240 General: Flushing cooling system

[Clifford Pope]

it seems a good idea to flush the system before draining and refilling with new antifreeze.
In the past I have just tipped in a bottle of the stuff, used the car the next day, then drained and refilled.
But reading the label I notice it now says pour it into the radiator, run up to temperature for 10 minutes, then cool and drain. But it isn't possible to pour it into the radiator, only the overflow reservoir, and that won't get circulated through the system until the engine has been through several heating and cooling cycles.

So is it OK to leave it in for a day of mixed running, or does it really mean only 10 minutes?

[cheshired5]

The only flush I'd ever use is deionised water unless a detergent was needed to remove oil deposits caused by some cross contamination.
Doing a couple of drain and fills using just deionised water over a couple of days would work fine so long as what comes out is clean and clear.
After your final drain, add 50% of your cooling capacity as neat coolant and top up with deionised water. The system will mix itself.
If you're interested, my coolant change/flush is here.
I use tap water followed by deionised. https://www.youtube.com/watch?v=CMkRdCUAlks

[Clifford Pope]

Ideally, yes, water alone should be sufficient. But if I suspect that there may be a certain amount of furring in the radiator or block, wouldn't a shot of the Holts defurrer be a good idea? Hence my question, how to mix it in 10 minutes, if that time actually matters.

[KBB]

Use a good cooling system descale and cleaner to remove mineral and acidic deposits and as mentioned mix with deionised water to prevent electrolysis.

[cheshired5]

Originally Posted by Clifford Pope

Ideally, yes, water alone should be sufficient. But if I suspect that there may be a certain amount of furring in the radiator or block

I would see what comes out first when running a tap water hose forwards and backwards through the radiator hoses.
If what comes out looks suspect and you want to use a suitable chemical, pour the correct concentration directly into the radiator through the disconnected top hose.
Then reconnect everything, top up the expansion with deionised water and do the cycle.
Speed up thermostat opening by reducing the cabin heater temp and turning on aircon if you have it.

[Stephen Edwin]

Putting Holts or similar in via the top hose sounds like a possile answer. Yes.

The advice on the link about cleaning out the hoses between the header tank and the radiator is a good point. Thank you.

I'm wondering, has anyone got a drain tap on the botom of their 240 radiator and/or found a drain tap for the engine block?

I am also wondering, is there any evidence from comparative tests as to any benefit from using de-ionised water as opposed to tap water?

[cheshired5]

Originally Posted by Stephen Edwin

I am also wondering, is there any evidence from comparative tests as to any benefit from using de-ionised water as opposed to tap water?

I've never sought any scientific comparisons but I've seen so much anecdotal evidence of what tap water mixes or tap water alone can do, I would never use it.
If you're in a soft water area, you may well be ok but deionised water can be had for less than a pound a litre and you need less than 10 litres to flush and fill a cooling system so I would look to make my savings elsewhere on the car.
Look in your kettle and you'll get an idea of the scale that can block the slim channels of a car radiator.

[wooble]

Originally Posted by Stephen Edwin

Putting Holts or similar in via the top hose sounds like a possile answer. Yes.

The advice on the link about cleaning out the hoses between the header tank and the radiator is a good point. Thank you.

I'm wondering, has anyone got a drain tap on the botom of their 240 radiator and/or found a drain tap for the engine block?

I am also wondering, is there any evidence from comparative tests as to any benefit from using de-ionised water as opposed to tap water?

There's a drain tap on the driver's side of the engine block, towards the rear. It even has a hose barb attached for easy draining, but may be clogged with sediment if you're long overdue a flush.

I flush mine by removing the thermostat and radiator, back flushing the block with a hose on the block drain tap, and flushing the radiator with a hose while it's off the car. I always fill with deionised water as I live in a hard water area and it's cheap peace of mind that I'm not furring up the cooling system.

[dingov70]

As a cheap alternative to de-ionised water , find a aquarium dealer & buy reverse osmosis water from them . Last time i bought 25lt it cost me about 50p per lt . The R.O. process removes dissolved mineral salts from the water so you end up with water you can pour into a battery with no side effects due to it's purity .

[Stephen Edwin]

Originally Posted by wooble

There's a drain tap on the driver's side of the engine block, towards the rear. It even has a hose barb attached for easy draining, but may be clogged with sediment if you're long overdue a flush.

I flush mine by removing the thermostat and radiator, back flushing the block with a hose on the block drain tap, and flushing the radiator with a hose while it's off the car. I always fill with deionised water as I live in a hard water area and it's cheap peace of mind that I'm not furring up the cooling system.

Thanks Wooble. I thought there is a drain tap somewhere there. Using it to put flushing water in is a great idea thanks.

I can see why one would perhaps use de-ioised water in a hard water area yes. Although I have seen it pointed out that a cooling system is rather different from say a kettle. In a kettle the water is frequently fully replenished, and the water does not get as hot as in a cooling system but is allowed to boil. The same applies to a steam iron. Anyway I've never had a furred up kettle or iron here and I am not tempted yet to use de-ionised water in the cooling system here.