Temp gauge climbs to 225 then quickly drops to 190?

After replacing the water pump i noticed that my 4.3 was still leaking coolant badly. I found that the intake manifold gaskets were the culprit and the the DEX COOL was probably to blame. You see, i believed GM when they told me that the dex-cool system was maintence free for 100k miles, I was wrong.. So after tearing the motor apart and replacing the intake gaskets the leak is gone and the truck seems to be running great again but... Last night and again this morning i noticed that the temp gauge rose all the way to 235 and then quickly dropped back to 190 and i am pretty sure that the coolant is full. I also hear the sound of running water inside the dashboard but i assume that is the coolant passing through the heater core. My question is weather or not this is "expected" behavior and i jsut didnt notice before my problems happened? Also, is there any way to stop that dam sloshing sound coming from the heater core?

I would suspect and air pocket. Try keeping the overflow tank at the full line. If there are no leaks in the system the air pocket will eventually work its way out.

I would suspect and air pocket. Try keeping the overflow tank at the full line. If there are no leaks in the system the air pocket will eventually work its way out.

that is what i was thinking but i needed someone to validate my idea..

BTW, i have a K1500 ex cab with the 4.3, not just the little S10 blazer in my Avatar.

I would say probably air in the system like has been mentioned. If you want to purge the air out remove the radiator cap when the engine is cold and start the engine. Look at the coolant level, you want to keep it full throughout the process in the radiator and the overflow tank. Turn on your heater so the air will purge out of the heater core. After the engine warms up and the thermistat opens the coolant may overflow just a little bit, I would run it for a few minutes after the thermastat open to bleed all the air out. Before you shut the engine off you should install the radiator cap and let it run for another minute or two, if you did not do this after you replaced a water pump you will have air in it for awhile, it may eventually work its way out, but it would take a lot longer

If you didn't refill the system the way Crasen directs. You have huge pockes of air... and it will take a long time to work them out.

Your thermostat may be sticking and taking that extra temp to open it. It would not hurt to replace it, especially if it has never been done. If you go to an auto parts store ask for the heavy duty one, it may cost a little more but will be well worth it.