My 77 F250 460 C6 is used mainly for towing a 7k 5th wheel with about 1k of "stuff" crammed into it. The tranny runs at about 210 degrees under normal towing. When under load as in pulling a long uphill grade the temp climbs to at least 250 sometimes even higher. The temperature gauge-sending unit is in the tranny pan so it is measuring the actual fluid temperature.

The factory radiator cooler has been bypassed and a Hayden Econo-Cool 241015 tranny cooler has been installed in front of the radiator in its place. I also installed a Hayden Max-Cool 243012 tranny cooler with a Hayden Rapid-cool 1150cfm 16-inch electric fan under the vehicle near the tranny. Both of these tranny coolers are rated at 10k towing capacity and are the largest tranny coolers that Hayden makes. Also the tranny pan has been replaced by an after market oversized pan that has the tubes running through it for additional cooling.

I have checked the temp gauge for accuracy with another gauge and sending unit and even used an infrared thermometer. The tranny is actually getting that hot. I have to change the fluid every 12k because it is burning.

I had the tranny rebuilt a few years ago because of a clunk I was getting in the torque converter. Except for the clunk the original tranny was working great. I didn't have a temperature probe in the original tranny so I don't know how hot it was running, but the fluid never burnt in the old one. I had the tranny shop put in a HD converter and a shift kit. The tranny works great except for this excessive heating.

Every time I try to probe a tranny shop for answers they start quoting 1200 bucks to go through it. I am hoping some of you tranny guru's out there can give me some ideas. I did check the intermediate band adjustment and it was pretty close to spec's.

I am sorry about making this post so darn long, but I didn't what a bunch of guys posting telling me to put a tranny cooler on it. Hopefully somebody has some ideas.

I forgot to mention that it has a 3.07 rear end in it. Any thoughts about this high of a ratio causing the tranny to lug down putting an extra load on it?

 

I have used old a/c condensors as coolers.

They are as wide as the rad and fit nicely.
You need more air flow at the front cooler.
Use an electric fan and make sure the air flow is not obstructed, like with a spare tire or such.
Yes the gear ratio will have an affect on it.

 

That is a pretty low # ratio for towing a significant load. But then I guess you had that ratio before the rebuild. It would tend to put more mechanical strain on the tranny and the rest of the drive line, but your problem started after the rebuild.

210 degrees under normal towing is about high normal in my experience with my 94 F250 E4OD 4.10 4x4. Mine runs more like 190 to 200. 250 is pretty high and I usually only see this kind of temp once in a great while after a long hot tow and only as I backup my slight incline driveway for about 600 feet. Otherwise my temp guage coming out of the cooler shows no more than 220 and usually less.

Unless your engine is overheating I think you lost some cooling capacity bypassing the radiator cooler. Water to air coolers are MUCH more efficient than air to air. Most auxilliary coolers if I recall are for X###s of load assuming the factory cooler is in the loop. You might need to find a really big cooler to make up for your loss. I have seen some in years past in JC Whitney that were something like 30,000#s. A quick look at my current catalog shows several approaching that rating.

Still, I think the problem is with the rebuild and no radiator cooling. You never burned fluid before, but after the rebuild you burned. Did they also bypass the radiator at that time? probably well past the warranty period from the rebuilder so you got to figure out how to bandaid(really beeg cooler and or radiator cooler) the problem or you might need a proper rebuild.

Good Luck,

Jim Henderson

 

I agree with Jim that by totally bypassing the radiator cooling stage you may have lost some very efficient means of 'first stage' cooling. My thought is that if you have a 250 degree fluid temp then you should try to utilize 'everything' avaliable on the vehicle to get that temp down. If it were me I would make the radiator the first in line cooler off the pressure side, the cooler in front of the radiator the second and the the underside coller the third.

Additionallly, how these are interconnected is important so as to minimuize restrictions to the flow. Connecting them with steel tubing using large radius bends instead of rubber hose and elimination of any 90 degree fittings where possible will increase flow and the steel will dissipate heat also.

If you haven't replaced your fan clutch in some time, now may be the time to do so. It could be that with three restrictors in line with the fan air flow you need additional fan capacity (HD Clutch) to work against the restriction. Remember that the coolers effiency is only as good as the volume of air moving acress them.

 

I removed the radiator cooler because of the overheating problem. The engine temp went down after I removed it, but there was no significant change in the tranny temp. As far as the fan clutch is concerned it is all new. I tried a flex fan on the truck and found that it didn't work for towing because high rpms at low speed would flatten the fan out and no air would move through the radiator. I replaced the flex fan with a new fan clutch and a six blade fan. This thing sucks so much air through the radiator that at idle I can place a 8.5 X 11 inch sheet of copy paper over the tranny cooler and it sticks in place. I am moving so much air over both coolers that it is hard to believe that the problem is external to the tranny. I still believe that the did something wrong when the put the tranny back together and yes the warranty period on the tranny is long past.

 

My C6 ran about 210-220 when hauling. What gear are you in when pulling these grades? I found my tranny ran much hotter when I pulled grades in 3rd gear at 55mph, I backed down to 2nd gear at 45mph and the tranny was a lot happier. I am also bypassing the rad. cooler and using my condenser as a cooler instead.

 

OK, so sounds like air flow is not the problem so it must be the fluid is not flowing in adequate volume so as to dissipate the heat. So, you must have a restriction somewhere.

You mentioned disconnecting the outlet line and observing what you thought was adequate flow. I presume you did thid observation at both the outlet directly out of the tranny and compared it to be the same flow at the line connecting to the inlet of the tranny which would eliminate possibilities of any cooler(s) restriction.

But you know that disconnecting a line to check for flow is cheating. The difference is that the system is running open loop and not closed loop as in normal operation. Just suppose the restriction is internal to the tranny at or near the inlet.

Best way I can tell you to check for adequate flow in the closed loop mode is to measure by hand touch the difference in temperature between the inlet connection and outlet connection of 'Each' cooler and in final try to assess the differential temperature between the inlet connection of the first cooler and outlet connection of the last cooler. With all of that air across the coolers you cannot help but but realize a dramatic temperature difference between these two points if there is adequate flow.

 

That transmission can't be too happy about pulling all of that weight with that 3.07:1 rear gear. What size tire are you using?
The compromise would be giving up some (empty) cruise rpm's, and keep it happy while it is loaded.

 

I know the high rear end can't be good for towing, but I towed for twenty years with the thing, so I doubt it is causing the massive heat problem. But I do plan on trying to find a sterling to put in this summer. The tires are standard 9.50 X 16.5 street thread 30" tires.

I am going to research the possible fluid flow restriction this weekend. I think the stall speed question is answered since I am not feeling any slip, so the fluid flow is the most likely suspect. I will post and let everybody know as soon as I get the results.

 

< I am going to research the possible fluid flow restriction this weekend. >

Good go on doing that... I suspect taht you will find your flow to be inadequate to perform the required or desired heat excange..

I can't help you much here, that is, I'm a pure novice at all of this but just suppose you try and find some specs for what the fluid flow (volume wise) sholud be and you find a way to actually maesure it within a closed loop system, and you find it to be within specs... then what ya gonna do?

I suspect you have a most serious point within the tranny that is generating heat beyond your wildest imagination and if not corrected soon then it could destroy other components.

If this is not the case and it's just an overlaod and this is for you and others who might want to investigate the feasibility if a pump that is arranged in mid stream , so as to cross conduct hot fluid before it ever reachedwhich would allow for higher circulation of a partial of the fluid that has yet to reach the tranny and then pump it back through the coolers as sorta a second chance cooling process. This of course would only work if the capacity of the coolant system (basically max flow/tubing size) and maximum flow capacity of the coolant lines were not already at max.

Anyone ever tried this?

 

The Dana61 3.07 is great for running down the road. Just use a lower gear for hills. Was the transmission replaced at some point?

The number of clutches, control pressures, and servo levers make a big difference in slippage. The C6 is not known for efficiency like some of the later transmissions. Improved thrust bearings are a big difference between the C6 and later transmissions. The C6 can be retrofitted with thrust bearings instead of washers and clutch plates can be added.

Thermostatic valves can be used in the cooling circuit that will help configure the cooling system for summer and winter use.

 

I think you need to flow test the cooler lines. Take the return line off the transmisson and place it in a bottle. According to TCI and B&M the cooler lines must flow 1 quart in 20 seconds. If not the cooling system is pointless. Check the lines for sharp bends small pieces of rotted rubber hose can also plug them. I have also seen a return line clogged with a check ball! The ball came from my Hayden cooler it was the size of a pea and shut the flow off. You can also destroy the tranny bearings in the rear with no return flow.

 

The test you describe will not reveal even the problem you were having with the ball stuck in the inlet. Your test only serves to determine if the source to the tranny pump is unrestricted and that the pump itself is actually working. As I described in an earlier post (in this thread) the problem could well be a restriction at the inlet but the only way to find out if that is the problem is to measure the fluid flow in the closed loop mode(without the normal flow path interrupted). Unless he has access to a fairly accurate in-line flowmeter (electronic vane type or differential pressure type) to measure the flow then the second best way is to check the differential temperatures between the tranny outlet and the tranny inlet and do a comparison with the results of a similar vehicle under the same conditions. According to him he has a whole lot of extra external cooling capacity (external coolers, external fans, HD radiator fan and clutch), so his results as far as temperature drop between those two points should far exceed that of a similar vehicle in temperature drop. If no, then yep... a definite flow problem...probably internal.

 

The problem that I tried to equate to everybody in my original post was that the truck went 165k on the original tranny. All that I had for cooling was the factory radiator cooler and an added external cooler in front of the radiator that, if I can remember right, had about three tubes in it. It was possibly 6” tall and 10” long. The tranny ran about 190 to 220 degrees all of the time towing or not.

After the rebuild the tranny started running hot. The problem is that I didn’t tow with it until the warranty period was over. I had no idea it was going to run that hot while towing or I would have taken it back to the shop and complained. I replaced the external tranny cooler with the largest one I could buy to try to cool it down. When that didn’t work, I added another of the largest tranny coolers I could find and put it in series with the other one.

I just drove up to Vegas yesterday. The temperature in Baker was around 85 so it wasn’t hot. The engine temp stayed at 190 and I ran the baker grade in 2nd. I tried running 65mph and the tranny temp was 300 degrees by the time I was 2/3 of the way up the grade. I tried backing down to 55mph with the engine at 2800rpms but the tranny never cooled down. I have a hard time believing that the problem is external cooling when the external coolers have about 500 percent more cooling than before the rebuild and I never had a heating problem before the rebuild.

I did get under the truck before I left and visually inspected the cooler lines and found no kinks or sharp bends. I didn’t get a chance to check the flow. I will check it as soon as I get back home.

 

I would be looking at the convertor then.

If the heat was caused from slippage in the transmission there would be lots of junk in the pan and it would have gone South and stayed there.