5R55E overheating in 4hi while under load???

'00 Explorer XLT 4x4

So here's my problem...
The last three times I've been out on the trails my trans will over heat every time it climbs a prolonged semi-steep hill. Has always happened while in 4hi and in 1st gear...and will eventually get to the point that the trans seems to stall and the Ex will no longer move even though the motor will rev to around 2k+ rpms...at least until I let it cool down...

Last week I had a aux trans cooler installed (rated for 22k GVW) and changed fuild/filter but it didn't seem to help. Took it back to a trans shop today and reexplained to the guy the signs/symptoms of my problem, the guy told me that I'd have to leave it with him for 2-3 days and that it probably needs to be rebuilt. After reminding him that he rebuilt it 60k ago, and that it still drive/shifts just fine under normal use he remarked "sorry, don't know what else to tell you". I told him thanks for his time, but even if it needs to be rebuilt, since his only last 60k, I'll need to find somewhere else...

What could be the problem, and/or could I be missing???

Thanks for any input...

Is the fluid level okay? Typically for off-roading, you can overfill the transmission by say a quart or so because at steep grades, the pickup in the transmission will just suck in air and the vehicle will feel as if it just went to Neutral.

What temperature is the ATF reaching when it "overheats"?

It might have been a little low the first time, but I've made a special point of checking the fluid level at the start of a trip since...

Unknown true temp since I have yet to install a temp gauge...overheating noted by fuild boiling/spilling out the top...

During these "overheat" conditions, how is the engine coolant temperature?

And it doesnt do this in 4LO? only in 4HI?

Engine coolant temp seemed within normal operating range...unknown exact temp.

Have not tried to engage 4lo as only 50/50 chance of t-case fully engaging...half the time t-case gets stuck in between 4hi-4lo.

I know this response from me has been posted in probably 30 threads, I cannot stress these points enough. There can be other things that can cause your tranny to over heat, (Like low fluid as IZ said) but I believe that the design of the stock transmission cooler is not sufficient for the 5r55e in anything but normal street driving. Add a temp gauge and you will see what I mean. The conditions you describe are probably one of the worst scenarios, slow driving while climbing a hill your transmission torque converter is constantly slipping for torque.

when I first hooked up the temp gauge to my tranny it didn't take me long to order the heavy duty cooler, transgo shift kit, and ford upgrades. Actually one drive with my camper hooked up and I knew I needed to do something to make sure this tranny would last.

In brand new condition the 5r55e may run cool enough to handle the very small cooler that it comes with. however once the parts start to wear especially the EPC it starts to slip more and heat up more.


Things that I would do to any auto transmission
1) full synthetic mercon V (mobil 1 or similar)
2) heavy duty stacked plate style tranny cooler
3) external tranny filter
4) transmission temp gauge

Things I would do specifically for the 5r55e
1) Check/replace worn EPC
2) Ford upgrade (solenoid bracket, sep plate, etc..)
3) Transgo Shift kit using the heavy duty towing setup
4) adjust the bands properly


If anything is slipping that will cause heat, keeping the tranmission fluid below 200 deg will greatly increase the life of the tranny and the fluid.


In your case I would recommend also thinking about using 4lo to muliply the torque output of the tranny and decrease slippage.

Geesh when I started typing that response there was only one reply to this thread
of course then I took a phone call.

you should also flush your tranmission coolant lines to make sure they are not clogged in anyway, also do a visual check to make sure they are not bent or crimped closed

I had a HD cooler added, but due to size they mounted it directly in front of the radiator...could that location seriously decrease the efficiency of the new cooler?

Will be taking the Ex out again tomorrow, and will manually engage t-case into 4lo to see if it makes a difference...

that is exactly were you want it, however I would make sure they hooked it up in the correct order. The fluid should flow into the radiator, then the stock cooler, then the heavy duty cooler. It almost sounds like you have a flow problem with your cooler lines.

What about installing an electric fan on the aux cooler? The location of the stock secondary cooler is not in a very good location to get much air from the radiator fan. Having the HD cooler directly in front of the radiator is where its sapposed to be but to me it seems like it would cause more restriction of air going threw radiator.

I've been running an idea threw my head for a while now and think I will finally get started. My idea is to install an aux trans cooler inside the fender and use an electric brake blower to pull outside air in threw a side vent. I'm going to use what they call a knacaduct (spelling?) in racing on the back side of the vent connected to brake hose with an electric blower. Parts are all freebies so if nothing else it won't hurt anything.

Just looked at the lines/routing and it looks fine (radiator to new cooler, then back to trans)...the shop removed the stock cooler...

what type of cooler is it? stacked plate or tube style?

here is the difference first one is a tube, second is stacked plate (the stock one was a small stacked plate) If they put a tube style in it could have actually reduced your cooling.

It's about the same as this one (same GVW, and overall size). http://www.importperformancetrans.c...iption&item_id=XW21J0FHbvEydtTh1BBsdrg0wxlfFL

...I don't recall the exact brand...

ok do this, get a drain pan, and disconnect the return line from the cooler, put the line over the drain pan or bucket and have someone start the car, fluid should be flowing, be ready to shut off the car right away as you don't want to waste too much of that liquid gold mercon V


If there is nothing flowing, you found the problem, if there is we can move onto other possible problems.

Boomer12 said:

It's about the same as this one (same GVW, and overall size). http://www.importperformancetrans.c...iption&item_id=XW21J0FHbvEydtTh1BBsdrg0wxlfFL

...I don't recall the exact brand...

Click to expand...

that's a good one, but I would have left the stock cooler on as well