My engine has been running heating up quicker than normal as of late. Normally my HINO has ice in it's veins, but around 380k I started having to drop gears in the hills to keep the heat off the engine.
I'm fairly sure its not the fan clutch, as the last time it heated up, I did the rolled up newspaper test, and it passed. (IE, when the engine is hotter than normal, insert rolled up paper magazine or sprts section into fan, if the speed decreases, your clutch is shot. If the speed stays the same, and the fan blade rips the paper out of your hand and pulls your arm into the fan, removing skin, your clutch in fine)
I have also replaced the radiator due to a leak recently and it is still heating up on pulls.
So I'm guessing maybe the water pump impeller may be worn.
Is there a way to test pump out put without removing the pump from the engine?