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Old 09-30-2002, 12:50 PM
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Draining and Flushing M103

I've been plowing through the archives but couldn't isolate answers to these questions.

1) How do you completely drain the coolant system on the M103? I've been refreshing some of the coolant by draining from the petcock on the bottom of the radiator but that won't get all of it.

2) How do you go about flushing the system using citric acid or just plain water? I've always tried to avoid using tap water but I guess that's the only way to flush the system.

Thanks in advance,
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Old 09-30-2002, 02:04 PM
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Join Date: Dec 2001
Posts: 571
This works for me - I have a 103 motor.

- The easiest way to drain a 103 radiator is to remove the hose at the passenger-side bottom of the radiator. This drains the radiator and the pressurized expansion tank. There is a red drain plug around the front, but in some cases it's really hard to get to.

- Drain the engine block by removing a 19mm drain plug on passenger side between the #5 and #6 cyl exh. manifold...thereabouts.

- Remove thermostat housing cover(three 10mm bolts) - lift off housing. In order to remove the thermostat, you'll need to get the t-stat gasket out. On some t-stats, it's fitted on to the t-stat and on others, it is merely pressed on to the top of it.

- Leave the t-stat out and temporarily reinstall the t-stat housing cover. You don't need to snug it down all that tight. This is temporary so you can flush with a garden hose.

- Hook up any hoses that are off. I flush thru the expansion tank and thru the block. Some say that flushing with a garden hose doesn't do that much good, but if you change out your coolant often enough, it helps to clean out residual junk.

- Drain out all flushing water from all points that you have drained coolant from. Reconnect all hoses.

- Remove t-stat housing cover and refill with pre-mixed MB coolant and H20. MB says to use a 50/50 mixture. This area often times turns into a heated debate as some say mix 60(water) and 40(coolant). It's your car and your call.

- Install a new t-stat with the air-bleeder hole on the t-stat in the highest position. Install gasket that accompanies it accordingly. Install the t-stat hosuing cover and bolts. DO NOT OVERTIGHTEN these bolts!!! I always coat mine with anti-sieze compound so they're easy to remove the next time.

- Refill your expansion tank until it's at the full mark.

- Leave expansion tank cap off and start car. Let it run 'til mtotor warms up. You do this to bleed air out of the system.

- Reinstall expansion tank cap.

You will likely have to top off the system a couple of times over the next few days. Check the level with the engine cold in the AM on a level surface.

There's a procedure in the 103 engine manual that involves removing a 14mm plug that's just to the left of the t-stat housing. The threads on this plug and the threads in the cyl. head housing can gets striped easily. I do not use this port to refill the system with for this reason. I simply refill thru the t-stat housing as dsecribed above.
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Old 09-30-2002, 02:18 PM
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Thanks Mike, great Info.

I've been changing as much as I can get out from the bottom of the radiator annually. I use a 50/50 mix of MB anti-freeze, distilled water and Water Wetter.

I've always had the theory that the thing that ruins cooling systems is tap water but I can't see any way to avoid it if I flush the system.

I recently sold my wife's 18 year old 190D and it never had tap water in it. The cooling system never required repair and worked fine up to the day I sold the car.

Best Regards,
Bud Cook
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Old 09-30-2002, 03:15 PM
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Join Date: Dec 2001
Posts: 571
There are two schools of thought on water.

One says use only coolant and distilled water.

The other says that only tap water should be used - distilled water is supposedly corrosive.

I've seen heated debates on this subject here and on the Ritter-Easley list.

It's my opinion that grocery-store-bought distilled water is not a problem. There are lab grades of water that supposedly eat thru metal pretty quick. I've often wondered if the .59 cent variety has been confused with the high $$$$ lab type.

I've used disitlled water and coolant for many years and the inside of my radiators stay very clean.

My 2 cents.
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Old 09-30-2002, 03:31 PM
I told you so!
Join Date: Jun 2002
Location: Motor City, MI
Posts: 2,804
For what it's worth, I've read in a respected automotive engineering journal that it's the calcium in tap water that is a mild poison to the cooling system. They didn't say how, but I surmise calcium may interfere with precipitation of the sodium silicate on the metal surfaces. Sodium silicate is a water glass that coats and protects the metals surfaces from corrosion.

For that reason I avoid tap water whenever I can when filling the cooling system. I think it's okay for flushing.

And yes, treat the thermostat housing bolts with never-sieze. I've already had to helicoil a pair.
95 E320 Cabriolet, 140K
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Old 09-30-2002, 03:32 PM
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Distilled water by itself is corrosive but when it's mixed with anti-freeze, it is not. There should be no debate.

This was explained over and over by the great Frank King who was the Techical Editor for the Star magazine for decades.

On the other hand, tap water varies tremendously depending on where you live. In Minnesota we had deep wells that produced hard and ancient water. In Arizona we get a lot of water that is stored in aquifers. The water in Arizona is so bad I had an RO system installed in my new home. The water here actually looks oily.

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