Hi.

Drained (some of) the coolant from my 85hp twinair today (actually a 500).

I'm flying blind with this engine, as there's no literature.

I wanted to flush it out with distilled water for a few days, but only got about 3.5 litres in, which means I left about 1.5 litres of coolant in.

I put the heater dial on full, and removed the cap off the expansion bottle, and opened the petcock.

There doesn't seem to be any bleed nipples in the system (??).

I've just looked at a parts diagram, and there may be a plug on the top of the rad, on the opposite side to the drain petcock.

Would removing this help?

Otherwise, does anyone know how to thoroughly empty the system?

Cheers in advance.

Never drained a coolant system in my life, only partly for repairs, like a new radiator, and even then i poor the same stuff back in. (No water but coolant fluid)

Coolant has a finite life. The modern OAT lasts 4 years and should be flushed out and and replaced.
One of the reasons for overheating and poor heater performance is sludging by poor cooling system maintenance.

Never have had that kind of problems, and my Panda's have all been driven like i stole them.

Its not going to suddenly give trouble on its 4th birthday as the process will take time, the first you'll notice the trouble will be climbing a long hill on a hot day and the temperature gauge rising close to the red section. My doblo had a badly silted radiator due to being ignored, even back flushing and rad cleaner was ineffective, a new radiator was needed.

Without stripping everything down, you'll never get it completely drained, but you can get all the old coolant out.
I've done this with a hose pipe in the past (though not done a TA), just used it to flush it out.

I've also watched Edd on Wheeler Dealers use compressed air to fire out the dregs, think it was the TR6 episode.

One of the big problems Is those that use tap water in the antifreeze mix, even so called soft water can cause sludging. Deionised or distilled water only when mixing up the coolant.

For those that don't keep their coolant clean and fresh, I once used radflush in a knackered old Cinquento.

Apart from the heater starting to work again, after about five miles the engine suddenly livened up.

I definitely got a couple of horsepowers back. Maybe more.

Did you ever manage to bleed the system, I've just replaced the thermostat on my wife's 0.9l twin air (that we only purchased yesterday) and the heater still doesn't seem to be very lively. I'm thinking there is an airlock in the system, as I only poured about 1l of coolant back into it, and it has remained at the maximum line. (even after getting the engine temp to "middle" of the range.

Hi.
Surely there is two bleed points. There is a black plastic threaded plug on the radiator that bleeds the radiator itself. This would normally be the first item to bleed, fill the header tank with coolant 50% mix until the coolant starts to run from the removed plug make sure you allow it to run while refitting the plug. There should also be a small black threaded plug with a screwdriver slot on a hose, which will be fairly high up again remove the plug and keep topping up the coolant till it runs free once doing that replace the plug. There will always be some loss of coolant doing like this but its the best way to purge air, there are also vacuum filling devices that are allegedly very good. It is also an idea to squeeze some of the bigger hoses a few times to help the air move around (assuming you actually do have air in the system).