Transmission idiot light

[vdub]

In a previous thread concerning transmissions, someone had mentioned that it isn't good to rely on the Dodge supplied trans overheat light and that I should get a seperate gauge. Why is this? Does the Dodge light not give sufficient warning? Is it set too high or incorrectly placed? Doesn't make sense to me that Dodge would put in a light that does you no good. Thanks.

 

[cummins_crewcab]

Doesn't make sense that they would put in a fake oil pressure gauge either but hey, they still do it...

 

[Fred Swanson]

The factory light will come on at 265 degrees internal trans temp. That would be a little late, in my opinion. A gauge is a nice way to know long before it fries.

 

[vdub]

Thanks for the replies. Didn't know the light was set to come on at 265. You would think something lower would be more useful. According to other information I have found, 265 is where seal damage begins to happen. 235 may have been a better setting.

 

[rbattelle]

If we knew the voltage signal from the transmission temperature sending unit could a small resistor be mounted inline to adjust the light trip signal?



I assume it's an RTD, so resistance rises (linearly) with temperature. Putting in a series resistor would easily fool the computer into tripping the light at any temperature you want!



-Ryan

 

[jwduke]

Thanks for the replies. Didn't know the light was set to come on at 265. You would think something lower would be more useful. According to other information I have found, 265 is where seal damage begins to happen. 235 may have been a better setting.

Hey, this way they can sell you a new transmission!

 

[nickleinonen]

If we knew the voltage signal from the transmission temperature sending unit could a small resistor be mounted inline to adjust the light trip signal?



I assume it's an RTD, so resistance rises (linearly) with temperature. Putting in a series resistor would easily fool the computer into tripping the light at any temperature you want!



-Ryan

pretty safe bet it is a 5vdc signal to the thermister. .



RTD??? i have never heard of that term?



i know of thermisters as NTC and PTC... negitive temp coeffecent and positive temp coeffecent. . ntc is common on north american equipment. resistance is high when cold, and gets lower when hot. a resistor in parallel with the ntc thermister could be used to mess with the trans warning lamp but how would the pcm react to reading a hotter than normal trans?...



as i understand it, the reason most manufactures want to use ntc is when the equipment gets hot, so does the wiring going to the sensors... as the wire temp increases, it's internal resistance increases. this is bad, so with the ntc getting lower resistance when hot, and the wires getting higher resistance, it sorta balances out so the ecm/pcm can still get a somewhat accurate reading.

 

[oldcrow]

Transmission Temp.

I just purchased a X-Monitor for my 2004 19000 miles (305- 555) auto,towing pkg. and plow pkg. I never worried about transmission temp. with the above options. I pull a 32' 8000lbs camper. The truck pulls wonderful and hills are no problems as well as the flats. I see temp. from the transmission now with the X Monitor towing hills at 175 -185* and on the flats 165-175* no problem. In stop and go traffic that's a different story --I had the tow and haul ingaged and the X-Monitor read as high as 285*but the engine temp was at 195-200*and no dash warning lights. The truck unloaded runs at about 210-220* in stop and go regular traffic with outside temp at 92* but the temp. jumps back and forth 2-10*. The reason I bring this problem up that I have read many posts of people having there trucks read 140-150*normal transmission temp. in normal stop and go traffic.

I am new to the Dodge Diesel and just learning how this truck reacts to different driving methods. My question is this where I should be with temp. or is the X-Monitor giving me false readings. The temps. are they normal for the Dodge and what is everyone else getting.

The X- Monitor is tapped to a wire going to the computer to get the temp reading.



Thanks

Oldcrow

 

[Dieselnerd]

Oldcrow, the X Monitor does tend to jump around. If you have not already done so, run the ground wire from the X Monitor control box directly to the negative terminal on your battery. This will settle your readings down considerably although you will still get little fluctuations.

 

[rbattelle]

RTD??? i have never heard of that term?

RTD = Resistance Temperature Device. They work opposite to thermistors (increase in heat -> increase in resistance for an RTD).



I guess step 1 would be to determine if it's an RTD or a thermistor. If it's an RTD, a simple series resistor will fool the ECM. If it's a thermistor, things get a lot more complex.



-Ryan

 

[nickleinonen]

so basically, a RTD is a PTC thermister with a different name then eh... ?

 

[ACerf]

I have an X-Moniter. Most of time pulling my 32' footer, I am reading about 160+ or - 5 degrees, to no more then 175 + or - 5 degrees pulling a long grade. Usually if I get the higher temps and down shift the temp will drop at least 5 degrees within minutes. Of course I must admit that having the Mag-Hytec transmission pan has made a big difference in the temps ranges.

Running solo it is running about 140's to 150's depending on the temp of the day. I have never had the X-monitor warning light come on, which I have set a 240 degrees! The key is to not push the rig! It is better to run slower up the hills and keep the RPM's up. This also brings down your exhaust temp and water temp!

 

[rbattelle]

so basically, a RTD is a PTC thermister with a different name then eh... ?

Yes, it sounds like it. I had never heard of a PTC thermister until you brought it up...



-Ryan

 

[Matt400]

If we knew the voltage signal from the transmission temperature sending unit could a small resistor be mounted inline to adjust the light trip signal?

I don't think that would be a good idea, it would also keep OD locked out longer as the ECM thinks the trans is cold and not warmed up.



I forget where I saw it but there is an inexpensive kit out now for a trans dummy lamp that will light up sooner.



The OEM dash led is 275 from what I remember.

 

[rbattelle]

I don't think that would be a good idea, it would also keep OD locked out longer as the ECM thinks the trans is cold and not warmed up.

True. I didn't think of that. Perhaps if the threading on the sending unit is "standard" you might be able to buy a new RTD/thermistor (from someone like www.omega.com) with a different calibration than the stock one.



Or, just get a guage.



-Ryan

 

[Matt400]

I was just re hashing this idea and found this thread again.

If the thermistor is NTC as Nick suspects then a better approach IMO would be to move the OEM thermistor to the output line.



In the 05 manual it says- at 260 the ECM will turn tow/haul on and shift out of OD.

This is useful info for those that want a switch to lock out O/D, some calculating will be needed with some trial and error but a toggle that would switch over from the thermistor to a resistor shorted to ground could fool the ECM into thinking its at 260 and you wouldn't get OD.



The ECM keeps O/D locked out and tow/haul on until 230 is achieved.

At 270 the warning lamp is commanded.

Also O/D is not allowed until 50 is seen for warm ups.



In looking at those numbers- 260-230 and 270 along with the 50 figure it seems like a good bomb to move the thermistor to the hot line.

So now how can that be done?

 

[nickleinonen]

I was just re hashing this idea and found this thread again.

If the thermistor is NTC as Nick suspects then a better approach IMO would be to move the OEM thermistor to the output line.

i still do suspect it being an NTC thermistor, but i can't prove it with the wiring diagrams or service manual. all i can dig out of the manual is that the resistence of it at room temp is suppose to be about ±2000 ohm [from 04 manual]...



***********



it is a PTC thermistor... from 05 manual



TYPICAL VALUES FOR TRANSMISSION TEMPERATURE SENSOR

TEMPERATURE MIN TO MAX OHM RANGE

-40° C (-40° F) 1094 to 1176 ohms

0. 0° C (32° F) 1587 to 1672 ohms

25° C (77° F) 1960 to 2040 ohms

70° C (158° F) 2709 to 2860 ohms

100° C (212° F) 3284 to 3500 ohms

120° C (120° F) 3684 to 3950 ohms

150° C (302° F) 4110 to 4450 ohms



so a simple trim pot or resistor in series with the sensor would make the transmission controller think it is hotter than it actually is...

 

[Matt400]

Hey Nick, where did you find that chart?

This would be slick to turn on the lamp where you want and have the ECM make the control changes before meltdown.

 

[nickleinonen]

Hey Nick, where did you find that chart?

page 21-811 in the 2005 manual

page 21-1109 in the 2006 manual



i can't find any chart like that in the 2003 or 2004 manuals

 

[Matt400]

Thanks Nick.

Looks like-

120° C (120° F) 3684 to 3950 ohms

should be-120° C (248° F) 3684 to 3950 ohms



If my head is working right. . I am thinking a 613 ohm resistor spliced into the DG/OR wire, either at the ECM or transmission would effectively turn on the lamp a 212 deg. which in the pan is pretty hot IMO.



Those temp vs ohm ranges seem pretty wide which puts doubt as to the accuracy of the actual temp the lamp does turn on.