mid-late 80's Black Max 175Hp Compression

[Tyannt]

I posted recently about having done a cold compression test on a Merc V6 175Hp Black Max, mid to late 80's.
Was real surprised to see only 90lbs compression! Figured it was worn out...


Compression tested an 87 Merc V6 150Hp Black Max today and results were 80psi across...


Are these lower compression motors to begin with, or both on their last leg?



Appreciate any input!!

 

[Glenn Kornett]

I posted recently about having done a cold compression test on a Merc V6 175Hp Black Max, mid to late 80's.
Was real surprised to see only 90lbs compression! Figured it was worn out...


Compression tested an 87 Merc V6 150Hp Black Max today and results were 80psi across...


Are these lower compression motors to begin with, or both on their last leg?



Appreciate any input!!

Just a thought but have you tried to connect your compression gauge to an air tank with say 120 psi in it and read what your gauge indicates? If you measured the compression cold, it will likely increase 20 psi hot so now you have 100 psi. If the gauge is out another 20 psi then you have 120. Or measure the compression of your car. You can look up the specs but it is likely in the 140 - 160 range. If your gauge says it is 100 - 120 psi that would also indicate an inaccurate gauge. Of course it is not impossible that both motors are tired but you would have to be rather unlucky I would think.

 

[Tyannt]

Just a thought but have you tried to connect your compression gauge to an air tank with say 120 psi in it and read what your gauge indicates? If you measured the compression cold, it will likely increase 20 psi hot so now you have 100 psi. If the gauge is out another 20 psi then you have 120. Or measure the compression of your car. You can look up the specs but it is likely in the 140 - 160 range. If your gauge says it is 100 - 120 psi that would also indicate an inaccurate gauge. Of course it is not impossible that both motors are tired but you would have to be rather unlucky I would think.

The way my luck has been lately! Lol
Great suggestion Glenn..i have a compressor so it should be easy enough to check the compression guage that way.



Thanks!

 

[Glenn Kornett]

The way my luck has been lately! Lol
Great suggestion Glenn..i have a compressor so it should be easy enough to check the compression guage that way.



Thanks!

Good Luck. It happened to me years ago on my drag car. Was going to pull the engine and freshen it but borrowed a friends gauge and mine was reading 40 lbs. low. Later measured my friends gauge and mine with the compressor tank and his was out about 5 lbs and mine about 40 lbs.