrees before I even got it out of my shop garage area. It then went to about 206 degrees which is normal then it went up to 215 and stayed there awhile. But what happens next is it starts to get really hot goes up to somewhere in the 220s and hangs there and then doesn't drop until you slow down. Sometimes it'll drop down to about 206 at that point. Then as soon as you accelerate within a few seconds it will go up to 215 or 217 or so and stay there. Then when you come to a stop it'll go up to about 228 and the fans will be running high speed and it will eventually drop down to about 217 once you start moving again. I wouldn't have known about any of this if I hadn't been watching the digital readout. The reason I began this post is because it acted totally different when it was new. It would vary between about 203 and 215 back and forth. The normal time it takes me to get out of my garage at this ambient temperature it would go up to about 120 degrees. It was usually a couple of minutes of a swing between 203 and 215 when it was new going down the freeway and I never noticed it shoot upwards as soon as I accelerate. The other surprise was when I changed thermostats the coolant smelled burned. I will probably take this somewhere and get a chemical block check done before I take it to the dealer. When I started this thread I was wondering if anyone else had these rapid temperature swings, and if this era Hemi was known for head gasket issues. Thank you.

I have the same issues, but mine hangs at 228 - 230 and won’t go back down it recently started doing this and it’s concerning.

 

[SD Rebel]

I have the same issues, but mine hangs at 228 - 230 and won’t go back down it recently started doing this and it’s concerning.

The 230F isn't a problem, but the not going back down since the fan should have turned on by then is. Definitely needs to be checked.

Question, at hot idle does it go beyond 230F or does it maintain that temp? When cruising at constant speed, what temp are you averaging?

 

[Rick3478]

The water pump is always turning and moving coolant. The thermostat being open or closed doesn't prevent coolant from flowing. There is a bypass hose and heter hoses/heater core that have coolant flowing constantly while engine is running. So has nothing to do with engine drag.

Yeah the thermostat only controls flow through the block and heads. I had an old Cheyenne that would never get up to temp and couldn't get any heat in the winter. Eventually figured out there was just way too much bypass flow going through the heater, and installed an adjustable valve to throttle the flow, problem solved.

 

[munozjavier48]

The 230F isn't a problem, but the not going back down since the fan should have turned on by then is. Definitely needs to be checked.

Question, at hot idle does it go beyond 230F or does it maintain that temp? When cruising at constant speed, what temp are you averaging?

Yes it goes beyond 230F up to like 256 or 260 when I really punch it enough for the truck to ding and initiate the red screen stating it’s overheating. I really have to throttle down to get it to come back down to the above degrees 228 - 230

 

[HSKR R/T]

Yeah the thermostat only controls flow through the block and heads. I had an old Cheyenne that would never get up to temp and couldn't get any heat in the winter. Eventually figured out there was just way too much bypass flow going through the heater, and installed an adjustable valve to throttle the flow, problem solved.

The thermostat only controls flow through the radiator. You always want coolant flowing through block and heads.

 

[HSKR R/T]

Yes it goes beyond 230F up to like 256 or 260 when I really punch it enough for the truck to ding and initiate the red screen stating it’s overheating. I really have to throttle down to get it to come back down to the above degrees 228 - 230

You got some problems. I'd start by verifying your water pump is working, then may e change thermostat.

 

[Rick3478]

The thermostat only controls flow through the radiator. You always want coolant flowing through block and heads.

Maybe I stated it awkwardly, but when closed the thermostat forces coolant to recirculate through a bypass, keeping heat in the engine, until it is hot enough to open and allow flow somewhere else, like radiator. It's just an inversion of perspective, no biggie.