Radiator Flush.

Lespaul1960

I have an issue with my Ford Focus diesel.  The heater no longer blows warm air , it may warm up a little on a fast run but as soon as I slow down it turns cold.  The engine temperature is fine.  I suspect the cooling system is in need of flushing out. My question is ,are  the chemical treatments available worth bothering with ?  Does anybody have any recommendations .  It's decades since I last used one !   Thanks for reading..

tr7phil

Probably the thermostat housing needs replacing, I had it happen on my S-Max and it also happened on my parents' Focus.  Engine didn't overheat on either car but heater wouldn't blow warm.  Not an expensive fix (if that's what it is).

Lespaul1960

Thanks for that Phil,  I never even considered that as a possibility..

Lespaul1960

One thing I forgot to mention the coolant has been in there for 12.5 years !!!

Goudy

First off, as already mentioned check/replace the thermostat.
Plenty of guides on Youtube if you need them.

The heater core could be blocked and there are flushing kits and solutions available from Prestone. https://prestone.com/
You can buy this stuff on Amazon/Ebay.

Another problem with some Fords is the heater control valve or it's motor failing so hot coolant just doesn't flow through it to the heater core as the broken valve motor has failed in the closed position.

Lespaul1960

Thanks Goudy, I think the thermostat is the most likely culprit.