John,

Measure from the top of the radiator grill to the ground. Then subtract from that the distance from the top of the tank to the ground. Add a few inches. 

You don't want it to be so tall that you can't get a good pour between the top of the bong and the roof. 

Jim

On Nov 29, 2012, at 7:37 PM, JRodgers <jrodgers113@GMAIL.COM> wrote:

> Have to change the coolant in both of my '88GL's. Have decided to make a
> "Libby Bong" for the task - but - I have found most of the recommended
> dimensions for the bong - the one that eludes me is  how long or tall to
> make it. I know instructions say tall enough to be over the height of
> the radiator vent - but just how tall/long/high is that? Does anyone know??
> 
> Bong PVC pipe - 2in. dia by "X"in long?
> 
> Other parts --
> Plumbqwik Reducer - 2 in down ti 1-1/2 in.
> Nylon tube - 1/2 dia X  "X" in. long
> Rubber band
> Sticky/pucky to seal nylon tube to te PVC pipe.
> 
> Thanks,
> 
> John Rodgers