Just curious why you want the bypass open on a Pantera water pump? I've had the Weiand on my Pantera for 10 years without issue. Warmup might have the temp needle climb and fall a couple of times, but engine gets to temp pretty quickly and then runs cool, regardless of the outside temps.
There are several threads on this subject on this forum. They are pretty old by now. Probably from around 2000.
As supplied new with the blocked bi-pass, the engine temp was erratic. Not something that I wanted in a Pantera.
In all honesty, I didn't know what was wrong initially until I read a thread here on this forum about the subject.
Upon opening the bypass in the pump, all returned to normal and relieved the additional tension associated with the running hot syndrome.
Interesting enough, I had a Boss 351 in my 68 Shelby GT350 for a few years. I had the pump installed as it came from Wieand.
In that application it showed none of the nasty tendencies it did in my Pantera.
It's a simple recommendation from me particularly to Pantera newbies. Use the bi-pass...you will probably live longer as a result.
The Wieand pump comes with it undrilled. I am not aware of the combinations of all of the others but I do believe that the Edelbrock has it drilled.
Here's one here. https://pantera.infopop.cc/top...er-pump-modifacation
There are others.