Summer of '69- Econoline Poptop Resto-Mod

[dwh]

Years ago I had a long discussion with an engineer from B&M. Temp was one of the topics discussed.

In terms of heat, he said in general, anything above 220F and the fluid starts to lose viscosity. At 320, viscosity same as water. At 420, it smokes and turns to varnish.

In terms of cooling, when the trans (or engine) cools off, moisture condenses inside and drips down into the oil. During operation, the machinery needs to get up to a temp sufficient to insure that all the moisture evaporates, so it doesn't build up in the oil.

As a result of that conversation, my standard auto trans setup goes like this:

Hot line out of torque converter, across temp sensor, through BigAss tranny cooler (to bring temp down), through radiator loop (to bring temp back up to engine temp), through remote 1qt filter, back into tranny (which dumps into the pan).

In this way, the engine thermostat regulates both engine and trans temp and they stay basically locked together.

 

[dwh]

The B&M (or Autometer) mechanical tranny temp sensor can be screwed into the center of a standard 1/2" plumbing T with the same threaded adapter that would be used to screw a temp sensor into an intake manifold. It places the temp sensor right in the center of the fluid flow.

Add flare fittings to both ends of the T, cut and flare the metal tranny cooler line, and that's how I tap the sensor into the hot/out line.

Gives a much more accurate read than sticking the sensor in the pan. The B&M guy said they just have people put it in the pan because it's easier for the home mechanic.

 

[Wes!]

The B&M (or Autometer) mechanical tranny temp sensor can be screwed into the center of a standard 1/2" plumbing T with the same threaded adapter that would be used to screw a temp sensor into an intake manifold. It places the temp sensor right in the center of the fluid flow.

Add flare fittings to both ends of the T, cut and flare the metal tranny cooler line, and that's how I tap the sensor into the hot/out line.

Gives a much more accurate read than sticking the sensor in the pan. The B&M guy said they just have people put it in the pan because it's easier for the home mechanic.

That's interesting he suggested that you put the sensor in the line instead of the pan. The guy I was talking with at the trans shop I got some parts from recommended instead to put it in the pan for a better reading of the overall trans temp. At the time I had bought a -6AN adapter that had a thermo switch in it (I still have it actually) to put in the feed line leaving the trans and going to the cooler to trigger the fan. Both that one and the one I have in the pan switch the fan on at 185* and back off at 165*.

Ultimatley the goal by next summer is to pull the C4 and drop in a 4r70w so that I will have an OD gear. But in the meantime I my take your setup to keep it happy. I think the threads for the radiator cooler are 1/2" flared, so I should be able to find a 1/2" flared to -6an fitting to route it back through there.

 

[Mwilliamshs]

Transmission fluid lubricates rotating bearings and bushings and meshing gears, sliding pistons and clutches, serves as the hyrdraulic fluid to pressurize clutches and bands as well as transfer the engines torque through the converter, and cools the whole thing, and is mostly made up of detergents to keep the works clean. It's the hardest working fluid in the vehicle. It's only capable of all those jobs when it's cool enough to cool (so the pan temp must be less than the output temp of the torque converter), warm enough to flow (most trans experts say get the fluid to 175* before working the trans hard) and clean enough to clean (the fluid has to be cleaner than the dirtiest part of the system). The fluid also has to get hot enough consistently to evaporate moisture from the system. The transmission is vented to the atmosphere so when it's hot and everything, including the fluid, expands some air is expelled through that vent. When the transmission cools again, that same volume of air will be drawn in through that vent. That air invariably contains moisture that will condense on a cold aluminum housing and become part of your transmission environment. If that moisture isn't "exhaled" its volume will increase with each heat cycle. The only way to reduce that volume is sufficiently heat the fluid to dehydrate it, or drain and replace the fluid.

In everyday driving, my C6 transmission runs right about coolant temperature thanks to being looped through my radiator. My OE 195° thermostat temperature rating makes sure it gets hot enough to drive moisture from the system. Under heavy loads like climbing grades or towing, that fluid does more work of every type, lubricating, hydraulic work under pressure, transferring energy, and cooling. That can increase the temperature of the fluid substantially. Leaving the torque converter, the hottest part of the transmission, the fluid can be 300°. That hot fluid is pumped through the radiator where it's rapidly cooled to the coolant temp, about 200°. Water cools 32x more effectively than air, so that 100° drop is important and possible only by liquid-to-liquid cooling. Next, that hot fluid is cooled as much as possible by an air-to-liquid cooler then returned to the transmission pan. Some cooling is possible in the pan but I don't count on that. Ideally, ATF lives between 175° and 300°. Colder and it won't work, hotter and it won't last. With two temperature sending units on a toggle switch to a single guage, I monitored both TC output and pan input and chose a cooler that keeps my fluid between about 195° and 280° in the hottest months, loaded for a trip and climbing Ozark roads on slow two-lane switchbacks behind RVs, and between 175° and 195° in Winter idling in traffic. That took some trial and error and 2 different coolers before I found what worked. I'm sure if I had a bigger engine or heavier van or drove more aggressively, I'd need a bigger cooler. I'm also sure that without AC or loaded less heavily or on flat ground, I could get by with a smaller one. I'm equally sure that unless I lived in a tropical climate, I would need that radiator loop to keep things within range year round. It cools very effectively and warms as necessary. Here in the South, having the air-to-liquid cooler last works because most of the year I need more cooling than heating and I block off some the grille for quicker warmups. In a colder climate, going air first then radiator works for the opposite reason.