waterpump blues

How do I test the water pump? I can not tell if coolant is circulating when I look under the fill cap. I can not tell if it is flowing or just jiggling from vibration.

Starting from cold, I'd rely on temperature. Your hand should tell you if the pump outlet is warming up.

I have one of those cheap little laser pointed temp sensors, check where water enters and exits radiator for temp difference.

With most systems, you won't see movement of the coolant in the radiator until the thermostat begins to open. As it opens more and more coolant flow will increase. When the upper hose is at operating temperature the flow will be clearly visible if the coolant level is high enough. Don't take the cap off to see when it's hot, take it off while it's cold.

It's possible it's not leaking and not pumping, but I rather doubt it. Why are you worried about it and what is it on?

I'd go farther and say run it a while and see if the neck of the radiator is hot. If it is just warm that tells you the coolant is at a slow constant cycle, not a quick open and close with pressure like a pump should have. This could point to the pump or thermostat.

I know there are cases due to hard water and such where impellers will be worn away or break and the pump not leak, but I have never been so "lucky". I'm more of a shooting water in the middle of planting season kind of guy.

It is a very rare occurrence for a water pump to stop pumping. It does happen, involves the impeller falling off, slipping on the shaft, rusting away... I've only seen one impeller fail in 50+ years of servicing vehicles.

If there is no circulation, you will find the engine gets hot, but the air through the radiator remains cold. That can be caused from a failed pump, but more likely to be:

A failed thermostat, blocking the circulation.

Airlock, some engines are designed that they can trap air. The coolant never reaches the thermostat or cavitates around the impeller. This usually happens following a drain and refill. Those will have bleeeder valves, usually around the upper plumbing, thermostat housing, pump housing, that you open and allow air to escape, then close when the bubbling stops. Sometimes a failed thermostat will cause airlock. If the thermostat doesn't open, steam will build and push the coolant down below the pump and back out the radiator.

A blocked radiator. This happens, but it is a progressive failure, happens over time. Usually will show as being able to feel cold spots on the core where there is no circulation. More common on older equipment that has not been properly maintained.

But, you say the coolant is just sitting there, can't tell if it's moving. As long as the engine is not overheating, and there is "some" heat coming through the radiator, it probably is OK. If you are trying to get circulation, and the weather is cold, the thermostat will only allow a small amount of coolant to circulate, especially on an idling engine. Might keep an eye on the temperature and the coolant level, put some load on the engine, work it, then carefully check the coolant to be sure it is full.

They do go bad in different ways. Here is one from my 96 dodge. It was having a heating problem. The pot metal had been eaten away. If you have a cast iron body I doubt this could happen.I broke the impellor away to take the picture. I have been using anti freeze since I have owned it. I don't know what the previous owner used. Stan