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Old 05-17-2003, 04:33 PM
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help with my coolant flush

I'm in the middle of flushing my coolant right now on my 1988 300e (m103) and I've run into a problem. So far I have emptied the radiator and expansion tank wih the radiator drain. Right now I need to drain the block but the drain plug is REALLY stuck. I can't get enough leverage on it because it's pretty tight in there and I don't want to go spraying wd-40 all over my engine.

The plan is to use the degreaser and citric acid and then flush. All of this seems necessary because the coolant that came out of the radiator was VERY dirty.

Anyway, I'm thinking right now that I will fill up the expansion tank with plain water, then drain the radiator again after running the engine. I want to continue this until it runs clear. Is there any problem with this besides taking a very long time?

Can anybody think of a better way to do the flush or to get the drain plug out?
Thanks for your time.


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Old 05-17-2003, 06:29 PM
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Join Date: Sep 2001
Location: Wrightsville Beach NC
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If you put the front of your car on jack stands and get it from underneath is should'nt be a problem. Find and open end wrench (15mm I think) and a breaker bar, maybe spray a little PB blaster on it! You really need to flush the block especially if the radiator was nasty. Its worth it to do it right the first time then you don't have to worry about it for a couple of years. Good luck, let me know if you need further help.

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Old 05-17-2003, 09:08 PM
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Join Date: Nov 2000
Location: Vernon, CT
Posts: 1,846
I was about to drain and flush my newly acquired W124 (300TD) but I can't find the radiator drain. The radiator in thisTD has the tanks on the sides of the radiator. Is this the correct style for this chassis? If so, where is the drain?
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Old 05-18-2003, 11:53 PM
1991300SEL's Avatar
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Join Date: May 2003
Posts: 545
The SOHC M103 engine block coolant drain plug is back near the #6 exh. and uses a 19mm socket to loosen. 6 point socket is better as it get a better grip.

Don't know about the '98 mentioned above, but on many radiators fitted to 103 motors, the radiator drain plug is fitted on the front of the radiator - passenger side and can be a real bear to get to. On the 103 motor, it's easiest to drain the radiator by simply pulling the hose off the lower inside of the radiator - passenger side. This drains the rdaiator and the expansion tank in one shot.

Some will argue that removal of the radiator drain plug is better as it's lower than the hose I just mentioned and I would not argue with that, but again, getting to it can be very interesting in some cases.
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Old 05-19-2003, 09:45 AM
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Location: Austin, TX
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Elevate the front end on ramps or jack stands. You can get to the drain plug from underneath. Forget WD40, use Liquid Wrench or PB Blaster. A 19mm wrench or socket will do the trick. BTW, the drain plug doesn't come out, it's a petcock.

It you simply can't loosen it, try this. Either open the drian valve or the feeder hose from the expansion tank at the bottom passenger side of the radiator. Remove the thermostat housing and the t-stat. Make sure the heater is on. Insert a hose into the t-stat housing and flush until it runs clear.

You may need to lower the front end to let gravity help drain the block. To refill: raise the front end and pour cooland mix into the t-stat housing until it overflows. Replace the t-stat and housing. then, fill through the rcovery tank the rest of the way. Start the engine and top off after the t-stat opens.

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