Hello,

My 2.5L is getting a new water pump. The pump is sealed up against the cast-iron block with a large o-ring. The sealing surface on the block is not exactly smooth, so I'm concerned about leakage after assembly. Do you think it would be a good idea to but a very thin skim coat of RTV on the o-ring to account for the surface irregularity or will the bare o-ring be sufficient?? BTW the official Ford shop manual makes no mention of RTV, but I think the manual assumes a pristine engine, not one from the real world.

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2000 Ford Ranger XL, 2.5L, Automatic, Bright Atlantic Blue. Former owner of a 2006 Ranger XLT, 2.3L, 5 speed

Check where the O-ring seats. It may be not where you think at first glance. Some have a groove they ride in, and when installed actually seal against the inner diameter of the opening, not the flat surface you see. A skim of RTV couldn't hurt as long as you don't slobber it all over the place so you have 'squeeze-out' that can leave blobs that can break loose and clog things up. I think I would let the RTV set up for an hour or so before adding the coolant, running the engine, etc. If you run too soon, the RTV could get pressurized and pushed around. Would it blow out? Not likely if you just spread a thin layer, but if you want it to do something without being affected by heat or pressure, setup time seems like a good idea to me.
tom

Use a little common sense.....if the seal worked on the old water pump then why are you worried about the seals on a replacement water pump.

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Thanks for the replies! My o-ring seals directly on the block. I cleaned up the sealing surface with scotchbrite and it now feels pretty smooth. So I opted to use just the o-ring with any RTV. I enjoy this site and appreciate the experience of its members.

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2000 Ford Ranger XL, 2.5L, Automatic, Bright Atlantic Blue. Former owner of a 2006 Ranger XLT, 2.3L, 5 speed