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Old 04-05-2003, 03:54 PM
seacoast_benz seacoast_benz is offline
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Join Date: Feb 2002
Location: SF Bay Area, CA
Posts: 180
Block drain and t-stat change, 380SL

Spring has sprung! Time to service cooling systems before the heat kicks in.

Doctoring up an '83 380SL here. The PO did some stuff right, like a double-row chain, and some very wrong. Part of the wrong was the coolant: classic green Prestone cut with tap water. Lots of mineral scale visible in the reserve tank.

(The 500E, thank goodness, has always had proper changes with the right stuff, is clean as a whistle, and runs cool as a cucumber. Praise to the PO.)

When I first began to work on this vehicle, it was a notorious hot runner. The first step, of what I thought was many, was just to get the old stuff out. I ran multiple plain water flushes, hot cycled each, ended with two distilled flushes, hot cycled, and finished with 50/50 Dex-cool and distilled.

(Yes, I know, MB coolant is preferable, but I thought I would be dumping this stuff in a month. And many of the Dex horror stories seem to be from people who left old coolant in the block and/or heater core. I have found that if you flush every last milliliter of non-Dex coolant out, Dex is well behaved stuff.)

The Dex/distilled combo instantly got rid of the borderline overheating and made the car into a merely warm runner. But it's had that for eighteen months now, summer is coming, and the driver of the car tells me it's starting to run to the hot side again.

I think I am going to citric-flush it, follow with some plain flushes, change out the thermostat and see. If that doesn't improve matters, I'll pull the rad for rodding and change the water pump.

Pulled the reserve tank for inspection yesterday. Interesting Dex-cool note: the mineral scale in the tank, which was hard, crusty and unrinsable when the car arrived, has now been softened up after Dex immersion. I reached in with a tool and found that the scale came away easily to the touch. A garden hose rinse took out 99% of the scale. Excellent.

Couple of questions here:

I couldn't find the block drain when I first did this job. Didn't have a 107 CD available. Now I have the CD, but it's in a box behind a stack of others. Can anyone point me to the drain plug?

The thermostat is obviously on the left side of the water pump. The two front bolts look easy with a box wrench. I can't even see the third one. Sidewinder ratchet, maybe? Not much room in there.

(I know that these bolts like to shed heads. I'll soak them in Kroil for a few days first, and use antiseize when I reassemble. Might sacrifice a goat, too. The last bolt I decapitated cost me a full week of annoyance.)

Is the rad just held in by the two clips at the bottom left and right? I attempted to lift it after draining, and it seems incredibly solid in place.

Thanks for any guidance anyone can send along!

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