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TOPIC: What's the max RPM I should cruise Mercruiser 5.0LX

What's the max RPM I should cruise Mercruiser 5.0LX 18 Jun 2017 14:55 #1

  • Francorosso
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I have a 2001 2455 Bayliner Ciera with a Mercruiser 5.0LX. The RPM gauge goes up to 6000 with no red line. When I push the throttle all the way up the RPM is at 6000 (5500 with a full tank of gas), and I'm wondering is it ok if I run it wide open all the time? I understand about how much more gas you use at high RPM for very little increase in speed, but what I care about is whether this engine is good to run at 6000 RPM all day long without any worries. It has always made me nervous running an engine at full throttle for extended periods but perhaps that's what these are made for. I welcome all opinion and your experiences but I'm most interested in what the manufacturer recommends which I can't seem to find online.
Frank

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What's the max RPM I should cruise Mercruiser 5.0LX 18 Jun 2017 16:02 #2

  • builderdude
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Don't run it there! WOT is used for testing purposes only.
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Dave
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What's the max RPM I should cruise Mercruiser 5.0LX 18 Jun 2017 16:38 #3

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builderdude wrote: Don't run it there! WOT is used for testing purposes only.


AGREED.

While not the same engine size or boat, I try and limit the RPM to about 75-80% of WOT. In my case when tested I reach 4,600 rpm on my carb'd 5.7's which equates to 3,600-3,700. This proves to be the sweet spot in my application for ride, performance and efficiency.
Hope that helps.
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What's the max RPM I should cruise Mercruiser 5.0LX 18 Jun 2017 17:04 #4

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I think most guys tend to run the rpm at the slowest speed at which the boat will plane or a touch above. The fellas that have fuel flow equipment will likely run the rpm at where they achieve the best fuel economy. My 2556 will plane around 2900 rpm (pending conditions) but I'm usually running around 3200-3400 rpm.

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Dave
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What's the max RPM I should cruise Mercruiser 5.0LX 18 Jun 2017 17:20 #5

  • Don77
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If you can run that engine up to 6000 RPM you are way under propped!!!
You need a prop that has a higher pitch! As in going from a 15 inch pitch to a 17 inch pitch!
Good luck and enjoy your boat but DO NOT run it at 6000 RPM! Run it at a much lower RPM! But you should change that prop!
Don

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What's the max RPM I should cruise Mercruiser 5.0LX 18 Jun 2017 17:56 #6

  • desuch
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mine also
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1988 flybridge trophy bayliner 2556 ,mercury 5.7 lit. OMC cobra out drive 76 hrs. on new package,
located in ketchikan ak,name DOMINION

What's the max RPM I should cruise Mercruiser 5.0LX 18 Jun 2017 17:58 #7

  • desuch
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I have contacted bayliner on this issue they have told me that 4600 rpm is max anymore you have the wrong prop.I run mine at 3200-3400 rpm using a 15.5 x 13 prop. that gives me 4100 rpm
5.7 liter mercury carbed. engine cobra drive
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1988 flybridge trophy bayliner 2556 ,mercury 5.7 lit. OMC cobra out drive 76 hrs. on new package,
located in ketchikan ak,name DOMINION
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What's the max RPM I should cruise Mercruiser 5.0LX 18 Jun 2017 19:48 #8

  • TerryW
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After 10 years with mine, the "comfortable" cruise RPM is 3600 to 3800 depending on the amount of slime on the underside and the amount of wave action trying to reduce your plane. I use my 8120 computer to monitor GPS speed and fuel flow to get a really good understanding where the engine is at its most economic at cruise. I run a 4 blade aluminium prop which was a revelation when I installed it.

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Terry (Retired Diving Instructor and Part Time IT Consultant)
1998 Bayliner 2452. 5.7l V8 - Edelbrock 1409 4bbl - Alpha1Gen2 - Solent UK.
MMSI 235061726
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What's the max RPM I should cruise Mercruiser 5.0LX 19 Jun 2017 05:54 #9

  • GrindKore
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You are certainly over-revving your engine past 4800RPM, you should get a prop with at least 2" more aggressive pitch to get that under control and get better top end efficiency. For me best cruising RPM is between 3800 and 4000, I have 2004 Mercruiser 5.0 TKS (its a 305 cid double barrel carb with automatic enrichment for turn key start). I currently run 3 blade 16x16 aluminum prop and when lightly loaded I reach max RPM just barely where limiter kicks in near 4800 RPM. When heavy, I can only get about 4600 RPM, this means my prop is ideal for the weight of my boat.

On second thought, before you spend any money on props. Get a calibrated shop tachometer and actually measure your WOT RPM. I just can't believe 305 mercruiser would spin that fast without puking valves out in a hot mess. The in dash gauges can be inaccurate or faulty.
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2005 Ciera 242EC
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Running Solas aluminum 4 blade 14.75x15 prop
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What's the max RPM I should cruise Mercruiser 5.0LX 02 Jul 2017 17:31 #10

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Great answer, how can I find the specs of my prop? Are they on it? And is there a website I can go to try and choose the right prop?

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Franco

What's the max RPM I should cruise Mercruiser 5.0LX 02 Jul 2017 17:33 #11

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I'm curious myself now. I have a shop tach but the leads are short, I'll have to figure something out to read the rpm while cruising.

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Franco

What's the max RPM I should cruise Mercruiser 5.0LX 03 Jul 2017 10:08 #12

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There's an RPM limiter on Mercruisers?

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Franco

What's the max RPM I should cruise Mercruiser 5.0LX 03 Jul 2017 17:51 #13

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Yes, but only on those newer MPIs & TB5
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What's the max RPM I should cruise Mercruiser 5.0LX 03 Jul 2017 18:20 #14

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My 5.0 2bbl is rpm limited to 4800
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1993 2452 5.0vortec 2bbl alpha gen 2

What's the max RPM I should cruise Mercruiser 5.0LX 03 Jul 2017 18:42 #15

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Jakeallred wrote: My 5.0 2bbl is rpm limited to 4800


If you have a TB V ignition system, yes the Rev-Limiter is set 50 RPM above the maximum engine RPM.
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What's the max RPM I should cruise Mercruiser 5.0LX 04 Jul 2017 15:16 #16

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Ruffryder wrote: Yes, but only on those newer MPIs & TB5[/quote

cruise RPMs: Properly set up, about 36-3800 RPMs should give you 26-28 MPH. That's the sweet spot. Should run about 2.3-2.5 MPG. Proper set up is: when at full throttle, the rpms should be just the max by Mercs specs. More RPMs= over revving; less means lugging the engine. Personally, I am more interested in the reliability of the engine; not how fast the boat goes.

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What's the max RPM I should cruise Mercruiser 5.0LX 08 Jul 2017 16:22 #17

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Thanks everyone for the answers. I checked the RPM and the tach is accurate so I need a new prop. Current prop is MI wheel vortex 4 blade 15x16. If I can peg the tach at over 6000 RPM when light can you recommend a new prop size?
2BBL Mercrusier 5.0 Alpha on a 2000 Bayliner Cierra 2455

Frank

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Franco

What's the max RPM I should cruise Mercruiser 5.0LX 08 Jul 2017 16:46 #18

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15X17 3 blade is what goes on that boat usually,
15X16 4 blade can't be that much off unless it was cupped...
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What's the max RPM I should cruise Mercruiser 5.0LX 09 Jul 2017 14:41 #19

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I had a pair of these motors in my 1993 3055.

Max WOT for them is 4200-4600. Either your tachometer is off or your prop situation is way off. I suspect your tach is not reading correctly. That could be a simple ground issue.

Bayliner OEM on the Alpha drives was 14 1/2 x 17 props. I switched to a 4 blade prop and was very pleased with the results.

My cruising RPM's were 3200-3400. WOT 4400.

Now, my boat/hull is different than your 2455 so your cruising RPM's could be a bit different.

First thing I would do is get your tach working correctly. They are inexpensive to replace if necessary. From there do some test runs with the boat loaded how you run it most of the time and see what you are achieving for max RPM's and cruising RPM's. I would be shocked if 6000 has been an accurate reading and you have been running it that hard without some type of failure.
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What's the max RPM I should cruise Mercruiser 5.0LX 09 Jul 2017 15:37 #20

  • nwboater62
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I have a hand held tach that I use for tuning. Maybe you could find one to verify. Also check the back or your tachometer for a 4,6,8 cylinder switch and make sure it's on 8.
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What's the max RPM I should cruise Mercruiser 5.0LX 10 Jul 2017 15:53 #21

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If your tach is accurate and your prop is close to original then your ratio in the outdrive may be wrong. Someone may have changed the outlive in the past and put the wrong ratio on. You won't make up 1000+ rpm with just a prop I don't believe.
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What's the max RPM I should cruise Mercruiser 5.0LX 11 Jul 2017 11:39 #22

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nwboater62 wrote: I have a hand held tach that I use for tuning. Maybe you could find one to verify. Also check the back or your tachometer for a 4,6,8 cylinder switch and make sure it's on 8.


That eas my thought to check as well. You never k
Now what the other guy did before you and called good.
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What's the max RPM I should cruise Mercruiser 5.0LX 11 Jul 2017 22:03 #23

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Check back here in a few weeks for the rest of the story. I have work and vacation and won't be boating for a little while but I intend to get to the bottom of this. The engine sounds great when the tach reads 6000 RPM. I don't suspect a modified outdrive. The prop is in perfect shape, looks like new. The engine is in perfect shape, like new. The guy I bought it from was obsessive about maintaining this boat. The tach reads like a normal tach, doesn't have any hiccups or sticking like my old boat did. There has to be an answer, so when I get back from some time off I'm gonna figure it out and let you all know.
Thanks again.
Frank

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Franco

What's the max RPM I should cruise Mercruiser 5.0LX 12 Jul 2017 19:26 #24

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My boat is a 1993 and when I bought it in 2012 I found all four tachs were set to 8 cylinders instead of 6 as they should have been. I have twin V6's from the factory. Surprised the previous owners never thought to check.

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1993 Bayliner 3058 Cierra
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Alpha 1 Gen II Drives
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What's the max RPM I should cruise Mercruiser 5.0LX 12 Jul 2017 21:20 #25

  • SteveInCal
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I bought a semi-cheap automotive multimeter from Harbor Freight: Cen-Tech LCD Automotive Multimeter with Tachometer Kit

It includes a tachometer kit and seems to be pretty accurate.

BTW, you mentioned that your motor is a 2 BBL. I thought the LX meant it's a 4 BBL.

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Steve M.
Marin County, CA
1989 Arriva 2050 KE
5.0LX, 230 HP Mercruiser, Alpha 1 drive
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