I just lost all the heat in my heater in my 92 740 as I was driving down the road. It worked great when I started the trip, and then just quit. At the same time the engine coolant temp gauge was creeping up towards the red. There is no visable leaks, the rad is not low, and there is no broken belts. I am thinking that this has to be my water pump. Any other suggestions??
Rare, but it happens. I put a used radiator in my 240 once and it turned out to have a pebble from the salvage yard in it, got into the water pump and jammed the impeller with similar results. A bad thermostat could conceivably cause that, but usually they fail open.
I have had the car for about 2 years, and there has not been any problems with the radiator. The thermostat is functioning since the upper hose gets hot after the engine heats up.
I wonder if something has got in there and clogged or jammed the pump? It's made in such a way as to let the impeller break loose if it gets jammed so that it doesn't snap the shaft and throw the belts.
I'm not sure what the easiest way to test this is, I suppose you could drain the coolant, remove the belt, disconnect the lower radiator hose from the pump and poke a wire in there while rotating the shaft to see if the impeller is turning. If you can find a piece of transparent hose you could patch that in temporarily to see the flow. There are not too many things to go wrong.
I found a parts place that have a pump in stock, so i figure that for $55 I might as well just change it.
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