Water Pump Pressure

Put a pressure gauge in any spare port you can find on the water pump outlet, specs depend on what engine you've got.

 

The small line thats comes off the top of motor and goes to the top of the radiator, disconnect from radiator, makes sure motor is not hot so you dont get burnt with hot coolant, put pressure gauge in line comming from motor cap the fitting on radiator,start engine rev to Hmmmm 1000 rpm check reading on gauge see if it is within specs. Not sure on how much pressure maybe 30-50.

 

minnium of 14psi at 1400rpm

 

Heat builds pressure and with the radiator cap it allows the system to pressurize to the cap rating which is usually 16-18 lb. The increased pressure raises the boiling point of the coolant/water to keep your system from boiling over. The 16- 18 lb cap also keeps the system from overpressuring to keep from blowing the radiator seams, water pump seal or even a head gasket. That's why you are getting different readings is from engine heat and not the pump. Checking for what it's pump pressure is irrelevent. Pumps will bypass when the thermostat is closed so you'll never get a performance pressure.

Water pumps are simple. Basically you have a shaft mounted on a bearing. One end of the shaft is an metal impellar that pumps your coolant. On the other end of the shaft is a drive pulley. The shaft runs through a housing with a seal by the bearing to prevent leakage.

Most water pump failures are from the bearing wearing out and the shaft wobbles causing the seal to wear out. When this happens, there is a weep hole on the bottom of the housing where the shaft comes through. It's about an 1/8th inch hole. You might not be able to see it until you get it off, but you can reach in there and feel it with your finger. If your finger comes out wet, you are in the early stages of failure. When a seal gives all the way, it's quite obvious as the coolant spews out. They are designed with the weep hole at the bottom to prevent the hot coolant from flying in your face while you are checking why you are overheating. With the pump off you can wiggle the water pump drive pulley on a bad pump.

Very rarely will the shaft break or even one time I seen the impeller blades flatten out where they hit the housing before the seal gave out. You can count on the weep hole for how the water pump is doing.

Another test you can do is catch the engine at it's highest temperature right when the thermostat opens, squeeze the upper radiator hose, then let it go. You'll feel the coolant surge through it. Or from a cold state feel the upper radiator hose. When the engine reaches operating temp and the thermostat opens you'll feel the hose go cold to hot in seconds. This insures your pump and thermostat are working.
If you are experiencing overheating problems, you could have a stuck thermostat, a dirty radiator outside or scaled inside. Or even a bad head gasket, etc.

Here's a good link with a video on the water pump weep hole. Click the water pump video, bottom left when there. Hope this helps.

http://www.cat.com/maintenance-and-support#

 

isthe 15-18 pound cap very common,I`ve only seen 5 pounder

 

Depends on the engine. I seen peterbilts with 4 lb caps and KW's with 10 lb caps. I was just giving pressure specs when you pressure test the system. This is done with pump air hooked to a 16- 18lb radiator cap adaptor not hooking to hoses or the waterpump. I was just giving the guy an idea how to check his water pump. Pressure tests are for leaks. Watch the video.


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