To make sure you plumb the heater up correctly?

Erich

So you can't hook them up backwards.

On Mon, 11 Oct 2004, it was written:

I see a lot of people saying "So you can't hook it up backwards". That's
an answer that sounds like it makes sense, and perhaps there are a few
oddball cases where that's the reason, but mostly not. The heater *valve*
knows and cares which way the water flows; the heater *core* does not.

In fact, the main reason is to reduce noise. Noise? Yep. Just as sometimes
you can get whistles and squeals from household hot water taps and pipes
when you turn them on, the same can happen under certain circumstances in
an auto heater system if the right resonance happens to be set up. The
different-size pipe on inlet vs. outlet greatly reduces the opportunity
for these kinds of resonances to get started and propagate.

DS

So they can sell you a proper hose vs you going and buying a generic
chunk of heater hose.

Oh, they are not different like the intake and out hoses are different,
they are different so one end of the hose is smaller and one is larger
thus needing a molded hose.

So if you hook up the larger to the larger, you are going to get it
wrong for flow.

I think the physics behind it are like Daniel describes.  Noise.

Naw, who are we kidding, it's money for the molded hose....

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's