overheating wild temp swings after new waterpump/thermostats!

[railroadboy]

1998 6.5l suburban been losing coolant for some time. Finally water pump seal blew out I think its been leaking. Changed pump and put in dual 195 degree new thermostats. Truck will not cool properly and I have not heat. Sitting idle stays about 180, driving about five minutes heat climbs and pegs gauge out to 260 then a few seconds later it will fall all the way to 160 and for a few seconds I got heat. Then slowly creeps to 210 or so and then falls back. I tryed to bleed it but I'm lost and really frustrated. Do I have head gasket problems. I don't have any smoke or water in oil.

[john8662]

what kind of thermostats did you install?

If you installed anything but a balanced sleeve thermostat, you're going to have problems. The AC Delco replacement Balanced Sleeve thermostats are the only thing to use.

How are the thermostats positioned? They could be backwards.

[Robyn]

Sounds like a leaking head gasket for sure.

Classic example. Top radiator hose gets hard as a rock, coolant pukes out the overflow.

Missy

[56pan]

I had the similar symptoms with my 6.5 with the temp. swings. Also, I had bubbling into the coolant reservoir immediately after shutdown. Wasn't long after that coolant started oozing out the outer side of the driver's side head where it mated to the block. Changed both head gaskets.

[railroadboy]

Update: Head gaskets were blown, precups cracked out to head gasket, and heads cracked between several valve sets. Some cracks between valves went into seats.