I’ve had an ND soft top and now an RF and have gone through the cleaning process for the roof drains on both.
They are slightly different at the top section of the drainage system but the same at the bottom section.
The hood drain cleaning brush from MX5 parts is the best piece of kit you can get for the job.
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Open the roof to a somewhat halfway position and leave it like that.
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Find the drainage grids on each side of the car. They guy in this video points out where they are between 1:20 and 1:30.
https://www.youtube.com/watch?app=desktop&v=wHmjMEICmDU -
Delicately push the drain brush down through this grid. If you feel any resistance, pull the brush back up slightly and twist and turn it a little and try to push it through the drain again. Brush up and down gently to clean the inside of the drain.
When doing mine, I took the brush out of the drain a few times and dipped it in a mixture of hot water and washing up liquid and then made another few passes with the brush to make sure I got rid of all the dirt and grime built up inside the drain. -
Once you have done both sides with the drain brush, you need to go to the rear window and clean out the rubber drainage section at the bottom of the rear window on both sides.
See picture below identifying this area…
Use some cotton buds to clean these and also get your drain brush and delicately push it through the drain.
Once you’ve done all this, you can close the roof of the car. Then get a small amount of water and pour it down the drains from the rear window. If you’re drains are unblocked then you should see the water splashing/dripping out on the ground under the car.
Hope this helps. Any questions feel free to ask.