3N71B auto trans operating temp

[Charlie69]

Does any one know what a safe operating temperature range for 3N71B automatic transmission is?

 

Has any one had any experience with this type of cooler?

 

 

http://www.summitracing.com/parts/DER-13262/

 

I am thinking of installing one of these on the front of my frame rail under the radiator behind the apron.

[datzenmike]

Yeah that would work. Be sure it gets lots of air flow past it. In stop and go traffic it would be best to mount in front of the rad so the fan does the work.

 

If you have ever cut an auto tranny rad apart you'll find to your surprise, as I did, that there is no exotic finned heat exchanger in there. I cut a Chev one open and there is a copper pipe just long enough to join the two external fittings...... that's it! Anything would be better. I admit it is surrounded with water which conducts better than air but but it is near boiling temp too.

 

I had an old '82 Omni and only a standard rad for it. I pulled an old home air conditioner heat exchanger and ran hoses and gear clamps to the two lines and mounted it in front of the rad. It worked perfectly and I drove it across the US states from Ontario to BC. The fluid flow runs through the 'cooler' and back into the pan in the automatic so there is no pressure build up only flow. There is no risk of the 'cooler' blowing out and leaking. This is not like an engine oil cooler that runs in the 60 PSI range. Hell a heater core would work too if you reduce the pipe sizes, just mount in front of the rad where the air flows best. Because air does not hold much heat you need air flow passing past the fins for best heat transfer.

 

 

Mine looked like this one if it was half as thin and twice as long. Mine was 2" by 5" by 18-20" and was likely way big enough.

 

 

 

Flat and thin would work best I think.

 

 

 

 

Best of all they are cheap and plentiful at scrap dealers and cost scrap copper prices. Get ones with copper inlets/outlets that will fit your hoses

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[Charlie69]

Hi Mike thank you for the fast reply. If you go to the link you will see these are marked as a "passive cooler, litle or no air flow needed".

 

I build computers and have used in the past a lot of "passive cooling heat sinks" for various chip & ram cooling. Any time you add a fan to a Passive cooler it does cool better.

 

I am thinking of hooking up a temp gauge on my transmission. This why I am wondering about the safe operating operating temp of the 3N71B transmission.

[datzenmike]

I would say about 180 or so under normal condition and 210- 220 when it gets hot, it can go to 280-300 but not for long. Generally if the temp is kept around 180 which it is designed for, it will last almost indefinitely (100K miles or more). For every 20 degrees above, this cut this in half. So if you run near rad temps half the time and 220 in the summer stop and go and higher if carrying a load or towing it will be much less. You should NEVER tow because it generates huge amounts of heat which breaks down the ATF.

 

Keep the outer case of the tranny clean of oil and mud so it can radiate heat as well. Change every 30K or 5 years, oftener if in hot, city driving. Do not tow without an external cooler, the bigger the better.

 

The biggest cause of tranny failure is over heating, next is owners that don't change their fluid.

[Charlie69]

Hi Mike I really appreciate your knowledge and willingness to share & help everyone.

 

This transmission I am going to run I pulled out of a 1976 620 pickup with the motor. The odometer showed 168000 miles. When my trrans guy tor it down he said it was in great shape so he put in a trans rebuild kit & a new torque convertor. This is why I am asking these questions, I want to besure that what ever cooler I run is doing its job.

 

I will post up running temps on the trans when I get this truck finished & on the road.

 

Thank you again Mike for sharing your knowledge.