Overheating Mariner Magnum 150

[Paul Jenkins]

I have a 1987 (or so) Mariner Magnum 150 that is overheating. I replaced the water pump a couple of years ago and have replaced the thermostats. It sat for a year without being used. It seems to be moving plenty of water as water is coming out of the little hole and it comes out warm. It only overheats when I am towing a skier or other toy. Please help.

 

[j_martin]

Re: Overheating Mariner Magnum 150

I have a 1987 (or so) Mariner Magnum 150 that is overheating. I replaced the water pump a couple of years ago and have replaced the thermostats. It sat for a year without being used. It seems to be moving plenty of water as water is coming out of the little hole and it comes out warm. It only overheats when I am towing a skier or other toy. Please help.

The tattletale water is all water that has gone through the thermostats. You actually normally get a very weak stream if the cooling system is strong and the supply water is cold.

Most of us V6 owners consider water pump service a spring annual maintainance item. That would be where to start. The impeller is always replaced, along with the housing gasket. Replace the faceplate and gasket, the housing, and the outlet seal as needed.

A water pressure gauge is by far the best way to monitor the performance of your cooling system.

hope it helps
John

 

[Paul Jenkins]

Re: Overheating Mariner Magnum 150

I appreciate any advice I can get. Thank you. I am not sure the impeller is the problem as it only has a couple of hours on it. I replace it two years ago and the boat did not get used last year. I also remembered something else after I posted the first note. There is a small amount of water coming out of the rectangular holes that are just below the power head covers. I am not sure if this is normal or not. Is it possible that I have a leak in the water jacket between the cooling and exhaust systems?

 

[j_martin]

Re: Overheating Mariner Magnum 150

I appreciate any advice I can get. Thank you. I am not sure the impeller is the problem as it only has a couple of hours on it. I replace it two years ago and the boat did not get used last year. I also remembered something else after I posted the first note. There is a small amount of water coming out of the rectangular holes that are just below the power head covers. I am not sure if this is normal or not. Is it possible that I have a leak in the water jacket between the cooling and exhaust systems?

Those are exhaust reliefs, and spent cooling water is sprayed into the exhaust just above them, so a spray out of them is normal.

The impeller will take a set when sitting. It's actually worse than running.

CHECK OUT THE WATER PUMP COMPLETELY NEXT. Odds are 10:1 that's where the trouble is.

Yes I yelled.

hope it helps
John

 

[Paul Jenkins]

Re: Overheating Mariner Magnum 150

Message received. Thanks for yelling, sometimes I just need that incentive. I will tear into it this weekend. Again, I appreciate the advice.

 

[pny212]

Re: Overheating Mariner Magnum 150

I have a 88 150 and I had a tiny sea shell stuck in the poppet valve and I was getting the overheat alarm when I was under load, double check that as I was peeing fine and that was my fix,

it's under the switch boxes on the starboard side

be very careful as I broke a stud pulling it though luckly my brother has a machine shop and we got it right out

good luck