Compression test on 1996 mercruiser 5.7 bluewater

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marylou

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guys need help engine compression test was done on a 1996 mercruiser 5.7 bluewater with 500 hours

here is the test results i would like to know what every one thinks opinions needed please tell me if these readings look normal and acceptable

#1 175 psi
#2 175 psi
#3 175 psi
#4 175 psi
#5 175 psi
#6 150 psi
#7 175 psi
#8 150 psi
 
Bondo

Bondo

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Re: Compression test on 1996 mercruiser 5.7 bluewater

marylou said:
guys need help engine compression test was done on a 1996 mercruiser 5.7 bluewater with 500 hours

here is the test results i would like to know what every one thinks opinions needed please tell me if these readings look normal and acceptable

#1 175 psi
#2 175 psi
#3 175 psi
#4 175 psi
#5 175 psi
#6 150 psi
#7 175 psi
#8 150 psi
Click to expand...

Ayuh,.... Welcome Aboard,.... That's no doubt Runnable,...

With 6, 'n 8 low, I'd suspect it's had a leaky riser before,...
 
tpenfield

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Re: Compression test on 1996 mercruiser 5.7 bluewater

166 psi would be an acceptable low value. So, I'm with Bondo on the assessment of 6 & 8 being a problem, but still usable.

is this pre-purchase?
 
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marylou

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Re: Compression test on 1996 mercruiser 5.7 bluewater

yes this was a pre purchase compression test. my mechanic said there is nothing wrong with the 2 cylinders being 150 and the rest 175 psi . something is telling me it does not look good for the 2 cylinders @ 150 but mechanic says if there was a problem it would be much lower than 150psi . thanks for your replies i am looking for opinions on this don't feel like buying a boat and going for a new engine 2 months later.
 
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beermak

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Re: Compression test on 1996 mercruiser 5.7 bluewater

if its in great shape the boat, price is excelent and ur happy buy it.. and prepare to address that issue sometime in the future

if not, walk away there are plentty of boats arround :)
 
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marylou

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Re: Compression test on 1996 mercruiser 5.7 bluewater

thanks guys,
just got off the phone with mercruiser engineer's they stated that these numbers are acceptable they are within the 70% that they now use by standard. engineer actually said they are great numbers and it does not signify a problem in the two cylinders that are 150psi just thought i would share with all . i owe the mechanic an apology and a case of beer lol
thanks
 
tpenfield

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Re: Compression test on 1996 mercruiser 5.7 bluewater

Mercruiser has a fairly wide tolerance on acceptable compression readings. Many folks look for a greater amount of consistency than the 70%. I generally like to see things in a 10% range. There is definitely something different about 6 & 8 and those 2 cylinders are next to each other.

there is an additional test that could shed more light on why 6 & 8 are different than the rest. A cylinder leak test. . .

so, definitely your call based on the sort of deal that you have arranged.
 
Last edited:
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marylou

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Re: Compression test on 1996 mercruiser 5.7 bluewater

tipenfield ,
i agree i just don't understand why all others go by 10% and mercruiser now goes by a whopping 70% with cylinders i just dont get it.
 
Volphin

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Re: Compression test on 1996 mercruiser 5.7 bluewater

Could be that 6 & 8 have the valves adjusted a little too tight. As far as compression tests, I do a dry test and a wet test and average the readings. Anything beyond 15% variance is noted as something to keep an eye on or repair, depending upon the situation.
 
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marylou

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Re: Compression test on 1996 mercruiser 5.7 bluewater

well guys i took a chance and bought it i loved it so much and got a great deal now the fun begins.
 
tpenfield

tpenfield

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Re: Compression test on 1996 mercruiser 5.7 bluewater

marylou said:
tpenfield ,
i agree i just don't understand why all others go by 10% and mercruiser now goes by a whopping 70% with cylinders i just dont get it.
Click to expand...

It may relate to warranty liability. If they put their spec at 10% variation (where it is now 30%), then they would open themselves up to a wider range of warranty claims. Most mechanics will work to a tighter range than the 30% (70%) that Mercruiser specifies.
 
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