Difference and Benefits of Diagnostic vs. Compression Test?

[Bavic]

Looking to buy a used boat.
Its coming with a 2000 Volvo 5.7 GSI 280 HP
200 hours.
Please offer a explanation of what a Diagnositc run through the computer does and also what a compression test does?
What are the benefits of both and are they both needed or one more than the other?
Also has anybody heard of Dianometer? It seems to be the newest testing device where it can simulate full load on the engine to give an accurate appraisal of how the engine will react in live use.

thanks alot.

 

[TilliamWe]

Re: Difference and Benefits of Diagnostic vs. Compression Test?

In my opinion a diagnostic on a cumputer is a waste of time. All it will tell you is stored codes of previous electronic malfunctions.
A compression test tells you whether the cylinders have excessive wear and can point to the valves if they are bad.
The only kind of dynometer you need to test a boat engine is called a "sea trial". And that's a test drive, on the water, with your "normal" load of passngers/equipment to see how the engine/outdrive performs.
If you are not sure how to do these things yourself, you need to look into a marine surveyor.

 

[Bavic]

Re: Difference and Benefits of Diagnostic vs. Compression Test?

In my opinion a diagnostic on a cumputer is a waste of time..

So there is no useful info given from a diagnositic? I can have faith in hour meter on dash, which is digital not analog?

If you are not sure how to do these things yourself, you need to look into a marine surveyor.

Is that the same as bringing a mechanic? are they going to perform the same functions?

Thanks for the info by the way.

 

[Don S]

Re: Difference and Benefits of Diagnostic vs. Compression Test?

So there is no useful info given from a diagnositic? I can have faith in hour meter on dash, which is digital not analog?

Hours mean very little. If it has 200 hours on it, that is only 20 hours per year, not very much. What you don't know is how those hours were put on the boat. Wide open throttle for 20 hours is a lot different at cruising around at 3500 to 4000 rpm. It also doesn't tell you how often maintenance was done, like oil changes, gear lube, impellers, etc.
You could get a compression test if you want, it's not a big deal. The sea trial is going to be the big deal. If it idles ok, picks up speed and rpm smoothly, and reaches the proper wide open throttle rpm, then you can bet the engine is in good shape. With EFI, if you have a low or dead cylinder, it will not idle smooth, it will not run right at any speed.
The best thing to do if you are not sure is get a mechanical survey by a certified Volvo Penta dealer AFTER the sea trial. No sense spending money on a survey if the boat won't pass the sea trial which is free.

 

[shoestring]

Re: Difference and Benefits of Diagnostic vs. Compression Test?

Both the dyno, and the diagnostic computer are mainly for solving problems. on my year model of boat the diagnostic computer will tell you how many of the total hours were used at what rpm range. just gives you an idea of how hard the motor was run. these hours come from the engine computer and can be used to confirm the clock on the dash. compression test is important to tell you if you have pending major engine repairs in your future. My advice is to use your senses, being sight, smell and hearing. if it looks like it has been well taken care of, it probably has, etc. Service records always help. a good boat mechanic could confirm any technical aspect you may not be comfortable doing yourself. I just bought a used boat last year. I made a deal with the person i bought it from. seller told me everything was great. the deal was, i would have a surveyor of my choice inspect the boat. if i got a good report, i paid the surveyor, if i got a bad report, the seller payed the surveyor. if you are going to drop some dough on a boat, spring for a surveyor. you will get over "springing" for things before too long. Awesome advice on the sea trial. not only to see if it runs good, but if the boat suits your needs, rides and drives the way you want. could help prevent buyers remorse. beware of " the boat only needs to have the (XYZ) part replaced and it would make it as good as new, the part only costs $100." MY opinion of this is, if the seller CAN'T afford the (XYZ) part, he DIDN'T afford an oil change either.

 

[Bavic]

Re: Difference and Benefits of Diagnostic vs. Compression Test?

Thanks alot on all the great info. The marina selling it is acting as a brokerage between the future buyer and seller who is their customer. They have done all seasonal maintanance on it for the last 3 years.
They are going to use their "Diacom" program on it. They have said that they only became Volvo certified in the last 5 years so they dont have the add ons for older engines,(not cost effective). But want to do it and charge me an hours worth of labor? Will the Diacom work on a older Volvo?
Can you do a compression and diagnositic test out of the water? The boat is in winter storage and they said they could do both next week. I thought the engine would be winterized and thus wouldnt be able to be run full out until it was prepared for the season? Am I wrong?
Would you trust a Volvo certified marina as your mechanic surveyor if they are the broker for the seller?

Thanks so much for the help everyone!

 

[Speakrdude]

Re: Difference and Benefits of Diagnostic vs. Compression Test?

Someday, I'm gonna have a boat engine with a computer....-)

 

[TilliamWe]

Re: Difference and Benefits of Diagnostic vs. Compression Test?

... The marina selling it is acting as a brokerage between the future buyer and seller who is their customer. They have done all seasonal maintanance on it for the last 3 years. ...
Can you do a compression and diagnositic test out of the water?
The boat is in winter storage and they said they could do both next week. I thought the engine would be winterized and thus wouldnt be able to be run full out until it was prepared for the season? Am I wrong?
Would you trust a Volvo certified marina as your mechanic surveyor if they are the broker for the seller?
...

I'd certainly want to see those maintanence records. To see if they skipped anything since it "didn't get enough hours" on it in any certain season.
Yes, you can do a compression test out of the water.
You can not sea trial the boat while it is winterized, no. But depending on how it was winterized, and how you did the test, you could do a compression check and not disturb anything. But most likely, the engine would have to be re-winterized after a compression check. If they have to start the engine to do their diagnostic test, it would DEFINATELY have to be re-winterized.
I can't say whether I would trust that mechanic/dealer, cause I don't know them. They should be willing to be completely truthful about any problems, on the chance that they would get paid to fix them. And judging by your probable lack of expertise and experience with these engines, you would have to rely on them for future service. So they should be trying to get you as a future customer.