eileeneh

Hi everyone, last summer I went to Nova Scotia and Quebec and I experienced three occasions when my trans temp gauge reached 280. The worst one was on the Cabot Trail in NS, climbing North Mountain. I was towing a 24-foot fifth wheel weighing a little over 8,000 lbs with a Dodge Ram 3500 2005 automatic. I had to stop 3 times and wait for the gauge to descend to near 220 (I think they were 10-minute stops each!). The problem is this: my trans temp sensor is located in the tube connecting the pan with the cooler. This is the hottest place. I don't know if 280 for that location is a danger signal or if I was freaking out over nothing terrible. Can any of you with experience advise me on this? I am aware that the Dodge transmission is probably the weakest mechanical part of the truck and I have been wondering if I should consider some additional cooling feature because I experienced this climb to 280 (it has a towing package cooler on it now). The dealer looked at the fluid and did not think it looked damaged. The dealers I visited en route and at home think I should not worry until the red light goes on (I was trying to avoid that situation!!). My truck only has a little over 10,000 on it now. I will be going West next summer (BIG MOUNTAINS!!) and would like to go well-prepared and with knowledge so that I know how to interpret my gauges correctly.

Thanks, Eileen

Patrick Campbell

You might want to just get a Mag Hytec double deep transmission pan and change the fluid while you put it in. The cost is something like $200 or $250. While I had my sensor in the pan, I never saw it get hot at all. I can't recall the range on my gauge at the moment. Another trick is when you are idling or letting it cool down, put it in neutral since rumor has it that the fluid circuilates in neutral but not in park.

http://www.genosgarage.com/CoastalDa...ID=600&CATID=1

Tfeore

Couple of things:

1) Change your tranny oil, if your sensor gets that hot; the oil gets that hot. 280 is the temperature you start to see significant oil break-down.

2) I had the same problem towing a large trailer up a long climb. If you can get a torque converter(TC) lock up switch you can "lock up" in 2nd gear witch you cannot do with a stock tranny and torque converter set up in most of our trucks. I did not see which truck you are towing with so your situation may be different. Basically if the TC does not lock up you get oil shear and that leads to very high tranny temps in a BIG hurry.

A TC lock up switch can start a whole new set of problems though. None temperature related, but possible early tranny failure if you don't maintenance your oil diligently.

sorry to ramble...
tom

eileeneh

Thanks everyone. Does the fact that I STOPPED IMMEDIATELY when it hit 280 have any significance? I read that if one just spikes (or some word like that) at 280 it's different from driving at that temp. It's expensive to change the fluid and I hate to do it unless it has been damaged. . .

Thanks, Eileen

HiJenks

This is from the 1998 Daimler-Chryler Manuel

TRANSMISSION FLUID TEMPERATURE
THERMISTOR
Transmission fluid temperature readings are supplied
to the transmission control module by the thermistor.
The temperature readings are used to control
engagement of the fourth gear overdrive clutch, the
converter clutch, and governor pressure. Normal
resistance value for the thermistor at room temperature
is approximately 1000 ohms.
The PCM prevents engagement of the converter
clutch and overdrive clutch, when fluid temperature
is below approximately 10°C (50°F).
If fluid temperature exceeds 126°C (260°F), the
PCM causes a 4-3 downshift and engage the converter
clutch. Engagement is according to the third
gear converter clutch engagement schedule.
The overdrive OFF lamp in the instrument panel
illuminates when the shift back to third occurs. The
transmission will not allow fourth gear operation
until fluid temperature decreases to approximately
110°C (230°F).
The thermistor is part of the governor pressure
sensor assembly and is immersed in transmission
fluid at all times.

Did your "transmission temp" light come on?

My sensor is located in the DD pan and on hard pull the "light" came on when the guage reached 270*.

67Charger383HP

For what its worth, I would be careful at that temp and not back up your TT until the tranny is cooler. The tranny temps can go up fast when backing up and if you are already hot, it could be too fast to prevent damage.

Good on you for taking note of the temps and keeping tranny wear to a minimum.

eileeneh

Thanks everyone. The light did not go on that I am aware of (I don't remember seeing a light, but I was really focused on the gauge). This happened several times and I never saw a light at all, any time. I just realized that when I was trying to back up into my driveway the other day I was up to 280 just with that hellish and time-consuming task. I hope that's not another problem (I didn't let it cool as much when I was backing up because I'm hardly moving). The light did not go on there either. I'm feeling confused. . .

Thanks, Eileen

RATTLINRAM

Eileen,
If your temp sensor is in the "hot line" coming out of the transmission like mine is, I would think it is very normal to see these kind of temps. One thing we need to remember is that we are seeing the temp of the fluid right after it comes out of the TC. This is before it has any chance to cool at all. After passing that sensor, the fluid starts cooling when it goes into the heat exchanger and then passes through the trans-oil-cooler up front by the radiator and then back into the pan. As Tfeore stated, the fluid builds heat rapidly when the TC is unlocked. This is normal. The only control that we have is to try and keep the converter in its locked-up condition as much as possible. Those of us who have the 47RE tranny have a little more control than those with the new 48RE (which is like yours) because we can lock out OD. However, some climbing conditions are going to require that the tranny unlock in third or even downshift into second which is an unlocked gear that will cause heat build-up. The new 48RE is suppose to be smart enough that the computer will control the shifting to keep it at its best performing level. If your "transmission temp" light did not come on, then apparently the fluid temp in the pan & valve body was not hot enough to alarm the computer. As far as installing a TC lock-up switch on your 2005, be assured that this will definitely void your warranty. I have just recently installed one on mine, but this was done only for use at specific times such as dyno testing and possible use when towing to give me a little more engine braking on down-hill runs. I also have 104k on the truck without the TC lock-up switch. I have seen my fluid temps at 280 in some towing conditions,,,,,, mountains,,, stop and go traffic,,,, and when backing up. I do believe that the transmission makes the most heat when in Reverse. I've never seen an Automatic that didn't. I maintain my fluid and filter changes and my fluid has never been burnt yet.
Final Conclusion in my opinion,,,
Your truck sounds as if it's running normal and you should have nothing to worry about. An extra trans cooler & deep pan won't hurt and if you really want to do some comparing, install a second temp sensor in the pan so you can monitor both temps.

P Kennedy

First off, is this temperature guage a DC factory special on the truck or a quality aftermarket item installed. Factory dash board guages are notorious for being inaccurate and if it is after market was it tested for accuracy with a certified guage. #2 and most important is the tranny cooler covered up, or dirty with poor circulation and just to clarify the torque converter will generate a lot of heat while backing as the transmission is not circulating oil efficiently while the transmission guts are not physically moving driving the tranny oil pump. Was the water temp on the trip high causing the residual cooling temperature available to the cooler which is fed hot coolant increasing the allowable ambient temperature of the cooler itself. If the problem is consistant on warm days when towing invest in a deep pan as suggested for additional oil capacity and an external cooler that has a by-pass system to stop the flow of coolant. This alone drops the possible temperature at the cooler 100F as you would be using outside air temp as your coldest point not coolant 200F. Chances are that is why your idiot light has not come on due to the better accuracy of the thermo coupler it works off of, or it too could be hooped or inaccurate. If your truck is 4 wheel drive and you are backing on loose surfaces put it in low range, your tranny will love you and allow for easier backing up in control. PK

J BODY

How fast were you going? What RPM were you trying to maintain? What % grade? Stopping on a grade for "cooldown" often doesn't help the situation. When you go to take off it generates a ton of heat to get moving again.


....yours is equipped with a 48re and is proving itself to be a pretty good transmission.



....as mentioned above. It's pretty important to keep the trans in lockup. If you were going slow enough that required the trans to be in 2nd, if you pull it down into manual second you can still acheive torque convertor lock up (one of the many nice features of the 48re.......NOT the 47 for those who are wondering, that's where the "rigged" lock up switches come in that you see mentioned)

Hannibal

I've always prefered to have the sending unit in the pan. It's not as entertaining there as the needle doesn't move as much but, you'll have a better idea of what the overall temperature of your transmission is. The high fluid temp out of the TC is only for a very brief period of time. Not long enough to cook the fluid. The temperature in the pan is long term and involves your valve body and clutch packs. One other concern is, if the anti-drainback valve sticks (they've been known to on occasion) you might read an acceptable temperature in the hot line with no fluid going through it while your transmission is burning up from no cooling. Your TCM is monitoring the hot fluid out of the TC. You'd enjoy the trip more watching the overall temperature of your tranny and have all the info you need to prevent overheating it. Just my ever so humble been there and towed heavy with three 47s, one NV4500 and now a 5-45RFE opinion.

eileeneh

Thanks everybody. I've been terribly busy the last few days and just tried to read and digest the newer posts, which I can't do in about 5 minutes!! So I'll come back later and read again and respond. There is a lot to think about in what you have said, and I still don't understand everything you said. . .

Thanks again and until later, Eileen

J BODY

....and the counterpoint: I like the hot line. Either your fluid is getting hot or it isn't. The output line will at least let you know if you are exceeding the limits that the fluid is designed to withstand. If you see it go 280+ a few times you'll be sure to change your fluid a little more often. Cooling the fluid does not magically make the addtives in the atf back to where they were. Also if the drain back valve or cooler plugged you would be more apt to see a change in fluid temp as it would not drop as drastically when the torque convertor locked up. Yes, the ECM monitors the "hot" side of the fluid and will change shift schedule and turn an indicator on if a certain temp threshold is met. Does the same with the coolant temp and I don't see anyone saying it's OK to run until that light comes on. If a light is coming on, you are in possible damage territory and need to fix or adjust accordingly.

Shovelhead

+1 What he said.

FiverBob

Eilleen didn't answer a question that might help you auto guys help her. North Mountain is 8% and about 6 or 7 miles long. It took me down to 4th, then down to 3rd (six speed) to keep the EGT's and engine temp down last year when I pulled it. I was 24,000 GCW. Eilleen was in 2nd on this pull on her auto.
Bob