Follow up on the "bucket of bolts"

[Pbeanbag]

Hi guys, just thought I would post a follow up after the whole ECM issue. The wire coming from the tranny was the problem. Since i repaired it, all good! woo hoo! however i thought i would share an intereting issue and repair.
I had a coolant issue ....when i would start the truck(after topping off the radiator every day) it would build up air like a head gasket problem but all checked out. after i purged the air it ran fine but wouls still leak.Especially after shut down. I know a little about pumps from work and know that any pump will suck air before fluid ,so with that in mind i deducted that the pump had a bad backing plate gasket. Asked many top mechanics in my area all said "never heard of such a thing" well, I was right.
so this is how it worked....at start up the pump immeadiately sucked air into the cooling system but as the pressure built up it stopped sucking and only leaked when pressure built up considerably. Then when shut down the pressure would push the excess coolant out running from up behind the hose. New pump, problem solved !
Just keep this in mind cuz these old trucks will drive you crazy with puzzling isues.
Thank you everyone for all your help.

 

[GoToGuy]

It wasn't sucking air. How ? It's operating in a fluid environment. Whatever area of the pump that's failed, between heat and pressure coolant is finding an exit. That coolant is gone . That volume of coolant is replaced by outside atmosphere. Not by the water pump. Water pump is not a pressure pump, it is a propellor moving water. There are no vanes , or gears pumping high pressurized water. The coolant is heated by engine, that heat creates pressure. Like a pressure cooker.

 

[Pbeanbag]

sorry but i must disagree. the backing plate gasket was bad and if you have ever had a collapsed lower hose you would know that the pump pulls fluid. I have trash pumps and jet pumps and the slightest leak at the housing or hose will suck air causing foaming and lack of suction pressure. If your theory is correct why did the replacement completely solve the issue. no bubbles in radiator , no pressure leak at shutdown,no loss of fluid
maybe i am not communicating well, but problem cured