Overheating while driving but not at idle.

[mossyhorn]

My 2016 1500 with 5.7 Hemi 117k began to overheat last week on way to work. Checked overflow and it was dry so I added coolant. On the way home that night I payed closer attention to the temp reading. It would fluctuate from 210 to 240 degrees. It seemed if I let off the gas a little the temp would come down. Once I got it home I inspected a little closer and found a small crack in radiator letting some coolant seep out. I replaced the radiator, thermostat, and radiator cap on Saturday and did a short test drive of a couple of miles and everything seemed to work fine. This morning on the way to work, it started the overheating again. The same scenario, temp would rise while driving down the road but if I let off the gas it would come back down. Never had any issues prior, the temp gauge would always read just below the halfway mark. Could this be the water pump starting to go out or maybe something else. Any help is appreciated.

 

[EdGs]

You might still have some air in the system.

After I replaced my radiator, it took quite a few checks after cooling off/ topping up with a few ounces each time, before it was finally full.

Temp rising like that scares me. Definately keep an eye on your temps. Make sure your efan and your clutch fan work as they should.


@mossyhorn, where did your radiator crack?

 

[rzr6-4]

You topped off the overflow, but did you refill the actual radiator? If you are a gallon low in the rad, topping off the overflow isn't going to fix that.

Pics of the crack in the rad? Could be a loose connection if you are lucky, but some of the seams are known to fail and it's new rad time.

My guess is you are getting some coolant flow as you didn't just nuke your engine, but not enough to keep it cool while working it. Hence getting hot under sustained driving but will cool down as you coast. Double check to make sure you actually filled the coolant, but you will likely need to spend some time making sure you get all of the air bubbles out that may be restricting fluid flow.

FYI, if I floor it down some back roads I might see 210 degrees, maybe. Or if I'm towing heavy. Anything above 210 is "overheating" and something is wrong.

 

[mossyhorn]

Thanks. The radiator has a hairline crack vertically just under the upper hose connection. I was able to bleed the system yesterday but unable to test it at hwy speeds. At idle it sat steady at 204 for 20 minutes or so. I will be taking it out for test drive when I get home tonight. Tried to upload the pic but it doesnt like the file.

 

[EdGs]

I have seen/heard of 7 or 8 now (including mine) that cracked on a seam in that very area.

Mine decided to fail 12 hours before an 800 mile road trip. That would have been a huge bill if it failed on the interstate out in the middle of BFE somewhere.

Mine after filling with 15 psi pressure test.


Replace the radiator, don't chance it.

 

[mossyhorn]

Yep, that is the same spot. Although mine was not to the degree of yours, just bubbles and little coolant coming through. I replaced it last saturday along with the thermostat. Thats why I was confused with the overheating issue yesterday along with the fluctuating temps. Hoping that bleeding it is the solution.

 

[EdGs]

Yep, that is the same spot. Although mine was not to the degree of yours, just bubbles and little coolant coming through. I replaced it last saturday along with the thermostat. Thats why I was confused with the overheating issue yesterday along with the fluctuating temps. Hoping that bleeding it is the solution.

After I replaced my radiator, it took me several times topping it up at the radiator after a cooldown, a few ounces each time, to get all the air out.

I keep my evic screen on the temp display page, and I've seen my coolant still go to 221° sometimes. I'm not sure why this happens, but I'm still on the original water pump and mechanical clutch fan at 202k miles.

 

[Wild one]

Yep, that is the same spot. Although mine was not to the degree of yours, just bubbles and little coolant coming through. I replaced it last saturday along with the thermostat. Thats why I was confused with the overheating issue yesterday along with the fluctuating temps. Hoping that bleeding it is the solution.

Did you test the new thermostat in hot water before installing it.Just cause it's new doesn't mean much these days,it can be a dud right out of the box.

 

[mossyhorn]

I didnt test it out of the box but it did open around 209° . The box stated it was a 203° thermostat. Im planning on bleeding it again tonight and then taking for a test drive to see how it acts at hwy speeds.

 

[EdGs]

Sometimes pointing the nose uphill will help get the air out.

 

[crackerjack1957]

Turn the heater on also

 

[mossyhorn]

Bled it again last night just to be sure and took it on test drive for about 10 miles. Temp stayed steady at 208°. Drove it in to work this morning (35 miles) and got up to 212° for a second or two if I floored it or going uphill but would settle right back down to 208° - 210°. Gonna pay close attention on the way home tonight as well but thinking this is the fix. Thanks for all the suggestions and assistance.

 

[mdc1990zr1]

Bled it again last night just to be sure and took it on test drive for about 10 miles. Temp stayed steady at 208°. Drove it in to work this morning (35 miles) and got up to 212° for a second or two if I floored it or going uphill but would settle right back down to 208° - 210°. Gonna pay close attention on the way home tonight as well but thinking this is the fix. Thanks for all the suggestions and assistance.

The temperature seems to be straddling the temperature you measured in the pan so the system seems to be working. You may want to measure up another thermostat closer to 203 just in case the current thermostat craps out.

 

[mossyhorn]

Thanks. Would it wise to get a thermostat with a lower temp threshold?

 

[EdGs]

Bled it again last night just to be sure and took it on test drive for about 10 miles. Temp stayed steady at 208°. Drove it in to work this morning (35 miles) and got up to 212° for a second or two if I floored it or going uphill but would settle right back down to 208° - 210°. Gonna pay close attention on the way home tonight as well but thinking this is the fix. Thanks for all the suggestions and assistance.

The temperature seems to be straddling the temperature you measured in the pan so the system seems to be working. You may want to measure up another thermostat closer to 203 just in case the current thermostat craps out.

Thanks. Would it wise to get a thermostat with a lower temp threshold?

@mossyhorn, I'm glad you got the system bled.

I put a 192° degree stat in my truck.

I still sometimes get to 210°, occaisionally 220°
Not sure if it's related to shock load, if the grille shutters play a role, and/or my original water pump and clutch fan with 202k miles on them is affecting it. Or, a combination of them.

I try to watch my evic temp screen like a hawk.