Someone who works on Northstar engines said the overheating problem on my 1994 Cadillac STS is due to one of 3 problems – a bad water pump, bad head gaskets, or a bum thermostat. I am looking for second opinions because he thought it probably was the head gaskets and that the cost would be over two thousand bucks. The car has overheated dozens of times over the last few months but not predictably. That is, I might drive under 10 miles and the thing will overheat – or I can drive many more miles than 10 without it overheating at all. Sometimes there will be a big puddle under the car when I go out in the morning – sometimes not. I add quite a bit of water to the overflow when this happens. I changed the thermostat myself a few weeks ago but that didn’t seem to make any difference. Do these symptoms give anyone an idea as to what the real problems is? Also, how can one tell whether the head gaskets are gone or whether the water pump is the culprit? Thanks very much for any observations.