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

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2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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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.

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

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

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?

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

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

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!