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6.9 creeping coolant loss

Started by Punker, 29 June 2020, 05:01 AM

Punker

Hi guys,

as reported I changed the radiator hoses and the thermostat on my 6.9. Unfortunately I am now losing cooling water. About 1.5 liters per 100 kilometers. Pretty stupid. I haven't found a leak although I suspected the control of the automatic air conditioning (it's always a bit wet there).

Does anybody have a tip how I can proceed to find the leak?

Thanks for your tips on this annoying topic
Bjorn

1978 Mercedes 6.9 # 4616 - black/black leather
BMW R 25/3

raueda1

If your leak just started when you changed hoses I doubt it's a coincidence.  Clamps need to be surprisingly tight or they absolutely will seep.  Loosen, wiggle the hose around to reseat and retighten.

Other than that?  Leaking heater core or heater hoses?  I had a kind of always-wet floor situation and that's what it turned out to be.  OTOH, 1.5L/100km is a lot, mine was much smaller.  Still, worth exploring.
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

daantjie

Maybe also replace the radiator cap, they are super cheap.
Daniel
1977 450 SEL 6.9 - Astralsilber

Punker

many thanks for your tips . I have already replaced the radiator cap. I will check the hoses. Is it actually possible to remove the control unit for the automatic air conditioning and kill the connected hoses?

Plan a longer tour to Berlin in 2 weeks. Then I can't lose that much water.

Greetings
Björn
1978 Mercedes 6.9 # 4616 - black/black leather
BMW R 25/3

raueda1

Quote from: Punker on 29 June 2020, 02:36 PM
many thanks for your tips . I have already replaced the radiator cap. I will check the hoses. Is it actually possible to remove the control unit for the automatic air conditioning and kill the connected hoses?

Plan a longer tour to Berlin in 2 weeks. Then I can't lose that much water.  Greetings
Björn
Can you clarify?  AC doesn't interact with the cooling system at all.
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Jed

I think he is referring to the heater servo for the ACC...yes that can definitely leak.....
1979 Mercedes 6.9 #5206 - restored
1979 Mercedes 6.9 #6424 - ongoing restoration
1976 Mercedes 6.9 #484 - restoration?

revilla

Yes, 1.5 litters/100 Km is a lot!
But coolant liquids are made to leave a white trace once dry. So it should be easy to identify the leaking spot.
If you suspect the acc servo, yes, you can isolate it (by-pass) for your trip. There was a recent post about it. I'll try to find it.
Better to find the leaking point(s) and fix rather than the frustrating path of changing parts left and right in a trail and error approach. That can be expensive and you might find yourself chasing shooting stars. Not good.
Cheers

revilla


Punker

Many thanks for the recommendations. In the next few days I will have time to tackle the problem with your recommendations. I'll keep you informed.
Many greetings
Bjorn
1978 Mercedes 6.9 # 4616 - black/black leather
BMW R 25/3

PosedgeClk

I am surprised that no one has suggested the fluorescent dye. There are fairly inexpensive kits whereby you purchase a dye and a UV illuminator and trace down the leak shortly after running the dye through the system.
1979 450SEL 6.9

Randys01

how about a little look into the motor?

Trapo

Quote from: Randys01 on 01 July 2020, 03:01 AM
how about a little look into the motor?

Randy's suggestion is sound.  I found coolant dripping into the oil pan through a hole behind the water pump. If your oil measuring stick comes out "mayonnaise" color as Randy called, you found your leak.
A Mini racer but an MB fan at heart.
My first MB: 220 1954
My second MB: 220S 1956
My third MB: 190 1961
W210 320 S, W210 270 CDI, 190 E
W116 450 SEL