Draining ALL the coolant, '90 burb

[Metalhead47]

I've read all the threads I can find on draining the coolant & they mention allen head plugs on the sides of the block.... um, where the HECK are they & how do I get to em?? Just poking around under there it looks like there's all sorts of stuff in the way of the side of the block.

Also, I've got the rear heater to drain too. I was thinking, what if I unplugged the lead from the coil to the distributor & then cranked the engine over with a radiator hose disconnected. Would that work to get out all/most of the old coolant without damaging anything?

 

[ryoken]

the block drains are right above the oil pan rail, 1/2way down each side.. they could be allens or pipe plugs (9/16 socket)... about 2" above the pan mounting surface..

got air and a blow gun? pull the hoses that run to the rear heater and blow it out...

 

[bigblock72]

On a 90 the passenger side plug is the knock sensor, the driver side plug will be in the same relative position as the passenger side.

Make sure you vent the top of the motor when refilling the coolant otherwise the it will air lock and overheat. I usually pull either the heater hose off of the intake if it has one or pull the coolant temp sensor out of the intake manifold.