Want to flush coolant on SDL - PeachParts Mercedes-Benz Forum

WANT '71 280SEL · #1 01-04-2005, 12:53 PM

1. Where is the block drain. Do I even need to drain the block or can I just pull a plug on the radiator to empty everything out?
2. Does the radiator have some sort of drain plug?
3. I want to use a citric flush agent from one of the chain stores. (Prestone)
4. After I've some how drained all the coolant out, I add the flushing agent (through the upper hose I figured) and just water or a coolant/water mix?

I would then run the car with the agent + water(and coolant?)mix with the heater on high? Don't I want to get the car up to temp? Should the thermostat be removed for this? Any special parts needed to temporarily remove thermostat (gaskts, o-rings)

I appreciate any help.
Thanks
David

Brian Carlton · #2 01-04-2005, 01:48 PM

Quote:

Originally Posted by WANT '71 280SEL

1. Where is the block drain. Do I even need to drain the block or can I just pull a plug on the radiator to empty everything out?
2. Does the radiator have some sort of drain plug?
3. I want to use a citric flush agent from one of the chain stores. (Prestone)
4. After I've some how drained all the coolant out, I add the flushing agent (through the upper hose I figured) and just water or a coolant/water mix?

1. The block drain is on the passenger side of the engine beneath the turbo. You will need to get underneath the vehicle to access it. The access is quite difficult and the plug has probably never been removed. Based upon discussion with Dave, it would be preferable to simply raise the rear of the vehicle and let the coolant drain via the lower hose or the radiator drain plug.

2. The radiator has a drain plug on the bottom. It is plastic and seals with an O-ring.

3. This would be fine. The better flushing agents will have you install the flush and drive the vehicle for six hours or so. This could be dangerous in January because you have no anti-freeze in there and I'm sure that you don't want to take it on a six hour trip especially for this purpose.

4. The best scenario is to connect a garden hose to the hose on the very aft end of the head. You let the garden hose run, with the heater on high, and allow the system to flush all the old coolant out through the bottom of the radiator. If you flow too fast, the expansion tank will overflow.

After flushing the engine with clean water, you add the citric acid solution to the radiator and fill the system. The vehicle should be raised in the front when you do this. I had to add some water to the upper hose and fill the head, otherwise the temperature would climb above normal.

After driving it with the flushing agent, you need to flush the engine again with the garden hose. When you do this, you will probably see some additional green coolant, thereby confirming that the flush is not 100% effective. So, my recommendation is to fill the system again and drive the vehicle for 10 miles or so. Then return and flush the system yet again. This will, hopefully, get rid of all the remaining citric acid in the system (or at least 95% of it).

Then drain the system via the radiator and add 1.25 gallons of pure Xerex G-05. I stress the need to add pure anti-freeze, and not the mix, because you cannot get the system completely drained of water and you will not be able to add 2.50 gallons of the mix. The system uses about 11 quarts IIRC and 5 quarts of the G-05 will provide you with more than enough protection. Furthermore, after driving it, it will be down on coolant by at least 1 quart, and possibly up to 2 quarts. Now is the time to add mix to the system.

It's a bit of an arduous process.

Good luck.

dieseldiehard · #3 01-04-2005, 04:55 PM

Following a chemical flush, I empty then refill the radiator, run the car until the thermostat opens (heater on) by driving it 2 miles or so, then I repeat the process as many as five (5) times, until the discharge water no longer feels slippery. The water will feel "slippery" if it still has any flushing agent in it. You really want to get all of the residual stuff out before you put in new antifreeze and cap 'er off. The factory procedure is so complicated you will want to read it and reread it fifteen times before attempting it, it tells you to first install a special dummy thermostat, attach a pressure cap and run water thru it, run the car flush in place and so on then re-install the normal thermostat and do some more filling and flushing and so on. It may not be a bad procedure but I've done well with out all of that mess using my self made >arduous< procedure

Brian Carlton · #4 01-04-2005, 05:09 PM

Quote:

Originally Posted by dieseldiehard

Following a chemical flush, I empty then refill the radiator, run the car until the thermostat opens (heater on) by driving it 2 miles or so, then I repeat the process as many as five (5) times, until the discharge water no longer feels slippery.

This is a law of diminishing returns. The first time you flush it, say you remove 80% of the flush solution. The remaining flush solution is down to 20%.

The second time removes 80% of the remaining 20% = 16%

The third time removes 80% of the remaining 16% = 13%

The fourth time removes 80% of the remaining 13% = 10%

The fifth time removes 80% of the remaining 10% = 8%

It would sure be nice to figure out where the remaining 20% is hiding. Dave does not believe that it is in the bottom of the block because removing the drain plug results in very little discharge.

So, where is it?

dieseldiehard · #5 01-04-2005, 05:17 PM

I think some stays in the heater and the lines to and from the mono valve.

Brian Carlton · #6 01-04-2005, 05:23 PM

Quote:

Originally Posted by dieseldiehard

I think some stays in the heater and the lines to and from the mono valve.

If so, I wonder if you could utilize compressed air to drive it out of there.
It would sure be nice to do the procedure one time!

dieseldiehard · #7 01-04-2005, 05:30 PM

Brian, I tried using compressed air once to blow out water when I had one end of the block-to-firewall hose disconnected in a W123. It hissed and blew but I don't think much liquid came out, besides I don't think that is wise to hit the mono valve with any pressure like that or the rubber diaphragm may be damaged.
Some shops have a closed loop flushing machine that might do a thorough job, I just like to DIY my way, even if it takes half an afternoon.

Brian Carlton · #8 01-04-2005, 05:38 PM

It might be the case that blowing compressed air through the heater core is not very effective. There is the additional risk of damaging the monovalve.

Five flushes..............................

speedy300Dturbo · #9 01-04-2005, 05:56 PM

Dave suggested that I blow through the heater hose (next to the intake manifold). Sure enough, that got another pint or three out of the system...

WANT '71 280SEL · #10 01-04-2005, 05:58 PM

Could I just keep adding water through the top radiator hose to flush all the flushing agent out with the car runnning, and heat on high?
Thanks
David

WANT '71 280SEL · #11 01-04-2005, 05:59 PM

Now that I think about it, I couldn't because then it wouldn't return to the radiator and the hose would be pushing "against current" per say. Is there a particular hose I should remove at the back to finish off the flushing?
Thanks
David

Brian Carlton · #12 01-04-2005, 06:07 PM

Quote:

Originally Posted by WANT '71 280SEL

Now that I think about it, I couldn't because then it wouldn't return to the radiator and the hose would be pushing "against current" per say. Is there a particular hose I should remove at the back to finish off the flushing?
Thanks
David

The hose that I referred to above is at the rear of the head, on the drivers side. You can disconnect it from the hard line and install one of those Prestone "flush T's". This allows you to connect a garden hose to the engine without getting too much water all over everything. You will need a short section of hose and suitable hose clamps to work with the flush T.

dieseldiehard · #13 01-04-2005, 06:23 PM

Oh dear! the infamous Prestone flushing tee

My brother almost had a divorce or something because of one of those things, they don't talk about the "incident" even in closed family circles any more. He confided in me that he bought the Prestone kit and installed the tee on his wife's Lexus. Flushed it and all and refilled no problem. A few months later he was driving along the freeway at 65 when the idiot lights all came on, check engine, etc. So by the time he could fight his way off the road and find a place to stop the engine was toast. Grinding sounds

Came to discover that the center of the cap blew out, just gone I don't know why it just was gone and all the coolant gushed out. I would have sued Prestone

He replaced the toasted engine with a used one that leaked and stained the drive, under duress he sold the car at a loss to please the wife. Good thing it wasn't a MB or I'd probably have bought it from him....
I suggest if you use the Prestone tee thing, remove it and replace it with a short pipe and hose clamps afterwards. Lesson to the wise HISTORY REPEATS ITSELF! ! ! ! !
Ooops I hope you don't have one on any of your cars, Brian or you'll lose sleep after this post

Addendum. I did a search for "Preston Tee Failure" and guess what? another tee cap blew! see : http://www.lunghd.com/Tech_Articles/Cooling/BurpAirMod.htm

1971 220 (gas) 4-spd manual 106441
1979 300TD w/ ’85 turbo engine 296650
1983 300D 243280
1985 300TD 223470
1987 300D 262300

Hatterasguy · #14 01-04-2005, 09:26 PM

When I did my SDL last spring I just drained all of the coolant out of the rad, and since I was changing a lot of the hoses the block drained to. I didn't mess with the plug, I just refilled with water ran that for a few days then added coolant. As long as you get most of the coolant, I will do mine every spring I don't want to mess with the block plug.

Btw replace the upper hose at least, it was only $13 last I checked. This is a 603 why chance it?

I think the Prestone says to add with water and then run the car for awhile, that should be good enough.

WANT '71 280SEL · #15 01-04-2005, 11:42 PM

Bought two bottles of the Prestone flushing agent. They also have a rust remover and cleaner for sale, but I just bought the flushing agent. I'm going to pour both bottles into the radiator via the top hose then top up with water enough to fill the rad and block, then run around and do some errands. I won't let it sit overnight or hardly even turn it off. Then, I'll go back to the shop (25 miles from my house exactly) and drain it out then keep flushing with water until the agent is out. Then, I'll add 1 gallon of straight antifreeze then top up with a mix. I don't know if the extra 1/4 gallon would matter much, but if it does, I don't mind.

When I bought the two bottles of flush at Autozone, they don't carry
Zerex-G05! I thought they use to since that;s where I bought it, but I think the Advance Auto Parts by the shop has it, if not, I'll keep looking till I do. Right now the car has green stuff in it.

That's what I thought when I saw it in there...
Thanks
David