Please Help Cat D8L Transmission Overheating

Thanks for the suggestions Mark & Nige, I do have a brand new water pump for the old girl. I bought it at an auction with some other spare parts before another D8L went up for sale (I ended up not getting that one). I'll look in the book, but I take it that I'll have to drain the radiator to change out the pump? I also bought a new sender unit for the torque converter as well as gauge and built three pressure test jigs (0-60psi), (1-160psi), (0-600psi) and got more testing nipples. I'll keep you all updated !!

Seeing as you have already purchased a replacement TC temp sender unit it might pay you to install it first and do a few tests to see if it makes any difference to the TC Out temp readings on the gauge before going after the water pump. It won't cost you anything.

Before removing the water pump I would drain the coolant first and then flush the system out with plenty of clean water until the drain is running really clean.
Refill the system with water until you are 100% sure that everything is leak-free, then drain and refill fill with 50/50 premix (red) ELC as coolant would be my choice. Anything that meets Cat EC-1 specification would work.

Heard a mechanic talk about the elc coolant today and using it in older machines. Said some with a lot of corrosion it would cause them to leak because the elc would dissolve the corrosion and allow it to leak in weak spots. Is this true?

So from all the pictures of gauges you’ve shown I haven’t seen one where the trans is overheating. If the lights coming on and flickering before the gauge hits 250 that is a problem with the temp switch for the trans light which is not the same as the gauge sender.
The early d8n crawlers would run over 230 all the time due to an undersized cooler . Cat factory rep said if the light isn’t on it isn’t hot.
I think you have more of an electrical problem. Have a look at 7n9560 converter temp swtch

If R&I water pump, also remove trans cooler and clean the tubes. Hanging down low, all of the fine crap settles in the tubes.

Oldcatpusher said:

Heard a mechanic talk about the elc coolant today and using it in older machines. Said some with a lot of corrosion it would cause them to leak because the elc would dissolve the corrosion and allow it to leak in weak spots. Is this true?

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A good flush job will/should reveal those weak spots without the ELC. If it does leak, that's not to blame the ELC, there was an existing issue to begin with that should be repaired. The last two truck engines I inframed had junk radiators in addition to the worn out engine, rotting tubes and fins.

Mobiltech said:

If the lights coming on and flickering before the gauge hits 250 that is a problem with the temp switch for the trans light which is not the same as the gauge sender.
I think you have more of an electrical problem. Have a look at 7n9560 converter temp switch

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Good point, the high temp light and the gauge are fed from separate senders. 7N-9560 replaced by 203-3221, price about $65.

Hello Stabber.
I'm not in the league of these chaps that are busy solving your problem with your D8,but I'm starting to think that there isn't much wrong with the beast.
Your temp gauges aren't giving me stress.Infact,they look cool to me.
Before you pull the water pump,I'd be buggering about with that water flow sensor.They can lead a man a merry dance if,like me,he's no fitter.
As for the jiggery pokery she gave you the other day after it had been stood a few weeks,remember that she is a big,old girl with a hard life behind her.
Treat it like a woman........Start it up,don't touch it at all,climb off,and leave it idling for 15 minute at least.
Go and have a nice cup of tea or something before even thinking of returning to operate it.
You'll probably find it in a whole different frame of mind,and will find it performs far better.
As for the cooler thing,It costs nowt but time.You must do this task.It will give you an indication of the innards of your cooling system.A good clean up,flush out,and the correct bit of coolant additive and I think you are good to go.
You've done all the heart stopping jobs already with the filters and torque.
I feel you're on the home run,and perhaps your limited experience with the beast has got you on your nerves and abit over cautious.
Nowt wrong with that though.

Thank you all very much for your help so far - I wanted to give you all an update. This weekend I didn't have much time but I was able to test the transmission pressures with the new better resolution gauges. All tests were inline, unfortunately I left my sheet of paper at the ranch, but I will take a picture of the results and post them. After the tests I ran the dozer with the new temperature gauge and sender (didn't have a chance to run to cat and get the converter temp switch that controls the light). The new gauge / sending unit did not jump around and seemed to be working much better. It was about 98 deg F outside (hot hot) and I ran it for 25 minutes before the transmission temperature read 225 deg C and the light started flickering. It took 70 seconds for the light to turn off at high idle neutral and about 4.5 minutes for it to cool down to 100 deg C (again high idle neutral). The coolant flow light flickered throughout the operation (coolant full and cap tight). I waited for the beast to cool down and took off the water pump (what a miserable job). The old pump didn't look to be in bad shape and the gear / impeller seemed to be very well connected. I didn't have all the right seals and was completely beat, so I cleaned up everything, but did not install the new pump that I had in inventory. This week over lunch I will run to cat and get the seals as well as the converter temperature switch (7N9560). One other thing, there appears to be a check valve (relief valve) on the transmission oil cooler (read in book). Is this something that could be closed shut, or only partially opened? I love this old girl, but she has taken a couple years off my life ……

98F ambient ain't hot - I would guess our max here is somewhere 90+ for most of the year (tropical climate). We're currently sitting at 95F @ 2pm local time.
Don't misunderstand me, ambient temperatures like that put a premium on cooling system performance so you have to make sure everything's top notch, but a system in good order should be able to deal with it. The thing is that the engine coolant temperature isn't skyrocketing therefore it would appear as though the coolant side of the system isn't the problem.

Nice to hear that the TC Out gauge fluctuation has disappeared with the installation of a new temp gauge and sender. Check one box ……
TC high temp flickering @ 225F TC temp, is too low. It should not come on until at least 127-133C (260-270F), so the obvious next step is a replacement sender unit (note that 7N9560 is replaced by 203-3221)

4.5 minutes for the TC temp to drop from 225F (I assume the C in your post above is F) to 100C/212F is waaaaaay too long IMHO.
The TC temp should fall like a stone from whatever it is when you select neutral to a temperature say 10-15F above whatever the coolant temperature is within 60 seconds or preferably less with the engine @ HI. From that point it will fall more slowly as the oil & coolant temperatures get closer together.
You're already into the water pump so if that doesn't solve the problem then the issue would appear to be somewhere in the oil side of the powertrain circuit. I guess at that point it could be worth a look in the cooler core but I'd be interested to hear what others think.
Not sure what you are referring to regarding a check/bypass valve in the powertrain oil cooler circuit. How about taking a photo of what's in your book and post up what you are looking at.? It also might pay to quote the Cat Publication Number of the book you are using.

Nige,
Remove Transmission and Torque Converter Oil Cooler 1375-11 page 30
Remove adapter (2) and disconnect line (3) from the torque converter pressure relief valve at the oil cooler. Location: oil cooler bonnet (lower side beneath oil cooler) to water pump inlet elbow. Form # SENR2334 3408 Vehicular Engine for D8L Tractor / for use in service manual D8L Tractor SENR2329

Found it in the D&A. Weirdly there is no trace of it either on the powertrain oil lines or the powertrain cooler & mounting....and it doesn't appear in the SysOp for the powertrain oil system either.

I guess the next question is does the OP's tractor actually have that valve installed..?

Thanks Stan, I just took a photo of the book page as in the image below. Do you know the PN for the relief valve? I can't find it in my parts manual.

That's why in my post above I was asking you to check is that valve actually installed on your machine...… 'cos I can't find it in the Parts Manual either,

Part Manual: 7N7023 LINES GP-WATER S/N 53Y1 thru 3101-Up page 46B-47 and 47.01 SEBP 1356

Adapter #7N6604 <rectangular block , 2ea Gasket #1F4417 and adapter #8H9819> round-ish bolted to rectangular block with 2 plugs.

I cannot fine a breakdown of the relief valve in the parts manual or specifications in the service manual either.
Edit:
Looks like the service manual is referencing the torque converter 'outlet relief valve' as torque converter pressure relief valve (line #3) @ the oil cooler. No valve exist @ the oil cooler, just a 4-bolt flange, o-ring and bolts. Per my memory.

With it taking that long to cool I would pull the cooler and check it out I use a piece of brazing rod with out the flux to rod out each port. flush out the oil side too if you get anything out of it I would replace the cooler

what the book is telling you about the location of the torque relief is wrong. Its on the back of the converter housing with the line going to the cooler coming out of it and it is a rectangle block with 2 sending units in it, easy to get off only 3, 3/8" bolt hold it on the converter and its all O-ring seals.
You don't have to mess with it to clean/ change the tranny cooler. I say this from experience with our 8L that is also a 53Y.
The picture the book is showing with arrow #2 pointing at it is the drain valve for the cooling system that is part of the cooler

I'm planning on going out tomorrow after work and will take a picture and see if I can find it. Stupidly I didn't when I was working on it …

You mean this one..? #15 & #19 are the two TC temp senders, one for the gauge, the other for the high TC temp warning light.

Turbo,
Do you have any experience with those valves sticking shut? Do you know the PN for the valve body? I'll climb under her tomorrow and take a picture, but when I changed the sending unit, it looked like it was attached to that? Will I get a ton of oil out of the system if I take out the relief valve without draining the system? Can I run it without the relief valve to test it (put in a plug?).