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Mr Richter I humbly ask for your expertise...

10434 Views 93 Replies 22 Participants Last post by  Dysfunctional
My trans temps have gone WAY up in the last two weeks. Prior to this, the highest temp I've ever seen was 180* driving like a PRICK on a 118* day over the crooked and steep mountain road I drive daily. Today I hit 230* in the morning with outside temps in the 50's :poke:

Tonight I came home, hooked up a snap-on MODIS I'm borrowing from a friend and went for a test drive. Trans temps with the scanner are +/- 10* of what my autometer gauge says, I even got it up to 240* with ambient in the high 90's. You can monitor alot with this scanner, but I just locked in trans temp, TCC%, TorqueConverterClutch (on/off) and gear. When I LUGGED it on hills with TC locked in 3rd, TCC% shows 100%. A downshift, TCC% drops to about 60% momentarily (this seems ok). If I climb a grade with 2nd gear manually selected, the TC never locks according to the scanner (TCC shows OFF the entire time to any MPH) and my temps rise FAST.

IMO something is wrong... My temps are sky high out of nowhere. So the other weekend I bypassed the bypass valve on the trans by removing it and adding fittings to adapt back to the threads in the trans. After that temps seemed lower and stayed in check a few days.

When I got back tonight and my trans temp was 240*!!! I started feeling the cooler lines and I didn't not burn myself. Seems to me with fluid that hot I should have 2nd degree burns on my hands right?

Tomorrow I'm going to my friends shop to have the transmission flushed with a machine, 10 times if necessary.

Short version of this babble... I'm thinking I have a blockage...? :swordfight:
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I'll make a couple of comments to further the discussion along. Just remember that I'm a non tranny expert, but who has read tons of tranny posts since 2001 so take these with whatever amount of salt you want and the last time I can remember staying at a Holiday Inn Express was over 10 years ago :redspotdance:

My understanding of this bypass based on the following information from someone I believe should know something in fact a lot about the 4R100 tranny ...

The bypass is a pressure relief valve. When it's very cold the fluid in the cooler gets vaery hard to move. Pressure in the cooler line goes up and nothing flows. Since the return from the cooler is used to lube the rear half of the transmission, no cooler flow causes big problems.
If the pressure gets high enough the bypass opens and sends fluid to the rear lube

The internal bypass came out with the TorqShift. The 4R100 is external.
Yes, the bypass was to fix a problem. The fluid in the coolers would get to thick to flow in extreme cold weather. This starved the rear half of the transmission for lube. The bypass allows rear lue to always have fluid.
I do agree that a bypass failure can send temps sky high and IMHO is one reason to have a good tranny temp gauge installed, know your baseline and if things go south find out why pronto and fix the issue. But if the temps are cold enough you could starve the rear of the tranny possibly before the temps got out of control. Also if you remove it and and in warmer weather have a blocked cooler as was the situation in this thread it seems the starvation issue could add to the problem, but maybe the temps go sky high before the starvation issue becomes the major factor in a tranny failure. :shrug: I can also see if the bypass gets stuck open then you will also have a heat issue since it will be bypassing the coolers :rolleyes: I'm not sure what the extreme temps quoted above mean, but I seem to recall a lot of folks seeing that bypass open even in mildly cold climites when trying to "flush" their trannies when they removed the return line from their trannies to do the flush. :( From my understanding during the normal "tranny" flush that we do in our driveway we want that bypass closed and during the procedure we aren't lubing the rear of the tranny so some lack of lubrication over time doesn't seem to be an issue the question is how long is too long and that I have no idea.

FWIW: My stock tranny has both the factory OTA and OTW coolers and the bypass and personally I wouldn't just remove it. :shrug: Of course I also have a spare bypass since a new one was put on when my BTS was built and I got the old one from the original tranny that was still working.

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Your concern is out of focus. You shouldn't focus on someone who doesn't build transmissions yet understands a couple of simple features about them. I'd be more concerned about those that do build them yet don't understand those simple things.
To be honest with you and we have had our disagreements over the years in another life I do agree with you 100% in this case. This is more than somewhat worrisome in this particular case at least from my view point.

My 95's BTS does NOT have the bypass. Neither does the 97.
My BTS built in April 2004 has a bypass and it was a new one that Brian put on it. IIRC the E40Ds didn't have a bypass in their stock form. :confused:

Larry, your probably correct. If the bypass is so great, why not install them on all the trannys leaving the shop? That was my point.
:shrug: maybe the final length/fittings??? or didn't try and fit them on earlier rebuilds :shrug: just WAGs on my part since we really don't know.

I guess alternatively my point was he did install one at least when he did mine. He didn't even mess with the old one, put a new one on and I kept the old one. IIRC the bypass was added to the 4R100 to solve a problem, maybe when they went to the OTA/OTW combo coolers ... again a complete WAG since I know of only one person that doesn't post here that could authoratively tell us who/what/why FORD did what they did. That person is who I basically quoted in my first reply to this thread. So I know why and what it's meant to do.

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