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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?
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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.