Morris Minor Owners Club

right, my friend has a 1990 Sierra 1.8, it is lovely and well loved, but it has this winter managed to have heaters which don't work! they get warm, not hot. the mechanic said that the heater is probably blocked(they lose no water so shouldn't be leaking), so basically my question...
what would people use to clear the heater matrix of what is believed to be hard sludgey stuff...yes, a PROPER term...!!

If its loose sludgy stuff then maybe just disconnecting to hoses and flushing through with a hose pipe will shift it. If its more solid then use rad flush. However, I think it may be air locked and so need bleeding anyway.....

sorry i didn't explain enough! my bad! 2 weekends ago i took off the rad hoses, flushed it, back flushed it, took out the thermostat, tested that. you can really reach the heater hoses very well at all as there is an engine in the way. i will speak to him though and see if he wants to give it a go(i didn't want to do it myself as i was scared i'd break it) so just a rad flush...hmm...might give that a go...

Can you get one or both heater pipes off at the engine end rather than the bulkhead end? If so that should be the ideal point to bunge a garden hose into. One of those spray nozzle things will often jam in the pipe nicely. Even if you can only get access to one pipe it will still be worth trying it, to shift/dilute the blockage.

yup get some rad flush if the hosepipe isnt working, it should loosen the sludge

Is it definitely a blocked heater, as a stuck open or part stuck open thermostat may stop the engine getting up to temperature and therefore not produce hot enough water for the heater.