overheating 75 supercab
Cargo Master
Joined: Dec 2008
Posts: 3,211
Likes: 321
From: SW PA
Trans cooling circuit is routed as follows and is the way its done by all oem manufacturers.
Trans to radiator
radiator to aux cooler
aux cooler to trans
This allows the hot output from the trans to drop the most heat to the radiator and also always the coolest return to the trans. If you go as prescribed above you lose the initial high temp cooling ability. You actually heat the fluid to coolant temp before returning to the transmission which isn't good. The gauge doesn't belong in the cooling circuit unless you have two gauges and are measuring cooling deltas. The gauge needs to be in the pan or some install in the test port. Remember the C6 has no lock up so torque converter output temp can be up to 70 degrees higher than sump temperature.
Trans to radiator
radiator to aux cooler
aux cooler to trans
This allows the hot output from the trans to drop the most heat to the radiator and also always the coolest return to the trans. If you go as prescribed above you lose the initial high temp cooling ability. You actually heat the fluid to coolant temp before returning to the transmission which isn't good. The gauge doesn't belong in the cooling circuit unless you have two gauges and are measuring cooling deltas. The gauge needs to be in the pan or some install in the test port. Remember the C6 has no lock up so torque converter output temp can be up to 70 degrees higher than sump temperature.
If the OEM's do it that way, hard to argue.
However, it is my understanding that just like engine oil temps, transmission oil temps also have a sweet spot.
By design, this is close to the engine coolant temp, or around 180-190F. The reason to hit the rad cooler last is because there is the best chance to get your trans temp closer to ideal, which could mean to actually increase the trans fluid temperature if the aux cooler is too large.
Laughing Gas
Joined: May 2011
Posts: 855
Likes: 40
From: SoCal
What about fan and shroud spacing? When I was running a stock clutch fan on my Bronco it worked best when the fan was located just inside of the shroud. Not to close to the radiator. Also the rubber deflectors on the core support are critical to forcing air through the radiator and not around it.
Post Fiend
Joined: Feb 2008
Posts: 5,831
Likes: 121
From: St Albert, Alberta
Ok,
I've tried adding fuel, its only a 2bbl so its pretty straitforward. No change. I also have tried more or less ignition timing, no change. It has a pertronix, so I think that's pretty reliable too. I haven't put in a timing chain, but it doesn't have much slop, so I think that's a reach. I'm going to start with a RS stat, and I think I might put the puller back on it that I already have. That won't give me room for a clutch fan though, so either back to the OE fan (my first choice) or nix the puller and go to a clutch fan? Votes? To the reply above, I've often wondered about the flex fan at speed, because I've been suspicious that it created turbulence and hurt air flow.
For the records: Coolant is very clean, I've had the heads off a few times, and I can vouch for the block and the flush. I've added surfactin as a crazy try also. I will add a trans temp guage, and I think this might be part of my problem, but I'm nervous that the trans temp will be pretty high with only an air cooler. Might try it and see.
I've got a rollback made out of a 64 f-350, with a healthy 312, 4spd, 3.73 gears. Been through the mountains over 20,000lbs with that a bunch, and Ive got nearly 300k on it now with only a 4core rad, shroud, and flex fan, (which I've never replaced) and it will barely pass 200deg.
I appreciate all the help here. I've been getting to the 3G conversion, but almost every trip my 65amper Napa rebuild fails, so I keep getting free ones. No excuse. Sometimes bearings, sometimes no charge, but I'm on like the 4th one in 50k miles. Shame about the quality of that stuff these days.
I've tried adding fuel, its only a 2bbl so its pretty straitforward. No change. I also have tried more or less ignition timing, no change. It has a pertronix, so I think that's pretty reliable too. I haven't put in a timing chain, but it doesn't have much slop, so I think that's a reach. I'm going to start with a RS stat, and I think I might put the puller back on it that I already have. That won't give me room for a clutch fan though, so either back to the OE fan (my first choice) or nix the puller and go to a clutch fan? Votes? To the reply above, I've often wondered about the flex fan at speed, because I've been suspicious that it created turbulence and hurt air flow.
For the records: Coolant is very clean, I've had the heads off a few times, and I can vouch for the block and the flush. I've added surfactin as a crazy try also. I will add a trans temp guage, and I think this might be part of my problem, but I'm nervous that the trans temp will be pretty high with only an air cooler. Might try it and see.
I've got a rollback made out of a 64 f-350, with a healthy 312, 4spd, 3.73 gears. Been through the mountains over 20,000lbs with that a bunch, and Ive got nearly 300k on it now with only a 4core rad, shroud, and flex fan, (which I've never replaced) and it will barely pass 200deg.
I appreciate all the help here. I've been getting to the 3G conversion, but almost every trip my 65amper Napa rebuild fails, so I keep getting free ones. No excuse. Sometimes bearings, sometimes no charge, but I'm on like the 4th one in 50k miles. Shame about the quality of that stuff these days.
Also install the heat core shut off this will have a big impact as you won't be dumping near engine temp coolant into the cooled coolant returning from the rad.
FTE Emeritus
Joined: Jan 2006
Posts: 2,288
Likes: 200
From: springfield Missouri area
About the water pump, I've owned the truck for 20 years, and about 60k miles. I've never replaced it, but it don't leak, flows well (visually in radiator) and seems happy. I've been hesitant to touch it, see the comment above about the alternator. Its hard to beat a known good part. If I DID have to replace it, any one use a high flow on these?
And is other than fuel mileage, what is the benefit of a flex fan over the fixed OE? I dislike the noise of the OE at road speed, but I got a bitchin radio and 2 backseat teenagers, so that might be less of a problem than its worth to fix.
And is other than fuel mileage, what is the benefit of a flex fan over the fixed OE? I dislike the noise of the OE at road speed, but I got a bitchin radio and 2 backseat teenagers, so that might be less of a problem than its worth to fix.
Back in the 80's I worked at a shop that had a similar issue. Delivery van, checked everything , just like you have, had good flow at idle but would overheat out on the deliveries. We finally pulled the water pump off because we had exhausted all other options. The water pump fins had rusted off and was just a flat plate with little nubs left for the fins. Only one I have ever seen that way in my forty + years as a technician. Just a thought.
Fleet Owner
Joined: Jan 2004
Posts: 26,007
Likes: 575
From: Brentwood,CA
What about fan and shroud spacing? When I was running a stock clutch fan on my Bronco it worked best when the fan was located just inside of the shroud. Not to close to the radiator. Also the rubber deflectors on the core support are critical to forcing air through the radiator and not around it.
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New User
Joined: Jul 2020
Posts: 20
Likes: 0
Man, this is a great thread, for me at least. Clever, I'm not worried about volume of air flow, just the turbulence. I'm putting the stock fan back on asap, per the reply above about the flex fan. I used to have a bike rack on the front of this, which I moved to the rear. You could see right through it, but it was totally undriveable with heat, so it must have created dead air. On that trip, we were in Nova Scotia, and I had the stock fan still, and it stayed cool most of the trip (closer to 200deg), and now with the flex fan its hot again. I attributed it to driving in mountains vs ocean flatlands, but who knows. Perhaps I missed that clue. I will probably buy a pan and gauge soon for the trans, but that makes good sense too, because I'm sure the trans is warm at speed under load with that much frontal area. Fluid is clean and smells good, but can't hurt to know.
I'm not putting the puller back on for road speed airflow, but it will also run warm sitting in traffic with the ac on. Turn off the ac, never gets over 200. Put it in neutral and hold it 2000rpm helps a little. Plus the A/C sucks sitting still.
I'm not putting the puller back on for road speed airflow, but it will also run warm sitting in traffic with the ac on. Turn off the ac, never gets over 200. Put it in neutral and hold it 2000rpm helps a little. Plus the A/C sucks sitting still.
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New User
Joined: Jul 2020
Posts: 20
Likes: 0
overheating supercab revisited
Guys,
Wanted to post some updates on this if it helps anyone in the future. I took the flex fan off my truck, and put the stock fixed 5 blade back on (because I had it easy available), and it flat out took 20deg out of it at highway speeds. Just drove it to NC with my camper, and you could run 75mph with temps never touching 200deg on a 90deg day. I then put in the RS thermostat, which did seem to make it happier in stop and go. I am still getting some higher temps sitting still with the AC on, but I put my puller fan back in, and it will idle for a long time under 210 now, so I'm pretty happy. I still need a new shroud, as mine is all taped/ zip tied together. For what its worth, the flex fan makes sense, but I've never had this experience before. Thanks for all the feedback. If anyone has a shroud, lmk. I need the narrower one, number on the shroud is D3TA-8146-BA.
Wanted to post some updates on this if it helps anyone in the future. I took the flex fan off my truck, and put the stock fixed 5 blade back on (because I had it easy available), and it flat out took 20deg out of it at highway speeds. Just drove it to NC with my camper, and you could run 75mph with temps never touching 200deg on a 90deg day. I then put in the RS thermostat, which did seem to make it happier in stop and go. I am still getting some higher temps sitting still with the AC on, but I put my puller fan back in, and it will idle for a long time under 210 now, so I'm pretty happy. I still need a new shroud, as mine is all taped/ zip tied together. For what its worth, the flex fan makes sense, but I've never had this experience before. Thanks for all the feedback. If anyone has a shroud, lmk. I need the narrower one, number on the shroud is D3TA-8146-BA.
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