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compression reading

A healthy 1995 Mercruiser 5.7 VORTEC should give you a cylinder pressure reading of approx 140 to 160 psi per cylinder, and with no more than a 10% differential between the lowest and highest reading.

If using this style cylinder pressure gauge, the pressure will be accumulative.
shopping


This means that you will want to cycle each cylinder through at lest 3 compression strokes per reading.
Healthy battery, good starter motor, all spark plugs removed, and with the throttle plates just partially open.

Be sure to disconnect the power to the ignition system. In other words, do not just simply remove the high tension lead from the distributor cap or ignition coil.




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Consistency from cylinder to cylinder is more important since different gauges can give far different readings. For example, if two cylinders side by side are down 20 pounds, there's a break in the head gasket between them. Or if one hole is very low, you have a problem there.

Jeff
 
RicardoMarine said:
A healthy 1995 Mercruiser 5.7 VORTEC should give you a cylinder pressure reading of approx 140 to 160 psi per cylinder, and with no more than a 10% differential between the lowest and highest reading.

If using this style cylinder pressure gauge, the pressure will be accumulative.
shopping


This means that you will want to cycle each cylinder through at lest 3 compression strokes per reading.
Healthy battery, good starter motor, all spark plugs removed, and with the throttle plates just partially open.

Be sure to disconnect the power to the ignition system. In other words, do not just simply remove the high tension lead from the distributor cap or ignition coil.




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Click to expand...
How is it that you know the OP is doing this test themself?
 
o2batsea said:
How is it that you know the OP is doing this test themself?
Click to expand...

Actually, it would be himself (not themself)!

But to answer your question..... I don't!
However, this is very simple. The OP said: "Does anyone know what the compression reading should be on a mercruiser 1995 5.7 VORTEC with a 4-bbl.?"

If the OP had a shop do it for him, the shop would have told him that the readings were either OK or low.
Since he is asking here, I'd say that he very likely took the readings himself, or he wants to double check what the shop told him.

 
Actually if the question was read right, I posted What the compression SHOULD be? I took the test and all cylinders came in good. But how far from knowing what the compression Should be. No manual I have states VORTEX in the specs.
 
trimta said:
Actually if the question was read right, I posted What the compression SHOULD be? I took the test and all cylinders came in good. But how far from knowing what the compression Should be. No manual I have states VORTEX in the specs.
Click to expand...

A healthy engine, Vortec or not should be around 150psi... 130 psi is starting to show wear but still acceptable. To really know the health of your engine, perform a leak down test...

IMO this test should be done on a hot engine, all plugs removed and throttle wide open.
 
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