i know this response is way late, but this is what we did in the 'olden days':
1. make sure the system is cold
2. drain the coolant out
3. remove the thermostat
4. remove the hoses from the heater core
5. connect the garden hose to to the heater core and a long heater hose to the other heater core connections and flush it w/the hose water
pay attention to what comes out
- if a lot of junk looking like sludge or corrosion or whatever comes out, then you have problems w/your heater core
- if it looks good, you may not have probs w/your heater core
- those were the days when heater cores were brass
- with the new alum/plastic heater cores, i'm not sure
6. connect the heater core hoses together w/a pipe
7. fill your system w/clean water and long-term flush that's certified to use w/alum heads and new style heater cores, radiators, coolant sensors, valves, etc.
8. after a few days of driving around (= many hours of hot/cold), drain the coolant system and observe what comes out
- if it's nasty or junk comes out or it's dark or smells and looks worse than mildly cloudy, then you probably got a clogged heater core
- if so, you may need a radiator, since when you do a long-term flush you can loosen up junk that's keeping your system from leaking
9. flush out all you can w/the garden hose until it comes out very clean
10. if you feel it's real bad, then do the flush again
11. now you probably cleaned out your radiator and engine good enough, and you have 3 options at this point:
a. change your heater core and radiator and refill your system per mfgr specs,
b. change only your heater core and refill your system to spec,
c. put everything back together and refull your system to spec.
12. you do:
"a." if you had a lot of bad junk come out after the flush,
"b." if you had some bad junk come out and want to guarantee your heater core is clean and full-flowing,
"c." if you had no bad junk come out, or did, and want to take your chances on your heater core leaking i/s your blower housing (b/c that's usually what happens when you do the long-term flushes).
BEWARE:
1. doing a long-term flush can cause leaking in a bad heater core and radiator, and
2. doing a short-term flush can loosen up enough junk in the system (= engine scale, rubber seal junk, flaking glue, plastic fiber scale, alum corrosion, etc) to CLOG UP your heater core and possibly your radiator.
That's how i'd deal with this problem IF I suspected it.
First thing though, I'd consult my HELM manual to see what they recommend.
If they recommend something else that I am unable to do, then I do it if i can afford it. Otherwise, I do what we did in the 'olden days' before all this complicated and convoluted computer controlled junk cars came into existance (you know, the auto cartel protection racket sponsered by DC).
Cheers ... Chris