where is the coolant drain for the block on the 117 engine?

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65 190d sold
85 380SE sold
87 560 SL 180K
84 380SE 96K (mint)

IIRC one on each side just ahead of the mounts. One bolt that pulls straight down on each side.

Sixto
87 300SDL

As important as freeze protection is CORROSION INHIBITION provided by the corrosion inhibitor chemicals in antifreeze. A concentration between 50 and 70 percent antifreeze will provide both freeze protection and proper corrosion protection.

The capacity of M103 systems is about 10-11 quarts, so you should start with 1.5 gallons of antifreeze and top off with distilled water.

Draining is simple. Pop out the small panel on the RH side of the valence to access the radiator drain. It has a nipple for about a 3/8" hose, so you can drain into a container.

The block drain has a nipple for about a 1/2" hose, and you simply turn it CCW to open. It's under the rear exhaust manifold and you can access it with a crescent wrench, box, or socket. IIRC the hex is 17 mm.

I also siphon some water into the overflow tank and then siphon it out to flush the overflow tank.

Remove the engine undercover for best access.

Fill the system slowly with antifreeze first, then start the engine and let it run until the thermostat opens. Add distilled water as required. I've never had to open the bleed plugs. It's alway self bled with no problems. There is an arrow on the outside of the expansion tank. This is the "full cold" mark and is just above the seam. (See the owners manual.)

You can use Zerex G-05 - about ten bucks a gallon at McParts. It's identical to MB antifreeze and meets the MB spec. Read the label.

You should drain and refill with fresh G-05 every three years, regardless of mileage if you want your cooling system to last and not be eaten away by corrosion, which can result in some VERY EXPENSIVE repairs.

A larger expansion tank is not necessary.

If you need more info or details, try the search function.

Duke

This could work in a Diesel or 119 with the thermostat in the radiator return line. How will the 103 thermostat open if there isn't liquid at the level of the thermostat?

Sixto
87 300SDL

Keep in mind that a water/anti-freeze mixture not only lower's the freezing point of the coolant, but also raises the boiling point. This is why all vehicles should run a 50/50 or thereabouts mix. Plus, anti-freeze has propertie's which reduce oxidative damage in the block/heads/radiator/heater core.

On the other hand antifreeze has less heat capacity than water. You need water in the mix to do the job of transferring heat from the block to the radiator.

Sixto
87 300SDL