1990 Mercury 115 head gasket question

[narmer2000]

How do you tell if your head gasket is blown without dismantling?

My 115 over heated and since then when you take out for 15-20 minutes the alarm goes off. New water pump installed and was peeing water. Picked up a miss as well. Is their an easy way to tell if this is the problem?

 

[Dave1027]

Re: 1990 Mercury 115 head gasket question

Do a compression test.

These don't have a head gasket in the normal automotive sense because they don't have heads. Remember that this is a 2 stroke and they don't have valves hence no heads.

How do you know it overheated? Those alarms don't mean gospel. Most of the time they go off it's because of a malfunction in sensors or a module. Merc makes crappy electronics that seems designed to fail.

 

[narmer2000]

Re: 1990 Mercury 115 head gasket question

Im not a mechanic by any means. Thanks for the info. My friend has a compression tester so I will give that a shot tomorrow night. I took the boat out a couple weeks ago and idled out of the harbor into the channel. Soon as I did this the alarm went off and the motor starting running rough. Luckily I was able to idle back into the harbor and trailer it home. I am not sure about the water pumping. Replaced the water pump two weeks ago, tested and water was peeing out. When I had this problem no water was coming out the hose. When I got home I tried to flush as well but still no water coming out. Runs rough too so I am about ready to give up the ghost.

 

[Dave1027]

Re: 1990 Mercury 115 head gasket question

So you replaced the water pump impeller after the overheat incident?

Do you have a temp gauge? If so what did it read?

So when it overheated you looked and no water was coming out pee hole?

How did you flush? Mine does not have a flush connection.

Was it a continuous tone alarm or a beeping?

 

[narmer2000]

Re: 1990 Mercury 115 head gasket question

Yup, after the overheat I replaced the impellor and thermostat. The boat doesnt have a temp guage so its hard to tell if it was hot. I did not see water coming out the pee hole when it over heated. I just used the muffs with a garden hose on the lower unit and attached to the lower unit in front of the prop and it did pee water after I replaced but did not this last time. It is pumping water as you can tell when the motor starts the stream of water leaking from around the muffs dissipates but just not enough to come out the hole. The alarm was a steady, annoying squeel.

 

[narmer2000]

Re: 1990 Mercury 115 head gasket question

Do a compression test.

These don't have a head gasket in the normal automotive sense because they don't have heads. Remember that this is a 2 stroke and they don't have valves hence no heads.

How do you know it overheated? Those alarms don't mean gospel. Most of the time they go off it's because of a malfunction in sensors or a module. Merc makes crappy electronics that seems designed to fail.

I borrowed a compression tester and each cylinder was around the 120-125 mark

 

[narmer2000]

Re: 1990 Mercury 115 head gasket question

Could I have sand somewhere that just wont come out?

 

[Dave1027]

Re: 1990 Mercury 115 head gasket question

It could be a lean mixture into one or more cylinders. That would explain all of your symptoms. Maybe replace the fuel filters, rebuild the fuel pump, test with another fuel source and primer, rebuild carbs? Make sure the intakes and carbs are torqued down properly. Check your oil pump. Have you been monitoring it's oil usage?

 

[zorak]

Re: 1990 Mercury 115 head gasket question

Did the old impeller come out in one piece or are there pieces missing.If so there could be a piece of the impeller blocking a water passage up inside the motor.The telltale would still pee a stream but the blockage could be causing an overheat condition at WOT.

 

[narmer2000]

Re: 1990 Mercury 115 head gasket question

Thanks for the ideas! When I took out the old impellor it was intact and actually looked to be in very good condition with little wear. As far as oil consumption, the tank was full this spring and is about half empty now with only three tanks of gas so that could be a problem. I will take off the carbs and have them rebuilt and rebuild the fuel pump this winter too. Might that explain the hard starting too?

 

[Dave1027]

Re: 1990 Mercury 115 head gasket question

Yes. A lean mixture can cause hard starting.

How big is your gas tank?

 

[narmer2000]

Re: 1990 Mercury 115 head gasket question

20 gallons I think