Oddly enough my SD was configured the same when I purchased it. I believe it was a 16mm fitting but use THIS guide to help you figure it out. Pictures are always cool!

On the issue of heat - check you mono valve -

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15 VW Passat TDI
00 E420
98 E300 DT
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97 S500
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86 Holden Jackaroo Turbo D
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