Hey Bolt, welcome to classicbroncos! Sorry to hear you're having an issue after what should have been a simple pump swap.
Just switched out a stocker gmb pump (leaking with less than 200 miles) to a high flow gmb pump and I’ve had nothing but problems.
Already sounds like the pump(s) are defective. Leaking out the weep hole at 200 miles is an example of the typical imported crap/junk we're being given these days. Lots of discussions about it with other parts. Not so much the water pumps.
But I thought GMB was Japanese? If so, I'm surprised that you got one, or two bad ones.
Is it leaking from the weep hole though? Or a gasket surface?
Temp now running 190+ at idle so I dropped a 165 stat in which didn’t help.
No, I wouldn't have expected it to. As said, 190 isn't much. But the fact that it did not do it before you made the change is strange. Maybe you knocked the coolant temp sensor wire while working on the pump and it changed the old readings? That's a long shot I know, but stranger things have happened.
It never got over 180 with the stock pump even if the coolant was a quart low.
Yeah, I've run mine almost empty and it did not overheat until I was at least 2/3 of a radiator low on coolant.
Did you change the ignition timing in any way perhaps? Did you mess with the distributor, or anything else for that matter?
I'm thinking about going back to a stock pump.
You could do that. It does not sound like you were having trouble with a stock replacement, but no matter what, you're having trouble with the quality of the pumps at this point. Leaking so soon? Not an engine issue, but a pump quality issue.
Unless it was indeed a gasket that was leaking. In that case, it could be a warped pump housing, or a warped engine housing.
Temp drops immediately in the wind. I figure it’s an airflow issue but confused because I didn’t have this issue prior to the high flow.
If you changed the water pump only, it's not an air flow issue. Remember that your water pump is running faster at this point too.
What about the fan? Double check it to make sure it's not on backwards.
If you're running a v-belt system, then the pump and fan turn clockwise. Make sure that the fins are pointing in the right direction.
About the pump, any chance that you didn't notice a possible difference in design/shape from your old one to the new one? Could it be a reverse rotation pump that's being used in a standard rotation setup?
Either the fan or the pump running backwards of intended would do strange things.
Ron Davis radiator with aluminum shroud: stock fan.
Should be good I would think. Maybe you also got a bad new thermostat?
That's the problem with the parts these days. You used to be able to count on a new part working so you could check it off the list of culprits. But now you not only have to look at the old parts with a keen eye, but the new ones as well.
Lots of bad thermostats around here too.
I'm always on about "coincidental failures" on our rigs. Where you go to fix one thing, and something else entirely decides to fail at that same time. So in your case, changing a water pump could be accompanied by a failing distributor timing mechanism, retarding the timing and causing the engine to run hotter.
But if the pump is the only thing you touched (other than the front accessories) then you still have to concentrate on those first.
So:
1. vacuum leaks.
2. ignition timing.
3. fan direction.
4. defective thermostat.
5. Defective new pump(s)
6. Best of luck! Check!
Paul