Coolant temp fluctuating???

[m25443]

I was watching my coolant, oil and trans temp on my EVIC screen the past several days while on a long road trip and saw something that seems strange. I have a 2015 PW w/6.4 hemi and was driving on the interstate, flat land, and outside temp 65-70 degrees. Was driving about 70-75.

The oil and trans temp stayed consistent at 215 and 165 respectively. The coolant was fluctuating between ~195 and 212 on a 90-120 second interval (full swing both ways). This would repeat over and over. Sometimes it would just stay at ~210 for long periods of time. Then it would start swinging back and forth again.

What the heck? Is my thermostat causing that issue or what else could be going on. Surely it's not normal.

-Mike

 

[HammerHead]

I was watching my coolant, oil and trans temp on my EVIC screen the past several days while on a long road trip and saw something that seems strange. I have a 2015 PW w/6.4 hemi and was driving on the interstate, flat land, and outside temp 65-70 degrees. Was driving about 70-75.

The oil and trans temp stayed consistent at 215 and 165 respectively. The coolant was fluctuating between ~195 and 212 on a 90-120 second interval (full swing both ways). This would repeat over and over. Sometimes it would just stay at ~210 for long periods of time. Then it would start swinging back and forth again.

What the heck? Is my thermostat causing that issue or what else could be going on. Surely it's not normal.

-Mike

I've almost posted the same thread a million times. I'm glad you did because your 6.4 and my 6.4 do the same thing. No rime or reason it jumps all over, up and down, makes no sense. It's been doing this since day one.
I'm in a 2018 tradesmen.

 

[HammerHead]

Another thing I find strange is when I run the heater my oil temps go down, if I run the heat on high my oil temps go way down. About 215 to 194.

 

[m25443]

Another thing I find strange is when I run the heater my oil temps go down, if I run the heat on high my oil temps go way down. About 215 to 194.

Interesting. When you turn the heater on I would expect the coolant temp to drop. Pretty common old school fix solution for those of us who used to drive cars that were in less than optimal running condition during the summer. Surprised to hear the oil temp drops, as it takes longer for the oil temps to go up/down than it does the coolant temps.

 

[HammerHead]

Interesting. When you turn the heater on I would expect the coolant temp to drop. Pretty common old school fix solution for those of us who used to drive cars that were in less than optimal running condition during the summer. Surprised to hear the oil temp drops, as it takes longer for the oil temps to go up/down than it does the coolant temps.

That's what's so strange; all my other vehicles over the years the heater core is connected to the coolent. My 6.4 does some strange things, I'm still trying to figure it out.

 

[guru1ofatl]

Excuse my ignorance but does the 2500 have the active grill shutters?
I have seen those cause temperature fluctuations on the highway on 1500s.

 

[m25443]

Excuse my ignorance but does the 2500 have the active grill shutters?
I have seen those cause temperature fluctuations on the highway on 1500s.

Good thought. Mine does not.

 

[500rider86]

Perhaps the sensors are not accurate?

 

[m25443]

Perhaps the sensors are not accurate?

Perhaps. But I would expect inaccurate to still be stable, just showing the incorrect temp. Or fluctuating immediately between wide ranges (like 190 for 2 seconds, then 215 for a second or two, etc... The temps always smoothly go up/down over 90 second to 2 minute intervals.

 

[turkeybird56]

Sounds like thermostat, unless a sensor issue, but I am no mechanic...

 

[huntergreen]

Like above, first thing I would do is replace the thermostat.

 

[Tach_tech]

The range of 195-212 is right in the range the thermostat is fully opening. What your seeing is likely that amongst with the electric fan cycling on/off to help maintain temperatures. The thermostat is also electronically controlled.

My 1500 coolant temp fluctuates as well, usually about 194-208.

 

[HammerHead]

The range of 195-212 is right in the range the thermostat is fully opening. What your seeing is likely that amongst with the electric fan cycling on/off to help maintain temperatures. The thermostat is also electronically controlled.

My 1500 coolant temp fluctuates as well, usually about 194-208.

Can you tell me why my engine oil temps go Down when I run the heater on my 6.4?

 

[m25443]

HH. That is normal behavior.

 

[smithwessn]

Can you tell me why my engine oil temps go Down when I run the heater on my 6.4?

When the heat is on, you're blowing air across the heater core, which, of course, contains engine coolant that is being circulated through the entire cooling system. The effect is basically the same as the radiator up front. The air passing through the heater core is cooling the coolant. Cooler coolant passing through the engine block results in a cooler block, which reduces the temp of the oil.

Oh, and its normal for coolant temp to fluctuate. I wouldn't worry about it.

 

[CVX20]

Normal Operation.Usually the manufactures dumb down the guages so that you don't see the fluctuations.

 

[Fitz-0518]

1. I need to find out what temp is the factory thermostat opening and closing. I suspect that our 6.4 run right in the open/close range of the thermostat. I want to see what others have put in when they change their thermostat. OOOPS just remembered we have a "integrated" housing, sensor, thermostat. Could be the sensor out of spec.
2. When we open the heater core (turn on the heat) we are allowing the radiator water to mix with heater core water which is cold. This effects the temp for a short time. Once both fluids are at the same temp, should be no fluctuation.

 

[smithwessn]

1. I need to find out what temp is the factory thermostat opening and closing. I suspect that our 6.4 run right in the open/close range of the thermostat. I want to see what others have put in when they change their thermostat. OOOPS just remembered we have a "integrated" housing, sensor, thermostat. Could be the sensor out of spec.
2. When we open the heater core (turn on the heat) we are allowing the radiator water to mix with heater core water which is cold. This effects the temp for a short time. Once both fluids are at the same temp, should be no fluctuation.

Um... Coolant circulates through the heater core constantly, regardless of the heat being on or off. If the engine is running, coolant is flowing through the heater core. When you turn on the heat, you're just blowing air across the heater core. You don't circulate any additional fluid anywhere by turning on the heat.

Coolant temp fluctuation is completely normal and will vary with engine load and air flow across the radiator. Both of which can and will change while driving.

 

[HammerHead]

Yeah I'm not referring to the coolant, I understand how it works. But in my 6.4 at normal operating temperature (212-219) if I turn on my heater full blast the engine oil temps drop into the low 190's. I've never seen this on any other vehicle I've owned. The coolant only fluctuates a little.

 

[Wild one]

Can you tell me why my engine oil temps go Down when I run the heater on my 6.4?

Yeah I'm not referring to the coolant, I understand how it works. But in my 6.4 at normal operating temperature (212-219) if I turn on my heater full blast the engine oil temps drop into the low 190's. I've never seen this on any other vehicle I've owned. The coolant only fluctuates a little.

I think the 6.4's use coolant to heat/cool the engine oil.If they do it'll be through the coolant bypass valve,which routes the majority of the coolant through the heater core then out to the engine oil heater and the transmission heater on the 8 speed 1500's.So turning the heater fan on,is going to cool the coolant that is routed to the engine oil cooler,which should drop your engine oil temps .