350 Mariner Top Speed / RPM?

G

gratcho

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We bought our 2001 350 Mariner last year. I believe we are not getting the full range of RPMs out of the Mercruiser 350 Mag MPI engines (especially our port engine). We're maxing out at around 3200 rpm and 20 knots. What are others getting in RPM and speed?

If I'm way off everybody else, I'll post for solutions in the engine forum. Thanks!
 
I am not sure about about that engine set up. On my Crusaders the wot RPM range is listed on the air intake cover.
Those RPM' do seem low??
 
Was it like this when you bought the boat? What did your surveyor say about it?
Yes, your RPM's are way low. Not sure what RPM's that engine runs but you are at least 1000 maybe 1500 RPM's too low.
Possible causes: wrong props, engines not running properly, bad fuel, boat overloaded with junk and/or a lot of water in the bilge, bottom and/or running gear fouled. (or a combination of any/all the above)
What have you done to check into the problem?
 
Yep, I think you are quite a bit low. Do you have any idea what size props are on her?

Bob
 
Top speed/RPM for our '99 Mariner 350 with twin Merc MPI 350 engines is around 3,600 rb2@gr5t 22 mph or so...I know that it is underpropped, surveyor said the same thing. For our little lake I'm not worried about it, we just putt around anyway.
 
Brad, for what it's worth, you are overpropped, not under.
 
I have the Merc catalog in front of me.

WOT for that engine = 5200 I/0 and 5000 IB. (Doesn't make sense, I know!)

You are way over propped

Agree with all of the above plus....possibly a combination of overpropped and damaged prop and/or fouling in the running gear and a fouled bottom.

You should be able to put a scanner on the 350MPI and get a readout of everything you need.
 
Some futher info below:

Was it like this when you bought the boat? Yes.

What did your surveyor say about it? Nothing - hmmm.

Yes, your RPM's are way low. Not sure what RPM's that engine runs but you are at least 1000 maybe 1500 RPM's too low.
Possible causes: wrong props, engines not running properly, bad fuel, boat overloaded with junk and/or a lot of water in the bilge, bottom and/or running gear fouled. (or a combination of any/all the above)

What have you done to check into the problem? Posted this message - I wasn't sure if I had a problem. Looks like I do. Would it make sense for me to see what the RPMs are in neutral so I can eliminate drive train possiblities, or would that cause a problem?
 
I don't think running up the engine in neutral will tell you much.
Start looking into all the possible problems we listed.
Is you boat filled up with junk? Have you checked the bilge to make sure you're not carrying around a couple hundred pounds of unwanted water? When was the last time the engines were looked at by a qualified mechanic? After you have done all that, your next move is to haul the boat to check the bottom to make sure your running gear isn't fouled up and check your props. Find out what size they are and if they are the right size for your boat. If everything else is ok, you are grossly overpropped.
 
cwms brings up a very good point. I had a lot of "GUNK" in Saint Max's bilge on the maiden voyage. At the first rest over night (RON) we poured a quart of OrPine and about a hundred gallons of fresh water to clean the bilge for the next leg. Cruise and RPM dropped dramatically. Pumped the holding tank and the bilges the next evening and all was well.

Are you sure all bilge holds are vacant?
 
Can someone please explain what over/under propped means and how you determine the right prop's size? Thanks
 
quote:
Originally posted by MarcJ

Can someone please explain what over/under propped means and how you determine the right prop's size? Thanks

Click to expand...


If your engine is designed to run WOT at 5000 RPM's and you can only get 4000 (assuming engine is running good and boat is not overloaded) than you are over-propped meaning you have too much pitch and/or diameter in your prop for your boat/engine combination.

Same engine and you now get 6000 RPM's means you are underpropped.

How to know what size prop to get? Go to your local prop shop and let them tell you. They are the experts.
 
I had the engines tuned up prior to splashing this year. I'll contact them to understand what they do to check the high end. This is our weekend condo, but doesn't strike me as being overloaded - the fridge is full, we have enough cloths for the weekend, not all storage is filled to the brim. Bilge is good, I checked out all three bilges. I'll start digging into the prop issue. KWN came with two additional props in their original boxes.... maybe I'll check w/Carver to see what size props they started out with. thanks for the advice!!
 
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