Will a 3/8 Hose Fit an 11/16 Inch Fitting to Install a Transmission Cooler on a 2006 GMC Sierra

Updated 05/22/2018 | Published 05/20/2018

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Derale Series 8000 Plate-Fin Transmission Cooler Kit w/Barb Inlets - Class III - Efficient

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Derale Series 9000 Plate-Fin Transmission Cooler Kit w/ NPT Inlets - Class V - Extra Efficient

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Question:

Please excuse me if this is a ridiculous question, but does 3/8inch rubber hose fit properly over the slightly smaller 11/32inch cooler fitting, or must I use 11/32inch hose? The existing steel cooler lines from the transmission of my 2006 Sierra 4.3 are a standard 3/8inch O.D. I would prefer to simply use hose clamps and connect a cooler to the lines with 3/8 rubber hose, bypassing the factory radiator cooler. I greatly prefer fewer, simpler connections.

asked by: Larry

Expert Reply:

There is a lot of pressure within the transmission lines of a vehicle, including your 2006 GMC Sierra so the tighter the fit the better. If an 11/32 inch hose is needed then I would go with it over a 3/8.

Cooler # D13503 isn't really large enough or efficient enough to allow you to bypass the factory cooler. That is why I recommend installing the cooler as a supplemental unit. If the fitting on your radiator has a 5/8" hex head then you can use special fitting # D13018 and not have to cut and flare metal lines.

If you do want to bypass the factory cooler then I recommend a larger and more efficient cooler such as # D13614. The stacked plate design is the most efficient design.

expert reply by: Michael H