Why wet test an outboard motor while it is in the water? What do I look for??

Take the cowl off & see if the engine is relatively clean (no oil indicating leaks), pull the plugs & see if there is any indication of lean mixture or too much oil build up. Make sure the engine idles good when u first start it & after the engine warms up, same with high RPM's. Look at the engine again & check for leaks, gas, etc. Put it in gear & make sure there r no funky clunking sounds.

Ask around about a good mechanic & get one to check it out, including the carbs & a compression check.

If u have remote steering make sure the cables r not freezing up, making it hard to steer. Check any under deck foam to see if it is water logged.

outboards have underwater exhaust & the backpressure puts a load on the engine. The motor might start & sound fine without the lower unit submerged & then run like crap when u put a load on it.

In fact, many outboards will idle just fine out of the water with one or even two cylinders not hitting at all, & u can not detect it from listening (unless u have a history with that motor & recognize the different sound).

Are u asking what u look for when purchasing a used motor? It needs to start with a bump of the key (warm start only), idle in neutral & in gear without dying, accelerate smoothly when power is applied, & cruise at full throttle without misfiring. Depending on vintage (the ignition technology of a particular model), a cold engine might need to spin for 2 or 3 or 5 seconds before it starts.

Never buy a used motor without (at a minimum) checking the compression. If the lowest PS l cylinder is not within 5% of the highest, walk away.

If the boats on a trailer, ask the owner to start it up. If he does so without hooking the lower unit up with a garden hose attachment, walk away - he does not know how to take care of an outboard.

Excuse me. but u r asking about a ''wet'' test r u not? Luckyone. must indeed be lucky. as u can do all that he mentioned on dry land. & still end up with a motor that runs like crap - or does not run at all when under load.

As for me. well, l agree with u totally. u need to give the engine a very good ''wet'' test.
Take the boat out, & really put it through its paces. What r u looking for? You want to make sure it performs up to par. All engines act differently & perform differently when they have a ''load'' on them. hooking a hose up, turning on the water & starting the engine, & giving it a few ''revs'' does not put a load on it.

When the engine is pushing a boat - now u have a measure of the engines true performance.
In addition. u want to make sure the engine is cooling system has a good flow on its water pickup & thus, u can see it as it squirts out. Is it a good strong stream, or is it just a trickle? Does the engine smoke? If so, is it a pack a day. or a 3 pack a day smoker. either case. that is a big clue to something wrong. u also want to make sure it is not dripping oil or fuel anywhere.

Yes, Murphy & l r old friends. & l am a big believer in Murphy is laws. So, in addition to having ur favorite mechanic look at it. take it out & put it thru its paces. that Murphy. he especially loves boats & boating as much as l do, & he is always looking for a new boating friend.

Happy & Safe Boating!

l presume u have a tachometer on the boat - if this is a fishing motor, maybe the other guys advice is more helpful.
the real basic thing is that at WOT it is supposed to tach at or just below max rated RPM. u can find this in the mfr engine manual or in any of the Seloc manuals - ur public library probably has one or can get one by borrowing it from another library.

That is it! - That is all u really want to check in a wet test.

Like one other said, everything else can be done dry - but no kidding do not run it dry without a water cuff attached or u will need a new impeller, maybe more.

you want to see how it runs under a load
they run diferant in water than on land