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Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10621
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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Submitted: 1 year ago.
Category: Boat
Customer: replied 1 year ago.
2 + 2 115 mercury. I believe it is a 1991 or 92. Had an issue with water in my gas tank. Ended up trying to run straight water through the motor last summer. Syphoned gas tank and boat seemed to be running fine. Using it this past week, after running on plane for about 1 minute, boat died. No prior indication, just going from full to nothing. Boat seems to run fine when keeping RPM under 2500.
Expert:  Tan replied 1 year ago.
Hello. My name is Tan. We need to start out with a spark and compression test to eliminate these as a possible cause for your issue. When running the boat choke it. Does it run better? Squeeze the primer bulb does it run better?
Customer: replied 1 year ago.
How can I choke it? It is a mechanical choke, controlled by the temp. Should the pumping be done at idle on muffs?
Expert:  Tan replied 1 year ago.
When you push in on the Key it activates the choke primer.
Customer: replied 1 year ago.
Will try this sometime this week. Am I allowed to keep an open dialog with you. Going to be running the motor on muffs. It does run better on high idle if I pump. Went from 1700-1800 up to over 2000 when pumping. Need to fix oil leak first. Drops like crazy when tilted up.
Expert:  Tan replied 1 year ago.
Yes the questions don't close. Just post back as you have been. The engine running better when squeezing the primer bulb indicates a fuel restriction or a weak fuel pump. If it runs better when you choke it then you have dirty carbs. Then do the spark and compression tests. Post back with questions and findings.
Customer: replied 1 year ago.
How do I do a spark and compression test?
Expert:  Tan replied 1 year ago.
To do a spark test you will need a spark gap tester. You can get these at the auto parts store. click here Then rent a compression gauge from the same store. Remove the spark plug wire from the spoark plug connect it to the gap tester and ground the tester. Set the gap of the tester at 7/16 now crank engine. It should spark. Do thios on all cylinders. If you find one that doesn't jump the gap swap that coil with one of the other cyulinders does the problem move. If the no spark moves that coil is bad. If it stays then we have another ignition component failing. This requires further testing with an ohm meter. To do a compression test remove all the spark plugs screw the tester in the spark plug hole crank engine till needle on tester quits moving. Register the number do this same test on all cylinders. Post back with findings.
Customer: replied 1 year ago.
I still haven't had a chance to test the spark gap and compression. I have a question about my motor. I disconnected the alarm module a couple of years ago due to a faulty high temp alarm. (It would go off immediately after starting). Anyway, with the large amount of oil leaking, is there a safety shut off for the motor in the event that pressure dropped in the oil pump due to sucking air into the pump?
Expert:  Tan replied 1 year ago.
No shut off.
Customer: replied 1 year ago.
test
Expert:  Tan replied 1 year ago.
Hello.
Customer: replied 1 year ago.
I fixed the oil leak and determined the hose from the reservoir to the pump was rather worn. I am afraid I may have run the engine with little or no oil. I think my fears were confirmed today when I ran the compression test.Bottom Cylinder 75
Next 120
Next 105
Top 120I know there is nothing I can do to change the compression short of a new power head, is it shot, or could it be run at this condition? Can I assume at this point the motor is shot, and is why it is barely idling?
Expert:  Tan replied 1 year ago.
With compression number like that you are correct. Now the engine can possibly be rebuilt but no way to tell till engine is torn down. Many times when the engine is starved for oil it takes out the crank shaft and all the bearings from lack of lubrication. That all depends on how severe it was starved. Due to the age of the engine it will cost more to rebuild the engine than it is worth.

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