Compression testing a potential boat. Smart or overkill?

[vetplus40]

I am a big fan of compression testing. I perform them on my current boat and jet ski at routine intervals. That said, I am unsure whether asking for one on a prospective boat buy is proper or a bit overkill? On one hand, I can see where a seller (that may not be mechanically inclined) wouldn't want a stranger performing diagnostics on their motor. On the other, wanting to ensure the cylinders are in good shape isn't unrealistic either- especially given the high price of boats these days.

What do you folks think?

 

[Scott Danforth]

the check list is a sticky for a reason https://forums.iboats.com/forum/gen...eeding-help-buying-a-boat-a-buyer-s-checklist

absolutely do a compression test. if the prospective buyer wont let you do it, hire a surveyor.

 

[tpenfield]

Wicked Smaht . . .

Compression tests are pretty customary on engine inspections. The only thing is that a seller may want a certified mechanic to do the actual compression test, rather than the buyer. So, there is a cost to the buyer. No different than the survey on the boat though.

 

[vetplus40]

Thanks for the input. Should have checked the "stickies". Not familiar with a "survey", so I will have to do some reading. Thanks again.

 

[JoLin]

Given my age, physical limitations, the difficulty I have getting the plugs in and out, and the problems I've had with compression testers over the years... I haven't done a compression test in a long time.

I look for oil leaks, water leaks and smoking. I listen to the engine for noises that shouldn't be there. I look for a smooth idle and smooth power delivery. I monitor oil pressure and water temperature.

I have 2 engines on my boat- a complete 2014 Merc reman and a 2003 "I'm not sure what"- I think it was a long block replacement. Both engines are serviced regularly. Both engines show normal temps and oil pressure of 35-40 psi at a hot idle, around 50 psi at cruise. No leaks, no smoke, no noises. The old engine will burn 1/2 quart during the season (50-100 hours). Do I need to know that a cylinder is more than 10% out of spec., or that the old engine is down to 100 psi? Nope.

My .02

 

[dingbat]

I agree with JoLin but that’s assuming you have the experiance to know what to listen for.

Compression iproblems exhibit symptoms that are easily diagnosed without a compression test.

 

[ThomW]

I would absolutely do a compression test. It's quick, not overly invasive, and ensures you're not buying a motor with a blown piston or worn rings! Explain that, and if the seller says no way...he's either hiding something from you or doesn't understand motors at all. Either way...not overkill at all.

 

[H20Rat]

Has anyone that is saying do it actually bought a boat and done a compression test, or had a seller do one? I have bought and sold a dozen boats. Not once did I do a compression test, nor did I ever have a seller do one. The only time it might be of any value is if you can't water test the boat. If you have it on the water and it performs as expected, why compression test?

In any case, I would absolutely never let a buyer do a compression test themselves on a boat. Keep your hands off my engine, plenty of ways to screw it up. The only way I would agree is with a dealer certified mechanic doing it at buyers cost, and only with a purchase agreement (and deposit) that says they are committed to the boat pending compression test results.

 

[JoLin]

I agree with JoLin but that’s assuming you have the experiance to know what to listen for.

Very true. I should have mentioned that. I've been around engines for a long, long time.

 

[tpenfield]

Has anyone that is saying do it actually bought a boat and done a compression test, or had a seller do one?

Yes, on both power boats that I bought, I had compression tests done.

 

[Alumarine]

Has anyone that is saying do it actually bought a boat and done a compression test, or had a seller do one? I have bought and sold a dozen boats. Not once did I do a compression test, nor did I ever have a seller do one. The only time it might be of any value is if you can't water test the boat. If you have it on the water and it performs as expected, why compression test?

In any case, I would absolutely never let a buyer do a compression test themselves on a boat. Keep your hands off my engine, plenty of ways to screw it up. The only way I would agree is with a dealer certified mechanic doing it at buyers cost, and only with a purchase agreement (and deposit) that says they are committed to the boat pending compression test results.

I've done them on boats, bikes, cars and trucks.
Not all the time. It depends on the circumstances.
If it's priced accordingly then it doesn't matter as much.
Never had anyone object.

 

[Old Ironmaker]

I simply ask the seller if he or she is familiar with a simple compression test. If yes the seller usually gives the go ahead if no I would explain step by step. If they refuse including being done by a Marine tech. I simply would walk away. No comp. test no sale. Simple as that. Also putting the boat in the water for a run is important. You can inspect every nook and cranny and still not find a leak without being in the water. Even then it may not show up if you don't give her a good run not a "NO WAKE" putt around. Putting around a river can mask many problems including engines, give it a WOT run. Be prepared to give the buyer a 100 bucks for a water test. I have had a few tire kickers wanting to take the family for a nice weekend boat ride, tell them it is going to cost them and they all of a sudden aren't interested. $100.00 for me probably doesn't cover the tow, the launch and the fuel, let alone my time for 2 hours minimum.

edit: A Survey is a full comprehensive boat inspection done by a certified Marine Surveyor. They are difficult to find around here and won't do a survey on a boat less than 25' or even larger, and not cheap.

drunkenWaterRat, I've seen O/B's and I/O's run just fine on the muffs, and even run well when cold in the lake with a bad cylinder. We learned our lesson 2 years ago. Installed a crate engine in a boat and when it got in the lake wouldn't go past 3000 RPM. Worked on the thing for weeks then got the brilliant idea to do a comp. test. Bad out of the crate, duhhhh.

 

[dingbat]

edit: A Survey is a full comprehensive boat inspection done by a certified Marine Surveyor. They are difficult to find around here and won't do a survey on a boat less than 25' or even larger, and not cheap.

Interesting....

Surveyors they are a dime a dozen around here. Most banks require a survey if the boat (any size) is used for collateral on a loan.

If I remember correctly, they charged me $15 per the foot. He spent a good 2 hours checking the integrity of every system on the boat. Plumbing, fuel, thru hulls, electrical, drains, etc. Took moisture readings of the transom, deck and other venerable locations around the hull.

A couple of days later I received a report (2 copies) presenting his findings complete with OEM specifications and detailed explanations, with pictures, of any issues he found in the boats sub-systems.

Overall I as very impressed with the thoroughness of the inspection. He found the boat to be in above average condition for a 4 yro boat. The only actionable items was the PO installed new live well drains and didn't double clamp the connections.

 

[Old Ironmaker]

Interesting....

Surveyors they are a dime a dozen around here. Most banks require a survey if the boat (any size) is used for collateral on a loan.

If I remember correctly, they charged me $15 per the foot. He spent a good 2 hours checking the integrity of every system on the boat. Plumbing, fuel, thru hulls, electrical, drains, etc. Took moisture readings of the transom, deck and other venerable locations around the hull.

A couple of days later I received a report (2 copies) presenting his findings complete with OEM specifications and detailed explanations, with pictures, of any issues he found in the boats sub-systems.

Overall I as very impressed with the thoroughness of the inspection. He found the boat to be in above average condition for a 4 yro boat. The only actionable items was the PO installed new live well drains and didn't double clamp the connections.

Interesting for sure. I would bet the closest certified Marine Surveyor would be in the Toronto area, oer 2 hours from us here on Erie. Yes you can hire a Marine mechanic off duty to go over a prospective but not an official survey per say. Like Home Inspections here in Ontario, no certification needed to do one. I can make up cards this morning, get a clipboard, a step ladder, a drone to inspect the roof (very professional looking eh?) and a tester and do Home Inspections for money this afternoon. I'd trust my inspection more than a "pro" here.

I can't remember where you are dingbat. Tell one of your boat inspectors to emigrate to Ontario and he can write his own ticket.

 

[H20Rat]

drunkenWaterRat, I've seen O/B's and I/O's run just fine on the muffs, and even run well when cold in the lake with a bad cylinder. We learned our lesson 2 years ago. Installed a crate engine in a boat and when it got in the lake wouldn't go past 3000 RPM. Worked on the thing for weeks then got the brilliant idea to do a comp. test. Bad out of the crate, duhhhh.

Yep, like you said, a good water test. (implied that but should have stated) Have yet to see an engine that has weak compression, but still starts and runs well and hits its rated rpm with a decent prop. Ironically, I bought yet another boat a month ago, and did a water test on a local river. Varied in between full throttle runs, idling, shutdown, restart, pretty much everything a normal boater would do in a typical day, condensed into 20 minutes.

 

[Leardriver]

I have owned 20 boats, and never done one, and would never let someone else start turned wrenches on my motor. Cross-threading a spark plug would be a drag. If the potential buyer doesn't like it, they can go buy someone else's boat.
I will always water test, and demonstrate top speed runs, which would quickly show a poor running motor.

 

[Old Ironmaker]

I Cross-threading a spark plug would be a drag. .

I never thought of that, good point. I would do it my self for them while they stand there but can tell you #4 cylinder on mine is a huge pain. One reason I am selling mine through a reputable Marine dealer.

 

[Leardriver]

I shouldn't say never allow, it sounds so absolute, but I would need to be convinced.

 

[MTboatguy]

I would say the average boat customer these days would not ask to do a compression test unless they know something about boats. I have a lot of friends call me to go look at boats with them because they don't know what they are looking and don't know how to tell a bad one with a good one. So if a guy shows up and asks me to do a compression check on a boat or a motor I am selling, I normally ask a few questions to see if they know how to properly do one and I let them do it if they sound like they know what they are doing. Normally before that they have already looked over the boat and poked and prodded in the proper places showing me they have some level of knowledge about boat.

 

[444]

I have never done one before buying. If I get there and the motor is already warmed up I walk away. I usually find a legit cold start followed by a hot start after warming it up tells me as much as I need to know. If a potential buyer wanted to do a compression test on my boat I would pull out my tools and do the test for them with my gauge as they watched.