Are these compression numbers okay?

[Tmakaro]

I just tested the compression on my 4.3 mercruiser tks (closed cooling) and this is what I got:

back
180 175
180 160
180 180
front

Temperature right near the water temp sending unit is 161 degrees
left riser temp is 92.6 degrees
right riser temp is 87.2 degrees
Tempurature gauge usually reads 170-175
I replaced the temp gauge and now its reading more like 175-180

I get the odd alarm sounding for a couple of secs. Gear lube bottle is full and and oil pressure is over 40

 

[emoney]

I would re-test the one cylinder that's at 160 lbs. That is an anomaly that needs to be looked at. Nothing wrong with the numbers but you usually expect there to be a 10% range among all cylinders. Did you run the test with the engine cold or warm?

 

[Tmakaro]

I check that cylinder 2 or 3 times. Engine was cold when I did the test.

 

[nickmo]

I would try a different gauge. Numbers seem high, but that doesn't change the one cylinder being much lower.

 

[Scott Danforth]

any number over 150-155 would be a bad gauge or oil/water in the cylinder

 

[Tmakaro]

ugh, I just bought the gauge.

 

[nickmo]

ugh, I just bought the gauge.

I don't know where you're located, but you can go to a local Auto Zone or Advance Auto and they'll loan you a compression gauge. You then could compare the 2 readings.

 

[QBhoy]

Are closed cooling engines not meant to have a 140oF t stat ?

 

[nola mike]

Closed cooling will run hotter

 

[QBhoy]

Closed cooling will run hotter

Ok. Out of interest then...what is the 140 t stat for on these engines ? I always had it in mind that the 160 is always raw water. Always has been in the half dozen GM V6 and V8s I’ve ever had. Always thought the 140 was for closed cooling.

 

[nola mike]

The 140 is for salt water primarily. Higher temps corrode quicker. I should have said closed cooling *can* run hotter. I'm not sure why they don't in a marine setting

 

[Tmakaro]

Oem thermostat for my engine is 160 for both closed and open.