Pajero heating?

my 1993 mitsubishi pajero with climate control works well blowing cold air but will not heat, even though the rad boils up occasionally so it IS hot!!
i have had the matrix cleaned twice, after each time it works for a while and then goes cold again
i suspect an air lock ,am i right ? if so anyone know how to bleed the air out?

Answers:
It sounds like it could be either the thermostat, or the heater core it's self. Both which would need replacing. As for the suspected air lock. Go to your local parts store, rent a pressure tester with the cap that fits your radiator. While cold, pressure test the system. If it holds pressure your good if it looses pressure it is the heater core. while the cap is off bring car to running temp. Shut off and pressure test the system again. Remember it shouldn't take but a few pumps and watching it to see if it is an air lock. Normal should be 6-7 pumps, blocked 3-4. If it is the latter, keep pressure on the system and go to the high point of your cooling system and loosen one of the clamps. Not to much but enough for fluid to escape, keep pressure on it and watch and listen to see if liquid or air is coming out. Tighten up when satisfied.
check the thermostat could have failed in the closed position
Hi it could an air lock but sounds more like a sticking thermostat to me. To check air lock remove the top hose from the rad ensure the heater position is on hot, then top up through the top hose until full, then put back onto the rad un do rad cap and top up until full there hold your hand over the rad top and squeeze the top hose with your other hand to eliminate any air top up again and that should be it.
To check the thermostat locate it normally where the top rad hose goes to the block inside a small casting undo the 3/4 bolts remove the thermo. disc object, boil a kettle and pour over the termo in a cup, it should open if not replace, or just put back housing with some sealer! and replace later it's not that necessary this time of year.
ONLY DO THESE TESTS WHEN THE ENGINE COLD!! NEVER WHEN HOT !!
Good luck.

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