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!

s/b

And actually, it dawns on me that maybe the thermostat cover would be easier to remove (and less likely to result in headless bolts) if I just took off the whole water pump assembly and then pulled the t-stat on the bench.

Hi seacoast, if you're gonna' drain the block, get your umbrella ready! There are two block drain bolts on the 116 engine. You can see them ( one on each side ) by looking straight up from the bottom. They're 6mm allen's (they look similar to trans' pan drain plugs ). It's difficult to describe their location. They're about mid-way from front to back, above the highest point of the main oil pan. If you look around you'll find'em. The tricky part is not making a mess when you remove them. There's no easy way to direct the coolant into the drain pan. Let us know what you come up with.

a long 1/4 inch ext with a swivel 10mm socket will get that therm cover out in a heart beat. just go under the alt. or just take the alt out. those drain plugs are soft. you may need to hit them or heat them up if they resist you. i would get spares if you don't have the time.

Thanks, guys!

The citric is marinating in the system now. Boy, does it take a *lot* of flushes to get the system fully changed with just the radiator drain! I ran nine cycles before getting clear water.

I'll do a couple of heat-up cool-down runs with the citric before draining and going after the thermostat. Fortunately, citric is far more environmentally benign than ethylene glycol, and I can just dump the block drains straight into the gutter.

The two front thermostat bolts have been Kroiled. I'll dose them again with Kroil every time I warm up the engine. As for the one in back, I'll have to take my chances -- can't see where to squirt the penetrant, and it's too expensive to just blast in there blindly.

s/b

Citric results: after one hot cycle, the reserve tank, which was spotless to start, filled up at the bottom with obvious large flakes of scale.

I sucked those out with a Mityvac and ran it to hot again. More scale, again extracted by suction. At this rate, I think I should just power-flush the whole system and start again with clean citric. Unfortunately, this batch was the very last of the citric powder.

Okay, I've got the car on ramps and I've eyeballed the block drains. One's a straight shot, the other has an trans line in the way and will probably need an angle joint on it, but no trouble.

Meanwhile...

I noticed a steady drip from under the car, *behind* the engine. I stuck my hand under it: clear water, which is what's in the system now.

First thought: "Oh, futz. Heater core is dying."

Scooted further in and got a halogen light up in there. The drip is coming from a rubber weep tube beside the transmission. There are two of them; only one is draining.

Any idea what that might be from?

most likely the fluid is condensation from the a/c.

Yeah, I typically think AC when I find a puddle of clear water, but right now, to circulate the flush everywhere including the heater core, I have the heater on full blast.

s/b

Hey seacoast, if only one A/C drain is working you should clean the one that's clogged. Use a coathanger to open the drain from the bottom, but be careful. You could get a face full of water/crud. Good luck

Roger wilco, I'll poke around in the other drain and see what comes out.

I just verified that turning the heat off stops the drip. Turning the heat back to full starts it again, about two drops/second. Turning the heat off again stops it.

Pretty definitely a compromised heater core, I would guess, draining through the same path that the AC evaporator would drain.

It probably had a rust leak plugged up with scale; the citric dissolved the scale and it's Katy bar the door. Drat.

s/b