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Very Low Compessions on Mercruiser 5.0 MPI Engine. with Exhaust Manifold, Thermostat Housing Removed.

R

Robertse

New member
Dear All, I have a Mercruiser 5.0 MPI Engine. I did a compression test with the left hand Exhaust Manifold and Riser removed, Sea Water Pump removed, Alternator removed, Thermostat housing removed. I removed these items because they was rusted or sezied and need replacing or unsezied or removal of rust. The Engine has not been started for over 4 years and some items have developed corrosion. (See the attached Photo of the intake manifold under the thermostat housing.

On the left hand side (Port Side) of the engine the results was Cylinder 1=100, Cylinder 2 =0, Cylinder 3 = 0 and Cylinder 4 = 170, this is a very low/bad result I have not tested the right side as yet. Does it make a difference that the hand Exhaust Manifold, Riser, Sea Water Pump, Alternator, Thermostat housing are all removed. As the results are bad, should I just pull of the head and inspect the head gasket and pistons, wall, values etc? Thank you in advance. Rob
 
Based on both sides showing zero,
It is likely that either the rings are not sealing and/or the valves are sealing or both.
Sitting for 4 years and based on a lot of rust on the outside suggests this was in salt water and IF it is NOT a closed cooling system, salt may have found its way into combustion chamber.
Also if you did not add some lubricant into combustion chamber and crank engine over many times to get lubricant all over the inside and get things warmed up some and just did a Cold compression check. That also could explain the poor results.

What were the remaining cylinder compression results?
 
The 170 psi would give me a bit of hope. You have done so much work pulling things apart, might as well finish the job. With any luck, bottom end will be okay. Good Luck, and when it's time to put back together. Make 200% you put manifold gaskets on correctly. Trust me on that.
 
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