Mercruiser 5.0L EFI Compression Test

[thompsdw]

I am looking at a 2001 boat with a 5.0L EFI Mercruiser engine with 55 hours. Here are the actual compression readings:<br />1: 210<br />2: 210<br />3: 205<br />4: 190<br />5: 215<br />6: 205<br />7: 205<br />8: 210<br /><br />What about cylinder #4? Is this cause for significant concern? What should I do to verify that damage has not occurred?

 

[WillyBWright]

Re: Mercruiser 5.0L EFI Compression Test

Run the motor and test it warm. I wouldn't worry too much. You're still within 10%. But if you're concerned, try testing it at running temperature.

 

[imported_Mike_M2]

Re: Mercruiser 5.0L EFI Compression Test

I know it's late on a Saturday night, but they sound awfull high. I don't have my Merc manuals here, but most smallblocks should be in the 150/160 range. Is there a problem with your guage maybe? In any case, it is always more important to get close readings, whether high or low. The one low cylinder is not that far off from the others, but again they all sound way high to me. If noone else chimes in here, i'll look at the book tomarrow.

 

[Squirterguy]

Re: Mercruiser 5.0L EFI Compression Test

Just searched some ... found an article agreeing with Mike ... normal 140 to 160 PSI but with caveat that performance engines may well be up to 220 PSI on gasoline. Check mfr. specs for certain. <br /> Also that a 10% tolerance is considered OK. Yes, #4 is a bit low, maybe the rings are not perfect, maybe a valve bleeds a bit too much, but it is OK.

 

[BRIAN03]

Re: Mercruiser 5.0L EFI Compression Test

Pistons and rings are fine. The valve seats are rusted and not seating well. Do a leak down test and listen out the exhaust make sure the cylinder is at TDC or pull the valve lash back when you do the leak down test.

 

[Walt T]

Re: Mercruiser 5.0L EFI Compression Test

Worry about something else.