When rebuilding a transmission, it is vitally important to also flush out the transmission cooler (which is either the lower part of the radiator, or a separate unit), and flush or replace the transmission cooler lines.

The Transmission Cooler (also known as Heat Exchanger) cools the transmission fluid from 400 - 500 degrees Fahrenheit to about 200 - 220 degrees Fahrenheit, circling through the fine wire mesh inside (see picture on the left, below) before the fluid goes back into the transmission.

The metal debris found inside the transmission is also contained in the transmission fluid, which travels through the cooler; this debris manifests itself in the fine wire mesh of the cooler and must be removed - otherwise it will be flushed back into the newly rebuilt transmission, and cause new damage.

Especially if small parts (as little as a dust corn) gets stuck in one of the many valves inside the valve body (the hydraulic ‘brain’ of the transmission), it can cause an immediate malfunction of the transmission.

We, of course, always flush out the cooler tank, and flush (or replace) the cooler lines.

For this purpose we have special “Hot Flush” machines with fine filters, which pump transmission fluid at 150 degrees Fahrenheit through the lines and the cooler for at least 2 hours.

During this process, we check and clean the fine flush filter, until the hot flush process does not get any more debris out of the cooler tank and lines.

The pictures on the left show:

• one of the machines,
• the connection to the cooler lines (blue and red; here hooked up to metal cooler lines on a Jeep Grand Cherokee)
• the radiator with both transmission and engine coolant lines
• samples of external transmission coolers (VW-type on top, old metal cooler with mesh wire exposed for demonstration off our counter in the lobby; shown with a replaced Mercedes-Benz transmission cooler line)
• and a close-up of a typical mesh wire inside a transmission cooler tank, from which the debris is flushed away

Read up on more in-depth information about the transmission diagnostic process, upgrades, and examples, on this web site.

SEE FILTER RESULTS BELOW!

“We used the first, manual ‘Model 100’ since 1995, upgraded to the ‘Model 200’ in 1997, and are now using several flushers of the latest, fully-automatic model ‘HF345S’ (see pictures above).

Over the years, the HotFlush machines have been perfected, and no vehicle in the shop for a transmission rebuild leaves the bay without having its transmission cooler / heat exchanger and hoses hotflushed.

The automatic flushing process ensures all debris is removed, and the filter kit allows us to show to the customer the amount of debris we found in the cooling system - very educational for the customer, and a competitive advantage for us to demonstrate how we differ from other transmission shops (it’s all in the details..).

We highly recommend the product, and demonstrate this by the extensive use of the machines in our 14-bay shop.”

Freddie Free

... and here is your best source for the machines: