This is my first year with my 1970 Mercury Thunderbolt 500 motor. What do I need to do with it to winterize it?

 

The boat and motor will be stored in my unheated garage. Do I need to remove the motor from the boat or should I anyway? What do I need to do to make sure the inside of the motor doesn't rust?

 

For a 1970 its in GREAT shape. Fires right over and has 140 psi across all 4 cylinders and I would like it to keep it that way!

Take it to a pro, and pay to have it done.

 

Back in the day, when that motor was built, the general practice to protect the innards was to pull the spark plugs, put a teaspoon of oil in each cylinder with the spark plug holes facing up, and rotate the flywheel a few times.

 

Now, the practice is to "fog" the engines which also gets lubrication/rust protection on the reeds and bearings as well as the cylinders and piston rings.  It's not a complicated process, but it has to be done correctly.

 

Not knowing the skills, or the knowledge of those who seek winterizing advice, I always tell them to have it done by a competent technician, who services outboards for a living.

 

It's cheap insurance.

I'm going to agree with Tom, take it to someone who does this for a living.

 

The only extra cost is going to be an hour worth of labor, and then you'll know it was done correctly.  A good mechanic also knows what to look for in the ways of trouble, line water in the lower unit. 

I'll add one more thing.  Have them lubricate all the pivot points on the engine.  That includes the shift and throttle linkages as well as the control cables. 

 

They can also check for play in those linkages and make sure everything is in proper adjustment.  When you "park" your boat for the winter, do not keep the engine tilted.  It may not allow all water to drain from the powerhead and/or the lower unit. 

I do both mine myself.  It depends on your comfort level with working on motors, but it's pretty simple.  There's more to it than the mechanical side, too.  There's a ton of articles and videos out there, but this will get you started: http://www.bassresource.com/fishing/Winter_boat.html