It looks like you have a restriction at the t area. But before that, lets assume your water pump is not pumping, the engine would overheat due to no coolant circulation. Is doesn't seem like your engine is overheating. Lets assume your water pump is weak. Two things, if the impeller is the cause of reduced pumping it is usually due to the fins on the impeller breaking (plastic and or rusted metal) second, if too much clearance is created between the impeller and water pump housing adjacent to the impeller it would reduce pumping (if this is the case usually it is due to water pump bearing failure and coolant leaks).
When the engine is warm, have someone rev the engine in park up to 2,000rpm and hold it there then check the t fitting again to see if the temperature changes. If it does, good if it doesn't change temperature you have a restriction. Do this at the heater connections at the RR of the vehicle to feel if it is hot also. Have the blower on hot and blowing to see if the temperature of heat blowing out the vents is hotter with revving.
It doesn't sound like a water pump issue to me it sounds like a restriction or air trapped in the heater core.
I hope this helps, let me know.
Wednesday, November 6th, 2013 AT 5:11 PM