Too bad you didn't take your Super Duty on vacation...

Believe me I have been kicking myself the whole vacation because I normally do take the truck


Thanks for all the help and suggestions guys.

 

I believe this is good advice. If you install a trans fluid temp gauge, you will see the fluid gets quite hot while climbing a grade. This is just a fact of towing life. All we can do is manage the temps best we can.

If you do a lot of towing then a supplemental cooler is highly recommended.

Towing with OD enabled on fairly flat terrain is quite alright and actually helps cool the trans fluid because having the torque converter locked up is best. As far as I know, the converter only locks up in 4th gear. (could be wrong though....)

When climbing a grade, the PCM will release the TC to get a bit more torque multiplication to help climb the hill. If the transmission doesn't downshift, then it will remain in 4th gear with the TC unlocked. Each time you lift off the throttle (sometimes only slightly), the TC will lock up. Then the engine might bog down a little bit, driver will depress the pedal further, TC unlocks and so on. This does cause the clutches in the converter get hot which in turn causes the fluid to heat up quickly. The problem increases when the transmission hunts for gears, which also creates quite a bit of heat for the same basic reason. Hunting for the next higher gear is easy to notice, it is not a subtle thing. The transmission will upshift, bog the engine, downshift and repeat the cycle. The more this happens, the higher the fluid temps climb.

So, I recommend towing with OD enabled if the terrain is fairly flat. Turn the OD off on large hills and steep grades to help keep the transmission fluid from not getting any warmer than necessary. This will ensure that your transmission doesn't look for 4th gear and keep your TC from cycling lock/unlock. If you encounter a really steep grade and your transmission downshifts to 2nd gear, then you may wish to pull down to 2nd manually to keep it from hunting for 3rd gear. This is a judgment call because only you can see what is down the road. If the climb is long, then pull down to 2nd and pull the hill. There is no shame in backing off the throttle to keep the revs from getting too high. Half throttle in 2nd gear is lower trans temps than full throttle in 3rd gear and lugging up the hill.

Since we are on the subject. As a general rule, use the same gear to hold your speed going down a hill as you would to climb up it.

I have found the factory temp sensor for the PCM to be quite accurate. In addition, it responds fairly quickly compared to a sensor mounted in the pan. If you have the ability to monitor the temps via scan gauge or DashDaq or something similar, then you will see the temps climb and fall depending on the conditions I mentioned above. If you choose to install an aftermarket gauge, then the best place for the sensor is the test port. The pan is the worst place to monitor the fluid temps. It takes quite a while for the fluid in the pan to match the fluid temps in the transmission itself so it's not an ideal place for the sensor.

Hope this helps.

 

Under my pillow, of course

 

No no no no, the o-w-n-e-r-s manual, not that other manual.

 

Great tip, reps coming your way.

 

Thanks for the reps!

 

First of all, the torque convertor DOES lock in third and fourth gears.

Second, trans temps do NOT rise rapidly just because you are pulling a grade. They will slowly rise IF you are running in a situation where the TC is unlocked.

I drive my Expy over the million dollar highway in SW Colorado regularly. These are REAL mountain grades, one pass over 11,000 feet, two over 10,000 feet. I put 500 miles a month on the truck driving this road. I tow a snowmobile trailer up and down it regularly in the winter. I have done the road in a multitude of vehicles. I have done it a lot in Dodge diesel trucks with trans temp gauges.

My experience is that you guys are worried about nothing. You would have to SERIOUSLY push the limits to have a problem. The only time I have had to stop to cool down was in a 34' Class A motorhome with a 460 Ford and E4OD trans loaded up with the family towing a 6000lb truck on a 2000lb trailer. It is highly unlikely you are going to get anywhere near that kind of stress towing anything with the Expy. The Expy comes with a trans cooler perfectly capable of sustained towing, on grades, at its rated limits.

I used to mess with the OD button when going uphill. I have found that it is a pointless gesture as the AUTOMATIC transmission automatically adjusts to the load, as I mentioned before. It will downshift and lock the convertor. The 4R100 never spends more than a few seconds on OD with the convertor unlocked, it either locks up or drops to third and locks up. If you are lugging it down further yet, it will run in third unlocked longer than OD unlocked but it still will automatically either go to second or back to third locked before any significant temp rise occurs. The fan clutch will lock to cool things down long before you are stressing the trans. You can mess with it if you like, I did, but I am hear to tell you, it isn't necessary. If you are paying attention, you can feel every move the trans makes, I can.

I previously mentioned dropping gears when going downhill. Good advice for sure. I smell lots of overheated brakes in the mountains, don't be that guy.

 

Okay so you're the world's GIFT to experienced towing, now what? Your advice CONTRADICTS not only MANY whom towed, but it also CONTRADICTS the MANUFACTURER'S recommendation. Given the RISK you're taking, I'd lay odds that NINE out of TEN people will turn off their OD on the grades and NOT risk cooking their tranny.

 

Turning the OD off while towing is an old wives tale from a bygone era of transmissions. Contradicts the manual? I doubt that, I will have to pull it out from under my pillow and check it.

I would venture to say that my actual towing experience does put me into the "expert" catagory, does that offend you? I have run hundreds of thousands of miles with trailers on in everything from semi tractors pulling 14 foot wide loads to just a couple sleds on an open trailer. I have towed heavy through the mountains of Colorado for well over a decade. I have monitored trans temps on a dozen or better vehicles. I have ridden with and diagnosed transmission issues with an engineer from Allison. My input was used as the base for a national reflash on the Allison trans introduced in the 2001 Chev Duramax trucks. I put over 200k heavy towing and snowplowing miles on a 4r100 in an F350 without a failure. Like it or not, I think I have this subject covered, unless you would like me to fill a couple more paragraphs with actual tangible experience.

Push the dang button if it makes you feel better. Fact is, it gains you exactly nothing UNLESS the trans is hunting for gears, or you are using the engine for braking on downgrades. Exactly as I mentioned in my first response. What towing in third will do is burn more gas, needlessly.

 

Addendum: I just read the section on towing in the owners manual. Nowhere in there does it ever even suggest that you should be towing with the OD off. So much for contradicting the manufacturers reccomendation

 

You forgot to list your time with the circus.

 

Sigh, when you want something done right, you gotta do it yourself. See the attachment with the information from the 98 owners manual (PDF version). Start at the last section of the first page.

 

OK, the '98 version you posted is essentially similar to my '99 version. Please show me exactly where it states that you should tow with the OD switched off.

It states the obvious, select a lower gear if you need to, but that is substantially different than the suggesting the manual reccomends towing with the OD switched off. It says to tow in "D", OK, when my truck is in "D" overdrive is enabled unless you use the shift lever mounted switch.

Again, NOWHERE does it state that you should tow with the OD off, which is contrary to your statment...

"Just make sure the OD is turned off unless you're doing a steady speed on a flat stretch of road."

Suck it up buddy, that is an outdated notion. It is NOT reccomended by the manufacturer as you claimed, and it is NOT a risk to your transmission. That is just plain old wrong advice.

 

Thanks for that info. I have wondered about this myself. I had my Auto Enginuity scan tool hooked up while towing but never saw the TC lock up with OD turned off. However, I keep my eyes on the road most times so it's hard to monitor the laptop all the time. I need to learn how to data log so I can look at the information later.

You are correct. However with my truck, the TC unlocks pretty quickly once a grade is encountered. Rapidly and slowly are subjective terms. A 20 degree change seems like a lot to me.

We have real mountain grades here in Arizona as well. Winter towing is completely different than summer towing as far as transmission temps go. Heck, it's hard to get the transmission fluid up to temp in the winter in the first place. There is a whole other discussion about waiting until the fluid is up to temp before you push the transmission hard (but that is another topic entirely).

How are you monitoring the temps? Meaning, where is the sensor placed? I have towed with my AE connected (laptop), a sensor in the pan and a sensor in the test port...all at the same time. I will tell you with absolute certainty that the location of the sensor makes a difference in how quickly the gauge moves. If you are monitoring fluid temps in the pan, then it will take quite a while before you see the gauge move.

My fifth wheel trailer weighs 16,480 lbs so I guess that qualifies as seriously pushing the limits. Interesting enough, my trans temps are the highest when towing on surface streets in town. Stop light to stop light shows slightly higher temps than observed while pulling steep grades. Obviously I don't pull a fifth wheel with our Expedition but we do pull a boat to the lake through the mountain canyons and I have observed the trans temps with the scan gauge. It gets hot quick. 170 degrees on flat road and we hit the first set of climbing switch backs and the temps get over 200 within minutes. We saw 220 one time and pulled over (but it was 113 outside as well). I added a True-Cool MAX cooler and the temps never get over 190 now. I think the Expedition is rated for 8800 lbs in tow but I'd have to check the manual to be sure. I think our boat and trailer weights about 6k-7k ish. I should probably have it weighed to verify.

I'll attach the page in my manual that recommends towing with OD disabled. 1999 F250 with 4R100 trans. It is a little bit vague because it really says that it is 'useful' to tow with OD disabled. It doesn't say you 'must' tow with it off.

Fan clutch locks up at 207-212 degrees. That is too hot for my preferences. I prefer to keep the trans fluid in the 160-180 range if possible.

I think the primary benefit of turning off the OD is to keep the transmission from hunting for gears. If it's not hunting, then you can probably just leave it engaged. I just prefer to go ahead and turn it off when I am starting a grade because I already know it's going to be a hard pull.

Good points. Disable OD to keep the trans from hunting and descending. This is probably where the owner's manual breaks down because the average person doesn't really want to know the specifics of how to use their transmission to tow. They just want to select the correct setting and head down the road. So, for those people, it's best to recommend turning off the OD, waste the extra fuel and err on the side of caution. If you are able to tell when the transmission is hunting and have accurate gauges, then by all means....leave the OD enabled and be smart about when it's time to turn if off. In the case of the OP for this thread, he is using his Expedition to tow a car and we are assuming he doesn't have a transmission fluid temp gauge to really monitor what is happening. So for his trip, it's good advice to disable OD when climbing and descending grades.

 

My kids try pulling these "I can't find it" games too whenever they know they're wrong.

Here is the exact quote from the manual, word for word:
When towing a trailer:
• Use D (Drive) or a lower gear when towing up or down steep hills. This will eliminate excessive downshifting and upshifting for optimum fuel economy and transmission cooling.

It doesn't say "we suggest", nor does it say, "it's a good idea", it says to use D (Drive) or a lower gear. OD is higher than D, so without question they're saying to not use OD when towing up or down steep grades.

Now if you want to leave your OD turned on with your AUTOMATIC transmission then be my guest. But when you're giving advice to other people and it's their transmission and repair bill you're dealing with, then you've got to tell them the fact and not your opinion.