Coolant flush on 94 LT1

[Art B.]

I am trying to determine the best way of flushing and replacing the coolant on my 94 LT1 without following the service manual procedure of removing the knock sensors and thermostat. Is it possible to install a Prestone flush kit in the heater hose and flush the old coolant out the expansion tank cap? Any pitfalls with this method? Any better suggestions? Also, the service manual states not to use a chemical flush. Does anyone know why or what might happen if I did? Any help would be appreciated. Thanks.

[Joe L.]

Re: Coolant flush on 94 LT1

Art------

Due to the configuration of the Gen 2 small block cooling system, I don't think that the flush-and-fill kit will work properly. I would recommend following the service manual procedure. Removing the knock sensors and thermostat are not very difficult and guarantee that you'll get a complete drain of the old fluid. When removing the knock sensors, make sure that you measure the breakaway torque. If it exceeds specifications, you'll need to replace the knock sensors. Retorque the old or the new ONLY to the specified torque.

The knock sensors and thermostat, if you need/want to replace them, are as follows:

knock sensor---GM #10456126 (Delco #213-96)----34.63 GM list

thermostat-----GM #12555290 (delco #131-100)---22.77 GM list

The above-referemced parts are available for a lot less through Delco or discount GM dealers.

I think that the principal reason that GM does not recommend the use of flushing agents is the possibility that some will not be compatible with alumimum, some might remain in the engine after flushing and the fact that they are not really needed. I agree, too. You shouldn't need to use them unless you have a really poorly previously maintained cooling system. In that case, I'd go ahead and use one that is SPECIFICALLY approved for use with aluminum systems and flush thoroughly afterwards.