Coolant flush. Can I check this procedure with you pls?

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Active Member
Oct 6, 2008
Surrey, United Kingdom
ML320 W163, E320 W210 & Jaguar X300-XJR6
Good morning all.

I am planning to flush my coolant system this weekend, to hopefully help my car maintain a more even temperature and to prepare it for the winter. I haven't done it on this car before and I wanted to get some feedback on the process I plan to follow to make sure I am not missing anything.

It’s a 1999 S320 LWB

1 Warm up the car turn & on the heater (with AC off)
2 Remove the plastic cover to gain access to the bottom of the rad, hoses etc & remove expansion cap
3 Remove bottom hose and drain coolant (hoping that this will remove more sludge than using the drain plug)
4 Flush through using a garden hose from the expansion tank (Should the engine be running??)
5 Replace the bottom hose, and refill using ordinary tap water and Forte coolant flush
6 Run for 20 minutes or so, to let the flush work and allow to cool
7 Drain again by remove the bottom hose
8 Final flush as per point 4
9 Reconnect bottom hose securely
10 Refill with proper mixture of quality coolant and distilled water
11 Reassemble everything, maybe add some coolant conditioner?
12 Test run

Do I need to do anything to remove airlocks or to ensure that the heater works ok after the procedure? I have had problems in the past (on Jaguar's) where air locks seem to gather in the heater matrix rendering it ineffective until they clear!

Does this sound ok to those with more Mercedes Benz experience than I?

Any advice is GREATLY appreciated!
I would not run the engine with no coolant present as water pump etc rely on the fluid to lubricate. Ideally you need to 'back flush' the rad but if thats not ideal then a hose at a reasonably low pressure will do. Flush until clean water is present!

Good luck!
Not sure about putting washing up liquid into my SClass though!!
On mine i just pulled the bottom hose off and refitted and refiiled and rechecked the next day and it took another 1/2 pint of coolant and has been steady ever since.

I have stuck ctfr in the truck engines at work when an oil cooler has blown then drained and refilled with plain water run again and drain then fill with coolant, they take ages to get hot unlike my merc.

I tried some of that coolant wetter agant in my last car and it didnt make a blind bit of difference not even one degree cooler.

Bit of a daft question, but how do the hoses come off??? They dont seem to have traditional Jubilee clips!!!
Mine had hose clips, but if its the springy steel clips you need pliers and the patience of the devil, you can get special pilers for these clips always handy to have, just drain it out of the drain screw, saves buying them.

I doubt that there is any sludge in your system - is the coolant in the header tank a nice clear blue /green colour? If it is then no harm in changing it but I doubt it is the cause of your hot running. Worth a try though. I use MB coolant additive (but other high quality ones will be fine) and distilled water - I think it was the hard tap water that may have furred up the radiator and for the cost of 5 litres from Halfords about £4 it is hardly expensive. Just drain it from the rad tap.

It is worth measuring the old fluid that drains out - then you will know if there are any air locks - which can sometimes happen. Re-fill slowly to avoid air locks.
i don't know then, its got to be the first stop before I get serious with the spanners!
I agree it is worth doing. I am not sure if the flushing agent will unblock a furred up radiator which is what my problem was with the same symptoms as you have.

I suppose you could remove the rad from the cars cooling system and put some sort of descaling solution in it and then flush it through 100% before re-connecting it to the cars cooling system. My view was that the rad was causing a problem; it was likely to get worse not better and at some point it would have done more damage to the engine - or if I started to mess around with this and that soluton then I would mess up a water pump or something - so I bit the bullet and put the new rad on.

Problem solved.

Do you live in a hard water area and has the coolant ben changed regularly?
I do live in a hard water area andthe car has spent its life in London. Now heres the problem, the car was an ex chauffeur's vehicle. I dont really now its history, but I got it at such a good price I foolishly didnt ask too many questions (I know the owner well, its a long story but anway!...). So snapped up an immaculate long wheelbase S320 for less than the cost of a secondhand fiesta..

Problem is it was treated as a tool by the previous owner, certainly no TLC went into maintaining it. As an example when I picked it up it was complaining about a lack of engine oil, when I got it home and checked after a few hours it was completely bone dry! Such a shame for a beautiful car,

So in a round about way my answer to your question about the coolant being changed is I very much doubt it!

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