I have a slight leak at my out flow barb on my B&M 70264, I think it's just a loose hose clamp there. I installed this trans cooler in 01/2015 at 152,336 mileage, bypassing my brand new radiator's trans cooling feature. This minor leak brings up the perfect time to re-route my lines and incorporate the radiator cooling portion in line with the B&M cooler, rather than bypassing. Not the place to discuss pros/cons of this method.

I noticed just now that the caps that were capping off the barbs on the radiator's portion of the trans cooler, are no longer attached and missing. I can 100% confirm they were in fact attached and in place, (albeit a bit cracked looking), on 11/5/2016 at 164560 mileage, when I drained the radiator to install a new thermostat and hoses.

Question: what would be the best way to "clean" out the radiator's portion of the trans cooler since it's been exposed to the elements etc. for a month and ~ 1,500 miles? I'm thinking hook up a garden hose and flush out the trans cooler portion, followed by excessive air drying and air compressor "blowings".

Regardless of pros/cons of running my trans cooler in line with my rad, am I opening a can of worms by potentially introducing foreign objects into my trans fluid because I didn't flush it properly?

Others will chime in, but I think you just need to run the garden hose water through it to clear out dust/bugs etc. Let it drip dry a bit (maybe park on an incline?) and proceed with connecting your lines.

If I recall, the transmission is not "sealed". So to the transmission, any bit of water left in the radiator reservoir after cleaning will just be handled the same as condensation moisture built up in the trans itself from parking overnight or something.

Trans runs hot enough to just boil/evaporate any water drops that get caught in the flow.

But my knowledge experience is limited.

Flushing with garden hose a t low pressure will be fine.
Not much stuff if any will have got in there.

Blow it out and let it sit overnight and it should be dry.
Or drive it on a dry day and the heat from the rad will dry it out.

I use paint thinner or mineral spirits in conjunction with an oil suction gun to flush the cooler, followed by compressed air. Water isn't a very good solvent for ATF.