Mercruiser 165 in over my head, help.

[Fourwins170]

So... My girlfriend went ahead and purchased a 1987 four wins 170 horizon with the mercruiser 165 motor and put me in charge of repairs (great) my issues right now after an oil change, new freeze plug for the closed loop cooling system and a new belt that fit with the alternator conversion include high oil pressure when over 3/4 throttle and a LOUD popping sound every 3 minutes or so after about 15 minutes of moderate use under load. Also when putting it into reverse the boat stalls (I’ve been told I need to adjust idle up by seller who claims he never had this issue) and last but not least after it warms up it doesn’t like to go into gear, it revs to about 1,500-2,000 rpm and then slams in. Please help as I am not 100% mechanically inclined and from what I read I may be in over my head with this engine

 

[Eric 3.7LX Alpha 1]

Welcome. Your engine went by different names over the years, with some things changing. I have the same engine but labeled 3.7LX and was the last year they were made in '89. The most common model would be the 470. It is a Mercruiser designed aluminum block designed around The Ford 460 head and piston. They have a lot of torque with the large cylinder bore and are good on fuel. The closed cooling system is a breeze to winterize. Just remove the Aft most plug on the bottom of the heat exchanger to drain out the seawater section.
These engines do have some issues that if you have it long enough, you will most likely deal with. I've had mine for near 20 years and I have experienced them all. There are 3 main issues:
With the block being AL and the head being cast, if they overheat it usually results in a blown head gasket. You will want to have a good working temp gauge and keep an eye on it. The heat exchanger originally came out as a 3" diameter that was later upgraded to 4". I have the 4" and it runs at 160 all day.
The charging system was a stator behind the harmonic balancer that incorporated a water cooled voltage regulator near the heat exchanger that was very expensive when it failed. The best fix was/is an aftermarket belt driven alternator.
The last issue is well written here: https://www.sterndrives.com/470information/470coolantleakrepair.html

Your popping could be bad fuel or timing. Being a new to you boat, I'd probably give it a tune up and check/set the points, dwell and timing. Others will be along to help..

 

[Scott Danforth]

You bought a boat with a motor that requires you to be 100% mechanically inclined or have really really really deep pockets to pay mechanics

There are no such things as freeze plugs. They are core plugs and their purpose is to close off the water jacket holes where the core sand was removed during the casting process. If a core plug was lost on a heat exchaneger cooled motor, the something seriously went wrong in the motors past.

As Eric indicated, start with servicing the points.

Suggest you look up the issues of the 470 engine

 

[Fourwins170]

You bought a boat with a motor that requires you to be 100% mechanically inclined or have really really really deep pockets to pay mechanics

There are no such things as freeze plugs. They are core plugs and their purpose is to close off the water jacket holes where the core sand was removed during the casting process. If a core plug was lost on a heat exchaneger cooled motor, the something seriously went wrong in the motors past.

As Eric indicated, start with servicing the points.

Suggest you look up the issues of the 470 engine

Thank you for your reply, pockets are NOT super deep at the moment but this forum has been a lot of help, have figured out I have some carb issues and will start with a carb rebuild which I have done plenty of in the past on other vehicles, bad fuel mixture seems to be the issue with the popping and my rough idle/reverse issue along with the going into gear late at high rpm. As far as the plug it wasn’t missing it was just so corroded that the outer edge was leaking fumes, ended up finding one after calling 14 marinas in my area so I picked up 2 to be safe got it in there and the engine sounds much better, anything else you would recommend? Trying to avoid bringing it to a mechanic if possible

 

[Fourwins170]

Welcome. Your engine went by different names over the years, with some things changing. I have the same engine but labeled 3.7LX and was the last year they were made in '89. The most common model would be the 470. It is a Mercruiser designed aluminum block designed around The Ford 460 head and piston. They have a lot of torque with the large cylinder bore and are good on fuel. The closed cooling system is a breeze to winterize. Just remove the Aft most plug on the bottom of the heat exchanger to drain out the seawater section.
These engines do have some issues that if you have it long enough, you will most likely deal with. I've had mine for near 20 years and I have experienced them all. There are 3 main issues:
With the block being AL and the head being cast, if they overheat it usually results in a blown head gasket. You will want to have a good working temp gauge and keep an eye on it. The heat exchanger originally came out as a 3" diameter that was later upgraded to 4". I have the 4" and it runs at 160 all day.
The charging system was a stator behind the harmonic balancer that incorporated a water cooled voltage regulator near the heat exchanger that was very expensive when it failed. The best fix was/is an aftermarket belt driven alternator.
The last issue is well written here: https://www.sterndrives.com/470information/470coolantleakrepair.html

Your popping could be bad fuel or timing. Being a new to you boat, I'd probably give it a tune up and check/set the points, dwell and timing. Others will be along to help..

Thank you for your reply, a carb rebuild seems to be where I need to start, luckily it already has the 4 inch conversion and the alternator kit which (I hope) shows that somebody before me did some of the dirty work for me and knew something about them, everything I’m experiencing seems to be carb related if I’m reading and understanding correctly. Hopefully that does the trick, again thank you for the reply. Also running on last years gas so I will add some ethanol free and see if that helps after the carb rebuild

 

[ccoon520]

Also running on last years gas so I will add some ethanol free and see if that helps after the carb rebuild

If it is bad gas I think you'd be better off just draining the tank, and fuel filter and starting new. Also consider changing the spark plugs at the same time. I had old fuel when I got my boat. It fouled brand new plugs. Drained the tank, new plugs, and it made a world of difference. Still chasing down some issues but no lie the motor went from almost 1/2 throttle to start and not holding idle to turn key with barely an hour of effort.

Also if you aren't going to be running the thing daily I am in the camp of ethanol free fuel and stabilizer will be your friend.