A-518 in-line thermo sensor

["Mad Max"]

on an A-518 and 727, the beginning transmission cooler line comes out of the forward port on the case, makes a 90* turn, goes a couple inches and makes another 90* turn, then over and up to the heat exchanger. Between those two first 90* turns is a bung welded onto the line itself, and a thermo sensor mounted there.



My first question is, what does that sensor 'control'?



Second is what would be the adverse affects of mounting that thermo sensor in the pan (more or less like a transmission temp gauge would be mounted)?





Thx,

- Sam

 

[Philip]

That switch is a high temp switch. If it sees a converter out temp of 275 the switch opens telling the PCM to drop out of OD. When the temp drops below 245 the switch resets and the PCM allows OD then.



Mounted in the pan would make the switch inop. If you would ever see temps of 275 inside the pan. That would mean the trans or the whole truck melted.

 

[Flexiheep]

Philip has it above.

I pulled mine out and installed my Isspro sender there, it is still sitting zip-tied to the wire harness under the truck. I figure I care a bit more than the computer does, so I just watch it and pull it out of OD if I need to.

 

[cerberusiam]

Mounted in the pan would make the switch inop. If you would ever see temps of 275 inside the pan. That would mean the trans or the whole truck melted.

Not really, sounded good though. :-laf



Starting in MY99 the temp sensor move to the pan and is set about 260 degrees. If one is running ATF+4 as recommended that is well within its operational parameters.



Whether or not 18-20 year olds seals are up to the task is another question.



The hottest fluid will always be right there on the front output line so it makes a good place to mount a gauge to monitor what is going on.

 

["Mad Max"]

alright soooo unplugging it would not cause the system to 'inop' itself, meaning the OD system will still work if one of the sensors is unplugged, ja?



I'm building a daily-driver 6BT Ramcharger and I'm converting transmission cooler system to 3/8" hardline - a bit of an experiment I've been wanting to run - and as such the line fitting becomes... . difficult to replicate. I may just eliminate the switch all together - this RC won't be towing anything heavy enough to cause that much heat, and like you said Flex I'll probably be popping out of overdrive manually before the computer will. Plus, I've had a long field study going on for the 'what to do when the computer craps out and there aren't any left' scenario, so this plays into that too.



Thanks for the replies fellas



- Sam

 

[Flexiheep]

Sam,

If you don't mind, why are you changing out the cooler lines to something smaller?

 

["Mad Max"]

couple reasons, mostly a theory I have had for a long time that these trucks do not need a 1/2" line to keep the transmission's cool. My theory is a 3/8" line will do the job equally as well, plus, add in the fact that buying new 1/2" lines is nearly impossible, coupled with the same issues with new 1/2" coolers and accessories.



I've been asking every transmission shop and forum for a couple years now and noone can tell me for a fact that it won't work. Actually most of the feedback is "I can't think of any reason why it wouldn't work". So, I guess I'll be the first to try it, at least to post the results. I ain't skee'rd



It all comes down to the transmission fittings - a 1/2" line is huge compared to the opening in the brass fitting it's plugged into. The transmission lines/cooler, etc can only flow the fluid as fast as the smallest point in the system, and the brass fittings are it. The line could care less how big it is unless it's smaller than the fitting.



The i. d. of the 3/8" hard lines is bigger than the hole through the stock 1/2" brass fittings on the transmission, which is what got me thinking about all this to start with. The opening in the 3/8" brass fittings, however, are just a hair smaller than the 1/2" fittings, and my personal risk assessment is... it won't make any difference - that is what I'm going to "test".



In other words... if my theory is correct, the size of the 1/2" hard line is not a factor in how well the transmission is cooled - a 3/8" line will do equally as well. That is my theory and stickin' to it.



I have found NAPA carries the brass fittings to replace the two on the transmission and the two on the heat exchanger as a single-stage to 3/8" system - IOW the transmission and exchanger threads are the same but the line threads are "3/8". - no adaptors or fabrication - just a simple fitting swap.



If my RC's transmission stays nice and cool (... and I have the perfect 'hill' to test it - The Rocky Mountains, I-70 west up to and back from Eisenhour Tunnel ) then I'll know the 3/8" 'system' is capable of doing the job, and I'll have gained all of the aftermarket/local parts store availability for anything I need for a 3/8" system. I am also thinking of testing the theory on my tug boat, swapping to 3/8" line and then pulling something big and heavy. Of course both my RC and my tug boat have great converters, and the RC actually has a 47RH with lockup, so producing heat is already minimized.



I take 100% accountability for this whole deal, and I recognize it may not work. That's partly how I got my call sign - I try stuff that may not work, which some think is silly and stupid, but I call it pioneering and is how I try to keep my rigs on the road without having to spend hugh cabbage fabricating things that could otherwise be bought locally on the cheap.



Less and less is available from the dealerships, so I'm trying to find ways around particular items on our old rigs. Things like heater controls, vacuum ports, even the factory computer - when those 'go'... what do we replace them with? I'm trying to find ways around all of the limfacs on our trucks, and the transmission cooler lines are just one of 'em .



I'm also looking at converting my 1st gen fuel heater and filter systems to 24-valve style, even aftermarket off-the-shelf - I think I saw someone do it - been searching the threads - I'll find it.



More to follow



- Sam

 

[Flexiheep]

I always figured that 1/2" line was used due to the length of the runs the lines made. I bet a stock system runs almost 25 feet, there is a lot of resistance to flow in that length (I haven't added in the runs of tube if you have an under bed cooler).



I bet the factory made it 1/2 inch because of the length of the system, not the flow rate being higher than normal for a transmission. The resistance to fluid flow due to wall friction over a long length can easily be larger than that of 1 or 2 restrictive fittings.



3/8" would be just fine I bet if you shortened the distance the fluid travels.





I wonder if Mystery Man has any insight on the use of 1/2" transmission cooler lines?

 

[JDancoe]

To add to the mix-- This past summer my brother & I retrofitted a 92 CTD into a 1986 D-250.
We fabbed the cooler lines out of 1/2" copper which we ran along the inside of the right frame rail, then across the front crossmember. We used about 11 feet of copper, and about 8 feet of 3/8" of rubber line for flexible connections from the frame to the trans.
return fitting, and from the engine mounted oil/water cooler to the frame, and to the factory cooler mounted at the left top of the radiator.
I also installed a deeper transmission pan from a 2006 Ram CTD, and machined an extension block to set the filter deeper.
We also installed a new Isspro trans temp. gauge in the pan, and during several trips up & down through the Colorado mountains, and a return trip to his home in Mississippi, he never saw transmission temps above 160 deg. In fact, I'm wondering if the trans temps might be too cool during the colder weather.
Possibly we should re-route the flow through the air/oil cooler first, and then through the oil/water cooler for reheat?
Oh, by the way, we did pull the temp gauge and check it against a calibrated thermometer. It's reading correctly.
Jack Dancoe