Last week I bought my first Miata. Its a 1991 with 91,000 miles and runs great. Last night it rained in Houston. When I drove to work I heard a splashing noise on the passenger side. The floor also got wet a little bit. I read a thread about a drain plug but I am not familiar with where it is and what to do. I need some info on how this water came in, how to take it out, and how to prevent it from happening again. Is this a serious issue?

 

Sounds like water trapped in the door(s). Open door(s), look up at underside, poke drain holes open with thin stiff wire (coathanger) or thin blade of screwdriver. Wipe water out of eyes and change shirt.

 

You probably have water trapped the side sills due to clogged drain holes. See pics below for location. Have marked them with a white line on the lower pinch weld seam. If you run your finger along the outer surface of this pinch weld you should feel two raised bumps in the otherwise smooth surface. The rear ones are located appro 9" and 12" forward of the rear wheel well opening. Front ones are located approx 4" and 7" rearward of the front wheel well opening. Use a good flat head screwdriver and force it up into the holes using a twisting and rocking motion and then get out of the way as water will come pouring out. If you have overflow into the interior it will probably be a couple of gallons.

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Rear drains marked with white

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Front drains marked with white.