High Transmission temps

[puller]

I was pulling our trailer up a very steep hill that went on for miles, and the transmission temps reached 280 degrees, the temp sender is on the hot line out of the transmission. I stopped and let it cool down before proceeding again. Several other times it started to get hot 220 to 240 range and once again I stopped to let it cool. Ever since it has been running in the normal ranges 160 to 190 degrees.



My question is do you think I hurt the transmission any by letting it run that hot for about 5 to 10 minutes?



Puller

 

[AH64ID]

You are probably fine, synthetic fluid should be okay like that for a few minutes but you can always smell it to be sure.

What gear were you in? Where was the shift lever?

 

[rscurtis]

That's the problem with putting the sender on the hot line. You are needlessly alarmed by what are normal high temperatures. Put it in the pan, and then you'll know when you're over taxing the transmission's cooling capacity.

 

[AH64ID]

I would say if its too hot in the hot line then you are over taxing the cooling capacity, fluid gets damaged from temp long before trans parts.

This is why hot line temps are the best to monitor.

But if the hill was pulled in 2nd unlocked it would explain a lot!

 

[BGlidewell]

I think you're ok, but the hotter the transmission oil gets, the more frequently it needs to be changed which is why you replace it every year/12k when towing a lot.

 

[p-Bar]

AH64ID and BGlidewell are both correct in my book . Don't you want to know what the highest temp of that fluid has reached? When this happens the fluids looses it's ability to function as it's supposed too thus shortening the lifespan of the fluid.

 

[puller]

Thanks for the replies, I did smell the fluid and it does not smell burnt. It also still looks red.

What is the best gear to pull long hills in?

Puller

 

[SDrake]

Thanks for the replies, I did smell the fluid and it does not smell burnt. It also still looks red.



What is the best gear to pull long hills in?



Puller

What ever gear that pulls in a reasonably happy RPM range as long as converter is locked. The secret is, -- with converter locked it is just about impossible to overheat.

 

[HBarlow]

Mine in an '06 never overheated like that pulling heavy trailers. It is common for the automatic transmission fluid to run at engine operating temperature because the transmission is cooled by engine coolant but I don't know why yours would be that hot.

Were you in third gear, Tow Haul mode, converter locked?

 

[RMertens]

I was pulling our trailer up a very steep hill that went on for miles, and the transmission temps reached 280 degrees, the temp sender is on the hot line out of the transmission. I stopped and let it cool down before proceeding again. Several other times it started to get hot 220 to 240 range and once again I stopped to let it cool. Ever since it has been running in the normal ranges 160 to 190 degrees.



My question is do you think I hurt the transmission any by letting it run that hot for about 5 to 10 minutes?



Puller

Definately check the transmission fluid. I'm sure running it at those temps had to have burned the fluid. Do yourself a favor and do a fluid change. You should be alright for awhile, but transmissions don't like high temps at all!!!!

 

[puller]

What gear would be the best to climb these mountains in, to keep the torque converter in lock?



I was in tow/haul mode, if I should be in overdrive off and 2nd or 1st gear can someone tell me what is right.

I am in no hurry to get to the top and I take my time on the hills it just concerns me about the high temps.



Puller

 

[HBarlow]

The '06 will not lock the TC in first gear but will lock it in second gear above a certain speed which I don't remember and varies with differential gearing.

If you run the speed up in 2nd gear you'll feel it lock and engine rpm will drop then you'll know you're okay to continue climbing for miles.

Unless you're pulling a very heavy trailer up a very steep ascent 3rd locked should probably be enough rpm to keep the mighty Cummins hummin.

It would normally be better to pull steep grades heavily loaded in T/H mode because shift points up and down are improved and line pressure may be a little higher for tighter holding. I'm not a transmission mechanic so am not sure about the line pressure comment.

 

[SDrake]

The '06 will not lock the TC in first gear but will lock it in second gear above a certain speed which I don't remember and varies with differential gearing.



If you run the speed up in 2nd gear you'll feel it lock and engine rpm will drop then you'll know you're okay to continue climbing for miles.



Unless you're pulling a very heavy trailer up a very steep ascent 3rd locked should probably be enough rpm to keep the mighty Cummins hummin.



It would normally be better to pull steep grades heavily loaded in T/H mode because shift points up and down are improved and line pressure may be a little higher for tighter holding. I'm not a transmission mechanic so am not sure about the line pressure comment.

I discovered the 2nd gear lockup you mention. Somewhat inconvenient is that you have to get to a pretty high rpm and speed before it will lockup. But once in lockup it will pull down to a much lower RPM before dropping out of lockup. I wired in a lockup switch so I can manually lock up when I want to and now I just get up to the speedometer speed where the 2nd gear lockup RPM is high enough and back off the throttle (baby the clutch) and throw the switch and then pour on the coals. Get some happy pulling that way.

 

[Bill Stockard]

I discovered the 2nd gear lockup you mention. Somewhat inconvenient is that you have to get to a pretty high rpm and speed before it will lockup.

My '03 will lock the torque converter in 2nd gear at approximately 20 MPH if I manually shift the transmission down to 2nd gear.



Bill

 

[SDrake]

My '03 will lock the torque converter in 2nd gear at approximately 20 MPH if I manually shift the transmission down to 2nd gear.



Bill

Slick!! Were you not locked up when you down shifted to 2nd?



Something I noticed, is when you are in lockup, say in third, with OD off, when you switch OD "on" it shifts to forth and stays in lockup. I was at light acceleration and it felt like a shift with no unlock. I wasn't sure if it briefly unlocked, because it felt pretty solid. I have done this several times by accident and was not under heavy acceleration. Don't like the idea of shifting while pulling in lockup.



I am wondering if the controls are doing a quick unlock to keep the stresses down but locking up quickly so as to give maximum power to the wheels. If so it would be handy for maintaining momentum.

 

[BGlidewell]

With a cooler line probe, if you watch your temperature gauge when in heavy traffic, doing a lot of mild to hard acceleration/deceleration you may notice the temperature can swing like a rocket up, then down again. Mine can go from 100->200->120 in the span of a minute or two. I have a double deep pan and a cooler line probe.

 

[AH64ID]

My '03 will lock the torque converter in 2nd gear at approximately 20 MPH if I manually shift the transmission down to 2nd gear.



Bill

Exactly, if you have the shifter in 2nd it will lockup much easier/sooner.

 

[BGlidewell]

Exactly, if you have the shifter in 2nd it will lockup much easier/sooner.

I think this holds true for most automatics diesel or gas.

 

[SDrake]

As I learn about this the OD lockout switch has become less necessary but so far it is still quite useful. Occasionally get caught running at a speed that will not lockup unless I can speed up a bit, but instead I just use the switch.

 

[cerberusiam]

I think this holds true for most automatics diesel or gas.

Newer ones yes, older 47's, no. You had to actually change parts to get most of the 47RE's to lockup in 2nd.



Even with the 48RE the 2nd lockup it is not as aggressive it could be. It will NOT lock under heavy throttle and load and once it is locked if you push it hard it will drop it again.