How Long Can You Safely Run a Mercruiser 260 at WOT

[greg82255]

Hello, I have a Merc 260/Alpha One with about ~800 hours. With a 21" prop the WOT RPM is about 4400 (52 mph) and with a 19" prop I also get 52mph, but at about 4800 rpm. I'm wondering how long I can safely run at WOT without damaging anything. I ask this because I am driving the boat about 23 miles in Lake Winnipesaukee in NH this weekend, and I'd like to get to where I am going in a reasonable amount of time. I'd like to go 50mph the whole way if it's safe, but I don't want to wreck the motor on my way down there (or on my way back). I also assume it's better to use the 21" prop so the RPMs are not turning as high? This is the last time I will use the boat this year, and I am re-powering this winter, in case that changes anyone's answer.

 

[Don S]

Re: How Long Can You Safely Run a Mercruiser 260 at WOT

Until it blows up.

 

[tswiczko]

Re: How Long Can You Safely Run a Mercruiser 260 at WOT

What year is the motor?

My 89 5.7 has a recomended WOT of 4500, I have heard of later models having a recomended WOT rpm of closer to 5k.

I would find out what the factory recomended WOT rpm is and not exceed that, but run as close to that as I could.

as far as how long you can run at that rpm is a matter of the condition of the equipment. Personally I would not run WOT all the time as it increases wear and fatigue on moving parts.

 

[tswiczko]

Re: How Long Can You Safely Run a Mercruiser 260 at WOT

Until it blows up.

I like that answer better

 

[greg82255]

Re: How Long Can You Safely Run a Mercruiser 260 at WOT

Don I suppose you are right. I suppose what I'd really like to know is what is safe, and how long can I safely run at what RPM on a 23 mile trip. I've never stayed on plane for more than 15 minutes with my boat. Please forgive my ignorance here - I've heard stories of people running outboards forever at WOT with no problems, but I realize I/O's are a different story. My uncle has a 500 EFI in his Fountain and he runs 75 mph at 5300 RPM for 45 minutes at a time and also has no problems. Again, that's a high performance motor. But he also told me about his cousin buying a new 350 back in the 90s and running it for 15 minutes at WOT and it blew up, but I thought that was because it wasn't broken in properly before he decided to race around the lake.

Not sure who asked but it's a 1986.

 

[greg82255]

Re: How Long Can You Safely Run a Mercruiser 260 at WOT

A few people just posted while I was writing the last reply. Bubba - I believe the engine is healthy, as it's my first year with the boat. The oil is very clean (I actually just changed it about 3 days ago) and there are no cooling issues - I changed the impeller this year and have never had a problem. So you are saying that using the 19" prop, I should be able to safely run 3500-4000 as long as I want, and give it the gas every 10 minutes or so?

Thank you all for your replies.

 

[Don S]

Re: How Long Can You Safely Run a Mercruiser 260 at WOT

My answer would be the same had you ask how long you could run at 3500 rpm. No one here knows.

The engines are designed for sustained running at WOT rpm, but there is no rule as to how long it will last at those rpms.
Put another way, if an engine under warranty was run at max WOT rpm for 8 straight hours and then blew up, the manufacturer could not void your warranty for it.

 

[greg82255]

Re: How Long Can You Safely Run a Mercruiser 260 at WOT

Put another way, if an engine under warranty was run at max WOT rpm for 8 straight hours and then blew up, the manufacturer could not void your warranty for it.

That's exactly what happened to my uncle's friend. I was told he ran his boat at WOT for ~15 minutes and it started to make clicking noises and had other problems, so Merc gave him a new engine. I don't know all the details but that was what I was told.

 

[ohioriverat]

Re: How Long Can You Safely Run a Mercruiser 260 at WOT

I have a friend with a 98 sea ray 4.3 and he runs it wot everywhere and never lets it rest, wot is 4500 for him, i would never run mine wot for any period of time, i run at 4k rpm's and always make it home!

 

[bnicov]

Re: How Long Can You Safely Run a Mercruiser 260 at WOT

Running at WOT for that long and you have to start worrying about whether or not you have enough fuel on the boat. I'd keep it around 3500rpm so you'll be running in the 30odd mph range SAFELY. You don't have to worry about breaking anything. Just because you CAN run at WOT, does not mean that you SHOULD, esp. with an old motor. Go with the 21p prop, you'll cruise better, you will get a bit better mph for the given rpms giving you slightly better fuel economy.

 

[Volphin]

Re: How Long Can You Safely Run a Mercruiser 260 at WOT

I'd be right at 4000 rpm and call it good.

Check your fluids before you go.

V

 

[Volphin]

Re: How Long Can You Safely Run a Mercruiser 260 at WOT

Oh, and with the 19 pitch... sorry

V

 

[HT32BSX115]

Re: How Long Can You Safely Run a Mercruiser 260 at WOT

Reciprocating aircraft engines are designed to produce either maximum rated power for 5 min and then MUST reduced to a lower rated "continuous" power.



Automotive engines (and marine engines) aren't designed to produce MAX power indefinitely. (it's the main reason they're de-rated when people put them in airplanes)

Boat manufacturers don't rate the engines to produce MAX continuous power.........they just rate them for MAX power and call it good. Send Mercury Marine a letter and ask them how long you can run their engines at WOT!

How long can you run it at MAX power?

DonS had the best answer!!

Until it blows up.

Let us know when that happens!

We can start a spread sheet of how long IB engines last at WOT.

 

[greg82255]

Re: How Long Can You Safely Run a Mercruiser 260 at WOT

Replacing the engine after this weekend............. Anyone up in lake winnipesaukee this weekend willing to tow me back to Lakeport Landing.....? lol

 

[geneseo1911]

Re: How Long Can You Safely Run a Mercruiser 260 at WOT

I have a 19' '82 Cobalt with a 260 Merc 21pitch SS. On my boat, 3500 RPM is 40 mph. Top speed is 50-52. I don't know for certain, but I'd guess it burns twice the fuel for those 10 mph. You aren't going to save that much time by running WOT, and the fuel burn will be astronomical, but I doubt you will harm the engine so long as she doesn't overheat.