Thread: Coolant Flush Questions

Originally Posted by LandRohan

Hey guys,

Just about to attempt my first coolant flush but from what I can tell there seems to be two different ways to do this.

The first way is via my Haynes workshop manual. Basically it says that after draining the radiator you should then remove the alternator in order to gain access to the the cylinder block drain plug, drain coolant from there and then also remove the thermostat and then using a garden hose, flush out both the radiator via the radiator top hose connection point and the rest of the engine via thermostat connection point. Then refill system with coolant.

The second way and the way most people seem to be doing it is to simply drain the radiator. Fill the system with water (and a radiator flush cleaner solution if you want) and then run the car for 10mins with heater on full blast. Drain again and then re fill system with coolant.

I'd much rather do the second method but just wanted to check I'm not going to ruin anything that way?

It's a 02 TD5 Disco 2...

No idea what coolant is currently in there so need to get it all out before switching to my new stuff.

Keen to hear your thoughts. Thanks in advance!

Rohan

Doing it the second way could leave rad cleaner in the system, it's not possible to drain everything out so you'd need to flush several times if using rad cleaner.
Not draining the block leaves a lot of coolant in the system. Topping up with water and running dilutes this but there will still be some left in the system when you drain the rad again.

If I don't know the history of the vehicle I tend to drain then remove top & bottom radiator hose and flush bottom up.
I drain the block but flush through the top hose (too lazy to remove thermostat) but it means it's a slow process as the thermostat is closed. You can also flush up the bottom hose (doesn't hurt). When it runs clear you can stop.
Again if the vehicle is unknown then replacing the thermostat might be an idea.

Once you know what's in there there is less of a problem if you can't be bothered to drain the block. The only proviso is to always add the correct amount of new coolant. The percentage the manufacturer lists is to ensure the correct amount of corrosion inhibitor, reduce this and you compromise the corrosion protection.


Colin

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Rohan,
the cooling system for the 10P also has two lower hoses below the radiator outlet and the actual drain hole on the rail across the bottom of the engine which the thermostat sits above.
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You mention that you have no idea as to the coolant or such. Having just done the head and everything else on a TD5 which was well looked after except the coolant it would appear, if the service history does not support the fact it has been done, maybe be a good thing not to assume.

It may be an opportune moment to take off some hoses and investigate the state of the system, just for reference this is what I found on 260k country road driven TD5 with service history
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The second way and the way most people seem to be doing it is to simply drain the radiator. Fill the system with water (and a radiator flush cleaner solution if you want) and then run the car for 10mins with heater on full blast. Drain again and then re fill system with coolant.

Hi, first of all the heater's setting has noting to do with the coolant at all cos the circuit is not affected by that on a D2. Here's a verified method: Simply put a can of Liqui Moly radiator cleaner in the tank into the existing coolant(if it's full remove 300ml of it to make room for the additive), drive it one day like that, remove the drain plug from the bottom rail, insert a garden hose into the tank, let it flow and start the engine, keep the revs above 1500rpm for few seconds few times as to open the bypass valve, watch untill clean water comes out below then let the water out, some clean water will be trapped so fill with 6.5l of clean OAT then the rest with distilled water untill it comes out at the bleed hole, bleed with tank raised as in the book... job done

I drained mine with the drain plug on the radiator, filled with fresh water, ran to temp, drained and repeated a few times until the water came out cleanish.

I add this to the other posts - how you flush will depend on how much corrosion is in the block - this depends if the previous owner changed the coolant regularly. If at any stage the anti corrosion property of the existing coolant depleted or mostly water was used then you will have plenty of rust in the block. You will note some rust scum in the overflow bottle or in extreme case via the images of the water pump in one of the above posts.
This later situation is almost unrecoverable with your usual flushing additive from the local parts store. I have had such as car recently and I used a notable brand flush and it did not remove anywhere enough rust from the block. After using this product and then observing the flush water clear - using fresh rain water pumped from a rainwater tank - I then refilled with fresh coolant only to find rust sludge in the coolant bottle again after 6 months.
Corrosion inhibitors in coolant only work with blocks that are not already corroded. With a steel block there are 2 layers of rust in the cooling jacket. There is the soft ferrous oxide coating which acts as a barrier to heat transfer. Underneath that will be flakes of harder ferrous oxide. Both layers need to be removed through chemical action and heat. Once there is rust in the system your new coolant cannot get to the metal surface and so it will not stop further corrosion – it will slow it to some extent - my experience.

There are products and very lengthy flush procedures that will remove rust completely - see liquid intelligence – but it is a hell of a procedure to complete.

BTW never take the vehicle for a drive with chemical cleaners in the block – it will release gasses and cause huge pressure increase in the cooling system which will burst hoses or burst the heater matrix. Dont believe me - take it for a drive with the flush in it and then try to compress the radiator hose - most of the chinese pressure caps are faulty - of the 6 caps I tested, 50% would not release until at least 25 psi - and I have tested eurospares; britpart etc and most of then are not on spec - the other 50% leak continually and never reach correct pressure - the only one that passed testing was a german one marked Reuter under the cap. They are stamped 140kPa which is 20 psi in the old school - yes your TD5 cooling system is designed to run up to 20 psi - if your hoses are easy to squeeze you have a cheap cap releasing pressure at around 10 psi.

You will need to back flush and forward flush the matrix and the radiator and the block after removing the rust scale (if any in your vehicle).
See images below of rust and sludge accumulation areas in the radiator and matrix.