How to Paint the Stern Drive on a Mercruiserby Chris Stevenson
Stern drives, also called outdrives, are a significant investment for the boat owner. Stern drives, which sit outside the transom and remain partially submerged, endure salt water, oxides, marine growth and other harmful elements that destroy their metal surface. If left unattended for too long, they can deteriorate, causing the lower unit case to ingest water into the transmission gears, hoses and seals. Frequent inspection and preventive maintenance on the stern drive include a good cleaning and repainting of the surface metal. New paint not only offers a protective surface to the stern drive, it also provides less friction in the water, which aids performance.
Remove the boat from the water and move it to a convenient work location for preparation and painting. Place the boat under a car port or structure that gets little or no wind gusts. Rinse the stern drive with water. Put on the gloves and the respirator. Mix a solution of commercial marine acid wash or muriatic acid in a coffee can.
Apply the acid solution over the exterior surface of the lower unit, using an engine brush. Make sure not to get any acid on the steering linkage or inside the prop housing. Let it sit and bubble for 20 minutes. The solution will kill microscopic organisms.
Rinse the stern drive with a high-pressure hose nozzle, removing any oxide corrosion and peeled paint. Wipe dry with a clean towel. Use a wire brush to loosen and remove the heaviest buildup, as well as in in the tight corners and crevices. Rinse with a high-pressure hose. Towel the stern drive dry.
Sand the surface of the stern drive down to bare metal, using 150-grit sandpaper. Sand firmly over any patches that have white oxidized crust to remove the corrosive pitting. Sand lightly around sharp seams and leading edges, such as the cavitation plate on the bottom of the lower unit. Use a gasket scraper to shave away any small barnacles. Be sure to sand the underside of the lower unit, including the underside of the cavitation plate. Rinse with a high-pressure hose.
Sand the stern drive with 400-grit sandpaper over the all the areas you covered with the coarser grit. Use finger pressure to get into the hard-to-reach seams and corners. Rinse the stern drive with a high-pressure hose.
Open a can of pre-primer wash and pour the contents into a bucket. Add water according to the directions. Wash the stern drive with the pre-primer wash and a towel. Rinse with a high-pressure hose. Use masking tape to cover the outside edges of the transom engine mount. Wrap the propeller and input shaft opening with masking paper and tape.
Open a can of epoxy primer paint and stir the contents. Begin painting the top of the stern drive unit, using a fine-bristle paint brush. Apply a light, thin coat. Cover the entire stern drive, sides, top and bottom. Let the paint cure and dry according to directions. Apply a second coat of epoxy primer paint, applying an equally thin coat. Let the paint cure and dry according to directions.
Sand lightly any surface that shows runs, drips or irregularities. Wipe with a clean towel. Open a can of anti-fouling paint and stir the contents. Apply a thin, even coat of paint over all primed paint surfaces, top, bottom and sides with a clean, fine-bristle paint brush. Allow to cure and dry according to directions.
Apply a second coat of anti-fouling paint for thicker protection and a deeper luster. Allow to cure and dry according to directions. Remove all masking tape and paper.
- You can use aerosol cans to paint the stern drive, or a spray gun and compressor. Simply buy the product for that application.
Things You'll Need
- Muriatic acid wash solution
- Coffee can
- Engine brush
- Wire brush
- Gasket scraper
- Masking tape
- Masking paper
- Marine acid wash
- Sandpaper (various heavy and fine grits)
- Pre-primer wash
- Epoxy filler paint
- Fine-bristle paint brush
- Anti-fouling paint
- Always be very careful when using an acid wash. Wear the proper protection.
Chris Stevenson has been writing since 1988. His automotive vocation has spanned more than 35 years and he authored the auto repair manual "Auto Repair Shams and Scams" in 1990. Stevenson holds a P.D.S Toyota certificate, ASE brake certification, Clean Air Act certification and a California smog license.