WHy is my OMC 5.7 liter engine knocking at full throttle after It had over heated

[Christian3]

I am new to this forum and this thread seem like an easy start to get help. My name is Christian and I have a 1986 24.5' Marathon with a OMC 5.7 liter engine in it. I over heated it due to a bad empellers. I replaced it. Once I started it to test it I then noticed the water pump/circulator on the engine was leaking. I replaced it, it was rusted out. The next time out it ran good for a 20 a min. drive and then at the end of the day it had trouble starting and then ran at half speed back home. Smooth, no bucking just half speed at full throttle. I replaced all 8 plugs at least 2 were totally blown. It ran fine for 10 min then back to half speed. I treated gas with "Heet" and stabalizer and I replaced plugs again and two of them were bad again. It is now running fine at slow speed but if I give it full throttle it knocks hard and is still only going half speed at best. Any ideas?

 

[superbenk]

Re: WHy is my OMC 5.7 liter engine knocking at full throttle after It had over heate

Did you check your oil? You may have cracked something & let water into a cylinder or two causing hydro-lock & bent a valve or something.

 

[bruceb58]

Re: WHy is my OMC 5.7 liter engine knocking at full throttle after It had over heate

How old is your fuel? You may also have a very lean condition which is causing the knocking and may be why your plugs are failing. If you keep running the engine in this condition, you are going to burn through the pistons.

 

[Christian3]

Re: WHy is my OMC 5.7 liter engine knocking at full throttle after It had over heate

http://www.steelseal.com/testimonials.asp

The oil is not milky and I just took the gas to nothing and then filled it with super. I am going to try this product; check it out, they say it fixes bad head gaskets, I hope so...I will let you know.

 

[Howard Sterndrive]

Re: WHy is my OMC 5.7 liter engine knocking at full throttle after It had over heate

you have a closed cooling system? or ^ you gonna buy 10,000 bottles of that stuff and fill the lake? waste of time and money either way.

do a compression test on the motor. then remove and cut open the oil filter with a proper filter cutter.

pull the outdrive and check u-joints and gimbal bearing

 

[Christian3]

Re: WHy is my OMC 5.7 liter engine knocking at full throttle after It had over heate

I talked to the mechanic at the place that sells the Steel Seal and he told me that it will work if you are cooling with antifreeze, or if it is dry docked and you can run it in a closed circuit, like with the outdrive in a bucket. You have to run the steel seal through the engine at 1000rpm for 1 hour and get your engine to 200 degree for that duration to activate the ingredients to seal the head gasket. So, this is not for me since I am unable to pull the boat at this time. I understand you should do a compression test to see if your head gasket is blown but what is the reson for cutting the oil filter?

 

[91rr]

Re: WHy is my OMC 5.7 liter engine knocking at full throttle after It had over heate

but what is the reson for cutting the oil filter?

To see if you have any metal if so you are looking at a rebuild.