Best location to flush heater core?

[Klawrence]

Heating in my mk2 has been struggling to warm up for a long time now. I replaced the thermostat (I know the heater is on a different loop but the stat was sticking open anyway) and flushed/bled the cooling system (a couple of times) as per the Ky2 article and the BGB but even when the levels are all correct and no more bubbles are present, the heater still stays cool-ish.

I tried another bleed today and the rad/heater bleeding hoses came up completely level with the funnel on the filler at the back, no bubbles at all.

Im guessing the heater core is maybe blocked with debris as one hose at the front feels hot and the other is much cooler. Going to try flushing it and I was wondering the best place to do this? Should I pull off the hoses in the frunk where they go into the core and do it there or should I pull them off at the rear firewall and do it there? I guess doing it at the rear would flush out the hard lines too.

[jimi]

I'd start in the engine bay, easier to get rid of the water, no chance of making a mess in the front luggage compartment + it will do all the hoses/pipes & heater core.

[Klawrence]

I'd start in the engine bay, easier to get rid of the water, no chance of making a mess in the front luggage compartment + it will do all the hoses/pipes & heater core.

Good point about getting rid of the water and yea it would be a good idea to make sure the pipes are flushed at the same time.

Do you know offhand what diameter of tubing would be required to connect to the pipes coming through the engine bay? If not I’ll try and get a calliper on them to check.

[BYRNEY1984]

16mm. Or 5/8””. I would personally disconnect both the feed and return from the engine and from the hard pipes that go to the heater matrix above the battery. Join a piece of hose to the frunk end and put it in a bucket so you can drain the water without making a mess and also see what comes out of the pipes. The flush the feed and return hose one at a time. Then connect some hose to the matrix hard pipes and flush it through into a bucket.

[jimi]

The MK1 setup is very similar to the MK2, last time time I flushed mine I did all from the engine bay, I disconnected the heater hoses from the engine and flushed from there in both directions until water was running clear.
Make sure the heater valve is open by checking the actual valve (just in case the dash control isn't working properly)

[jimi]

FYI Trev's thread in MK2 Useful Info has many useful pictures of the cooling system that may be useful to you LINKY