Purging the GREEN AF stuff? - PeachParts Mercedes-Benz Forum

Dervman · #1 11-03-2004, 09:47 AM

OK, I have searched and read many threads regarding the recommendadtions for coolant in our Diesel engines. My SDL came to me filled with the GREEN STUFF

and I am planning on putting in the correct M-B PINK AF in the next week or so.

My question is, are there any recommended flushing or 'treatments' required to totally remove the Green AF before re-filling with the OEM coolant? I have read references to citric acid and de-oiling flushes, but these are only recommended if you have corrosion or oil in the coolant, which I don't appear to have. Radiator & Water Pump were both replaced in 2000.

Thanks

dieseldiehard · #2 11-03-2004, 01:43 PM

If your system is already free of scale and crud, just drain the radiator and attach a hose to the heater line (that is the hose that fits to a nipple on the left side of the head) and back flush it at least 2 or 3 minutes (engine cold of course).

I also made up a cable with a 2-pin connector that fits the motor at the heater (aux) pump. This clips to the battery and runs it during the flushing process to carry clean water to the heater core. There is a MB service bulletin that illustrates this, I just looked for it but can't find it.

Following a flush, I always operate the engine (driving the car about 1 mile) until the thermostat opens, then let it cool about 30 minutes and then repeat the drain/flush procedure until the water runs clear. I had to do this 5 times following a citric acid descaling attempt once, until the water did not feel slippery. You can't judge the acidity of the stuff by looking at it, you have to check it with litmus paper or by feeling it with your bare hands. What a PITA that was, 5 X 45 minutes = 4 hours. Some shops own a special flushing machine that attaches to the cooling system and runs under pressure while filtering the coolant out. They don't have the time to spend draining and refilling and running the car like I do, and there are probably restrictions that prevent dumping even tiny amounts of antifreeze down the drain. I catch the coolant from the first draining and carry it to the local recycling center where they accept it at no charge, but I let additional flushings go on the ground "out back", hoping it might kill some weeds there. If you have a well nearby you might not want to do this

I just reread your post and see you refer to a W126 chassis, right? That is slightly different than I described as applying to the iron head 617 engines. But similar technique can be used with the exception of where to back flush the engine. How many miles on your '87?
1971 220 (gas) 4-spd manual 106441
1979 300TD w/ ’85 turbo engine 295530
1983 300D 243280
1985 300TD 217300
1987 300D 258230

Dervman · #3 11-03-2004, 02:46 PM

Thanks Dieseldiehard for all the info.
Yes, this is for my '87 W126 300SDL.
The car just rolled over 193,000 miles. I bought the car in Texas in August and have been enjoying it ever since. I am slowly catching up on all the things on my "to do" list. The car was very well maintained and I have all the service records from new. It only had 2 previous owners. I haven't found any record of the Vacuum Pump being replaced so that is high on my priority list.

Do I need to remove the Thermostat to properly flush the system?

Dervman

The Warden · #4 11-03-2004, 03:04 PM

Quote:

Originally Posted by dieseldiehard

I also made up a cable with a 2-pin connector that fits the motor at the heater (aux) pump. This clips to the battery and runs it during the flushing process to carry clean water to the heater core. There is a MB service bulletin that illustrates this, I just looked for it but can't find it.

Did you also find a way to make sure the monovalve is open and allowing coolant to circulate through the system? Or does backpressure on it open it automatically?

I'm going to need to do a cooling flush before too long...and after the garbage that came out last year, I'm thinking long and hard about doing a citric acid flush this time, then adding a coolant filter into the system...

dieseldiehard · #5 11-03-2004, 04:15 PM

Hi Warden, I believe you will find that the mono valve is normally open. It closes when current is applied that is why there is a burst of moisture in the W123 car like your wagon when you start up after parking it for a while and it briefly is in defrost mode.

A citric acid flush is primarily to descale the radiator tubes, IMHO its calcium and magnesium that comes out of tap water that causes most of this.
If your radiator is old (meaning over say 4 or 5 years) then a acid treatment should improve its thermal efficiency.
I've seen radiator fluid that looked like tea leaves floating around in it, brownish in color due to rust. The mechanics at my friend's shop really were having fun describing radiator fluid in one car recently (sorry I can't repeat the wording they used here but I think you know!)

dieseldiehard · #6 11-03-2004, 04:31 PM

OK Dervman thanks for the data, sounds like a good car. Service records are important. Big question would be, does it still have a trap oxidizer in the exhaust line?

As for the thermostat I would remove it if it hasn't been replaced in order to look for crud in there. If it has been replaced in the past 3 years leave it be. There are reports of factory new thermostats sticking

MB coolant flush recommendations are very complex, they use a dummy thermostat (no one I know ever owned one of them!) and calls for a lot of stuff that will leave you wondering what the Germans were thinking of when they developed the factory service bulletins.

OTOH, I did have to burp my cooling system the first time I replaced coolant, you will too after you fill it and run the heater without that clever cable adapter thing.

RE: Vac Pump - very good subject for engine longevity!
The new style vacuum pump has four (or is it 5?) bolts on the front cover, better check and see what you have before too long, hopefully it was upgraded already.

And you may want to consider a transmission fluid and filter service if there is no record of it having been done in say 15K miles. The transmissions in these tend to fail in about 100K+/- according to someone here in the Shopforum. I haven't experienced any trans problems, fortunately my '87 had a rebuilt transmission installed shortly before the PO decided to sell the car and that was one big reason I bought the thing

256Kmiles and going STRONG! Love that '87 turbo !

Dervman · #7 11-03-2004, 05:03 PM

No Trap Oxidiser - it was removed on recall back in the mid-nineties. Can't tell if the Turbo was changed as well as there is no detailed record of the recall itself, only a note on an M-B Service sheet that it was done.

I was planning to put in a new Thermostat (OEM from M-B) but after your comment I'm having second thoughts. I can't find any recent reference to the existing one having been changed although it may have been done when the Rad and WP were done.

My Aux. Water Pump was seized when I got the car (I knew about it) and the power supply disconnected. I really should replace it but its a real PITA to get at buried under the monovalve and heater coolant hoses between the firewalls.

Transmission fluid was changed (inc. torque converter) about 6k ago along with a complete 30k Service. I plan on changing to Synthetic Mobil-ATF next time around. I did that in my wife's BMW325ix and I couldn't believe how much smoother the transmission was.

I will check the Vac Pump to see if it is the later design cover.

Thanks again for all the advice.

dieseldiehard · #8 11-03-2004, 05:12 PM

Gkad you are ahead on the trap business!
Records on my car showed the factory replaced the turbo and the entire exhaust line when they original trap recall was performed.

There is a picture of the later design Vac pump somewhere in the forum, lurking in the digital realm.
re: OE thermostats, here are two interesting readings:
oem thermostat vs. original equipment manuf.
and
Replaced T-Stat Engine now getting real hot

psfred · #9 11-03-2004, 07:08 PM

If you are only flushing out old coolant and not chemically cleaning, don't bother removing the thermostat.

When filling, there is a plug in the head next to the valve cover, up front, that can be removed ("sensor strip" -- I assume this is where temp sensors for this or that can be screwed in) to vent the air out of the head.

Drains are on the right rear of block, probably have to reach from underneath to get to it, and behind the tow hook cover on the radiator. You can attach at hose to both of them, much nicer than dumping coolant all over the place.

I'm gonna take a look at the 300D tonight when I put new sway bar bushing in it (or attempt to, we'll see what condition the bolts on the carriers are in!).

May go ahead and replace the coolant if I have time, else this weekend -- it's coming up on three years since I got it, and the coolant is (of course) green...

Same job on the TE this weekend, too.

Peter