Compression Test Results

LakeStClairDave

New Member
Dec 28, 2020
9
Boat Info
2006 320 Sundancer
Engines
Twin 350s
I'm in the process of purchasing a '06 320 DA, 350 mags, vdrive, trying to anyway...Just got the compression test results back today...
Port - 195, 180, 190, 185, 160, 200, 190, 200
Stb - 205, 210, 190, 180, 185, 200, 205, 190
The engines only have about 365 hours on them and the boat has been in heated (57 degree) storage since October. The mechanic is telling me the numbers are fine and should balance out more after running. He also said that 160 is plenty of compression....I know I'd prefer the results be closer together, but the 160 is the concerning number for me. Should I be asking for some additional testing to be done or just see how she runs in the spring when I can do a sea trial? Thank you for any advice...
 
Numbers sound a bit high across the board. Better high than low. Running it will tell the story
 
For a cold test not bad at all... Don't like the 160 but I'm sure it will come back, These 320s run and get up on plane really easy... I think ur be ok..
 
Agreed that for cold engines those are acceptable. Put it in the water a run it hard for an hour and do a hot compression test and it will check out fine.
 
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FYI - On my 340 with 7.4's the Mercruiser spec was 30% between the top and bottom compression. 160 is only 20% so well within the tolerance. I would assume that the 350's are similar.
 
I've got the same Port cylinder at 158.

kirkfreakout.gif
 
I have a 1992 Mercruiser 454 with 1300 hours. It burns zero oil and seems to run strong, besides an oil pump issue. My mechanic did a compression test and got the below results. Is it worth fixing the oil pump (cost for the repair is 3000 plus pulling the boat out the water)?

Environmentals readings
AOT 74F Battery readings 13.2v engine temp 150F

Compression Port Engine
Cylinder# Reading (PSI)
1 182
2 135
3 150
4 130
5 145
6 142
7 150
8 150
 
Never seen a compression reading as high as 182 on a 454. 160 tops. I'd disregard the 182 as wrong. Other than that they are fine. Were they taken cold or warm? 3k to replace an oil pump sounds like a lot.
 
He mentioned engine temp @150 and I agree that the 182 is a phony.

It’s worth fixing but 3 grand seems about 30% too much.

Can you do some of the preliminary disassembly yourself and get it back together? Maybe only pay the marina thieves to swing it in and out.
 
My mechanic has no skin in the game, but when he sent me the compression test results, I needed validation that those numbers were correct. He did both engines warm and for the forum below is the results from the starboard engine.
Compression Starboard Engine
Cylinder# Readings (PSI)
1 148
2 145
3 145
4 151
5 145
6 145
7 147
8 150
 
I have a 1992 Mercruiser 454 with 1300 hours. It burns zero oil and seems to run strong, besides an oil pump issue. My mechanic did a compression test and got the below results. Is it worth fixing the oil pump (cost for the repair is 3000 plus pulling the boat out the water)?

Unfortunately, pulling the engine is necessary to replace the oil pump. Once it's up on the hoist, pull the pan and change the pump - a very easy, quick job. Maybe 20 minutes. While it's out, check the pan for rust. New pan gasket, bolt it up and drop the motor back in. $3,000 sounds like a lot for this job.
 
I'm in the process of purchasing a '06 320 DA, 350 mags, vdrive, trying to anyway...Just got the compression test results back today...
Port - 195, 180, 190, 185, 160, 200, 190, 200
Stb - 205, 210, 190, 180, 185, 200, 205, 190
The engines only have about 365 hours on them and the boat has been in heated (57 degree) storage since October. The mechanic is telling me the numbers are fine and should balance out more after running. He also said that 160 is plenty of compression....I know I'd prefer the results be closer together, but the 160 is the concerning number for me. Should I be asking for some additional testing to be done or just see how she runs in the spring when I can do a sea trial? Thank you for any advice...

Nothing wrong with that engine!
 
Same happened to me. Compression test on twin 350s revealed one or 2 cylinders with low compression. Every mechanic I talked to said they don’t use compression testing for diagnostic purposes, and asked, how does it run? I bought mine with stupid low hours and it’s been fine for 5 years and and I’m now at 600 hours. (230 hours on a 9 year old boat, next time I will pass on low hour boats and look for 50-100 hours per year, assuming a FL year round boat...). My issues have all been external issues, water pumps, IAC (Merc recommends replacing these each year as part of annual maintenance, so no more issues since this started), fuel pump relays, water pressure sensors, and I’ll be doing the elbows this year, but I’m in salt.
 
Same happened to me. Compression test on twin 350s revealed one or 2 cylinders with low compression. Every mechanic I talked to said they don’t use compression testing for diagnostic purposes, and asked, how does it run? I bought mine with stupid low hours and it’s been fine for 5 years and and I’m now at 600 hours. (230 hours on a 9 year old boat, next time I will pass on low hour boats and look for 50-100 hours per year, assuming a FL year round boat...). My issues have all been external issues, water pumps, IAC (Merc recommends replacing these each year as part of annual maintenance, so no more issues since this started), fuel pump relays, water pressure sensors, and I’ll be doing the elbows this year, but I’m in salt.

Its been my experience than any engine with compression issues would have a difficult time hitting wot rpm. If it runs poorly do a leak down test. I don't read much into compression tests. There is a wide spec range for a reason.
 

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