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Discussion Starter #1
I thought I understood the procedure Mark has laid out but I must have misunderstood or missed something.
I drained pan, cleaned magnet, changed filter, reinstalled pan, added 7 qts Mobil 1, disconnected rear transmission line- rear- passenger side, hooked up latex hose, had bucket marked for gallon & 1/2, started truck, fluid pumping into bucket, last I looked had about 3/4 gallon, started shifting through gears, 5 sec. each one, looked down, no oil going to bucket- shut off truck, all over the floor!
Checked hose and OK, added few more qts., started truck, looked underneath, oil just pouring out of the fitting on the transmission where the flare end of line and nut go in.
Transmission fluid everywhere, I’m soaked—hooked line back up. Cleaned the worst of the mess, calling it quits tonight.
I don’t know what I did wrong?
I’ll will check transmission level tomorrow, will it hurt to have Mobil 1 and conventional mixed?
Any help appreciated. Maybe things will look better after a good nights sleep- Lol.

BTW- drove truck 6 hr round trip yesterday- no problems- transmission temp was good. Old transmission fluid little dirty butter didn’t look bad- no burn smell.
 

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There are two possibilities. The most likely is that the cooler bypass needs to be rebuilt. It's an easy job and the parts are around $25 at Summit Racing. The second possibility is that you have a restriction in the cooler circuit. Either a damaged hose or a plugged cooler.
 

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This is a rebuild kit for a failing bypass as Mark described above.

Cooler Bypass Valve Kit
Part No. 36605-02K

https://www.sonnax.com/parts/2078-cooler-bypass-valve-kit

They are available at Summit and also on EBay for $20.

The manufacturer is Sonnax and it helps to print out the pdf in case its missing from the kit.

Its not a difficult rebuild but you have to pay close attention to the o-ring removal and replacement. It is also easy to crossthread into the aluminum 4R100 so be slow & deliberate.
 

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Discussion Starter #4
Thanks guys, I will order the bypass rebuild kit. I am also going to check the cooler circuit today, send low pressure air through it to see if it is open.
I should have stopped and asked some questions— when I removed the return cooler line at the back of the 4R100 there was a constant, slow stream of fluid coming out of the port that never did stop, I’m assuming that’s because the bypass is bad and wasn’t shutting off all the way- now that Mark and ArcticDriver responded and I’ve looked at the schematic of the bypass valve.

So I’m not familiar with the bypass valve. Where I removed the line—is there just one bolt there that removes the bypass? I know in the rebuild kit it refers to the banjo and tube—-I’ll try to look up in my Chiltons for a disassembly/assembly pictures unless someone can offer a description.

If the cooler ends up being plugged up it no big deal as I have not installed the new 6.0 cooler sitting in my shop yet. If (and I hope not) find a restriction in my radiator what would the course of action be?

Thanks—. Once I get it figured out I’ll send an update.
 

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The bypass valve assembly has a front and rear banjo bolt setup and is prone to failure after 100k IMO. Search for my adventure and don't repeat my mistakes. Also, do thread the front one first as it is smaller and more prone to cross threading...
I'm not sure why the trans circuit would all of the sudden get plugged without a major failure within the trans itself.
 

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Discussion Starter #6
Small update: thank you gentlemen, removed pressure relief tube/ got better light and could see the line and banjo at both ends.Tube is open.
Hooked up 15psi to line/cooler circuit and flows freely/ no blockages.
Now just waiting on parts in the mail/ valve rebuild.
Being I’m not towing anything heavy yet what would be an indicator that cooler pressure relief valve is bad? Or isn’t there?
 

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There wouldn't be any indication.
 

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My indication was unexplained increase in trans temps. I actually think it had been going on for quite a while to some degree and then a lot more all of the sudden. You know something is up when even the large cooler doesn't seem to help like it used to.
 

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Discussion Starter #9
Mark Kovalsky—- Mark, if you will indulge me I have one more question. I don’t know how much old fluid is left in the tranny since the old and a lot of the new went through by-pass onto floor. Most of the oil I cleaned up looked new (really bright red). I do know tranny pumped about 1 gallon into bucket initially before bypass opened up.
Now that I have pan empty again (fill plug- recovered the fresh Mobil 1) , am assuming mostly new in torque converter, and have lines and cooler blown out, I am going to install the 6.0 cooler, and spin on external filter while I have the down time. After pressure valve rebuild, and complete reassembly of system I will fill back up. When I blew air through the cooler system this morning to check for any obstructions the oil I caught in bucket looked new. Would there be any need to purge more fluid through return line and into bucket? I’m not sure why there would be or even know how many more quarts. Or just fill system and check level after driving tranny at operating temp. and call it good until my next flush/fill. Thanks!!

BTW— I did a search and read a lot of your posts on another forum around (2011?) about the pressure relief valve and it’s purpose— made a lot of sense.
 

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Yes, I'd run more through it. The system holds 18 quarts. And now you have fresh Mobil 1 mixed with whatever was in there.
 

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So would it be a good maintenance item to rebuild the bypass every 100k miles?
 

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Discussion Starter #12
Not answering for Mark, I had thought about that earlier today. Once I get everything worked out I’ll be on a 60k Trans fluid change. I had thought about Rebuilding pressure release valve every other flush which would be 120k between valve rebuilds.
 

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I changed mine around 175K as a precaution (and because I had moved to a congested traffic area in FL towing boats). There is some risk involved of cross-threading and improper o-ring removal/replacement.
From my own experience, I don’t think the risk/benefit is worth it being a 100K-mile maintenance item for me.

I will need a rebuilt 4R100 soon enough and just include it then.

Thats just my 2 cents.
 

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Discussion Starter #14
So would “putting a big catch pan underneath, disconnect return line, hook up latex hose directed into bottle, start engine, and make sure only fluid coming out is through hose and not banjo fitting, pump about 1/2 gallon and shut off engine” be a simple enough test or am I over simplifying it?
 

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That pretty well sums it up.
 

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Discussion Starter #16
Update: to everyone, especially Mark—thank you!

•Got rebuild kit for by-pass pressure relief valve
•Rebuilt valve—it was a snap/very easy
•By-pass tube, banjo bolts lined up perfect
•Assemble snug-finger tight- per specs-24 ft.lbs.
•Hooked up latex hose to return line & ran test
•Fluid pumping through hose- no leaks at banjo
•Bought cheap dexron 3 to refill for start point
•Drained pan, add 7 qts Mobil 1-
•Pump out 1-1/2 gal. while Shift through all gears
•Pour in 6 qts. Mobil 1 - pump out 1-1/2 gal.
•Add 6 qts. Mobil 1 Check level - was on dipstick

PERFECT!! Just like you said Mark.

Tomorrow I’m taking out the OEM cooler and installing 6.0 cooler and spin on external filter.
Then I’ll recheck fluid level, run truck on road and check again.

Procedure works very slick! I probably didn’t need to test by-pass first but I was a little jumpy after dumping ATF all over my shop floor...Lol
 

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Discussion Starter #17
Couple things that might help someone first time:

4R100 fill tube is at a very shallow angle and I found tedious pouring in ATF slowly even with transmission funnel — I bought a larger funnel that a 1/2” latex hose would fit over spout, ran long latex hose down fill tube 10”, suspended funnel from engine hood with vice grips and s- hook (welding rod) towards front of the truck—- think “IV” pole” . Very easy to get to as I had the truck on jack stands. Could dump whole quart in quickly, fluid went in slow due to restriction of funnel spout/ and hose.

As procedure is based on measurements in (qts.) and out (approx. 1-1/2 gallons) I took a 2 gallon pail befor I started, found the line of Point where 1-1/2 gallon would fill. Took a welding rod and bent a loop in the middle and bent the ends down again (forming a big paper clip) that hung on inside of pail. When fluid reached loop - exactly 1-1/2 gallon. After each start/stop pull clip off small 2 gallon pail, dump into larger bucket, rehang clip on pail and ready for next start up, transfer of fluid.
 

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I have bookmarked this thread for future reference....Thanks
 

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Discussion Starter #19
I have bookmarked this thread for future reference....Thanks
Note: Be sure to find Marks Kovalsky’s original write up for changing fluid in the 4R100 if you haven’t already seen it.
 
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