Compression Tests, what it can really tell me...

[FAV453]

I am looking at a used boat that has a Johnson ocean pro 225 (1998). The broker says there is no hour meter, but will provide a compression test. Let's say the compression test comes back 100% within specs, what does that tell me about the engine's projected life? To me it says everything related to compression is functioning normally (now), but for how long and what about the other systems of the engine?

 

[wayne h]

Re: Compression Tests, what it can really tell me...

really hard to say just like a car anything can go wrong at any time.new or used.compression tells u that the powerhead is pretty sound.i say pretty sound because it can still have a rod knock or internal damage and still have good compresstion.but remember there is other things that can fail like carbs,starter,ignition, lowerend,water pump the list goes on and on any time you buy used it BUYER BEWARE.see if he will let you take it out and run it also what kinda warrenty?but if the price is right.just remember its a boat.a hole in the water you throw money into.we all have done it or are going to do it because boating is a sickness there is no other play i can think of better then being on the water.with all that said make sure you look it over well and adjust the price according to what you find. good luck

 

[FAV453]

Re: Compression Tests, what it can really tell me...

Thanks for the info. Kinda what I figured. On the same engine is there a way to check the water pump (impeller) easily? I heard you can look at how well the water comes out the telltale, but how about a mre scientific method?

 

[andrewkafp]

Re: Compression Tests, what it can really tell me...

Compression is important, but the hour meter can be disconnected for years.<br />I think that absence of corrosion and evidence of regular maintenance are good measures. If the owner has reciepts of work thats been done.. all the better..<br />You can usually tell if a motor has been neglected by just looking it over.. corroded metal, wires, oil leaks, water in L/U burnt parts, like rectifier or wires. And general appearance of outer covers. Has it been patched up to sell or is it original and been looked after ?

 

[Solittle]

Re: Compression Tests, what it can really tell me...

FAV - Don't sweat the water pump as you should replace it anyway. You can do it yourself and it is not expensive to do.<br /><br />Water pump impellers "should" be replaced every couple of years. The telltale only tells you that it is pumping but not how well or how old the impeller is. Some boats have a pressure guage but it dosen't tell you how old the impeller is either. The pressure guages on my OMC V4s show 8-12 lbs with muffs in the driveway.