5.0fl running hot

[chartersj]

My buddy just bought a 1994 20ft chris craft with a 5.0fl omc in it. Did the first test run yesterday and the engine run around 140-150 while cruising, but then when he started pushing it, it jumped right up to 200-220 and did not want to cool down. The exhaust manifolds and risers are both staying cool, but the bottom of the thermostat housing and the large hose from the engine circulating pump are both hot. Is it safe to say the thermostat is shot?

 

[alldodge]

Is it safe to say the thermostat is shot?

Not really, would start with verifying that the temp is actually reaching 200+ degrees. At 200 I would expect the oil and paint on the motor to start to smell and/or smoke. You might have a bad gauge or sender. Get a IR temp gun and measure the thermostat housing.

Has the water pump impeller been replaced, and pump inspected?

 

[chartersj]

Not really, would start with verifying that the temp is actually reaching 200+ degrees. At 200 I would expect the oil and paint on the motor to start to smell and/or smoke. You might have a bad gauge or sender. Get a IR temp gun and measure the thermostat housing.

Has the water pump impeller been replaced, and pump inspected?

Ok the motor did not seem to smell or smoke, I do have a temp gun though so we will try that. We did have the raw water pump apart, impeller was fine and housing didn't have an abnormal amount of grooving. Is there anyway to verify the gauge or sender other then replace it?

 

[alldodge]

Is there anyway to verify the gauge or sender other then replace it?

Yes, once you verify the gauge is not correct using the IR temp gun.

If gauge is inaccurate, you need a volt ohm meter. Remove the sender and place in a pan of water on the stove. Connect the ohm meter to the top stud and other probe on the casing. Sender should read 240 ohms when cold and 33 ohms around 215 degrees (give or take a little)

Put a thermometer in the pan or use the IR gun to verify temp