Quote:
Originally Posted by 97 SL320
It looks like BSPP ( British Standard Pipe Parallel ) but could be a DIN / ISO / German equivalent. Go to Discount Hydraulic Hose and look at their thread ID PDF.
On the plug, where the threads hit the under head hex, there should be a slight taper from the hex to the threads. ( this is a reverse of a tapered seat spark plug. ) The outer sharp edge bites into the soft aluminum cooler boss. This is typical for BSPP in soft metals. If used on steel, a sealing washer is used.
This should plug screw in easily until the under head hits the boss so you have a thread issue that needs addressed.
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Doubt Behr would have used a British thread! Looking at that DHH pdf, it looks like my screw plug may be designed to have an o-ring. But I don't know if it is an original screw plug MB part A0019971530. No pictures on net that I could find. I am able to screw the plug all the way in. I am sure it had no crush washer on when I removed it. It may not do any harm to have an aluminum washer plus a little sealant. Just went out and picked up two washers. Probably use flat one plus some Permatex HT sealant.
New rad and cooler now in. Job complete. No leaks yet!
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Graham
85 300D
,72 350SL, 98 E320, Outback 2.5