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Discussion Starter · #1 ·
My 2003 E-350 PSD 3.55 rear, owners manual says:

• Use when driving conditions cause excessive shifting from O/D to other gears. Examples: city traffic, hilly terrain, heavy loads, trailer towing and when engine braking is required.

Well, driving thru moderately hilly terrain (Traverse City) between 55-65 mph with OD "OFF" and 9000lb trailer in tow, I watched my trans temp crawl up to 215!
Switched OD back on, and it dropped back down to 185-190, and stayed there.

No difference at all in performance.

Good thing I installed the aftermarket trans temp gauge.
 

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You only need to lock it out when it's "hunting" between gears.
When the converter is unlocked, Temps will rise.
It's working exactly like designed.

Sent from my SAMSUNG-SM-G935A using Tapatalk
 

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Whenever i pull my 16k toy hauler with my 2002 ford 7.3 f-250 i turn OD off. overdrive is just like 5th gear, when you turn it off, your truck becomes a 4 speed, therefore there is less shifting and your RPMs will be higher (when pulling a trailer you need the power). But once i get on the highway, i turn it back on and my RPMs drop to 1300 or so. Your tranny temp is directly related to your RPMs, if you stomp on the gas up a hill pulling a ton of weight, temp goes up. Also 215 is not that hot for your transmission. depending on where you have the sensor, (i have mine right when fluid comes out of tranny) and In my case i can run up to 230 or even 240 for a short time. I have even seen my gauge right on 240 at the crest of a long steep hill and she feels right at home. I wouldn't let it get over 250 though, things may get too hot. Hope this helps.
 

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SI tend to agree with the majority of people that 225 is Max temperature for the 4r100 transmission but if it's maintained properly with new filter and fluid every 50,000 miles, a short burst of higher temps from time to time I don't think will cause significant damage. Remember accelerated wear will happen regardless at increased temps.
As for overdrive or not, I just left mine on 90% of the time when I towed my 7500lbs travel trailer. The few rare occasions I would take it off was when I encountered slow speeds and sharp hilly areas to prevent "gear hunting".

I would suggest adding a transmission cooler at the earliest convenience if you plan on towing in the future. Even a small size like I have reduced 20 degrees.
 

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Whenever i pull my 16k toy hauler with my 2002 ford 7.3 f-250 i turn OD off. overdrive is just like 5th gear, when you turn it off, your truck becomes a 4 speed,
The transmission only has four speeds. When you turn off overdrive it can only use 1, 2, and 3. It doesn't have a fifth gear.

Also 215 is not that hot for your transmission. depending on where you have the sensor, (i have mine right when fluid comes out of tranny) and In my case i can run up to 230 or even 240 for a short time. I have even seen my gauge right on 240 at the crest of a long steep hill and she feels right at home. I wouldn't let it get over 250 though, things may get too hot. Hope this helps.
With the sensor in the hot line (not my first choice of where to put it) 250F is not all that hot. I've had the temps there reach 300F, while the internal sensor and a sensor at the test port will still down around 220-230F.

SI tend to agree with the majority of people that 225 is Max temperature for the 4r100 transmission
The 4R100 can run as high as 220F all day long with NO problems. You can go as high as 250F for no more than a half hour at a time.
 

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Discussion Starter · #6 ·
The transmission only has four speeds. When you turn off overdrive it can only use 1, 2, and 3. It doesn't have a fifth gear.


With the sensor in the hot line (not my first choice of where to put it) 250F is not all that hot. I've had the temps there reach 300F, while the internal sensor and a sensor at the test port will still down around 220-230F.


The 4R100 can run as high as 220F all day long with NO problems. You can go as high as 250F for no more than a half hour at a time.
Thanks Mark

Sensor is in the test port.

With OD on it would drop down a gear on an uphill if I wanted to maintain speed and went WOT- I don't consider that "hunting". If I didn't mat the accelerator, the truck would simply slow down. Depending on the grade, I would be around 40mph at the crest.
I'm still learning engine/speed management, as this is my first diesel truck, but staying in the right lane getting passed up makes me a little anxious. Always felt like somebody cruising along posting a Tweet about how awesome their mountain trip is will plow into my rear end.

Anyhow, back to my original post, with OD OFF all it did was get hotter, and most likely crappier mpg.

With that said, Traverse City and even Blue Ridge Parkway are child's play compared to Big Horn and Continental Divide that I used my gasser over. I don't feel confident at all to use this truck as a tow vehicle for out west, and I'm assuming (hoping) it's because of the 3.55 rear.
I don't know. Maybe those grades are where "hunting" happens?

Sorry if my post is a little scattered. Still trying to figure it all out.
 

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Most people I've encountered say 4.10 gears and the 7.3 are a good match for towing most of the times. The 7.3 doesn't mind working hard or being revved. I've towed my TT with 3.55 LSD and was more than satisfied even in the sharp hills of PA /NJ. I just need a cooler because I used to tow fast lol.
But regardless a cooler is good, towing or not (Mark might disagree or not) I feel lower trans temps = longer and happier...
I don't tow anyone but have 4.10 LSD gears with my 7.3 I haven't seen trans guage go past 185 yet (with the cooler).
 

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These trucks, from mid year 2000 and newer, come with a cooler in the radiator and an aux cooler. You don't want to add any more coolers. It is helpful to replace the aux cooler with a larger one. The best one I know of is from a 6.0L truck.
 

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Discussion Starter · #9 ·
Most people I've encountered say 4.10 gears and the 7.3 are a good match for towing most of the times. The 7.3 doesn't mind working hard or being revved. I've towed my TT with 3.55 LSD and was more than satisfied even in the sharp hills of PA /NJ. I just need a cooler because I used to tow fast lol.
But regardless a cooler is good, towing or not (Mark might disagree or not) I feel lower trans temps = longer and happier...
I don't tow anyone but have 4.10 LSD gears with my 7.3 I haven't seen trans guage go past 185 yet (with the cooler).
Yeah, been researching a 4.10 swap for a while, now. Picking up some tools and books here and there, so I can do it myself. Looks a little bit intimidating because it seems to be as much "art" as "science", to get it right.

Right now I've got a consistent 15.5mpg city (unhitched), and 11.5 highway hitched up. I guess I can assume much lower mileage with a 4.10 rear?
 

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Whoa, your mpg seem to be on the low side. With the 3.55 in my other past two E350 7.3L I used to get about 18-22 mpg speed depending.
Are you loaded heavy or have hilly terrain?
 

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That milage does sound low I got 12mpg hauling my 17,000 triple slide out fifth wheel rv this weekend. That was on flat land running 65mph at 1200 rpm.
 

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The transmission only has four speeds. When you turn off overdrive it can only use 1, 2, and 3. It doesn't have a fifth gear.


With the sensor in the hot line (not my first choice of where to put it) 250F is not all that hot. I've had the temps there reach 300F, while the internal sensor and a sensor at the test port will still down around 220-230F.


The 4R100 can run as high as 220F all day long with NO problems. You can go as high as 250F for no more than a half hour at a time.
Mark, where would your first choice be to put the sensor, I am putting a trans gauge on my other truck and i would like your opinion before i put the sensor in. Thanks
 

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Discussion Starter · #13 ·
Great.
No hills in Detroit, and loaded with no more than a few souls.
And I thought 15mpg was good (compared to 9 with my 8.1L 'Burb)

So, where do I start?
 

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There already is a trans temp sensor, not sure where.... but something like scanguage or torque pro app can read it.
(Btw, I have a scanguage f/s)
 

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Great.
No hills in Detroit, and loaded with no more than a few souls.
And I thought 15mpg was good (compared to 9 with my 8.1L 'Burb)

So, where do I start?
All the maintenance items including tire psi.
 

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Mark, where would your first choice be to put the sensor, I am putting a trans gauge on my other truck and i would like your opinion before i put the sensor in. Thanks
For an external gauge use the test port on the driver's side of the trans. That location is almost as good as the internal sensor that the computer reads, and is available on the OBDII port.
 

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Discussion Starter · #17 ·
OK, this is everything I've done since buying off original owner last June. The only thing he had in the way of service records was a page in diesel supplemental owners manual, that showed 3 oil changes over 54k miles. Yikes.

Tires are at bone jarring 80psi, front and rear



Service 0.0 2016-04-07 76,700 Trans Temp Gauge
Service 0.0 2016-03-30 76,806 Shocks, rear
Service 0.0 2016-03-26 76,680 Oil Change
Service 0.0 2016-03-18 76,160 Fuel Tank
Service 0.0 2016-03-17 76,160 Fuel Filter
Service 0.0 2016-03-15 76,028 Trans cooler filter
Service 0.0 2016-03-11 75,805 Antifreeze flush
Service 0.0 2016-03-06 75,375 Fuel pump
Service 0.0 2016-03-05 75,140 Fuel pump
Service 0.0 2016-02-27 73,605 Vacuum Pump
Service 0.0 2016-02-27 73,605 Air Filter
Service 0.0 2016-02-21 72,925 Windshield Wipers
Service 0.0 2016-02-21 72,900 Oil Change
Service 0.0 2015-11-11 68,236 Oil Change
Service 0.0 2015-10-25 67,230 Sway bar bushings
Service 0.0 2015-10-23 67,180 Brakes Front
Service 0.0 2015-10-23 67,180 Front coil springs
Service 0.0 2015-09-11 64,732 Oil Change
Service 0.0 2015-06-13 58,200 Shocks, front
Service 0.0 2015-06-09 58,184 Tire balance
Service 0.0 2015-06-04 58,190 Tow Mirrors
Service 0.0 2015-06-03 57,957 Trans fluid change, Fuel Filter, Oil Change
 

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That milage does sound low I got 12mpg hauling my 17,000 triple slide out fifth wheel rv this weekend. That was on flat land running 65mph at 1200 rpm.
Wow, you must have really large tires or a GearVendors overdrive. My automatic with a 3.55 differential and stock tire size runs about 1680 RPM at 55.

Towing a 17,000-pound trailer with that gearing sounds like what an 18-wheeler could do.
 

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How are you guys measuring RPM?
Was a tach available for your E-350?
I would like a way to see what RPM our 2000 w/ 3.55 is running.
 

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I have 305 70r16 and I miss wrote the rpm I ment to say 2000rpm sorry about that
 
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