Alde fluid - my plan

Not if you used ready mixed.

You should only use ready mixed if you have the system empty and are refilling it totally.

For a 13 litre system to be 40% glycol, you need to use 5.2 litres of concentrated glycol.

If the system does hold 13 litres then if you added 5 litres of diluted you are well under strength. No idea of dilution rate but even if 50% was the mix as bought you will have less than half the required strength in your system. 

I would recommend checking the strength and if needed emptying some fluid (probably a fair amount if as you state the system holds 13 litres) and topping with neat antifreeze to obtain the correct concentration.  

I should think the Lunar system might be a bit under 13 litres, our twin axle Sterling is 13 litres and the Lunar is smaller I think.

Even so, using a 50/50 mix, the concentration as you say will be too low.

As an aside. When I was at Alde the technician refilling my system said that they used the diluted mix to flush as they topped up. Although the materials were dearer that way it actually worked out cheaper for the company compared to the cost of labour in flushing with distilled and then adding antifreeze etc. 

If I get my system refilled before I get rid of the van I feel a trip to Wellingborough coming on.

Yes, thanks for that, I will get some concentrate tomorrow.

I recon KjeIINN has this job by the scruff of the neck. I would go along with his method but add a 50/50 mixture. If the mixture is to thin you could get "kettling", a siuation where the fluid boil's just like central heating. It took the suplier a year to sort my caravan heating noise and Alde one telephone call to diagnose the issue.Hope this helps

I had a problem with Kettling. Only happened on 2kw not 1kw electric. Dealer new the problem and did a fluid change. They failed to get the right concentration and problem not solved. I took 'van to Alde who sorted it (Lunar picked up the bill). Alde contacted the dealer and explaine dwhy they had been unsuccessful.

I flushed with a 60/40 mix so stronger than required. antifreeze/deionised water.

I flushed with a 60/40 mix so stronger than required. antifreeze/deionised water.

You can have too much of a good thing ...... 😉 that's  why you don't need/want 100% antifreeze