Fishing & Boating News

On the Dock

Winterize Now

by: Rick Smith,

(Nov. 23, 2010 - Temple, TX) The weatherman is telling us our first freeze of the season is headed to Central Texas over the Thanksgiving weekend so let's talk winterization. This is a job you can do yourself or take your boat to your local marine dealer, but do not think you have nothing to worry about. Last winter we had some really cold weather and Marine Outlet in Temple had dozens of phone calls from concerned boaters who damaged their inboard engines due to freezing water cracking their engine blocks and manifolds. This happened because most inboards and stern drives have raw water cooling systems. This means that the lake water is drawn up into the engine and is used to keep the engine in a safe operating temperature range while running. When the boat is hauled out of the water, water remains inside manifolds, fuel and transmission coolers and engine blocks. Water expands when frozen and this will typically crack the cast iron blocks, manifolds and housings.

Keeping your boat in a heated garage is one solution, but if there is a loss of electrical power, you're not protected. So let's discuss the basics of winterization.

Fuel Treatment

Since the gas that you purchase now has ethanol added (E10), you will need to add an ethanol/fuel stabilizer like StarTron, Phaser 3000, Quickstor 3 or Sta-Bil ET. The purpose of these fuel conditioners is to keep the gas from going "sour" and to prevent phase separation of the ethanol from the gasoline. Top off the fuel tank (be careful not to overfill) and run the engine in the water for a few minutes to allow the product to work its way into the engine's fuel system.

Water Purging

On most modern Mercruiser inboards and inboard/outboards the water drain plugs are plastic and blue in color to make them easier to find. The carbureted, 3.0L inline 4 cylinder engine, will have two blue hoses attached to a t-handle near the thermostat housing on the port side of the engine. Simply remove these two hoses and use the t-handle to push them down into the bilge. Watch for water to drain out.

The V6 and V8 Mercruiser conversions have two different systems:

1. The carbureted models will have two blue plugs on the lower engine block, two more on the manifolds, and possibly a vent plug on the thermostat housing.

2. The Multi Port Fuel Injected (MPI) models have a blue round "faucet style" knob on the front of the engine, a blue drain plug below this knob on the water distribution housing and a thermostat vent.

Always make sure water does drain out as sometimes debris will block the passages. You can place a small wire into the orifices to confirm that there is no blockage.

If the boat is an inboard-outboard or outboard, you will need to check the lower unit making sure there is no water in it. You can do this by loosening the lower screw on the stern drive unit and letting a little fluid drain out on your fingers. If water comes out or if the fluid is mocha colored then you have water contamination. You will need to have a lower unit seal pressure test performed by a marine dealer to confirm which seals are defective. If you do not have time to take the boat to a service center, then drain the oil/water mixture by removing the vent screw making sure to properly dispose of the liquid. Refill with the recommended weight of oil. If the oil comes out black, then it needs to be drained and refilled, but the pressure test is not necessary. If the oil is normal in color then top it off.

Check the trim and power steering fluid reservoirs for water contamination. (Not all Mercruiser 3.0L engines have power steering.) Purge and refill if necessary.

If you have a fuel water separator filter, then now is the time to replace it with a new one.


Fogging is lubricating the internal engine components with a light mineral oil. This is done to protect the pistons, rings and bearings from moisture. Typically this is performed by spraying the oil through the intake while turning over the engine. This should be done with the "kill" safety switch disconnected so that the engine does not start or backfire.


Disconnect the negative terminal from the battery. This will reduce the battery drain. It's necessary to periodically charge the battery to keep up the specific gravity so that it does not freeze or sulfate the plates. Trailer Brakes & Bearings

If your trailer has brakes, they are probably surge, and there is a master brake cylinder on the tongue. Check the fluid making sure it is not contaminated with water. Check your trailer hubs, especially oil bath hubs, for water. Lube as necessary.

Disclaimer (here come the lawyers!)

The above is intended to be a guide to help protect your boat. It's in no way meant to be complete as boats are unique. Inboards, sailboats, houseboats, walk-arounds, bass boats and cruisers will require additional maintenance. All of this information should be readily available in your owner's manual, but if you feel uncomfortable performing these tasks, then take your boat to a certified dealer. The small price you'll pay is much less than replacing a complete engine or lower unit. Your boat gives you a huge amount of fun so give it lots of love.