thought this thread was something to read...(stole from another site)


.....I'll start with the short version.

At 20,000lbs my '99 F350 7.3L/ZF6 will hit 230-deg on the manual transmission temp gauge at 75mph within 40 miles.

Empty, it takes 100 miles to get in that ballpark.

At 230-deg, I pull over to the side of the road, and grab both cooler lines at the radiator.

Both sides are cold. Not warm and hot, not hot and hot, cold and cold.

50mph in 5th gear at 20,000lbs keeps the temperature around 195. 55mph and it creeps up.

Bad bump/drive? Bad pressure relief?

I confirmed the cooler is clear - disconnecting the lines from the transmission, I was able to blow through the circuit with nothing more than pucker power.

I also got a squirt of fluid out of the ZF6 when I let the clutch out, but can't really say much more about it (I was in the truck, wife was keeping an eye on the ATF puddle)

Adding an auxiliary cooler did nothing to change the situation.

I did not completely bypass the factory cooler though. But as noted, confirmed I can blow through the cooler.

Now the back story.

2nd owner of an e99 7.3L F350. 183k miles.

I loaded my gooseneck with a Scout II 4x4 and hauled it to Spokane for a car show. Transmission saw 230 or so. Driving empty, it had never moved within the first 100 miles, and had never gone above 150. This was the first tow.

230 or so going over the hills to Spokane. It had me worried, but it was OK.

I changed the fluid when I got home - it was probably due.

Left for Colorado, same load, with another 3,000lbs of pop-up camper.

Transmission approached 230 the first day. Second day, saw it again.

While pulling a modest grade at 70mph with the cruise on, I heard a pop/smack. I chalked it up to a very bad thrown-rock, because what else could it be?

Well, it was the throwing bearing taking a bump, and/or one of the springs from the clutch disc coming out, and/or a few of the other things that got bounced around inside the bellhousing in the ensuing melee.

450 miles of no-clutch was ahead of me. Aside from the transmission running hot, no big deal.

Transmission ran hot. And hotter. Saw 240 and I was concerned, but needed to get to my destination. Saw 250, at which point the gauge numbering stops - that must be a bad number since they didn't bother to mark the gauge after that.

I can confirm that north of 250, and by 260 in particular, the shifter rattles pretty good.

So I had the clutch replaced, and had the ZF6 opened up and found it was smoked, and a reman was installed.

Transmission shop confirmed the cooler was in good shape and free flowing, and talked me out of an auxiliary cooler. They said I'd be fine.

Thus, on the return trip, 43 miles out, I pulled over to let the transmission cool, and after another jaunt, I was installing an auxiliary cooler in the CarQuest parking lot, which ultimately did nothing for me.

I drove home in 5th gear, 2000rpm, 50mph. 12.3mpg wasn't too bad, but the two days of driving took the fun out of it.

Confirmed on multiple occasions that I had cold cooler lines, both sides.

After I got home, I went for a 75mph drive 100 miles away, and watched the transmission temperature climb - hotter than the original ZF6 ever got driving empty.

My conclusion - the pump drive key isn't installed correctly, or the pressure relief on the pump output is too low.

Of course, the nearest service shop for the warranty work is 250 miles away..

I'm not sure why the original ZF6 ran hot - part of me wants to blame it on the transmission being damaged before I got my hands on it (~3000 miles ago) and that contributed to the heat buildup, but I'm not sure.

I never stopped to check the cooler lines on the original transmission, that I can remember. I remember checking that the transmission was too hot to touch, but I don't recall checking the lines.

If I need to be concerned about the ZF6s temperatures when loaded to GCWR, then I'll go back to insisting I run an aux cooler - once the pump is confirmed to be working well.

What else am I missing? Is this fairly common?

My friends run 80+ in their ZF6 equipped trucks pulling comparable loads and do this all day.

The SD was nice with the quieter cab, air conditioning, and the 12mpg loaded.. but I was yearning for my '74 IH Travelette I'd left at home.. sure, 6mpg hurts the pocket book, but the old T-35 stick shift wouldn't have complained, and I could've bought a lot more fuel for the cost of the ZF6.

Both trucks pull the same. The T444E just gets 2x the fuel economy of the old SV392.

 

Those temps are too high obviously. I'm surprised the empty temps were getting that high. Are you absolutely sure the cooler was hooked up and not bypassed in any way? It's really weird that both trans got that hot empty. I could see if one of the pumps had failed it would get that hot, but what are the odds both trans had bad pumps? It will take me a long time driving in summer to get my trans up to 150, but I have an external cooler I installed. Before the cooler I saw temps in the 235 range but my fan clutch was not working. Is your fan clutch working? What are your coolant temps?

 

sounds like he has a big problem.

 

FATS...its not my thread. It was one, i came across this morning, and thought it would be a good topic to "comment" on, here. Since, its been noted, that the zf6 runs cool enough, not to even monitor it, but unfortunetly, seems its one that should not be overlooked. I posted it in the sense of "us" handshakers, might consider a temp sensor install...I have a place for one (trans by-pass), but yet to get the gauge..

 

Ahh ok. I use one gauge for my water temp, trans temp, and diff temp. They all have their sending units wired into a rotary switch.

 

Interesting read. Wonder what came of it and what happened to the old ZF-6? Also wonder what the outside temps were at the time to feel cold cooler lines? 100+ in the shade around here lately so there's no cold anything around my truck.

As for the gauge, I guess it's a little late for me to worry about that. Of course I live out in the flat lands, but every 50k when I change my fluid it comes out shiny and new looking. With almost 450,000 miles under it's belt, it's a little late for me to worry about the temps in my ZF-6.

 

When I swapped trannys a couple of yrs ago, I added a 40K oil cooler and a FastCool extension housing. My thought was manual tranny or not, cool is better. Empty, I rarely see anything over 40 degrees above ambient. Towing with a gross weight right at 30K I have only seen 70 degrees over ambient. And If I stop and let it idle it will drop to within 10 degrees of ambient within 15 minutes. This dude has a problem.

Barney

 

==============

 

I'm looking at getting gauges and this has me wondering if I should order a tranny temp gauge for my zf6. What do you guys think? Is there even a place to hook it up on the tranny?

It also has me wondering if I should do a complete flush of the tranny. Is there a right up for the zf6 out there?

 

flushing is no more than removing the bottom drain plug, and let it pour out. You can then, "tap" that drain plug and install the temp sensor, or, install an external inline filtration and install the sensor in the filter base.

 

..........then, replace the plug, pull the plug on the side and add fluid until it starts to run out the hole on the side where you're filling. Replace side plug and you're done.

 

Thanks, this is my first vehicle with a manual transmission so I didn't know if it took an actual flush like the automatic. Just draining and filling sounds a lot nicer!

 

Baatzy, its your discretion on what "fluid" to use. F350-6 bangs out wwith regular ole' Mercon V, for the last 450k miles. I've tried the Amsoil approach, but think, my zf didnt inject it well. I'm back to Mercon V.

 

My 99 had an automatic fluid changer for a while. Well, actually it just let some out over time, and then I would top it off every 1000 miles or so. That fluid was brown. I recently changed it, and fixed the leak (seal around the gear shift). I don't know how hot it actually gets, but when I would get home and check the fluid, it was way too hot to touch! My typical trip would be 100 miles one way.

 

not sure if it was mentioned in OP'er thread, but wonder how the shifting was. I know when mines' warmed up, damn is it tough to get in gears ,especially when rpms are up. Cold or otherwise, getting warmed up, its like a brand-new tranny, under there.