Cooling System Cleaning Kit

An engine that runs hot in stop-start city traffic, idling at the lights on a hot day or on a long hill climb, with the temperature gauge creeping past centre, is a strong sign that its cooling system is compromised by a build-up of calcium and rust scale. Hot spots in the block and head cause detonation, or pinging, and whenever the temperature climbs past normal the engine is running in the danger zone.

Why a quick flush won't fix it

A 300 mL bottle of fast radiator flush won't remove what took years and thousands of kilometres to build up, and most fast flushes contain acids that damage copper, aluminium, brass and zinc alloys.

Why new parts won't fix it either

The usual next step is new parts: a new or larger radiator, a thermostat, hoses, fresh coolant, perhaps a water pump or an electric fan. They mask the symptoms, but if the radiator needed cleaning or replacing because of deposits, the engine block and cylinder head are coated with the same deposits.

Anything with a liquid-cooled engine, whether it runs on coolant or plain water: vintage, classic and late-model cars; work and recreational vehicles; light and heavy commercial vehicles and road haulage; earthmoving, mining and construction equipment, cranes and forklifts; tractors and farm machinery; generators and stationary engines; boats and ships.

NRG Automotive Repairs in Rydalmere, NSW, cleaned a badly corroded cooling system with 239 and photographed the job. As they point out, corrosion eats a cooling system from the inside, and cleaning it out can uncover damage that was hidden. On this one, the corrosion had eaten away the pipe ends where the hoses seal.

How long the clean takes depends on how much scale is in there: from a few hours for a late-model engine with a light dusting of rust, to as long as ten days for a badly scaled one. The colour of the liquid tells you where you are, so read this through before you start.

1. Prepare the vehicle

1. Drain the old coolant and flush the system out as thoroughly as you can, so only Part A and water go in.
2. Take the thermostat out. You'll be idling the engine, and with the thermostat out the solution flows from the start. Flow, turbulence and heat are what make 239 work.
3. Fit a filter in the top hose. Part A breaks down the soft top layer of rust quickly, releasing flakes of shale and scale that the water pump can carry into the radiator tubes or the heater core and block them. A proprietary in-line top hose filter works, or do as we do and use a thin, summer-weight cotton-nylon business sock: its weave stops anything big enough to block a radiator tube but lets the coolant flow freely. Disconnect the top hose from the radiator, push the sock toe-first into the top tank, fold its cuff back over the outlet, then refit the hose over it and clamp it. With the engine running, the sock balloons open inside the tank and catches the debris.

2. Mix and add Part A

1. Use one heaped spoonful of Part A per litre of cooling system capacity: a 10 litre system, such as a Falcon's, takes 10 heaped spoonfuls. Be generous, and don't level them off.
2. Dissolve it in a bucket with a couple of litres of hot water, from the kettle or the hot tap, and stir until it has fully dissolved. It must be hot: in cold water it takes an age to dissolve.
3. Pour the solution into the empty cooling system, top it up from the garden hose and refit the cap.

3. Run Part A until the liquid runs clear

Part A is ten times more effective at removing scale at 70°C or higher than at room temperature, so the more heat, flow and turbulence, the faster it works. We don't recommend driving the vehicle with Part A in, in case something goes wrong away from home: idle it instead.

1. Start the engine and idle it up to the centre of the temperature gauge, then switch off and let it cool. Repeat, again and again, to keep the solution moving and reacting. A weekend suits: start on Saturday morning and check it on Sunday afternoon.
2. Watch the colour. The solution goes in clear. As Part A breaks down the soft top layer of rust it turns a murky brown, like pea soup. As it reaches the harder, denser scale below, it lightens to the colour of light beer. As it gets back to bare cast iron, it goes clear again.
3. Once it's clear, Part A has done its job. It may still look a little muddy from dirt and clay in the system, which is fine; it shouldn't look rusty. If it still has colour, keep going a day at a time until it clears.

4. Flush out Part A

Drain Part A and flush the system every way you can, but don't worry if it won't all come out. Part A breaks the rust down into iron salts, a fine orange-red powder that clings to metal (on the top of the radiator tank it looks like surface rust), and a garden hose won't reach the back of the engine or the head. Part B deals with what's left.

5. Mix and run Part B

1. Dissolve the same number of heaped spoonfuls of Part B as you used of Part A in a couple of litres of hot water. Pour it into the empty system, top up from the hose and refit the cap.
2. Bring the engine up to temperature and switch off, two or three times, so the water pump circulates it.
3. Leave it overnight to soak. In the morning, bring it up to temperature once more, then drain it.

Part B turns the iron salts from orange-red to black and loosens their hold on the metal, so they flush out far more easily. It comes out dark, if not black, and that's where most of the debris comes away. Drain it on gravel rather than clean or coloured concrete, which it will stain.

6. Flush until it runs clean

1. Flush out what you can with the hose, then fill the system with water and run the engine with the cap off for a short time, so the water pump stirs the remaining particles up.
2. Switch off and drop the bottom radiator hose before the engine gets too hot, so you can refill with cold water straight away.
3. Catch the water in a bucket or saucepan tilted under the outlet. It will overflow, but the heavy iron salts settle in the bottom, so you can see how much came out.
4. Refill, run and drain again. Each flush brings out less. Keep going until nothing comes out but clean, clear water.
5. Remove the filter sock, refit the thermostat and fill with the correct mix of coolant.

Don't skip the final flushes. Leftover iron salts do no harm, but they turn fresh coolant brown within a day or so. Flushed out properly, the new coolant stays bright and clean.

Every cooling system is different, so call us before you start if you're unsure about any of it, and as often as you need to along the way. Advice is free, 7am–7pm, seven days, on 1800 441 163.