I have a 1997 4.3L 4 x 4 with 106k and it just started bubbling in the reservoir. THe Temp gauge pegs after about 5 minute of warm up. My gut reaction is to replace the thermostat... I don't have a repair manual, so I am not sure if this is my first step. Any suggestions or feedback would be greatly appreciated.

 

Bubbling in the reservior would suggest that you are getting pressurized air from someplace. One source is a bad head gasket forcing air from the cylinder(s) under the compression of the piston into the cooling system. This very well could cause the quick over heating.

Are you getting any coolant out of the exhaust? Have you pulled your plugs to have a look at them? Is the cooling system full?

 

I checked the oil with the dipstick, not milky. I did not notice any leakage of any kind. Did not check the plug. So is the thermostat not likely? System is full and clean

 

It still is a possibility, but it pays to check everything over first.

When you replace the thermostat, also replace your radiator cap.

 

Thanks for the advice... I'll pull a plug then replace the thermostat and cap if i see no issues

 

filled with coolant, boiling sound in or around the water pump. leaking (slow steady drip) under front end of engine. skid plat makes it difficult to pinpoint the origin of the leak. Should the next step be a pressure test?