6.9 coolant flush and block drain plugs

[raueda1]

Greetings,

I'm doing the citric acid coolant flush after replacing radiator hoses.  I know I'm supposed to drain the block but can't find the plugs.  Actually I haven't even looked yet because I've found that the mere act posting causes me to immediately find what I'm looking for whether anybody responds or not.  If anybody knows, of course, feel free to respond! 

But here's my real question:  If I drain, refill the radiator, run the engine till hot (i.e., coolant circulating through radiator and block)  and repeat several times, is this sufficient to mix out the coolant solution in the block?  Any other special caveats on flushing and refilling?  thanks much!

[daantjie]

Dave I have not done this myself so hopefully more learned members will chime in. I can check the engine manual when I get home. I think it only has welch plugs/freeze plugs. 

After all these years I would proceed with caution as this seems like one job that can turn into a bit of a wrench dance with tight clearances.

[raueda1]

Thanks, any info is useful.  Supposedly the car takes 19 liters of coolant, ca. 4.5 gallons.  I drained radiator and got about 2 gallons so it stands to reason that the rest is in the block.  Didn't see any details on the online manual. 

Wow, you got an ENGINE manual!  Nice.

[TJ 450]

Yes, there's two plugs for draining the block, left and right. They are 6mm inhex from memory and a bit of a challenge. I would definitely open these as there will be lots of crud at the bottom, in fact the sediment often blocks the drains.

Location is to the rear of the engine mounting arms, possibly obscured by the exhaust manifolds.

Tim

[oversize]

I've had some success by simply draining, disconnecting heater hoses and blasting out the crud with clean highish pressure water from the garden hose.  Of course that depends on you local water quality and pressure.  You can also achieve a reasonable 'flush' by filling and draining with clean water, repeating the process several times before filling with premix coolant or concentrate and distilled water in the correct ratio.

Pulling block drains can be a disastrous exercise, although Benzes will be better than any other manufacturer.

[raueda1]

OK, thanks all.  I've had countless cars over the years and this seems like the worst coolant flush process I can remember.   The way I'm set up at the moment there's no way I can get under the car enough to find, much less remove, the block drains, so that's out.  I guess I'll do the heater hose trick with several flushes. 

It looks like I may be lucky with the sludge in there anyway.  The hoses are old but no rust or gunk in them, in fact they're amazingly clean.  Old engines with a lot of rust and scale usually have crap in the hoses too.  Regardless, I'll just live with the results.  The car has no overheating issues even under load, at altitude, in triple digit temperatures.  Now on to the next issue.     Cheers,

[ptashek]

If memory serves right, the service manual procedure calls for an alkaline solution (5% caustic soda?) flush, before the citric acid flush. This is to degrease the coolant passages, in case there ever was any contamination.

Any grease in there will cause the acid to be ineffective.

[Squiggle Dog]

Apparently dishwasher detergent tabs are good to break up and drop in the cooling system (alone with water, before doing an acid flush) as it contains a caustic soda and cleans out oils. Then, I think the next step is drain, rinse, use citric or oxalic acid (wood bleach powder), followed by draining, rinsing, and then washing soda to neutralize the acid, then draining, rinsing very well, and finally adding the proper coolant. If you can't get the block drains out, I would worry about all these extra steps as there may be some residual detergent, acid, or soda in the system.

I tried flushing the cooling system in a 1960 Ford F-100 without removing the block drains, as it has an automatic transmission and uses the block drains to connect tubes which run back to a heat exchanger on the transmission. It was not at all effective, even using a flush-n-fill kit. I ended up disconnecting the transmission cooler lines and couldn't believe all the rust and goop that came out of the block. It took lots of rinsing before the fluid would run clear.

Anyway, it sounds like your cooling system is pretty clean, so you should be fine just buttoning it up and installing new coolant.

[daantjie]

Thanks, any info is useful.  Supposedly the car takes 19 liters of coolant, ca. 4.5 gallons.  I drained radiator and got about 2 gallons so it stands to reason that the rest is in the block.  Didn't see any details on the online manual. 

Wow, you got an ENGINE manual!  Nice.

Dave yes I have the engine manual but it is the crappy Microfische version so pics are useless.
It speaks to 2 methods draining and filling depending on if you have manual or auto climate control. You can jump the Aux water pump and run the ACC to DEFROST and use the pump to run fresh coolant in. Cap is 16 litres of 50/50 premix coolant.