Hi. I have an '08 Mk2 +FL, does anyone happen to know the outside diameter of the pipes from the heater matrix please?

I'm preparing to do a coolant flush and wish to buy some PVC tubing to use when flushing the heater matrix, but I don't know precisely what size of PVC tube would fit. The connectors from the rubber hoses are of course extremely difficult to detach, and are right up against the firewall, making it difficult to simply measure.

7 hours ago, rd457 said:

...wish to buy some PVC tubing to use when flushing the heater matrix, ...

I have never heard of anyone doing this. Would be interested in the result so keep us posted...

when flushing the cooling system there is no need to disconnect anything.

Just open the drain valve at the bottom of the radiator and flush the system (preferably with coolant) from the coolant reservoir. 

A 2008 Focus that is correctly serviced and when the correct coolant is used should not have the need to perform a cooling system flush. 

17 hours ago, StephenFord said:

I have never heard of anyone doing this. Would be interested in the result so keep us posted...

Really, oh... I'm uncertain, being new here, whether that's due to lack of knowledge on different flushing techniques on your part or because what my intentions are were not very clear from what I wrote, so please forgive me if in the following I'm preaching to the choir. Let me explain...

There are multiple techniques for accomplishing a flush, as per the Haynes manual and the many videos I've come across on youtube. (FWIW I don't find the section in the Haynes manual on this to be very good).

• A vacuum based flush involves using special equipment to accomplish the task in such a way as to avoid air pockets, which is necessary in some vehicle designs, but thankfully not mine.
• There's the technique of draining, filling with water, then running the engine until warm (to open the thermostat and thus circulate through the radiator), and repeating these three steps in sequence over and over until the fluid looks clear, then finally (having just drained) refilling with fresh coolant (in such a way as to end up with the right antifreeze-concentrate-to-water mixture). Draining only removes an estimated 2/3rds of the system's contents (I'm sceptical in my car's design it would be as much as that), so each time you repeat the drain+add-water+circulate sequence you're diluting what remains of the old fluid further and further until you decide it's diluted enough. This method has the benefit of avoiding disconnecting hoses, but the downside is how much fluid it requires, and it's only suitable if the system has been well maintained such that there is no concern over contamination / choked pipes. Since tap water is not ideal for use in cooling systems, strictly speaking you should only perform this method with distilled/de-ionised water, though this of course costs more.
• Then there's the technique of disconnecting hoses and flushing out individual components of the system with distilled/de-ionised water, reassembling and refilling. This in some ways is more difficult, but has the benefits of perhaps more thoroughly removing the old fluid and of potentially requiring less water overall, and is supposedly more appropriate for a poorly maintained system, especially if is it choked up (in which case you'd need to flush water through individual components with a certain amount of pressure in reverse to try to dislodge things).

Partly in the interest of being more economical I'm intending to use the third technique. I'll essentially be disconnecting hoses, flushing with de-ionised water (using as little as possible), reassembling (in as careful a way as possible to avoid air bubbles), adding in 1/2 the system volume in antifreeze concentrate, topping up with de-ionised water, and then running the engine a bit to circulate and mix the antifreeze and water. Then I intend to do a pressure test to determine whether or not to replace the expansion tank pressure cap.

In the interest of minimising mess I'd like some clear PVC tubing for flushing the heater matrix, as you can see demonstrated in the following ChrisFix video: https://www.youtube.com/watch?v=M9SIafVsqyc. But of course I need to know what diameter of PVC pipe to actually buy first, which is the problem... (My pipes may not turn out to be the same size as his).

16 hours ago, JW1982 said:

when flushing the cooling system there is no need to disconnect anything.

Just open the drain valve at the bottom of the radiator and flush the system (preferably with coolant) from the coolant reservoir. 

A 2008 Focus that is correctly serviced and when the correct coolant is used should not have the need to perform a cooling system flush. 

Yes, I know there's no strict need to disconnect things for a flush but I'm specifically interested in using the method described above that does involve this.

My Focus, I am ashamed to say, has not always been well serviced. I've just recently replaced my water pump and managed to loose about 0.5 litres of coolant in the process of doing so. Rather than just top up, since the first coolant renewal interval is supposedly 10 years (contrary to the information given by Haynes) and my coolant is now 14 years old, and partly just for the experience, I'm opting to renew with a full flush.

Update as promised. I finally got around to doing the flush the other week.

Heater matrix pipe outer diameter turned out to be 18mm.

All went well, though with a few difficulties.

- I managed to get the unusual heater matrix pipe fixings undone by gently hammering a small length of wood against the bit that rotates.

- Handling the clips on the pipes was a pain since I only had a pair of adjustable pliers to do it with, but I managed.

- Accessing the bottom radiator pipe was the hardest. The air conditioning pipes block the most obvious access point. I ended up having to remove the bottom shield beneath the front bumper to reach the pipe's retaining clip. Refitting was particularly frustrating without a proper tool and required two hands which required raising the vehicle. The lower engine block connections required removing the alternator.

Having disassembled the pipes, flushing everything out was easy. I used up something like 5-10 litres of de-ionised water for that.

When refilling I twice had to start the engine to get new fluid moved into the system from the expansion tank. I roughly followed the Haynes manual instructions on reflling, taking it for a drive though for part of it to avoid annoying the neighbours too much, topping up with de-ionised water during and after. Of a total 5.8 litre capacity, which requires 2.9 litres of coolant concentrate and 2.9 litres of de-ionised water to fill for a 50:50 mix, I ultimately put in the full 2.9 litres of concentrate along with 2 litres of de-ionised water, which has left it at the maximum mark, suggesting 0.9 litres of de-ionised water was left within system components from the flush.