Author Topic: Draining and cleaning the cooling system 6.9  (Read 368 times)

Jan S

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Draining and cleaning the cooling system 6.9
« on: 07 October 2021, 04:06 PM »
M100 6.9 US version 1977

I need to replace my thermostat and a few aging hoses. While I'm at it, I might as well flush the entire cooling system (I do not know if this has been done by previous owners).

I have searched the forum and found the following recipe: 

https://forum.w116.org/mechanicals/cleaning-the-cooling-system/msg41188/#msg41188

- Any experience with this procedure?
- The recipe is referring to "a mild alcaline cleaner" ...... a dishwasher detergent?
- I have a "blue" anti-freeze and should probably use the same when refilling. I have heard Mercedes recommends a special blue for models prior to 2014 and a different blue for later models?
- Is draining the block a must?
- When revving the car from 0-50 km/h I believe I can hear some "bubbles" under the dash, maybe from the heater ..... could that be trapped air somewhere? By the way, my AC is not working .... e.g. compressor and condenser is missing.
- Anything special to be aware of during this procedure?

I'm trying to do the job before the winter sets in. Hopefully I will find suitable hoses.

Tips & tricks highly appreciated.
1975-mod W116 450 SE with 6.9 engine

ptashek

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Re: Draining and cleaning the cooling system 6.9
« Reply #1 on: 07 October 2021, 05:29 PM »
- The recipe is referring to "a mild alcaline cleaner" ...... a dishwasher detergent?

Don't use any detergent, especially one that crates tons of foam :)
MB still sell the appropriate cleaning agent: A0029864271 (only 200EUR for 10kg... LOL  :o :o)
5% solution of caustic soda should be fine too - the engine is all cast-iron.
If the 6.9 has anything made from aluminium in that path, don't use caustic soda.

Job reference from the tech manual: https://cdn.w116.org/cd/Engine/617/20-015.pdf

Quote
- I have a "blue" anti-freeze and should probably use the same when refilling. I have heard Mercedes recommends a special blue for models prior to 2014 and a different blue for later models?
You need a BASF Glysantin based coolant - a lot of them have "G48" in the name, and are blue in colour. Comma Xstreme G48 is what I use. Or anything else that has MB 325.0 approval. Post-2013 models use a different coolant type, normally pink in colour.

Quote
- Is draining the block a must?

Can't tell about the M100, but on the M117 there's barely anything in the block.
« Last Edit: 07 October 2021, 05:36 PM by ptashek »
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daantjie

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Re: Draining and cleaning the cooling system 6.9
« Reply #2 on: 07 October 2021, 06:18 PM »
Lots of guys run Zerex G-05 coolant, good stuff.  I would not touch the drain plugs if I were you, the chances of them being stuck fast are high and if you mess up the threads you will be crying :'(
Daniel
1977 450 SEL 6.9 - Astralsilber

Randys01

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Re: Draining and cleaning the cooling system 6.9
« Reply #3 on: 07 October 2021, 11:11 PM »
Good luck with the hoses. You will find that you have to cut them from generic hoses.
That water gurgling sound you hear is air in the system.
Ive just done a complete overhaul of my cooling system:
you will  find it is a weeping hose somewhere. Its quite a job replacing hoses ...in addition to making them,,..new clamps/thermostat out and checked/AAV  etc.

There is something very screwy with the hoses for these tubs,. My spare parts manual hardly goes near them..and when it does it has no part no but a no of xxx?
When I contacted Tom H at MBCC he said they only had one of them and no picture?!!...so I took it sight unseen and I reckon it is the one that goes from the back of the head to the heater valve.

daantjie

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Re: Draining and cleaning the cooling system 6.9
« Reply #4 on: 08 October 2021, 07:30 AM »
The upper and lower radiator hoses for the 6.9 should still be readily available and not too pricey.  I bought some a while ago and from memory it was painless.  Now if you are talking about the hoses for the dreaded ACC system, then yes, part numbers for those are shall we say an "interesting" challenge ::)
Daniel
1977 450 SEL 6.9 - Astralsilber

Jan S

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Re: Draining and cleaning the cooling system 6.9
« Reply #5 on: 08 October 2021, 08:53 AM »
Thanks to all of you for advice!

ptashek; good to know that your attached link points at the same recipe I was referring to. The 6.9 has a cast iron block and aluminum alloy heads. I shouldn't use caustic soda, I guess  :-\ And Comma sound good!

daantjie; thanks, I will leave the drain plugs for now - I hate messed up threads, a nightmare

Randys01; yes, I suspect I have to improvise with the hoses. An additional challenge .... the previous owner let the 4.5 liter engine radiator remain in the car for the 6.9 engine, and the two cars have different hoses at a few places.  >:(

How can I get rid of the gurgling? "Bleeding" the system? Please don't tell me I have to open the dash?  :'( The aging hoses I have to replace are at the front. I need to find the dimensions (inner diameter etc.) and buy some fairly good cooling hoses.
1975-mod W116 450 SE with 6.9 engine

Jan S

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Re: Draining and cleaning the cooling system 6.9
« Reply #6 on: 08 October 2021, 08:59 AM »
The upper and lower radiator hoses for the 6.9 should still be readily available and not too pricey.  I bought some a while ago and from memory it was painless.  Now if you are talking about the hoses for the dreaded ACC system, then yes, part numbers for those are shall we say an "interesting" challenge ::)

I have a 6.9 in a 450 SE with a 4.5 liter engine radiator  :'( It will be trial and error.

I'm not psychologically prepared to tackle the AC, yet.  ;) I just need to do main things for now .... and rid the gurgling would be nice
1975-mod W116 450 SE with 6.9 engine

TNNBENZ

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Re: Draining and cleaning the cooling system 6.9
« Reply #7 on: 08 October 2021, 09:50 AM »
The upper and lower radiator hoses for the 6.9 should still be readily available and not too pricey.  I bought some a while ago and from memory it was painless.  Now if you are talking about the hoses for the dreaded ACC system, then yes, part numbers for those are shall we say an "interesting" challenge ::)

I have a 6.9 in a 450 SE with a 4.5 liter engine radiator  :'( It will be trial and error.

I'm not psychologically prepared to tackle the AC, yet.  ;) I just need to do main things for now .... and rid the gurgling would be nice
I am impressed with your progress !!!  You have inspired me !!!
I know how you feel about the A/C.  I feel overwhelmed many times.  Sometimes a little break, helps a lot........I think your progress proves you will do fine with the A/C.  Just take your time.  Get you a BIG fan until then............ha, lol..........
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UTn_boy

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Re: Draining and cleaning the cooling system 6.9
« Reply #8 on: 08 October 2021, 01:29 PM »
- The recipe is referring to "a mild alcaline cleaner" ...... a dishwasher detergent?

Don't use any detergent, especially one that crates tons of foam :)
MB still sell the appropriate cleaning agent: A0029864271 (only 200EUR for 10kg... LOL  :o :o)
5% solution of caustic soda should be fine too - the engine is all cast-iron.
If the 6.9 has anything made from aluminium in that path, don't use caustic soda.

Job reference from the tech manual: https://cdn.w116.org/cd/Engine/617/20-015.pdf

Quote
- I have a "blue" anti-freeze and should probably use the same when refilling. I have heard Mercedes recommends a special blue for models prior to 2014 and a different blue for later models?
You need a BASF Glysantin based coolant - a lot of them have "G48" in the name, and are blue in colour. Comma Xstreme G48 is what I use. Or anything else that has MB 325.0 approval. Post-2013 models use a different coolant type, normally pink in colour.

Quote
- Is draining the block a must?

Can't tell about the M100, but on the M117 there's barely anything in the block.

The cylinder heads and intake manifold on a 6.3 and 6.9 are aluminum.  Only the block is cast iron. 

The block holds a gallon on the 6.9 and about three quarters of a gallon in the 4.5.  It's a significant enough of an amount to drain if the coolant hasn't been changed on more than 2 years.  Otherwise, draining the block isn't necessary. 

The cleaning agent you refer to, part number 002-986-42-71, is the cleaner used ONLY for when oil has contaminated the cooling system from blown or leaking head gaskets.  The correct cleaner for general flushing is part number 000-989-10-25-11.  It's a citric acid power that you mix with water, run in the engine, and then flush until it runs clean.  This cleaner is only about 15 Euros or $20 USD. 

When using the citric aid power to flush with, you must procure some litmus paper strips to test the pH of the water being used to flush out the engine.  Essentially, the pH needs to be neutral or slightly alkaline.  Otherwise, too much acidity will cause corrosion.  So be sure to flush well.  It may take 10 flushes, but it's necessary. 
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Jan S

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Re: Draining and cleaning the cooling system 6.9
« Reply #9 on: 08 October 2021, 04:50 PM »
I guess I will go directly to the citrus acid stuff, skip the alcaline cleaner.

Will the new coolant mix up well with the clean water trapped in the block and the heater? I guess everything will circulate and mix well as soon as I start the engine?

Is there an easy way to get rid of the gurgling under the dash? Probably trapped air somewhere .....
1975-mod W116 450 SE with 6.9 engine

nathan

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Re: Draining and cleaning the cooling system 6.9
« Reply #10 on: 09 October 2021, 04:38 AM »
Hi Jan,

this is a short video I made when I changed the coolant only my 6.9
https://www.youtube.com/watch?v=lDRRM_ELl4k

not sure if it helps.
regards
Nathan
Western Australia
6.9 79 #6436
6.9 79 #6290
6.9 79 #6181
6.9 78 #4764
6.9 77 #3096
6.9 76 #1741
6.9 76 #0902
6.9 75 #0018

ptashek

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Re: Draining and cleaning the cooling system 6.9
« Reply #11 on: 09 October 2021, 08:53 AM »
Thanks for the correction UTn_boy :)
I wasn't sure if the M100 had aluminium heads.

On the degreaser - recommended it based on the fact this is a transplant engine, with potentially unknown maintenance records / history.
It won't harm, might help.
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Jan S

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Re: Draining and cleaning the cooling system 6.9
« Reply #12 on: 09 October 2021, 04:52 PM »
Thanks, nathan, superb video and a really nice car you have!

Any trouble getting those two bolts in the block out/in? Your engine has been rebuilt - mine hasn't been "touched" in those areas since .... God knows when  :-\
1975-mod W116 450 SE with 6.9 engine

nathan

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Re: Draining and cleaning the cooling system 6.9
« Reply #13 on: 10 October 2021, 05:53 AM »
Cheers Jan,

The block bolts weren't actually too hard, its just that you get a coolant shower which will be even worse if you dont have access to a hoist! wear your wife's shower cap!

Crikey, anything could come out if it hadn't been done in a while. 

That darn car took (I forget how much!) a bucket load of coolant!

Good luck Jan
6.9 79 #6436
6.9 79 #6290
6.9 79 #6181
6.9 78 #4764
6.9 77 #3096
6.9 76 #1741
6.9 76 #0902
6.9 75 #0018

UTn_boy

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Re: Draining and cleaning the cooling system 6.9
« Reply #14 on: 10 October 2021, 01:25 PM »
To add to Jan's commentary, if the coolant hasn't been changed in a long while, there may be sediment built up above the block drain plugs.  When/If this happens, you'll know it because when you remove the block drain plugs either nothing will come out or a drip/dribble will show itself.  To remedy this, just get a long slender screw driver or something of the like and ream the drain holes out.  You'll still get a shower, but the drain will be open now. 
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1971 280sel Black/black leather
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1976 280s astral silver/blue MB Tex