6.4 hemi fluctuating coolant temps. Running hot?

Brianedgestone · Jan 13, 2018

I had the Tstat changed on my 2015 6.4 because it was not reaching operating temps. Now it fluctuates between 220 and 186 pretty rapidly. 15 seconds or so. It will not run at a steady temp. Air temps here are around 20 degrees. Does this seem normal?

Rampant · Jan 13, 2018

Brianedgestone said:
I had the Tstat changed on my 2015 6.4 because it was not reaching operating temps. Now it fluctuates between 220 and 186 pretty rapidly. 15 seconds or so. It will not run at a steady temp. Air temps here are around 20 degrees. Does this seem normal?

Definitely not normal.

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crackerjack1957 · Jan 13, 2018

Brianedgestone said:
I had the Tstat changed on my 2015 6.4 because it was not reaching operating temps. Now it fluctuates between 220 and 186 pretty rapidly. 15 seconds or so. It will not run at a steady temp. Air temps here are around 20 degrees. Does this seem normal?

What were the temps before change?
Has it overheated?
Sounds like a bad or wrong temp Tstat, think I would try another.
Also could be water pump, clogged radiator from mixing wrong type coolants together, radiator cap, & air bubbles in coolant.

huntergreen · Jan 13, 2018

Possibly air in the line or a faulty temp gauge.

Brianedgestone · Jan 13, 2018

I have only owned the truck for 4 months. Temp before the new tstat was around 208. The new t-stat is a factory 216 degree. I’m fine with the temp. I’m just concerned with the fluctuating. I’ve tried to find a relief valve to purge the air but I can not find one on this 6.4. It’s not on the tstat housing. Any ideas on how to get an air pocket out. Radiator doesn’t have a cap it’s only on the overflow tank.

crackerjack1957 · Jan 13, 2018

It's own my 2014 5.7 Ram, should be on 6.4 also.

Brianedgestone · Jan 15, 2018

Apparently it is not the same in the 6.4. I can’t find a relief valve anywhere. Anyone have any idea? Olso one other symptom I should have mentioned is my heat blows somewhat warm on the driver side vents and really hot on the passengers side. And below 190 I don’t have much heat on the drivers side.

crackerjack1957 · Jan 15, 2018

h**p://***.challengertalk.com/forums/f489/cooling-system-bleed-598321/

smurfs_of_war · Jan 17, 2018

Once I get mine on the highway and get her running my temp goes up and down. 88c or so up to 98c or so. But it does it at a slower pace and eventually evens out. I just sluffed it off to the tstat opening and closing. Maybe an issue too?

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Brianedgestone · Jan 17, 2018

I think it is opening and not closing completely. But the kinda warm air coming out of the drivers side and hot air on the passenger side has me stumped. Also the fan speed coming out of the vent is really low. I think I have compounding problems. I dropped it off t the dealer this morning and haven’t heard anything yet. But I know a fluctuation of 30degrees is not normal.

68PowerWagon · Jan 17, 2018

Sounds like you have other issues going on but my 16' Ram 2500 with the 6.4 temp will go up & down like that. It is much more drastic in this really cold single digit temps we have been having. After 20-30 minutes of driving it will settle in a little. On mine it's just the thermostat opening bringing in all of the cooled coolant from the radiator.
Seems odd that you are having cooling system issues already.

smurfs_of_war · Jan 17, 2018

68PowerWagon said:
Sounds like you have other issues going on but my 16' Ram 2500 with the 6.4 temp will go up & down like that. It is much more drastic in this really cold single digit temps we have been having. After 20-30 minutes of driving it will settle in a little. On mine it's just the thermostat opening bringing in all of the cooled coolant from the radiator.
Seems odd that you are having cooling system issues already.

This is exactly what mine does so I suspect normal. Good

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grizzstang · Jan 17, 2018

It is probably air in the system like huntergreen mentioned. After replacing the T-stat I am betting the tech topped off the coolant overflow reservoir and shoved it out the door. Time is money.

Raise the front end up (ramps, jack or park on a hill) pull the reservoir cap off and let it run until the T-stat opens and all the air is purged, top off the system, put the cap back on.

Brianedgestone · Jan 17, 2018

Mine is a ‘15 2500 and on the way in to the dealer this morn it only fluctuated from 190 to 217. Those are the extremes. I would say the average slot was 200-208. Sounds like you guys think that is normal. Are any of you noticing cooler air on the drivers side? When down to the 190ish mark the air is really cool on drivers side. I should have plenty of heat above 160. Frustrating indeed on a 2yr old truck with 50k.

MeatCurtains · Jan 17, 2018

Burp the system. AutoZone used to have a funnel that was just for this I'd venture they still do.

It attaches to the radiator cap and you fill it with coolsnt and let the engine running until bubbles stop appearing.

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Dodge4x4810 · Jan 17, 2018

It sounds to me like it is air bound. The warm and hot problem with the drivers/pass side seems like that is air trapped in the heater core. I am going to assume that when they did the thermostat, they did not have the heat on. When you burp a system you should always have the heat on so it, burps all of the air trapped in the heater core. I highly doubt that the heater core would be clogged, even if you used the wrong coolant. The truck is too new.

yoda · Jan 17, 2018

Coolant runs through the heater core any time the truck is running. Having the heat on or off doesn't matter. Its been many years since any Chrysler products used a heater core shut off. 80s if I remember correctly.
The 6.4 uses a degas bottle, not a conventional overflow bottle, as long as it is full the air should work its way out on its own.
Hate to say it but sounds like classic partially plugged heater core. The way the airflow flows through the HVAC box, the bottom of the heater core air flow goes to the drivers side the top to the passenger side, all the gunk settles to the bottom of the core, that's why the drivers side is cooler.

Dodge4x4810 · Jan 17, 2018

I'm sorry, you're right. I don't know why I was thinking these trucks had heater valves. This is my third ram too. It sounds like a clogged heater core, it is just not that old, but it is possible. I usually flush cores out by taking the hoses off at the firewall and putting a hose through and just keep pressure until clear water comes out.

Brianedgestone · Jan 17, 2018

I told the dealer to flush the system. Still haven’t heard anything hung from them. I will call tomorrow and get an update. I have been leaning toward air in the system and clogged heater core. I have tried letting it run with the res. lid off and it didn’t seam to help. Could a partially clogged heater core give me fluctuating temps?

smurfs_of_war · Jan 18, 2018

Is it possible some **** made its way into the system when they changed the tstat? Old gasket material or something?

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6.4 hemi fluctuating coolant temps. Running hot?

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