Practically Classics Forum

Can anyone recommend a decent radiator flushing agent? I found tea coloured sludge underneath the radiator cap and as the age of the coolant is unknown (more than 12 months old) I'm going to replace it and because of the sludge I found I want to flush the cooling system. The cooling system is in good order so I don't feel the need to use a hose. The cap had seen better days and wasn't pressurising so I've repalced it with a brand new one.

The car? One of my Triumph Acclaims. These have the Honda EN4 engine which has an aluminium alloy block & head.

I'm very wary about using flushing agents, particularly on alloy engines. By their nature they are very aggressive. I would simply take off the rad and back flush with a hose, and also run the hose through the heater matrix, no need to remove it.

I degunked my rad by putting HOT cola in to it until it cooled. the amount of crud that freed up was unreal! (I did rince it thorougly before putting it back in the car)

TerryG wrote:I degunked my rad by putting HOT cola in to it until it cooled. the amount of crud that freed up was unreal! (I did filter it thorougly before putting it back in the bottle)

There, I've corrected that for you.

Cola? If it's good enough for cleaning the bog then it might just work a treat. The cheapest stuff from Lidl or the Sainsbury's Basics cola would be perfect. The only thing that bothers me is the sugar/sweetener contant. Should I dilute the cola or do I just use it neat?

Because I reckon the coolant is just in need of replacing, I've decided not to use a flushing agent as I had problems the last time I used one (on one of my other Acclaims).

My plan is to drain the radiator, refill with plain water (using said cheap cola instead is tempting), run it up to temperature, drain and refill with fresh coolant. Everything's working exactly as it should and the heater's putting out plenty of heat so this is the way to go.

I have never run a rad flush through a running engine. As i was replacing the engine but keeping the radiator i did used "neat" cola (tesco value), i let it go flat over night then got it REALLY hot on the hob before pouring it in to the rad.
I don't see how it could damage the engine if you run it to warm with coke in it, drain it out, fill it with water, run it, drain it out then fill it with coolant.
I'm sure someone will correct me if it is a really bad idea.

Mercedes Benz recommend citric acid flush. I've done it before on my 6.9 with no ill effects.

I didn't bother with a flushing agent. I drained the cooling system (the old coolant wasn't too bad but needed replacing), filled up with clean water, ran it up to temperature, drained it and refilled with fresh coolant. I also cleaned the overflow bottle out and put fresh coolant in. Job done!

I've used Cola to clean out the waterways before with excellent results.