150 Mariner running hot

[Fishslick]

Hello fellow boaters. This is only my second post, and after the results of my first I know this is the place to find answers.

I have a 1996 251 Proline with twin 1996 150 Mariners. I have been having problems with the starboard motor running hotter that what I think it should be. I have replaced the water pump, including all gaskets, wear plates and upper housing. I have replaced the stats and poppet valve (reason for first post). The motor will run at around 180 degrees until it is put under pressure (around 2500 rpm), then it gets up to about 210 degrees. The temp guage works correclty.

I did notice while flushing engines with the flush (not running) that is mounted by the tell tale that the the port motor does NOT have water coming out of the water intake, but DOES drain out around the anodes on the lower unit. The starboard (one running hot) motor DOES have water running out from the water intake and does NOT have any coming out around the anodes on the lower unit. It is just the opposite of the port. I did not put any silicone on the exhaust plate that divides the water pump housing and the exhaust tube. Would that cause the motor to run hotter than normal and the water to flow back out of the water intake? The engine does not overheat enough to sound the alarm, but it does get very hot to the touch. I did install the grommet on the drive shaft next to the upper water pump housing. The water pump tube seems to fit tight.

Is the silicone the problem?
Did I accidentally install the wear plate wrong?
COuld I have the fins on the impeller runningthe wrong way?

 

[j_martin]

Re: 150 Mariner running hot

I used to train field engineers for computer work. The one thing that was hardest to get them to know was this.

If you walk up to a running machine, do something to it, and it now does not run, IT'S WHAT YOU DID!

Something ain't right. Take it back off and check it out.

hope it helps
John

 

[Fishslick]

Re: 150 Mariner running hot

Hey John,

Thanks for the response.
I am not sure if it is something I did not do right, or something that I haven't done yet, just can't figure out which one it may be.

It was running hot before I started changing parts. I was working through a process of elimination, and I started with the easiest thing first. The first was the stats. Didn't work second was the poppet valve. No change in temp there. The final was the water pump with no success.

I am not sure if the water flow was doing the same thing before or not. I did not notice the difference until after I had put the L/U back on.

I was just wondering if the scenarios I had mentioned would cause the that problem or not.

 

[Fishslick]

Re: 150 Mariner running hot

Update:
I pulled the L/U off this morning. I removed the upper pump housing to look at the impeller. I noticed that the splines were staying curved counter clockwise. This is bad as they should have straightened out some.

I just installed the whole water pump kit about 6 months ago, and it only has about 15 hours on it. This was a aftermarket kit not a Mercury kit. I looked at a Mercury impeller I had and the aftermarket impeller. The aftermarket splines were alot softer and more flexible than the mercury impeller. I won't mention the name of the aftermarket brand, but it is a very common brand. Since I did not have a new impeller I re-installed the old mercury impeller. After all it was in better shape than the one that was in there.

I made sure that the water pump pipe all lined up correctly and it was a good tight fit while I was putting it back together. The only other thing I did different was to put silicone on the water pump and exhaust divider. I let it set for about 2 hours before I bolted it back in to make sure I had a good seal between the two.

Now while running water through the flush out connection ( motor not running ) there is very little water that comes out of the water intake on the foot. Also there is alot more water coming out from around the anodes on the lower unit. Time to test it.

Instead of running the motor with the muffs, I used a large tub that the lower unit would fit in. Fired it up and the tell tale started peeing, first good sign. After a minute or so the temp got up to about 165 degrees and then dropped to about 150 (stats opened), and remainded there for 10 minutes or so while at idle. Increased rpms to 2000 and the temp went up to about 180, then dropped to about 140 and stayed there (poppet valve opened). SUCCESS!!!!!!!!!!!!!!!

Two things I will take from this:
I will always purchase true Mercury parts and not aftermarket.
I will always use a silicone sealer to fill in the gap on the exhaust divider.

I would have to assume that the gap was allowing water from the pump to push out of the exhaust which was decreasing the water pressure from the pump. Since this is a XL shaft that little bit of water pressure loss was all it was taking to not allow enough water to circulate through the engine.

I have read several threads on the silicone. It was about 50/50 as to whether seal the gap or not. Some say you have to, others say it is not necessary.

Based on my experience with this one, it may not be necessary but you will notice a big difference in the running temp. Maybe on newer models where everything is still a good tight fit and no build up in the cooling chambers as time will do, it would probably run fine without doing this. But on older models, that has seen years and hours of use I think "IMHO" it is a necessary thing to do.

I am not a mechanic so take this advice for what it is worth.


Regards and thanks for the replies.

 

[j_martin]

Re: 150 Mariner running hot

On the sillycone seal. The OEM manual says put it in. They invented the machine. I'm inclined to believe them.

Now I know why it's important.

John