Jerry Posted February 10, 2013 Share Posted February 10, 2013 Thanks in advance :) Link to comment Share on other sites More sharing options...
dasbulliwagen Posted February 11, 2013 Share Posted February 11, 2013 I think we need more details. I'm not sure what a block coolant drain plug is, and I'm a professional mechanic. Do you mean the block freeze plugs? They are round discs that get hammered into the block and use an interference fit to seal the coolant in, but are made to be a weak point if the coolant in the block freezes. If thats what youre talking about, you take a punch and a hammer, and knock one side of it into the block to turn it sideways, then pull it out with some pliers, clean the hole and install a new one the same size with a freeze plug installer, or a socket that will fit snugly inside the freeze plug cup, and hammer it in so it is just under flush with the block. Hope this helps. If not let us know what ya got! Link to comment Share on other sites More sharing options...
mvusse Posted February 11, 2013 Share Posted February 11, 2013 Every engine I have worked on has had a drain plug to drain the coolant. Problem is they are usually so rusted in they will break before it will unscrew. Therefore I use pressurized air to evacuate coolant from the block. Link to comment Share on other sites More sharing options...
HOrnbrod Posted February 11, 2013 Share Posted February 11, 2013 EDIT: The one on my 91 is a recessed 12mm 8mm plug. I have a combination metric plug tool that I used on Benz's that fits it fine. You can also get a socket or grind down a 1/2" 3/8" ratchet extension. If you get it out be sure to use anti-seize when re-installing. I went and looked. Haven't pulled it in years............ Link to comment Share on other sites More sharing options...
gogmorgo Posted February 11, 2013 Share Posted February 11, 2013 I looked it up online when I noticed my owner's manual said I had a block drain plug. I remember it being 8mm square? Didn't have an 8mm square so I didn't even bother looking for where the drain plug was. Just pulled all the hoses off the block and let it drain out. Link to comment Share on other sites More sharing options...
flint54 Posted February 11, 2013 Share Posted February 11, 2013 If it's the recessed block drain plug as described, good luck. You may wish to save the aggravation and not bother. I applied a great deal of force, heat, penetrant, and no small amount of foul incantations without budging that litlle ba$t$rd one bit. Link to comment Share on other sites More sharing options...
cruiser54 Posted February 11, 2013 Share Posted February 11, 2013 5/16" square drive. An 8mm or 5/16" allen wrench can be ground down to fit. Link to comment Share on other sites More sharing options...
gogmorgo Posted February 11, 2013 Share Posted February 11, 2013 If it's the recessed block drain plug as described, good luck. You may wish to save the aggravation and not bother. I applied a great deal of force, heat, penetrant, and no small amount of foul incantations without budging that litlle ba$t$rd one bit. Heat might actually make this one worse. You'd expand the plug much faster than you'd expand the block around it. Link to comment Share on other sites More sharing options...
HOrnbrod Posted February 11, 2013 Share Posted February 11, 2013 Mine came out pretty easily with the Benz metric plug tool. Soaked it overnight with PB, had to tap in the tool and use a short cheater, but it came out. It's 3/8" NPT, so if you do get it out you can replace with a more conventional plug. I only pulled it once, and as I remember no crud came out that you couldn't get out easier via the lower radiator hose and flushing from above w/ the stat removed. Link to comment Share on other sites More sharing options...
Jerry Posted February 11, 2013 Author Share Posted February 11, 2013 Great, thanks for the info guys. To clarify, I'm talking about the plug as shown in the diagram (thanks mvusse). I flushed the cooling system couple years back and when I went to re-fill I could only get half the specified amount of coolant back in. I think that was because I didn't take out the block drain plug and that must have left quite a lot of water in the system and crud sitting in the bottom of the block. I've just checked it yesterday and there's a ton of brown sediment in the coolant, probably rust so I want to give the system a real good clear out. I have an airline. Recommendations? Bottom and top hoses off at block and blast away with the air line? Rinse and repeat? Sound like a plan? Avoids having to extract a probably very rusty and inaccessible drain plug. TIA :) Link to comment Share on other sites More sharing options...
mvusse Posted February 12, 2013 Share Posted February 12, 2013 Brown sediment from rust means you used tap water (and have hard water) instead of distilled as is specified in the manual. Link to comment Share on other sites More sharing options...
gogmorgo Posted February 12, 2013 Share Posted February 12, 2013 Even distilled water will cause rusting. Unless you've managed to extract all the dissolved O2 you'll get some rust. But yeah, you're still much better off avoiding the minerals and using distilled water. Link to comment Share on other sites More sharing options...
mvusse Posted February 12, 2013 Share Posted February 12, 2013 The biggest problem with hard tap water is not that it causes rust, it is that it has iron in it (that's what makes it "hard") that will separate out as rust gunk. This will happen within days if not hours of filling it. I plugged up two radiators before I learned to use distilled water. Link to comment Share on other sites More sharing options...
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