if the boat appears to be well cared for and the engine runs and sounds smooth and develops expected power i would not care about compression test numbers . if the engine has running issues walk away .

224 hours should be nothing for a 6.2

 

was this a dry or wet compression test?

cliff

 

who did the test? doesnt sound like it was run first....how long has it sat? are the two low cylinders next to each other? center? did the tester squirt any oil in the cylinders? my bet is rust on the valves/seats due to not being used or fogged when layed up.....this may "go away" when it is run, but obviously some damage will have been done necessitating a valve job at some point....i would probably either adjust my offer accordingly or cut my losses and walk a this point...

 

According to Mercruiser on a cold compression test all cylinders should exceed 100psi and the lowest cylinder should be within 70% of the highest. In your case it is close the low cylinder is 71% of the high. I did a compression test on my engine last year (Merc 4.3 600hrs) cold all the cylinders were between 120-125psi warm they were all 145-150psi. If the boat has been winterized and not run, it needs to be run first. Then I would do a warm test. If you still have that much difference between the high and low I would be thinking something is up with the low cylinders.

 

thank you for the quick responses. This was a dry test - boat has sat through the winter. It's a seacroe engine and not sure if it made a difference. The test was done by the shop mechanic while surveyor observing. I asked the surveyor to do oil samples and observe compression test so if there are issues, I would have shop address before i buy. Sea trial and another compression test after sea trial. Make sense?

 

Yep, that makes good sense. Also, make sure it reaches W.O.T. on sea trial. Good luck.

 

Also make sure when you do a compression test the throttle is wide open if not this can drastically change the numbers

 

+1

 

I'd pass, healthy vortec headed motor should be in the 180 range. 150 for non vortec engines. A leak down test would give you more insight as to where your losing it. Cold or hot the leakdown is way more accurate

 

The port engine broke the sparkplug so we could not so the compression test at this time

The numbers will come up after its been run, I'm sure. How did the spark plug break?

 

the mechanic was trying to take it out to do the compression test of the port engine.

 

Plus throttle wide open have all the spark plugs removed.
And leak-down test is a much better indicator.

 

Doesn't need to be to long but at least a minute or 2. What is most important is that it gets to the spec. for your boat and engine package. with normal load. Also, pay close attention to your gauges.
Look for oil press. to be within spec. and not drop, temp to be in spec. and not rise.

 

Thanks. Will do for sure. Any other tools that i can use to get or capture readings during the ride?

 

Here are the results.

• Cylinder #1: 100
• Cylinder #3: 100
• Cylinder #5: 115
• Cylinder #7: 120
• Cylinder #2: 140
• Cylinder #4: 135
• Cylinder #6: 120
• Cylinder #8: 120

 

Here are the results.

• Cylinder #1: 100
• Cylinder #3: 100
• Cylinder #5: 115
• Cylinder #7: 120
• Cylinder #2: 140
• Cylinder #4: 135
• Cylinder #6: 120
• Cylinder #8: 120

100-140 range is too much IMO. This boat needs/is going to need soon, a valve job. That's not cheap. If it were me, I'd pass.

 

Not a big fan of doing just a top end rebuild... plenty more boats out there......sorry

 

Just got the oil analysis results and metals reads quite low across the board. The port engine has 2.5% fuel, however the lab indicated that its normal operation as fuel was present in both engines. The genset results were excellent. Compression test result were from the port engine. Thoughts?

 

 

Unless the engines were rebuilt since your first post a week ago, your compression numbers suck.
Now if you want to get serious about why your numbers are so low....do a leakdown test.

 

Looking for some guidance, did a compression test and results were: two at 100, one at 115, and three at 120. The others are 140 and 135. I'm looking to buy this boat and this is my initial test - will do another compression test after the sea trial in a couple of weeks. Engine is Mercruiser horizons 6.2 with 224 hours - 2008. This was out of the water test. The port engine broke the sparkplug so we could not so the compression test at this time. Oil samples being tested. Looking for guidance on this.

I figured they needed to between 140 and 150.

Guess I was thinking after sea trial numbers.

 

I agree with scoflaw.... Those number's ain't great if you can do a leak down test go for it.... Otherwise i would start with a Top end and while ur there do manifolds and rises...

 

Leak down test is the only way you really know, Done on piston aircraft every year, Mandatory on the yearly inspection.

 

Thanks for the great feedback. I received all the maintenance records, the boat (SR310 2008 powered by 6.2l - SC & Axius) was maintained and repaired by the shop (looks like with open check book). The shop is going to do the prep, detail and necessary repairs, do the sea trial, WOT and then perform the compression test again.

Sounds reasonable? What else should I be asking for?

 

Like it has been suggested before a leak down test is a true indicator of where a problem is compression test is just a snapshot of overall health you are at the low-end of normal for a motor that’s not that old ,this are my compression numbers of my port motor last year upon inspection of the cylinder heads the exhausts ports were no looking to good so I replaced the motor keep in mind my motors were 20 years old with better numbers than what you’re looking at

 

Had a motor couple of boats ago, that had
#2 175
#4 150
#6 150
#8 175
#1 180
#3 150
#5 150
#7 175

Boat ran alright, I thought, pulled engine out to do a rotten oil pan. Had the exhaust manifold off and did a leakdown, and could see into the ports that the exhaust valves were leaking. Pulled the heads and discovered both heads had a crack between the center exhaust valves, from a previous overheat that was recorded with the dealer that had been doing the PO's work.

A healthy vortec headed engine should be 175 +. They are thin castings and it doesn't take much to crack them

 

Not a mechanic. Was told consistency is more important than the numbers as one may have a gauge out of calibration. One is 140 the rest around 100+. I would assume 140 was last tested and oil may have filled voids in cylinder. I once had twin 3.8 V 6s on a 28 footer. Some how one spark plug tip got bent in and shorted. We were at the north end of Vancouver Island and the person beside be at the dock was a Class A Drag racer with his mechanic. His comment was it was probably a brass screw form the carburetor that went through the engine. Took out plug bent tip back engine did not sound correct. He asked if I wanted to take the carbon out of the engine. Yes. He told me to hold RPM at 1500 while he poured a quart of water over 10 minutes into the engine. He said the water turned to stream and would loosen the carbon in the rings and valves. It worked. More power. I had done a compression test a year before and readings were 95 to 120. I did one again and they were 145 to 160. Was it a good idea? After he did it he said you can blow an engine doing that if it is not in good condition. He said they use the water trick for the last run of the day if the engine does not seem good.

 

thanks for sharing, that sounds very interesting, how did you pour into the engine?

 

I'm trying to educate myself by reading and watching youtube about leak down test. The low compression number indicate an air leak and by doing a leak down test the mechanics are trying to identify where the leaks are. There could be a number of reasons why and where. since the shop said they will do what it take to address this, i will defiantly suggest or ask if they have done a leak down test, what followup questions should I be asking?

 

They don't have to do all 16 cylinders, do your worst ones, and it will tell the story. I would want to be there so they don't BS there way out of it.

 

The 3.8 V6 were carb engines. No idea how one would do it on a non carb engine and what effect it would have.

 

Make sure whom ever is performing the compression test takes the boat out for a drive first and puts some good heat into the motor specifically the exhaust. I have seen several times some mechanics just warm the engines in the slip for 7-12mins; then poor readings result. Why because boat motors, unlike cars, have exhaust systems that use an intake water system to keep cool and when not heated properly it tends to impact the compression readings of the cylinders accross the engine. I always test in the following manner:
1.) Heat motors with a good cruise
2.) Test in order 1-8
3.) Heat motors again with a good cruise
4.) Test again but in reverse order 8-1
5.) Compare testing results and retest any cylinders which have a number that is 12-20% below your highest number.
Two other important factors when testing:
(1)make sure the oil in the engine is clean (testing after a oil change is ideal)
(2) Testing at WOT