6.4 NOT Getting up to Temp?

[NickTF]

Ok, since day one of owning this truck until the past month it has always gotten up to temp easily which is usually 205-210 within about 8-10 minutes of run time despite the outside temps. I had a lifter fail over the summer and the dealer warrantied the truck which required removal of the entire top end of the motor (all 16 lifters were replaced). I've also undergone various updates and replaced the EGR valve myself.

Now, my truck will not exceed 185-188 degrees when less than 40 degrees outside. Further, when selecting heat and the dash vents option the air stream is very weak almost like the blend door isn't being commanded properly (possibly because coolant temps are too low). The thermostat on these trucks is electronically controlled (opposed to a normal spring loaded deal with a set temp of olden days) so I am leaning toward this being a programming issue associated with the multitude of updates my truck received during the lifter replacement and EGR/surge chasing efforts. A mechanical issue sounds unlikely but again i'm open to suggestions.

Anyone have any ideas. Truck is 3.75 years old with 62k on the clock and has a 5 year 100k powertrain warranty for what it's worth.

[Mule]

Had that problem a few years back. Pulling a trailer and I never got up to temp...


New t-stat and the problem was fixed.

[NickTF]

If the behavior persists and I suspect it will i'll likely look to replace the stat but figured with the electronic wizzardry associated with the 6.4's t-stat it might not be that simple.

[TheDirtRoad]

I had the issue with my '14 and it was a stuck t-stat. I had to convince the dealer-ship though the t-stat was stuck because it didn't show in their trouble shooting.

[NickTF]

Oh I have no doubt. Is the t-stat part of the 5-year 100k power train warranty?

[NickTF]

Looks like there are a few updates (surprise) for my truck. I'll get them done and see if this issue resolves (guessing it wont). T-stat is not a power train warranty item so i'll just replace myself.

[DamageWagon]

Sounds like thermostat. They don’t tend to last long in my truck. Definitely use Mopar.

I have not seen any evidence of the 6.4 having any electronics in the thermostatic system, maybe there is something in the heater core routing but I’ve never seen a stepper motor controlled gate valve or similar in the coolant system.

[NickTF]

I thought I read that but could certainly be wrong

[NickTF]

https://shop.advanceautoparts.com/p/mot ... *-49999546

Look at the above link for the pic of our themostat. Is that just a sensor plug or an actual actuator?

[olyelr]

Looks to me like aside from the electrical/sensor, there is a replaceable thermostat like always. The sensor may just be for reading the fluid temp?

[Reloaderguy]

That's just a sensor, the mechanical thermostat is sticking out of the bottom.

[NickTF]

Yes, you can see the spring just wasn't sure if the area where sensor plugged in imparted some force in addition to spring.

I'll add this too the list. Dragging 7500lbs of boat has kept the temps up to normal but it is definitely not getting to temp properly when unloaded in the morning.

[Retired BLM Rig]

Here's more pictures.
http://parts-catalog.moparrepairconnect ... /4893177ab
I haven't had to work on one yet, but based on the fact that it's strategically located over the center of the T-stat, I suspect that it's a position sensor providing info to the computer. A temp sensor could be installed anywhere at any angle. Odd that it's not setting a code P0128 for coolant temp rationality.

[NickTF]

Haven’t put a scanner on it but no codes to point where anything on dash is illuminated. I don’t have the most faith in the diagnostics built in to these trucks though.

[NickTF]

I installed a new thermostat tonight and temps are back to normal. Will snap a few shots of the old stat, I swear there is an electronically controlled stop preventing travel as commanded but could just be a position sensor like BLM said.

[NickTF]

Pulled my stat apart. A seal ripped in mine which is why I had low temps. The mystery electronic appears to be a heater, a long rod which travels through center of shaft spring surrounds. I will post pics tomorrow or there about. I googled coolant temp sensor for ram 6.4 and part numbers came up with a picture of what is a more standard coolant temp sensor which I assume is somewhere in the cylinder heads or block.

[NickTF]

Photo of top side where you can see seal torn.



Seal removed


Disassembled. Heater top left removed from spring shaft.


Heater placed in spring shaft which is how it is situated inside of housing normally.

[olyelr]

Looks like a position and or temp sensor to me.

Good on you for getting this fixed without dicking with the dealer. Im just about ready to do that with mine with the egr setup... got a writeup or any info on that?!

[RustyPW]

That's a wild set-up.

[NickTF]

Looks like a position and or temp sensor to me.

Good on you for getting this fixed without dicking with the dealer. Im just about ready to do that with mine with the egr setup... got a writeup or any info on that?!

How would it measure position? Magnetically? The shaft doesn't move.

Why have a temp sensor inside of the spring shaft not exposed directly to engine coolant when there is a separate engine coolant temperature sensor somewhere else in the motor? See below link:

https://www.rockauto.com/en/catalog/ram ... ensor,4748

My buddy who's a world class gm tech said he sees heated thermostats regularly now which is why, in conjunction with the questions/thinking above, I leaned toward it being a heater.

Have any specific questions on the EGR? It's a relatively easy swap but it didn't solve a thing for me.

[NickTF]

That's a wild set-up.

Just like the MDS lifters, a stupidly overcomplicated design which increases headaches by 80% and achieves a 2% improvement in it's intended function. Atleast when the thermostat fails it doesn't cause thousands of dollars of damage (assuming you don't drive around for 3 years with it not working properly).

[Retired BLM Rig]

Here’s an article on this new style of T-stat.

I haven’t seen one yet but the Euro guys I work with say they fail all the time.

[NickTF]

Here’s an article on this new style of T-stat.

I haven’t seen one yet but the Euro guys I work with say they fail all the time.

Very good info. So my suspicion it was controlled electronically was correct but I had the method all wrong. Definitely seems unnecessarily complex and prone to failure.

[DamageWagon]

Wow that is interesting. That is called a Wax Motor. They are used heavily in industry in HVAC and are considered extremely reliable in that setting. Maybe a big part of why they fail is that the coolant has so much more energy flowing past the wax that the heating element really has to dump heat into it to get it to work properly. Too much heat, too fast for that kind of motor. They usually have very little power and move slowly.

[NickTF]

For what it's worth (knock on wood) my failure was the seal and had nothing to do with the heating element/wax chamber.