I am redoing a build in my 79. I wish to install a transmission cooler. I have heard two schools of thought on how to run the cooling lines. Some factory diagrams that I have seen show the output line from the transmission go to the cooler in the radiator and leave the radiator to go to the cooler then back to the transmission again. It has also been recommended to me to run the cooling lines straight from the transmission to go directly to the cooler, thereby bypassing the radiator altogether. The logic is that the heat from the radiator will heat up the transmission fluid. Which is the most optimal configuration?

I am running a 700-R4. The transmission temperature gets up to around 200-205F. I feel that is too hot. Optimal Temps should be around 180F.
I am running factory hardlines from the transmission to the radiator on my stock setup.

 

Green,

Both of those theories of routing lines are correct. I too had mixed thoughts on which was the best.

A few yrs ago, I had bought a small B&M trans cooler and was looking over the owner's manual. There was a phone number for tech, so I had a chat with the pros.
First thing he asked was, Where Do You Live?

He suggested that those living in the northern climes should route from tranny to Rad first, then Cooler, then Return. He went on to say that cold ATF temps can do almost as much damage as too hot of ATF. He even had a range in Fahrenheit that the ATF should stay in.

So, in answering your question, looking at your region, I would incorporate the Radiators heating / cooling first, then remote cooler.

A small trans cooler will fit nicely in front of the Rad or A/C condenser.
Never double up clamps on the hoses. And use only rubber hose distinctly labeled for ATF.

Updated additional info for A/C Vettes with condensers:
Note that in the B&M cooler document below, post 11, that generally the coolers come in 1- & 1/2-inch thickness and slim line 3/4-inch thickness. Hint: More is not better.
If you plan on installing the cooler in front of the A/C condenser, always use the thinner 3/4 inch thick unit. Due to the leading edge of C3 hoods, the nose of the hood will strike the thicker cooler when fully open.
(Not a clearance issue with the thinner unit)

 

Not to nitpick. Are you sure about that order? By having the remote cooler as the last stop, you could get too much cooling. If your target temp is 180 deg F, shouldn't the pass through the radiator be the last stop? The radiator temp is likely to be close to that target temp, and would act to adjust it in either direction. If you have an LS swap and a 210 degree radiator, the advice given might make more sense.

Is there such a thing as a thermostat for trans coolers?

 

what is thermostat? normal 79 is 195f probably for emissions?.. i would go 180f and see if that helps keep temperature lower?

 

I think the ATF in our antique transmissions has a very wide range of operational temperatures. I can tell you in the winter that the same ATF in my 1994 pickup never gets to 180* or even close on a subzero day. Yet that transmission has 180,000 miles on it. So as far as being too cold? I would not sweat that.
Modern transmissions may be more picky. Still, how many of us idle the car in the winter until you feel the ATF is up to temp? I would venture no one does that. Perhaps a thermostat is integrated in some modern vehicles transmissions.
I have never seen a caution in any car I've ever owned regarding making sure the ATF is at some min temp prior to driving. I have had some that will not shift into an overdrive gear until some min temp is met however.

 

I also would first look into what temperature thermostat you have. If 195 use a 180.

 

Thanks for all of your input. In my research I have also found thermal bypass valves as well. My engine runs pretty hot as it is. I have a 180F thermostat installed. Again, two options. Run the output from the transmission into a thermal valve set to 180F and the bypass to a cooler. Or, run the output of the transmission to the radiator and have the discharge side of the radiator run to a thermal bypass valve with the bypass routed to the cooler then back to the transmission?
I live in Southern Illinois. I will drive the Vette to the point before the snow falls and no salt on the roads. Like I said before, my transmission temps are over 210F. with the stock set up. I have a 10" lock up converter. The temperature sending unit is on the output side of the Trans. and mounted about 4" away from it.

Thanks again for of your input. It is extremely helpful.

 

Yes. I am sure about that order. That is from B&M performance transmission technician.
You would never get TOO MUCH cooling from that little remote unit. You are just trying to knock down the temps from 220+.

But just for sake of argument, lets reverse the order. Cooler first (not good) then to the hot radiator (not good either) then on to the tranny? (terrible)
You see what's wrong with that? That is incorrect.
The idea is to warm the ATF slightly via the bottom of the radiator which is warm, then cool the ATF by remote unit, before returning to the trans pan.

Tech guy also pointed out that southern areas could easily avoid using the lower radiator portion all together. And just run the cooler only.

For what its worth, my daily driver pickup will not shift into O.D. until the gauge is quite warm.

 

Bikespace wrote:

Is there a thermostat for transmission coolers?

I don't believe so. However, somewhere I read that the more expensive coolers did have some type of "by-pass" built into them.
Not sure how it worked but, cold ATF would flow through less rows of tubes (by-pass) until hot. At which time an alternate route was taken for full cooling effect.

I don't believe the cheaper, little 7 X 11 units have that option.

 

You said your engine runs hot..maybe time for a new radiator if tuned up and timed ok? If so that should help transmission temps.

 

No, I don't see what's wrong with that, based on the OP's question. He stated that he wants his trans fluid to be 180 degrees. The only regulated temperature anywhere in this system is at the thermostat on his engine, where coolant leaves the engine and goes in to the radiator. Set that to 180, and work backwards. Use the aux cooler first to knock down the temp, then go through the radiator last. If you can't have "too much cooling", then why do OEMs run the trans fluid through the (temp regulated) radiator at all? Shouldn't we all have massive, unregulated transmission coolers on our automatics?

OP stated that "optimal temp" is 180 F. My C3 coolant temp can stay right at 175 degrees all day as it passes through the thermostat, and I've done the experiment to prove it. I don't have any ATF to cool, though.

FWIW, here are B&M's instructions, which agree with @HeadsU.P.
https://static.summitracing.com/glob...er_techdoc.pdf

OP: Can you post a part number or link for that bypass valve? I can find ones for later transmissions, but I didn't find one for your 700-R4

 

Well Bikespace,
First thanks for the B&M drawing.

Second. Why does OEM pump the ATF to the Rad bottom first?
Yes, the O.P. wants the ATF to be at 180* . . . . . and eventually stay there.

To clarify what I said and what B&M tech recommends:
We are talking about first thing in the morning. Cold out, ATF might be below zero. Cold clutch packs. You sure don't want to send the cold ATF to a cooler.
Remember, cold ATF can also harm trans parts.
So, how do you warm that cold-cold ATF? Send it to the Rad first.

Some time in the 90's I believe, about every American vehicle on the road had a transmission cooler behind the front bumper. This was about the same time a little P.S. fluid cooler was up front also. Some engineer figured out, too hot of fluids reduces longevity of expensive parts.
And today, thanks to remote coolers, automatics & PS systems can go 100,000 miles before servicing.

Why use the OEM bottom of rad at all? Like B&M tech said: Where do you live?
So in conclusion, this whole post is regional.

 

Living in the Northeast where the temperatures can get to below 0 and above 100 degrees in the summer, I have run stand alone (no radiator cooling at all) tranny coolers always on many many cars since my first Nova SS in 1978 and I have never had a tranny failure with many transmissions having over 200k miles on them.

The ideal transmission temp is around 140-160 degrees (dig deep and you will find those numbers) which is very difficult to achieve, even with stand alone coolers. Long Double stack coolers have built in temp control, based on the viscosity of the fluid. I have used mostly Dana/Long Double Stack coolers for 40 years.

Currently, my 2008 300 Chrysler with a 28,000 GVW cooler in the grille doing all the cooling has 175,000 miles on it and my recently departed 2001 Grand Prix had 240,000 miles on the OEM tranny when I scrapped her, transmission shifting like new on the way to salvage yard.

Change the fluid/filter often, keep the fluid around 160 degrees and the tranny will last forever.