How do you flush trans cooler in radiator after trans rebuild?


May 24, 2001
I have seen aerosol products for flushing, but wasnt sure if anyone had any luck with them. Would removing the radiator and having the cooler flushed be the only option?
Trans fluid is extremely detergent, and pretty much cleans out the cooler itself. But, if you want all of the old fluid out of th rad., take a piece of an old line and tighten it into one of the cooler lin holes, remove the other, and hose clamp a piece of 3/8" fuel hose over the piece of steel line. BLow through this with your air compressor on low pressure slowly increasing until you get only air. Trust me it makes a mess, but it works.
THe other way would be to go to a repair shop and have a trans tech run on the cooler. It hooks up to the cooler lines and forces old fluid out and new fluid in...this thing has virtually eliminated the tranny service of old. It changes 100% of the fluid. Take my advice don't let those a**holes sell you any additives. You dont need them. the fluid is detergent enough. Additives=slippage
Doing as National says in the first part will work very well . if you would like you can flush clean fluid thru or even a can of brakleen thru it.
National has it covered ............I am not fond of the flush machines... but thats me

I always thought that there is enought cleaning action in trans fluid to make flushing a valid cleaning.

The first trans I replaced, I just hooked up a drill powered pump and pumped lacquer thinner through the lines, from the ends that hook up to the trans so that I would get everything. I pumped about a quart, that I continued to cycle from the same container for several minutes. Then I switched to a fresh container, it ran clear almost immediately. I was convinced that my lines and cooler were clean, until I read many posts claiming on MUST replace the cooler.

Except for where the lines run CLOSE to exhaust and may cook fluid, I now believe that my technique is successful.
I LIKE the 1/4" steel cable idea I recently read about. Hook one end to a drill and run it through and it sure seems to be a serious line cleanning machine.

I finished up by running some trans fluid through the lines.

NOW how does one flush the converter? - here comes another thread.
You may be thinking about the engine oil cooler being a "must" to replace when you get bearing/engine damage. Not the tranny cooler.
This is because (or so I have been told) can't be properly flushed to get all the metal out due to its design.