I need your opinon...20 hp Merc issue


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ol sarge

Well-known member
Feb 1, 2012
Reaction score
Central Wisconsin
A little back story on my 1974 20 hp Mercury. I bought it last year and had a few minor issues with it. I paid $450 for it and had to put another $700 into it after various little things came up (broken pull start, new water pump,new shift linkage, ect) I had it winterized last fall and never took it back out until last Thursday. Before going out, I changed the fuel filter and filled the tank with ethanol free gas and added oil to the gas (50:1 mix as required). I motor started up on the 2nd pull and I got about 2 minutes down the lake and it started to bog and spit and sputter and then died on me. After a few minutes I got it to run but when I put it in gear it would spit, sputter and then die. I did not run the motor for more than 5 minutes total. I called the marine guy who worked on the motor last year and asked him what could be wrong with the motor and the first thing he said was bad gas. Well, it had fresh gas and oil. After a few minutes of back and forth he told me to bring the motor to him and he would look at it and not charge me any labor. Well I took the motor to him Thursday and he calls me today and says that he bore scoped the cylinders and the number 2 was cracked and it looked like it had been run with no oil. He said the motor was toast. Now, I am not stupid, and I did put the proper amount of oil into the fuel tank (I always add it before I fill so it will mix). Do you think this sounds right or is he just trying to get rid of me? I think it sounds a little suspicious to me (maybe they hooked straight gas up to it?) so I am looking for suggestions. I have another place that will look at it and do a diagnostic for $50 but I do not really want to keep throwing good money after bad. What do you think I should do? I do not trust this guy at all. Thanks for your input.
With what you already have invested in the motor, should be reason enough to get a second opinion if it's only $50, but if you don't trust the guy then I would definitely get a second opinion.
I would get a second opinion. It may be just bad gas. If you purchased the gas just before launching the boat does not mean the gas is good. There are shops that will tell you anything thinking you will just leave motor to them and then they will resell it or the parts in it. $50.00 for "piece of mind" is not bad.
Wont the mechanic let you look at the crack in the cylinder with his borescope? He owes you at least that much. If you see the crack, you don't need a second opinion.
A compression gauge is $15 or so from any autoparts store - screws in place of a spark plug. If there's a cracked cylinder preventing the motor from running under load then there's definitely compression loss.
Well I went and picked up the motor and the service manager would not even look at me, little lone talk to me. The kid at the front counter brought out the service sheet and he had put on in" ENGINE SHOT" and had a labor fee of $47 for the test he said they ran. Well I did not pay the $47 and I took my motor to another marine guy who is going to do a diagnostic check on it in the morning. I told him that it just stopped running and did not mention anything about the other guy or what he said. If it comes back with both cylinders good, I am going to have to call the owner and let him know what this guy is up to. I will let you all know tomorrow night what happens. On the good side of things, the wife told me to just go buy an new boat! Not for awhile.......
This has been very interesting so far. Have you heard anything yet?? I am hoping for the best.
I think you made a good call by just taking it to another mechanic and not saying anything about the other guy. On the other hand, if my wife gave me a green light on a new motor or boat................... =D>
The go buy a new motor is an old Jedi mind trick. Once I buy the motor the conversation will be I want to get such and such and I did not say a word when you spent that money on a motor. Aint falling for that one.

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