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#12646634 - 02/25/18 06:30 PM Low hour, low compression motor
Drobe0711 Offline
Green Horn

Registered: 02/10/18
Posts: 4
I am looking at a 2010 boat with a 150 Mercury Optimax. The motor has less than 200 hours on it with over half of that idling/trolling/low rpm. The engine report showed that all cylinders had 95 psi compression. This less than the service manual that say 110 - 130 psi for compression. All the mechanics I have talked too said that since the cylinders were even, that it is ok. Is it more likely for a low hours motor to have low compression/stuck or worn rings or that the test was done cold?

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#12646683 - 02/25/18 06:55 PM Re: Low hour, low compression motor [Re: Drobe0711]
Pat Goff Online   content
TFF Celebrity

Registered: 01/29/05
Posts: 5693
Loc: Marble Falls/Seadrift
Probably cold motor.
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Pat Goff
Marble Falls/Seadrift TX



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#12646843 - 02/25/18 08:07 PM Re: Low hour, low compression motor [Re: Drobe0711]
Capt. Andrew Offline
Extreme Angler

Registered: 07/28/11
Posts: 1162
Loc: Port Isabel/SPI
I had a motor test at 99lbs with one gauge and 130 with another. As long as they are all around 10% of each other and the motor runs smooth its goo.
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#12647515 - 02/26/18 10:24 AM Re: Low hour, low compression motor [Re: Drobe0711]
gary purdy Online   content
TFF Guru

Registered: 05/24/03
Posts: 11404
Loc: Littlefield Tx & Lake A. H. US...
Do a carbon cleaning on it.
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The world will not be destroyed by those who do evil, but by those who watch them without doing anything. Remember what He has done and remember that He is not done yet!-- GOD IS GOOD

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#12647608 - 02/26/18 11:19 AM Re: Low hour, low compression motor [Re: Drobe0711]
Curtbass Offline
Extreme Angler

Registered: 04/17/15
Posts: 1487
Loc: Grand Prairie, Tx
Check it usung another gauge just to see if there are different results. Then de carbon motor & do it again. Warm motor up, check with throttle in wide open position, for initial readings then do a leakdown test. A more comprehensive picture of motor health.
I would be leery about the lower results but hate to see someone miss a fair deal in a good even motor over a faulty gauge. Ask seller if hes willing to do that. Could benefit both of you. He makes a sale & you make a better purchasing decision.


Edited by Curtbass (02/26/18 11:26 AM)
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'94 Merc 200Xri

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#12648104 - 02/26/18 03:50 PM Re: Low hour, low compression motor [Re: Drobe0711]
Gamblinman Offline
TFF Team Angler

Registered: 11/26/02
Posts: 3412
Loc: Yantis, TX
Along with the above, you need to perform a leak down test to determine the actual condition of cylinder sealing.


Edited by Gamblinman (02/26/18 03:51 PM)

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#12648412 - 02/26/18 07:24 PM Re: Low hour, low compression motor [Re: Curtbass]
Curtbass Offline
Extreme Angler

Registered: 04/17/15
Posts: 1487
Loc: Grand Prairie, Tx
i mentioned leakdown test also.
_________________________
'98 Tr20 Triton
'94 Merc 200Xri

92' ChampioN 201DCR Elite
13' Yamaha250SHO

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#12649112 - 02/27/18 08:48 AM Re: Low hour, low compression motor [Re: Drobe0711]
Drobe0711 Offline
Green Horn

Registered: 02/10/18
Posts: 4
Thanks everybody for the suggestions. I was planning on having a leak down test completed when I went to look at the boat. I will ask the current owner if he can have a carbon cleaning done.

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