Need Help!!! 1993 70hp johnson

[pdaye7]

Ok. Got on the water today and overheated at high speed. Before I turned it on, keyed it up and overheat alarm went off. Unplugged temp sensor and because thought sensor was bad. Got on water at boat overheated at WOT. Prop is is rough condition(not horrible).

I have replaced:
Thermostat OEM
Impeller Assembly
Changed lower unit fluid

Compression: #1 95 #2 95 #120


I am stumped. Please help with any guidance.

 

[racerone]

The logical step is to remove the cylinder head.----Inspect cylinder walls.------This is a blown head gasket or more expensive.-----Likely a big $$$ fix here.

 

[pdaye7]

The logical step is to remove the cylinder head.----Inspect cylinder walls.------This is a blown head gasket or more expensive.-----Likely a big $$$ fix here.

Well I will remove and check for head gasket. What should I be looking for? Also what type of issue could be this $$$ fix lol

 

[racerone]

Inspect cylinder wall for scoring ( scratches ) instead of fine crosshatch pattern.----You would be shocked at what it costs at a dealer to rebuild that if you can find a shop that wants to take it on.

 

[pdaye7]

Inspect cylinder wall for scoring ( scratches ) instead of fine crosshatch pattern.----You would be shocked at what it costs at a dealer to rebuild that if you can find a shop that wants to take it on.

Thanks again! I took the head off and this is what i found. Bottom cylinder was wet, and seemed like it was holding a lot of fuel/possible water mixture. middle was dry, and top was dry. attached pictures as well. Also found he thermostat (pin) at the bottom of case in water passage. is that pin supposed to come out of the thermostat? any info is always appreciated. thank you.

 

[racerone]

Motor needs to come apart for rebuild.----It is junk now and will never run properly.----No surprise to me here.

 

[pdaye7]

Motor needs to come apart for rebuild.----It is junk now and will never run properly.----No surprise to me here.

How far down you thinking?

 

[racerone]

Needs to come apart.----Likely needs 2 cylinders bored and honed.------2 new o/s pistons and rings.-----It is called an overhaul to return cylinders to factory specification.-----Big $$$ at a boat shop.

 

[pdaye7]

Needs to come apart.----Likely needs 2 cylinders bored and honed.------2 new o/s pistons and rings.-----It is called an overhaul to return cylinders to factory specification.-----Big $$$ at a boat shop.

Yes. I see, my brother did his and ran beautiful afterwards. Could this have caused it to overheat?

 

[racerone]

Cylinders that are bone dry lost lubrication due to overheat.----The overheat caused this damage.------You need to find the cause or the fix will be short lived.----You will ruin the motor again.----So answer these questions.----Does the tell tale hose come off the side of the block or the top ?----Have you ever installed the latest greatest water pump kit along with cooling system mods ?---Is the oil injection in service and checked, yes , no or not sure ?----Or are you mixing at 50:1 in the fuel tank.

 

[oldboat1]

(edit)

 

[pdaye7]

Cylinders that are bone dry lost lubrication due to overheat.----The overheat caused this damage.------You need to find the cause or the fix will be short lived.----You will ruin the motor again.----So answer these questions.----Does the tell tale hose come off the side of the block or the top ?----Have you ever installed the latest greatest water pump kit along with cooling system mods ?---Is the oil injection in service and checked, yes , no or not sure ?----Or are you mixing at 50:1 in the fuel tank.

How's is on top no side, replaced with updated water pump, oil injection not in service, I mix 50:1. What other cooling system mods are there for this engine? I believe I have found the cause of the overheating. I read the service manual and looks like the previous owner had the thermostat in backwards and when I replaced it I installed the new one in backwards as well.(all before I got the service manual). Manual clearly states thermostat should be installed with pin side facing out. Thanks again for you advice!

 

[racerone]

Motor needs to be rebuilt.------Tear it down completely.----Inspect all parts.----Rebuild or order a rebuilt / exchange power head if you can not do the work yourself.

 

[pdaye7]

Motor needs to be rebuilt.------Tear it down completely.----Inspect all parts.----Rebuild or order a rebuilt / exchange power head if you can not do the work yourself.

Thanks again for your help!