Test Merc 25 HP Four Stroke Jet

[walk-on]

Hi Guys,

I'm about to purchase a used boat with a 2008 Merc 25 HP four stroke jet motor. Being it is less than a year old and still under warranty, I was not concerned about hearing it run, however I'm starting to get that nagging feeling that I need to know that it runs okay.

The weather outside is frightful at 6 degrees F here in PA and I'd like to know if this motor can be started briefly without water. I don't even know if it will start, or if I should try to start it since it is so cold. I'm thinking if there is an impeller that has ice around it, I might cause damage by trying to start it. Having only ever owned two stroke prop motors, I don't know how these four stroke jets cooling system works.

Thanks for your thoughts.

walk-on

 

[tashasdaddy]

Re: Test Merc 25 HP Four Stroke Jet

be aware when buying a 25 hp jet, you are loosing about 30% of the actual hp in the jet transition. they are usually rated like 90/60 90 hp powerhead, 60 hp jet output. so with a 25 hp power head, you are only getting around 15 hp thrust.

 

[TOHATSU GURU]

Re: Test Merc 25 HP Four Stroke Jet

What he said and no, you have to have water going into the engine to RUN it. You can start the engine without water to see if it does start. That should be limited to turning the key and hearing the engine start, then shutting it off very quickly. Figure 1 to 2 seconds, before you turn it off.

 

[walk-on]

Re: Test Merc 25 HP Four Stroke Jet

According to the Mercury web site, the prop shaft rated horsepower is 25 HP.

For the 40 HP Jet the features area states:

"Based on the powerful 60 hp FourStroke (60.8 Cu. In.) delivering 40hp at the jet pump."

It wouldn't make sense to me to rate the 40 HP at the jet and the 25 HP at the powerhead.

The specs for the 25 HP four stroke jet show 32.1 Cu. In. (526 cc) which leads me to believe the outboard is actually a 25 HP or slightly less at the jet. Can anyone confirm?

Thanks again.

 

[TOHATSU GURU]

Re: Test Merc 25 HP Four Stroke Jet

It's supposed to have the 30 ECM which allows it to turn a 21 hp eqilivant hp at the jet output. The powerhead puts out between 31 and 32.

 

[tashasdaddy]

Re: Test Merc 25 HP Four Stroke Jet

"It's supposed to have the 30 ECM which allows it to turn a 21 hp eqilivant hp at the jet output. The powerhead puts out between 31 and 32." which is a 30% loss.

 

[ondarvr]

Re: Test Merc 25 HP Four Stroke Jet

What type of boat is it? Most jets that small barely get the boat on plan with just one person, add some gear, a cooler and another person and it may not plane at all.

 

[walk-on]

Re: Test Merc 25 HP Four Stroke Jet

The boat is a 1648 aluminum jon with side console, 70 inch beam and 428 lb. hull weight. My current boat is a small 1432 jon with an old 3HP Evinrude duckhunter that moves pretty slow so I'm thinking the 25 jet is going to be an upgrade!

 

[Wee Hooker]

Re: Test Merc 25 HP Four Stroke Jet

If your within a few hours of the coast/ unfrozen water, I think I'd still want a test run. IT will tell you how it runs under load (vs ideling in a bucket) and show you what she has for power, speed and ride.

Is warrenty on the engine transerable?

 

[walk-on]

Re: Test Merc 25 HP Four Stroke Jet

I think the warranty is transferrable for $50 but I'll have to check with the local dealer to make sure.

 

[ondarvr]

Re: Test Merc 25 HP Four Stroke Jet

Sounds under powered, I have 16' G3 with a 60/40 Yamaha jet on it. With one person its great, two its good, three its slow. I also have 15' (but heavier) boat with a 90/60hp Evinrude jet, with one or two people its great, three is good, four is slow and at the limit.

Test run it with buddy and some junk in the boat before you buy it.

With a 35HP rating for that hull you aren't even close to getting good performance with 25HP prop, let alone a 25 converted to a jet. You need a 50 converted to a jet to get good performance.

Is this a jet from the factory? If so it should be a 40HP power head with a 25HP rating at the pump. I didn't look up the displacement of each to see which it is. If it is 40HP power head then it won't be as bad.

 

[walk-on]

Re: Test Merc 25 HP Four Stroke Jet

I bought the boat today. The previous owner stated that I could take the boat to the river (without him) if I wanted to. I settled for hearing the motor run in the bucket in the garage. It started right up and sounded good, but then again it only has two months of run time on it.

The max HP for this boat is 35 HP and it was purchased brand new as a package from the local marine in August of 2008. The motor warranty is transferrable for $50. Now I'll have to wait a couple months for the ice to melt so I can get it out on the water.

According to the chart at outboardjets.com the minimum size would be approximately 30 HP at the powerhead. I realize this boat won't run 40 MPH but it will run over 20 MPH which will be fine for what I need.

Thanks for all the input!

 

[Green-Hornet]

Re: Test Merc 25 HP Four Stroke Jet

outboard jets have been rated at the jet instead of the powerehead for a while now so when a merc,honda, yamaha say X amount of HP on a current jet it means at the jet. also the newer jets like the merc in this discussion will have a SS impeller and in general the latest most effeciant design . There seems to be a number of jet improvements over the last few years as more areas area are increasing the limits on power and size of boats in alaska and other places.

 

[walk-on]

Re: Test Merc 25 HP Four Stroke Jet

I just remembered this post so I thought I'd come back with an update. The 25 Jet runs very good but for some of you it would be considered underpowered. The only time I don't like the jet/boat combo is when I have most of the people weight toward the back of the boat. My buddy is 250lb and I am 150 lb. If he is in the middle or front of the boat, it comes on plane immediately and runs between 20 mph and 25 mph WOT.

I'm not unhappy with this motor on this boat. I just need to make sure my weight distribution is ideal to make it work the best.

 

[ondarvr]

Re: Test Merc 25 HP Four Stroke Jet

outboard jets have been rated at the jet instead of the powerehead for a while now so when a merc,honda, yamaha say X amount of HP on a current jet it means at the jet. also the newer jets like the merc in this discussion will have a SS impeller and in general the latest most effeciant design . There seems to be a number of jet improvements over the last few years as more areas area are increasing the limits on power and size of boats in alaska and other places.

The HP is rated at the jet only if it "is" from the factory, many are converted at a later date, which was already asked. There have been very few improvements, if any, to outboard jet pumps over the years, the only real changes have been in the high HP models. Stainless impellors don't help low HP models much if at all, they do help in the 150+ HP range though. Stainless impellors will last a lot longer and it most likely has a stainless sleeve too, my Yamaha does.

The is no need for these jets to be improved, at least from the manufacturers perspective, they're the only company that makes an OB jet, so there's no competition to force them to improve the design.


Good to see it works for, that?s the only thing that counts.