Not good.

The front bank drain plug came out fine, and the rear one came out when I changed the coolant 2 years ago, but it's well and truly stuck now. I can get a short swing with my torque wrench and have also tried an impact gun.

The head of the plug is starting to become mis-shapen... any ideas or tips?

yeah, stop it! Leave it in!

An absurd thought but if it is on the back of the engine are you sure you are trying to turn it the correct direction?

I checked the rotation direction so many times today!

I think I'll fill/empty a few times tomorrow with tap water and then distilled. Then when it seems to be clean I'll fill with the coolant and top up with water. With a few dilutions the old coolant will be at very low concentration.

Can you pull a heater hose off, attach it to your garden hose and flush it that way. I did it this way to get rid of the pink coolant in my daughter's corolla before I put the real coolant in.

Try hitting the plug with a drift and hammer, don't smash it, just just firm hits, probably 10 at a time then re-try to undo after each 10 probably take 3 or 4 rounds. if you get it out replace it with a new 1 and put some non hardening thread sealing compound on it, that will make it easier next time.

Cheers Dave

Thanks Dave. I've done the x 10 dilution workaround this time, and will pay for it to be removed and replaced at the next coolant change.

Get a new one and try an Irwin bolt grip on the old one

Hey they look like the business! http://www.warburtons.com.au/p-784-irwin-bolt-grip.aspx

I've never taken those drain plugs out in any cars I've owned, just done the flush method with tap water (drain from bottom radiator hose (I lie, radiator has a tap on it), refill with tap water, run the engine warm, let cool, repeat twice) and used the correct amount of concentrated coolant. I don't trust those plugs, they are in too tight, snap one off or strip the thread and you have real problems.

Last time I pulled bits off my 15 year old TS V6 at 240,000 km, there was no corrosion on any of the alloy parts, (heads, water pump) so this method is just fine. Coolant gets changed every 2 years.

I've never taken those drain plugs out in any cars I've owned, just done the flush method with tap water (drain from bottom radiator hose (I lie, radiator has a tap on it), refill with tap water, run the engine warm, let cool, repeat twice) and used the correct amount of concentrated coolant. I don't trust those plugs, they are in too tight, snap one off or strip the thread and you have real problems.

Last time I pulled bits off my 15 year old TS V6 at 240,000 km, there was no corrosion on any of the alloy parts, (heads, water pump) so this method is just fine. Coolant gets changed every 2 years.

I left the rear one in with my previous change and just did a fill with SCA coolant, ran for a while, drained front bank and radiator again and filled with SCA coolant again.
Then I found the SCA coolant is crud and created sludge, finally got the rear plug out with a breaker bar and it was clogged to the max with sludge.
Hopefully they're easier to get to with extractors rather than the stock manifolds?

In regards to Irwin bolt grips, I have a set, they are fantastic!!