Temperature Reading

[rekabeka]

I have a 2000 Dodge RAM 2500 Cummins / 6 speed. Problem: Engine is at operating temp and all seems OK then the gauge creeps down to the cold side and slowly creeps back to normal. This problem may happen multiple times at anytime during the course of operation. I have changed thermostat, sending unit, and radiator cap. I'm running Evans waterless coolant in a Mishimoto radiator with a 19 lb. cap. I realize on a 2000 that the reading is produced by an electronic impulse rather than mechanical. Any thoughts? Thanks.

 

[RBeard]

I have a 2001 and it goes to about 210 and then(when the t-stat opens) goes down to about 185. It does that maybe 3-4 times before all the coolant sort of warms up and it stabilizes at 195. It also depends on the load and terrain your driving on.

 

[GAmes]

Temp fluctuation is normal in a 12 valve. It swings because when the engine isn't loaded the radiator cools more than the engine requires, so the t-stat closes until the engine heats up again. It looks like a lot but in reality it is only 20 or 30 degrees change. I have read that Dodge rigged the 24 valve to be idiot gauges that don't swing back and forth. Maybe they didn't. I look for my gauge to swing, it tells me that the thermostat is working.

 

[Michaelsloft]

Temp fluctuation is normal in a 12 valve. It swings because when the engine isn't loaded the radiator cools more than the engine requires, so the t-stat closes until the engine heats up again. It looks like a lot but in reality it is only 20 or 30 degrees change. I have read that Dodge rigged the 24 valve to be idiot gauges that don't swing back and forth. Maybe they didn't. I look for my gauge to swing, it tells me that the thermostat is working.

The temp fluctuates on my '99 24 valve like you are describing your 12 valve does. And yes it does tell me my thermostat is working! I too have read some posts over the years indicating the idiot gauges.....might be do to different computer flashes, reflashes and programming etc.

 

[rekabeka]

OK, Thanks for all the replies. I guess as long as it doesn't go towards the hot side I shouldn't worry too much. I really like mechanical gauges on my motors. Enough of this computer and electronic crap! Thanks again. Rekabeka or -- email address removed --

 

[GAmes]

I haven't ever seen a mechanical coolant temp gauge on anything. I can't imagine how it would work. My 50 year old Chev pickup has the same type temp sensor as my Dodge. It is an electrical signal, not a mechanical gauge. From the FSM;

The coolant temperature gauge gives an indication
of the engine coolant temperature. The coolant temperature
sending unit is a thermistor that changes
electrical resistance with changes in the engine coolant
temperature. Some gauge needle cycling, depending
upon the vehicle load, is normal on models
equipped with the diesel engine option. High sending
unit resistance causes low coolant temperature readings.
Low resistance causes high coolant temperature
readings. The sending unit resistance values are
shown in a chart in Specifications at the back of this
group.

 

[NIsaacs]

Here ya go Gary: They use a line similar to a thermocouple on a gas furnace. They were used forever on off highway equipment.

 

[GAmes]

Really Nick? It is still an electrical signal, just self contained. To me, a mechanical gauge is like a pressure gauge that has a billows connected to a needle. Pressure moves the billows, they are connected to the needle. The needle moves mechanically, thus a mechanical gauge.

 

[NIsaacs]

Really Nick? It is still an electrical signal, just self contained. To me, a mechanical gauge is like a pressure gauge that has a billows connected to a needle. Pressure moves the billows, they are connected to the needle. The needle moves mechanically, thus a mechanical gauge.

No...not electric at all, just mechanical....here is a link to Summit Racing, they list 124 mechanical water temp gauges. Read the specs, no 12volt signal, as in a sender with a wire. What do you mean self contained electric signal? How do 12 volts get in there? https://www.summitracing.com/search...N=4294951097+4294951021+4294944911+4294951006

 

[GAmes]

It isn't 12 volts. It is millivolts produced by a bi-metal probe.

 

[NIsaacs]

It isn't 12 volts. It is millivolts produced by a bi-metal probe.

Okay, maybe you call it electric but I call it mechanical, as does every one that sells that type. If you ask for an electric water temp gauge you will get one that requires 12 volts, if you ask for a mechanical, you will get one that doesn't.

 

[GAmes]

A better comparison is a speedometer. My '54 Ford speedo has a cable that drives a gear in the gauge. Truly mechanical. The speedo in my Dodge doesn't utilize 12 volts, it is another self contained system. So is it mechanical too?
SPEEDOMETER/ODOMETER
The speedometer/odometer gives an indication of
the current vehicle speed, and displays a cumulative
total of the distance the vehicle has traveled. The
speedometer/odometer unit receives a vehicle speed
pulse signal from the Vehicle Speed Sensor (VSS). An
electronic integrated circuit contained within the
speedometer/odometer unit reads and analyzes the
pulse signal. It then adjusts the ground path resistance
of one electromagnet in the gauge to control
speedometer needle movement. It also sends signals
to an electric stepper motor to control movement of
the odometer number rolls. The frequency values for
the pulse signal are shown in a chart in Specifications
at the back of this group.

 

[NIsaacs]

Now you are getting over my head. I am pretty sure your Dodge's speedometer will not work if you coast it off a hill in neutral with the engine off and the batteries removed. I think the OP was talking about mechanical like I am. I don't think he said a mechanical water temp gauge as one that needed gears and a drive shaft.

 

[GAmes]

Now you are getting over my head. I am pretty sure your Dodge's speedometer will not work if you coast it off a hill in neutral with the engine off and the batteries removed. I think the OP was talking about mechanical like I am. I don't think he said a mechanical water temp gauge as one that needed gears and a drive shaft.

LOL, I'd try it if I had a place to do it. I have a mechanical injection pump and mechanical injectors. They don't require any electricity to operate. I don't consider anything that has an electrical current involved to be mechanical.

 

[NIsaacs]

Okay, no problem

 

[NIsaacs]

It isn't 12 volts. It is millivolts produced by a bi-metal probe.

Is this how a pyrometer without an amplifier works?

So, after a good nights sleep, I found this, no reference to millivolts?

The web quickly answered my many questions. The mechanical temperature gauge is a marvel of thermodynamics and is not a relic, but still in use - thankfully. it turns out that the solid "wire" that was cut is actually a capillary tube - a hollow tube. The sender is a probe, a bulb that sits in the coolant stream. The system is sealed and filled with ether. When the system heats up, the ether expands and the vapor pressure with the ether-charged system increases. The increased pressure causes an element within the gauge head (a Bourdon tube) to deflect the indicator needle to the appropriate temperature reading on the gauge face. Very freaking cool and elegant. Also voltage independent, so useful in a 12 volt or 24 volt vehicle, and not dependent upon a voltage stabilizer like the fuel gauge or electrical temperature gauge. This explains why I could not find the oil and water temperature gauges on the 12 volt wiring diagram (or 24 volt diagram) for the Lightweight.

And this:

http://www.mgaguru.com/mgtech/dash/dt101.htm

 

[GAmes]

I stand corrected and learned something. Good job.

 

[GAmes]

In the process of this exchange we failed to note to the OP that even if he had a mechanical gauge it would still swing. I wonder how long it would take to wear one out with all that movement.