Subaru Water Pump / Running Temperture - 98 Outback

Make: Subaru
Model: Outback
Year: 98
Mileage: 125,500

Recently I had an overheating problem with my Outback. My mechanic, who I've been using for 10 years, dianosed the problem as a bad water pump and themostat. Just to be sure he further check to make sure the problem was not a cracked head gasket. The problem was the water pump. He replaced the pump, changed the thermostat, and replaced the timing belt.

After the repair things ran well until just recent. Now, when I watch the temperature guage on the dashboard, I see the needle bounce from the lower level or normal operational temperature to 3/4 way up the gauge and then back down. It does not happen fast, but I will see the it start bouncing like this 10 miles into my drive. The bounce cycle seems to occur in 5-10 mile intervals with continous driving. In stop & go traffic it is more frequent. ( After the repair, I continued to monitor my coolent level in the overflow bottle to make sure I was not looseing any. I did not see any reduction at the time)

More concerning was last night I had a 90 mile trip. I had no major issues during the trip with the exception of the temperature bounce. When I arrived at my destination, the temperature guage jumped. I checked my coolent overflow bottle and it had bubbled to the top.

Later that evening I returned, I again saw the bounce and the spike in temperature at the end of my drive. However, the coolent in the overflow was significantly less. I also saw what looked to be leaked coolent under my overflow and in the underside engine carriage guard near what I beleive is the water pump.

I have two questions:

1) What could be causing the temperature bounce?

2) What would cause the difference in coolent level between the first leg of the trip and the return? Is there a relief in the water pump? I did not notice any pooling of the Coolent under the car at any of my stoping destinations.

Also note today everything ran with the same bounce during my normal daily trip. And the coolent level looked unchanged.


Thanks,

I will wait for a replay.