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#12266867 - 05/28/17 03:30 PM Boat motor compression help
chas1 Offline
Angler

Registered: 04/01/06
Posts: 359
Loc: Stephenville tx.
Boat motor compression help
I'm not an expert on boat motors but I picked up a compression tool at the local auto parts store and did a compression test on a 2003, 75 hp Mercury tracker, all three cylinders test around 80 or psi ,I assume this is too low so I passed on the boat did I do the right thing
Thanks

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#12266869 - 05/28/17 03:33 PM Re: Boat motor compression help [Re: chas1]
tmd11111 Online   content
Outdoorsman

Registered: 04/30/17
Posts: 229
Loc: San Angelo
First you need to run the engine and get it up to operating temperature. Next is make sure you have the throttle wide open. A closed throttle creates a vacuum and will give a low reading. Good thing is all three cylinders are reading close to one another.


Edited by tmd11111 (05/28/17 03:35 PM)

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#12267101 - 05/28/17 07:17 PM Re: Boat motor compression help [Re: chas1]
chas1 Offline
Angler

Registered: 04/01/06
Posts: 359
Loc: Stephenville tx.
Thanks

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#12267114 - 05/28/17 07:22 PM Re: Boat motor compression help [Re: chas1]
chas1 Offline
Angler

Registered: 04/01/06
Posts: 359
Loc: Stephenville tx.
One more question if I am running Ears with the water hose how long do you think it would take a motor to warm up ?

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#12267818 - 05/29/17 11:07 AM Re: Boat motor compression help [Re: chas1]
Muzzlebrake Online   content
Extreme Angler

Registered: 12/26/14
Posts: 1523
Loc: Euless
80 is too low for me. Hot engine the psi might come up another 5 lbs.
That motor new would be about 120 give or take. The 2001 50 elpto I just sold last year was still 115 is all holes.
I think you did the right thing. I would have passed too.


Edited by Muzzlebrake (05/29/17 11:08 AM)
_________________________
From Genesis: "And God promised men that good and obedient wives would be found in all corners of the earth."

Then He made the earth round...and He laughed and laughed and laughed!


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#12268158 - 05/29/17 04:15 PM Re: Boat motor compression help [Re: Muzzlebrake]
tmd11111 Online   content
Outdoorsman

Registered: 04/30/17
Posts: 229
Loc: San Angelo
Originally Posted By: Muzzlebrake
80 is too low for me. Hot engine the psi might come up another 5 lbs.
That motor new would be about 120 give or take. The 2001 50 elpto I just sold last year was still 115 is all holes.
I think you did the right thing. I would have passed too.


If the compression test was done without having the throttle held wide open then 80psi wouldn't be out of line. Now if it was done with the throttle open and motor warmed up then yes 80 is definitely on the low side. It take about 50-60psi just to get the fuel mixture to ignite.

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#12363938 - 07/29/17 01:45 PM Re: Boat motor compression help [Re: chas1]
Curtbass Offline
Extreme Angler

Registered: 04/17/15
Posts: 1059
Loc: Grand Prairie, Tx
Is it a cheaper quality (not Well known Chinese built) compression gauge? A quality gauge is worth it If you use one regularly. If just using it for looking at a boat, i can understand NOT spending a lot on one. You can possibly find a mechanic that would have a good one to just compare it to just to see how accurate it is. Ive seen cheap ones actually be off by 20#'s & that might cause you to pass on a good motor. Yours probably isnt that far off , but...if it is ???


Edited by Curtbass (07/29/17 01:52 PM)
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'98 Tr20 Triton completly updated & rigged, 05 Magnum c-channeltrailer
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