Old boat engine fixup

I have a boat with an old 170 Mercruiser 3.7L engine, it hasn’t been run in like 5-10 years and im hoping to see if there is still life in the old gal or if i need to spend the almost $3500 on a total engine replacement.

Hoping to find someone who might be able to come check it out and walk me through care of the engine. I have limited Mechanical knowledge. I can do the oil change on a car, and that is about it.

First big check: does it rotate when you trn the starter.

  • If it does, then at least it isn’t frozen.
  • If it doesn’t. pull the plugs and squirt something like Marvel Mystery Oil into the cylinders and let it soak a couple of days to break the rings free. Then try again. If it turns you’ll probably still need to pull the heads or borescope to see how much damage to cylinder walls

If it is still locked up, probably need a total rebuild or replacement.
Others can give their recommendations of what to do, there are various approaches. But “Is the engine frozen?” the first big diagnostic.

ok probably should have stated this in the original:
no key, (lost to the same place odd socks go and pocket change comes from)
there is NO battery

is there anything i can do to see if i can get it working? I have all sorts of fine machine oils. really just want to see if the shaft turns

There’s probably a large bolt on crank pulley, see if you can get it to rotate that way using a socket and long handled ratchet with or without cheater bar.

You can by-pass ignition to just try starter: Negative to the engine block, follow the cable from starter to solenoid and touch positive to it.

should i still remove the spark plugs before turning it?

also what else should i try before manually turning

It would make it easier to manually turn over if you removed the spark plugs and I would be tempted to spray some oil in each cylinder beforehand to. Either use some oil that you already have or pick up a can of fogging oil from an auto parts store and let it soak and coat everything before attempting to turn it over. You should also check to make sure there is oil in the crankcase, and preferably change it out before getting too overzealous with turning it over.

well i did check the dip stick and there is some oil in there, and the gas tank smells of gas fumes… though the “blower” needs total hose replacement. now, to find where the spark plugs are.

should i put the oil down the spark plug hole? and would high grade gun oil work? its the highest refined oil i have and works wonders for the 150 year old revolver i have.

Whatever weight oil the engine normally takes, pour a tea/tablespoon full down each spark plugs hole then rotate it by hand. I would also drain the gas if you can or worst case put a good quantity of fresh gas in it. If the engine was stored somewhere inside or covered, you probably won’t have any issues. I had a motorcycle that sat for 5-6 year and did the same procedure. She fired right up and ran just fine

its been sitting out in the sun and rain for the whole time… sadly. its previous owner didnt have the desire or funds to maintain it.

the engine is from 1985, should i use synthetic oil or conventional?

At this point, I would use whatever oil you can find for cheap/on sale, which will probably be conventional. I say that because it would be wise to change it again after getting a little run time in case any gunk gets flushed out and into the oil. After that, it will really be up to you, though I would probably stick with conventional.

When you say the gas tank smells of gasoline, is there any in there? Gas tends to settle out some solids, which are Not Good for combustion. That’s about the extent of my knowledge re: old gasoline…

tbh i dont know, i tried to shake the boat and couldn’t hear anything sloshing, if anything im going to have to purge the fuel lines and oil anyways

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well someone came over, and the drive shaft turns, but it need a total replacement of all the hoses. they appear to be original with the engine, 35 years ago, and most are fairly decayed. does anyone recommend where i might be able to find a mechanic or someone who knows what they be doing to help do this? I have no idea what id be doing, but i have the money to buy new hoses.

id normally use a mechanic, but most are 6 weeks lagging behind, and charge $180 just to look at the boat.

Here’s a biggie: The water pump impeller needs to be replaced. They are made out of rubber and rot. Most are located on the inside of the lower leg (typically just above the cavitation plate) But they get old, dry, brittle and, disintegrate.
I would also recommend you get the type of water hose attachment to get water into the engine vs putting lower leg in a tank of water. Several types:

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