Heater core flush

[Jon Blaze]

I change the coolant every 30,000 miles. 06 trailblazer 4.2 4/4 reg. wheel base and has rear stereo and heat/ac controls 73,000 miles owned since new and i would like to know if and how to flush the heater core and should it be done? Just want to try and keep up on it. When i change the coolant i just drain rad. and refill with new 50/50 mix. I dont flush with water.
Also looking to put a block heater in any info on it good or bad?
Thank you for all the help possible.

 

[NJTB]

If you change your coolant every 30,000 miles, you really don't need to flush the heater core unless the coolant has problems. When you did the original flush, did the coolant have lots of debris in it? If not, you're good to go.
If you insist on flushing, you have to know which direction the coolant is going in the heater core, and flush the opposite way. I used to use a garden hose with the end cut off, but on the 4.2 engine I don't know anymore. I do know they use a 'reverse' flow for some reason.
I had a 97 Blazer with the red coolant, and for some reason, when I took off the radiator cap one day, the radiator was full of these rust colored balls. I should have replaced the radiator but decided to back flush the system (worked for me for the last 20 years, why not now?) and drove for an entire winter with no heat (where I learned about reverse flow). Once I figured that out, the garden hose in the outlet of the heater core thing got lots of crap out, in the summer naturally.