Bad water pump?

[Radwelder]

I only overheat when at highway speed‘s past 10 mile drives but when I stop at a stoplight the temperature comes back down. I thought I might not be getting enough circulation through the cooling system so I set up a hose to check flow. If I’m flowing this much water with the engine off is it possible my water pump impeller is spinning freely so when the engine is running it’s not flowing water under pressure? I did remove thermostat for this test.

 

[Michael Hanson]

Hi, pump looks ok. RAdiator cap check ok? How old is radiator? Is your temp gauge actually working correctly ? Mike

 

[FJACS]

overheating at speed - I’d start by seeing if anything is blocking airflow to the radiator - like is the A/C evaporator packed full of dirt & debris...

 

[Radwelder]

Hi, pump looks ok. RAdiator cap check ok? How old is radiator? Is your temp gauge actually working correctly ? Mike

Water pump looks good and 9 months old, replaced when head redone. Pressure test system last week and holds 17psi per FSM. Radiator has no leaks, just flushed and seems to flow water no problem. Temp sender and sensor replace with head. Gauge varies between mid level and line below red when I call it hot. Fan clutch is original but has tension when cold but loosens up once cruiser up to temp.

 

[Radwelder]

overheating at speed - I’d start by seeing if anything is blocking airflow to the radiator - like is the A/C evaporator packed full of dirt & debris...

Pressure washed through both radiator and AC. You can see through them somewhat.

 

[Radwelder]

Hi, pump looks ok. RAdiator cap check ok? How old is radiator? Is your temp gauge actually working correctly ? Mike

So pump will bypass this volume of water if it’s not spinning? This picture is with engine off. Thanks

 

[OSS]

The pump is a direct drive shaft on the impeller. If the pully is turning, so is the impeller. There is a thread in the 40s section I read a long time ago of a guy who had cooling problems with his 40 w 2F and he went through everything, replacing everything (except the water pump) yet the engine still ran too hot.
Frustrated that nothing helped, he decided to change the water pump as the last resort. When he pulled the pump, he discovered that the pump was completely clogged with some sort of sludge that was blocking the flow.

Vane pumps (like the water pump) can pump a lot of volume but they don't generate much pressure, so congealed sludge is tenacious enough to block the flow. The impeller spins but no water flows.

While your pump may be fine. Don't rule out the possibility. I'd definitely check it.

 

[Seth S]

Maybe I missed it but have you replaced the thermostat?