Returning from a weekend camp this weekend, the 175 mile freeway trip back home was made in 100-110 degree temps. Since I was hauling the camper, and since there are a few decent grades to climb, I had Torque App running to monitor real-time engine and tranny coolant temps. I wanted to post my results and see if they jive with others on here.

Running on the flats at 65-68mph, 3rd gear (drive), 2650rpm, engine and tranny coolant were both right at 200 degrees.

On one of the longer/steeper climbs, I got behind a couple of semi's and speed dropped to 50mph or so. I pulled into 2nd gear for a couple of miles to get back up to and hold 60mph. 3800rpm, engine coolant climbed to 210, tranny went to 220 or so. Once on flat land again, coolant came down to 200, tranny stayed at 210 for the rest of the way home.

I was actually expecting higher tranny temps than this so I was pleasantly surprised.

 

Those temps are nothing to be too concerned about while towing in those kind of air temps. I have hit 210 on my coolant temp on a few occasions while towing our 35 footer. Also, as for the tranny temp, one of our members on this forum that is a transmission engineer for Ford has told several members that these trannies can run at 220 all day long... its when you hit close to 230 and above that you have a problem...

I wouldn't be worried about it. Those numbers seem normal to me if you are running the stock factory tranny cooler.

James

 

our 2012 winnibago 28ft I run around 200-202 regularly this is with 2700 towd vehicle. I did get to 215 once or twice climbing in colorado foothills up to around 10000 ft or so. Fan came on a couple of times. 204 or so on slight climbs OAT was in mid 80-90's I would guess. I dont monitor the trans temps, its the same trans as in my F350 and it never gets hot even on the same pulls as we had the rv on.

 

Normal but I would increase the trans oil cooler capacity for longer life of the ATF. I have read that a 10* decrease in this range will double the life of the ATF. If the ATF were constantly at this temp it is said the life would be 10K miles.

 

Interesting to me that the temp climbed in 2nd, not knowing better, i hypothesized it would be better at the higher rpm in second than lugging in 3rd for those times when its borderline as to what gear to use.

 

Yes, I should've stated that my tranny cooler is the stock one.

I did see a recent post by Mark K (the former tranny engineer) wherein he stated that temps of 220 are not a problem at all - that the tranny can run at this temp all day long. But I believe that specific statement was made in reference to the 5-speed 5R110, and I don't know if the 4R100 is any different when it comes to running temps.

 

You are correct regarding which tranny he was talking about in that post.
However, I have seen other posts by him and others that have suggested that 230 and above are really the cut off point for the danger area with the 4R100.... I think for most auto tranny's this is the case.

Am I comfortable driving at 220 for long periods of time? Not really, but hitting it and then it backing off to 200 - 210 for awhile while towing heavy in hot weather doesn't make me nervous. If my tranny was hitting those temps with just my family and gear inside, then I would start looking for a problem. Mine runs at 169 - 185 with my family and gear while driving through the Blue Ridge Mountains in August.

Maybe Mark will see this and correct anything that I have said that is wrong.... (I hope he does join in... I like to hear it directly from an expert)

James

 

That temperature is also good for the 4R100. You can go as high as 250F for no more than a half hour at a time, too.

 

Thanks for the info Mark. I really appreciate it.

A follow-up question: if tranny temp does spike to 250, do you recommend replacing the fluid? (above question assumes non-synthetic Mercon V fluid)

 

Thank you for joining in Mark!! g I was hoping you would.

James

 

No, I do not. There is no reason to replace the fluid more often because it saw 250F for a short time. I recommend changing the fluid at least every 30k miles regardless of the temperatures.