Where's the coolant drain plug on the engine block? 78 450sl

[jnanasakti]

So I have this overheat problem. When I originally bought the 78, it was in Oct of 04, being it was cold outside, I think that although there might have been an overheat problem then, it was less apparent because of outside temps (live in chicago). Long story short, I think it's had an overheat problem ever since I've been the owner.

First thing I did was I replaced the thermostat; inexpensive solution, if thats the problem. No noticeable change, still overheating.

So, know I have three major things, the fan clutch, the waterpump, and the radiator.

While the engine was running, I slowly pushed the fan shroud against the fan to see what kind of resistance; the fan did not slow down or stop, so I figure the fan clutch is fine.

That leaves me with either the water pump, or the radiator. Can anyone tell me how to test the water pump if that can be done. The waterpump costs ~140; the radiator 800...thats a huge difference.

So now, I wanna do a citric acid flush, but in order to do that, as suggested by many, I should drain the coolant out the block as well. Does anyone know where the drain plug/hose is for the block on a 78 450sl?

Any thoughts or advice on these issues is appreciated.

...also, whenever I keep the car moving, the temp drops. The temp drops are better on the highway, but decent (drop to about 200) at 30mph

[Lexxani]

when I flushed my 117.985 I just removed the drain plug on the lower right of the radiator and let it drain, to remove any left over sediment I added a couppla gallons of distilled water to address any thing left behind as well as to dilute any remaining coolant, filled up with Zerex G-05 (correct coolant for MB's) and mixed 50/50 with distilled water.

I dont believe there is a block drain plug for coolant, but the radiator drain is the easiest and most accessable, you need not even take a jack to the car.

One more thing, does your aux fan work? you'd know if it did, it is a fairly loud. Mine usually doesent engage except when the engine gets really hot during the summer here in florida.

[jnanasakti]

Originally Posted by Lexxani

when I flushed my 117.985 I just removed the drain plug on the lower right of the radiator and let it drain, to remove any left over sediment I added a couppla gallons of distilled water to address any thing left behind as well as to dilute any remaining coolant, filled up with Zerex G-05 (correct coolant for MB's) and mixed 50/50 with distilled water.

I dont believe there is a block drain plug for coolant, but the radiator drain is the easiest and most accessable, you need not even take a jack to the car.

One more thing, does your aux fan work? you'd know if it did, it is a fairly loud. Mine usually doesent engage except when the engine gets really hot during the summer here in florida.

If there's no block drain for coolant, then that's good and I won't worry about that. I'm still gonna move forward with the citric acid flush. If there's gunk in the coolant spaces or radiator, my understanding is that it'll fix it (or worse, create a leak...risk I'm willing to take; I think).

You know, I think that my aux fan does not work. I think I'll definitely have to look into that.

[Lexxani]

check your relay, its located above the fuse box, you have to remove the hardboard panel as well as the doorsill trim to get at it. There are 6 fuses, I believe the fan relay is the top or the one below it (in the middle) on the column nearest to the seat. . .

No aux fan is definitely a contributing factor to ****ty cooling. . let me guess your a/c isnt all that cold either?