Thermostat or coolant temperature sensor? Po128 code on 04 Ram 5.7

[Harry Paratestes]

Got a PO128 code for my 04 Ram with 5.7. My heat in cab is hot but temp gauge is only about 1/4 of the way on the needle. How do I tell if its the coolant temp sensor or thermostat? I figured itd be the temp sensor since the heat coming from my vents is hot? Any advice? Thanks

 

[Slinge]

thermostat stuck open
thats what is what was in my Jeep
But check coolant level, if low could also be cause
Doubt its the sensor

 

[Harry Paratestes]

thermostat stuck open
thats what is what was in my Jeep
But check coolant level, if low could also be cause
Doubt its the sensor

coolant level is good. You get good heat even if the thermostat is stuck open?

 

[Slinge]

the fault code is telling you
your coolant is not reaching the expected temp
without reaching operating temp
you will not get max heat
you may get acceptable heat

 

[Dean2]

Take a infrared heat gun and measure the temp on the return hose and top of the block. T stat stuck open the motor and hose will be below the proper temp.

 

[Harry Paratestes]

Take a infrared heat gun and measure the temp on the return hose and top of the block. T stat stuck open the motor and hose will be below the proper temp.

Is the oem thermostat a 203 or 195? I searched all over and couldnt find a straight answer.
I have one of those guns. What should the temps be at on the return hose and top of the block?

 

[Slinge]

reach out to Benny at Allmoparts
he is a vendor on this sight
AllMoparParts

 

[jws123]

Is the oem thermostat a 203 or 195? I searched all over and couldnt find a straight answer.
I have one of those guns. What should the temps be at on the return hose and top of the block?

I always use the 195.

 

[Dean2]

The upper hose should be 190 or better if Tstat is working.

 

[Harry Paratestes]

I confirmed with benny that its a 195 degree thermostat for oem temperature

 

[Harry Paratestes]

The upper hose should be 190 or better if Tstat is working.

So i just replaced the thermostat on my 08 4.7 ram today with a 195 degree one and the top hose is only reading about 128 after driving 10 miles. do you think coolant temperature sensor is bad?

 

[Harry Paratestes]

Great. So i replaced the thermostat with a 195 one today. Top radiator hose coming out of thermostat is 130 running or 150 after i turn the truck off and let it sit for a few min in my garage. the needle on the gauge is in basically the same spot as before i replaced the thermostat.

I havent got a check engine light yet but only drove it maybe 10 or 15 miles or so. All of the readings are on my infrared thermometer in 28 or so degree weather.

It looks like i might have replaced the thermostat for no reason just like i did for my 08 4.7 ram. Probably the coolant temperature sensor is bad in this 5.7 just like i am suspecting the same on my 4.7.

This is exactly why i asked how do you tell whether the thermostat is bad or the coolant temperature sensor. Frustrating that i replaced both thermostats this weekend when more than likely the coolant temperature sensors are bad on both and the thermostats were fine

Im not upset at anyone on the forum and am greatful for the help on my thread. On the positive side I guess now i know the thermostats are good on both

 

[Dean2]

Take a infrared heat gun and measure the temp on the return hose and top of the block. T stat stuck open the motor and hose will be below the proper temp.

You were given good advice on how to check WITHOUT replacing the T-stat. You say you drove it 10 to 15 miles and the upper hose is still only 130 degrees, 150 after sitting. By the way, the upper hose is hot water returning to the T-Stat and the radiator. Thus, that hose should get to 195 before the T-stat opens.

The temperatures you are getting are too low with a 195 T-stat if the engine is completely warmed up. Take it for a much longer drive and measure the hose temp. On my 2021 I can see the temp go up to 103 Centigrade, it then drops back to 96C when the T-stat opens, shows right on my dash. Just so you know, 100 C is the boiling point of water, so it is the same as 212 F, at sea level and normal atmospheric pressure. You cooling system is at 14 or so PSI so boiling point is higher and that boiling point is further raised due to the antifreeze mixed in with the water. As far as the sensors being bad, your gauge looks like it is reading pretty normal to me for the temperatures you are getting with the temp gun. I do not see any evidence of too high or too low a temp for what you measured and what the gauge on your dash is showing. The heat gauge should be in the middle or close when that upper hose is at 195 degrees.

You are the one choosing to fire the parts cannon without doing the proper diagnostics or really understanding how your cooling system works, or how your gauges should read at various engine temperatures, so if you want to be frustrated and pissed off, you only have yourself to blame.

 

[jws123]

is your fan clutch stuck on?

 

[Harry Paratestes]

You were given good advice on how to check WITHOUT replacing the T-stat. You say you drove it 10 to 15 miles and the upper hose is still only 130 degrees, 150 after sitting. By the way, the upper hose is hot water returning to the T-Stat and the radiator. Thus, that hose should get to 195 before the T-stat opens.

The temperatures you are getting are too low with a 195 T-stat if the engine is completely warmed up. Take it for a much longer drive and measure the hose temp. On my 2021 I can see the temp go up to 103 Centigrade, it then drops back to 96C when the T-stat opens, shows right on my dash. Just so you know, 100 C is the boiling point of water, so it is the same as 212 F, at sea level and normal atmospheric pressure. You cooling system is at 14 or so PSI so boiling point is higher and that boiling point is further raised due to the antifreeze mixed in with the water. As far as the sensors being bad, your gauge looks like it is reading pretty normal to me for the temperatures you are getting with the temp gun. I do not see any evidence of too high or too low a temp for what you measured and what the gauge on your dash is showing. The heat gauge should be in the middle or close when that upper hose is at 195 degrees.

You are the one choosing to fire the parts cannon without doing the proper diagnostics or really understanding how your cooling system works, or how your gauges should read at various engine temperatures, so if you want to be frustrated and pissed off, you only have yourself to blame.

Did you read my post #11 or just skip it before you made this post?

 

[Harry Paratestes]

is your fan clutch stuck on?

No its not

 

[Harry Paratestes]

You were given good advice on how to check WITHOUT replacing the T-stat. You say you drove it 10 to 15 miles and the upper hose is still only 130 degrees, 150 after sitting. By the way, the upper hose is hot water returning to the T-Stat and the radiator. Thus, that hose should get to 195 before the T-stat opens.

The temperatures you are getting are too low with a 195 T-stat if the engine is completely warmed up. Take it for a much longer drive and measure the hose temp. On my 2021 I can see the temp go up to 103 Centigrade, it then drops back to 96C when the T-stat opens, shows right on my dash. Just so you know, 100 C is the boiling point of water, so it is the same as 212 F, at sea level and normal atmospheric pressure. You cooling system is at 14 or so PSI so boiling point is higher and that boiling point is further raised due to the antifreeze mixed in with the water. As far as the sensors being bad, your gauge looks like it is reading pretty normal to me for the temperatures you are getting with the temp gun. I do not see any evidence of too high or too low a temp for what you measured and what the gauge on your dash is showing. The heat gauge should be in the middle or close when that upper hose is at 195 degrees.

You are the one choosing to fire the parts cannon without doing the proper diagnostics or really understanding how your cooling system works, or how your gauges should read at various engine temperatures, so if you want to be frustrated and pissed off, you only have yourself to blame.

Also forgot to mention the gauge in my 03 hemi ram almost touches the middle point with the needle and they both take a 195 tstat. Maybe ill do a longer drive and see what temps are at. I believe my scanner might tell coolant temperature too but ill check

 

[Wild one]

Did you read my post #11 or just skip it before you made this post?

With answers like that,you'll be lucky if anybody tries to help you out.
Appears like you're in over your head,take it to a shop

 

[Dean2]

Did you read my post #11 or just skip it before you made this post?

Yep, I read it too. Despite you thinking you know everything, all that post proves is you are way out of your realm. Since you have no use for my input and cant seem to understand even my cooling 101 level explanations, then adios amigo. Short plank, long walk off pier, seem to be in your immediate future. Have a nice week.

 

[Harry Paratestes]

With answers like that,you'll be lucky if anybody tries to help you out.
Appears like you're in over your head,take it to a shop

What was wrong with my question?