Get P0712 and P1738 codes. Transmission seems to shift okay, no other issues other than the codes, "transmission failure" and blinking OD light. Fluid level is good, no signs of burnt smell. Pulled lines off of the temperature controlled bypass valve for the transmission, little blue box, on the transmission lines and blew air through the radiator to see if it may have been clogged, air went through just fine and blew out the remainder of the fluid in the radiator.



Is there a way to test this temperature controlled bypass to see if it is working properly? I am thinking of just taking it out and to see if that changes my symptoms. Still warm enough here that it shouldn't effect the shifting of the transmission, at this time.
If this isn't the problem, what else could cause the transmission, to overheat when everything else seems to be working properly?
I did measure the bottom of the transmission pan with a thermal thermometer, when the code was set and got a reading of 290 degrees! Unless that is not a good way to check the temperature, it tells me the fluid is indeed getting overheated.
I am at a loss since there doesn't seem to be any other issues.

Oh, I noticed there was a arrow etched into the side of the blue box. Which transmission line should be connected to this port, the top or bottom line coming out of the transmission? Or does it matter? I didn't etch the arrow, it was done when the transmission was replaced several years ago.

 

Have you considered adding a trans temp gauge?

 

Yes, I have considered that option. However, I have to order one as no one in this area stocks transmission temp kits. Is there a manufacturer you recommend?

I believe the clutch pack may be slipping while the transmission is under load, pulling extra weight, but not during normal driving. This slipping is causing the overheat condition.

 

Does it have a tow package. It should have an extra cooler in front of radiator . I would at least tie wrap a ac temp gauge to that . Anything getting to 200 f is trouble .
I don't know why a aftermarket bypass would be a plus .
I have given aftermarket coolers to friends towing too much load , sometimes people will use it when they wont buy it . Why --I don't know .

 

Yes it does have the tow package installed on it.

I'm trying to understand why I am having this issue and if there is anything I can do to rectify it, short of rebuilding or replacing transmission.

Seems I am able to use truck as a normal daily driver, without any issues, I don't get a transmission failure error. However, if I put the truck under load the transmission error code comes up. Drove it yesterday and had no issues. Couple of days ago, I pulled a Honda Civic out of the sand, in reverse, not a hard pull, for about 50 yards and directly afterwards the transmission overheat error came on. Later that same day, I was dragging my dirt road, which I have done hundreds of times, and the transmission error came on again.

I don't feel or hear the transmission slipping and would think I would get an error indicating a difference between the input shaft speed and the output shaft speed, if this were happening.

If my thinking is wrong on any of this, please enlighten me.

I am going to remove the bypass valve and try to install a makeshift temp gauge, until I can get the one I want (something is better than nothing).

Have a three hundred mile trip to make on Friday and hoping I don't end up sitting on the side of the road....

 

Installed a temp gauge today. Wasn't able to locate a transmission temp gauge so adapted a water temp gauge into the line set. It should work until the correct gauge set comes in.

Drove truck around for a bit, about five miles or so and the temperature was sitting at about 150. Which led me to my next question, what is an average temperature for the transmission to operate at?

Oh, I also got rid of the bypass valve. I don't really see a reason to have it where I live. It isn't ever going to get cold enough here to require one.

 

I find that normal temp on mine runs around 160 f not doing any heavy towing . I take it very easy when hauling a heavy tractor , I do have the tow package. I am a firm believer in an extra trans cooler, I put a aftermarket drain pan on my trans so i could change fluid 4-5 quarts at a time then over some weeks i could run thru 20 quarts or so .
New fluid wont fix it but may prevent damage . It better be red and not smell burnt . Don't try to climb a mountain at 70 pulling a load . Slow it down and give it rest break to cool .

 

If you have the sensor in the cooler line, you can expect anywhere from 150-300°F, depending on operating conditions. And those are normal temperatures.

If you have the sensor in the test port, which is what I recommend, the average temperature will be about 150-200°F. The maximum continuous temperature is 220°F. You cann go up to 250°F for up to a half hour at a time.

 

If you have the sensor in the cooler line, you can expect anywhere from 150-300°F, depending on operating conditions. And those are normal temperatures.

If you have the sensor in the test port, which is what I recommend, the average temperature will be about 150-200°F. The maximum continuous temperature is 220°F. You can go up to 250°F for up to a half hour at a time.

 

Okay, I'm happy with the results I got today, but they don't add up with what I was expecting or what you all have said.

I drove a little over 300 miles today. Average outside temperature was probably around 70 - 75 degrees, average speed was about the same , some hills and all that. The water temp gauge that I am using starts at 130 degrees and the majority of the time the needle was sitting there, so temp was =< 130 degrees. On one hill the temp did rise to about 140 degrees and again while I was in a traffic jam, stop and go on the freeway. I even got home and hooked up my drag to see if that would raise the temp, outside temp is at 80 degrees. Pulling the drag it did raise the temp to about 145 degrees and pretty much held steady there.

The sensor is in the transmission line that feeds the radiator, so should be the temperature of the fluid leaving the transmission, not coming back from radiator. I am thinking the bypass valve was my problem and by taking it out of the system the fluid is now able to flow.

@Mark Kovalsky I read somewhere .... "problem with the test port is that it is a dead end fluid port. It will be slow to respond to temp changes."

The fluid is red and doesn't smell burnt, it is in good condition.

I think I will invest in the correct temperature sensor and gauge, install an additional trans cooler and drop the pan to change fluid and filter. Like Redfish said, this isn't going to fix any problems, but it may prevent them from getting any worse.

Was driving and thinking about ways to help cool the trans and thought about a off-the-wall thing that may work. What if you could run your condensation line from your AC to drain onto the trans cooler? It would be free water and help cool the cooler. Not sure if you could maintain the required drop for the water to flow, or prevent the air from blowing the water back up the tubing, but in my mind it sounded good....

 

And there is your "overheating" problem. Your sensor is in the wrong place.

Ford doesn't have temperature limits for the fluid leaving the trans to the cooler. From my years as an automatic transmission cooling engineer, I can tell you that anything below 320°F. IS ABSOLUTELY NORMAL. You will not be able to change this by adding more cooling, or replacing the bypass. It's normal. The only way to prevent high temperatures here is to never work the truck hard. And this is true for every vehicle with a torque converter.

Put the sensor in the test port on the side of the transmission. It's true that you won't see the wild temperature swings that happen in the cooler line, but so what? What does it gain you to know those temperature swings when you can't do anything about it?


Don't remove the bypass valve.

The return from the cooler is used to lube the rear half of the transmission. The purpose of the bypass is to maintain this lube flow if the cooler gets restricted. If this happens the trans runs hot, but doesn't fail. If there is no bypass and the cooler gets restricted your first clue that something is wrong is that the transmission self destructs.

You can get a bypass rebuild kit for very little money. Then you'll know that the bypass isn't the problem.

 

If this is true, how do you explain this chart? This is just one of many available from different manufacturers websites:



This makes sense, I guess a rebuild for the bypass would be a good idea.

However, it doesn't mean the bypass wasn't causing my overheating issue. If the bypass is faulty, it will bypass the trans cooler (or partially bypass the cooler) and the transmission will overheat, which is what was happening. I removed the bypass and the problem seems to have gone away.

As far as the temp measurements go, there seems to be some confusion, as to, where to measure the temperature. Is there a manufacturer document that states the proper place to measure for temperature variations? The factory temperature sensor for this transmission is part of the ribbon cable inside the transmission, sitting in the pan of fluid. What temperature is considered to be a over temp condition?

 

It's easy to explain that chart. It was developed in the 1960s for fluids and seals that existed then. It is completely false for modern fluids and materials. But it is an excellent sales tool for people selling cooling products.

That chart also refers to internal temperatures, not cooling line temperatures. You can't compare the two. I've seen 300°F in the cooler line while the internal sensor and test port were near 200°F. Would you call the trans temp 200 or 300 in this case? I say it's 200°F.

The Ford spec on transmission temperatures measured at the internal sensor is anything at or below 220°F is fine for continuous operation. You can run all day at 220°F with no heat problems. You can go up to 250°F for no more than a half hour at a time. A sensor in the test port will read very close to the internal sensor. I've measured this and compared them on many trucks and cars. That was part of my job as a cooling engineer for several years.

 

That is what I was eluding too earlier. Where you place, the temp sensor is going to give you different temperature readings.

I was surprised that my temperature reading spent most of the time in the =<130 degree mark, I just figured the line temperature reading would be lower than the test port temperature reading. Can you tell me where the actual test port is located on a 4r70w transmission? I don't want to remove the wrong bolt and hear a spring release inside the transmission!

I think we can all agree that anything you can do to decrease the temperature of the transmission is a good idea, an additional cooler can't hurt.

 

The test port on a 4R70W transmission is on the driver's side, towards the front of the trans, just above the pan. It has a black hex head plug in it from the factory.

An additional cooler CAN hurt. If it adds restriction there may be less flow to the coolers, and you'll have less cooling than without the additional cooler.