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Mercruiser 7.4 Replacement/Upgrade

S

Scottd21

Member
I have a 2001 Sea Ray 260 BR bowrider with a Mercruiser 7.4 MPI Bravo 3. I recently got stuck and was told the engine needs replacing.

I'm not sure what happened as I heard a clicking sound that got louder and louder and then the engine seized. No alarms. Mechanic said there was oil everywhere and engine can't be repaired.

It only had about 800 hours and no signs of any problems (compression test and oil analysis) I've only had it for 3 seasons. I'm going to get a second opinion on the engine but I was wondering what possible upgrade options I would have with a 7.4 with Bravo 3.

I've read good things about the 6.2. The new 8.2 looks like a great engine but says it's compatible with the Bravo 3 X so I'm not sure if that would require replacing the drive unless extra work can be done to compensate for that difference.

The boat is 27 ft and weighs 4450 dry. If the engine needs replacing I'd like to future proof my boat as much as possible.

Any ideas or suggestions would be appreciated and if you have a ballpark price.

Thanks

Scott
 
I would suggest to get a brand new Long block exactly like the one you have now, All accessories can be reused and you will have a fresh engine which may get another 800+ hours.

I would suspect a new Marine 454 HO long block would be in the range of $5000.00-$7000.00 range but that is an estimate.

A brand new Mercruiser complete block would be wel over $10,000 range.........
 
The 6.2 is not a replacement for the 7.4... The 8.2 is $$$$ and has issues with cracking manifolds constantly.....

Like Jack said, get a 7.4 long block along with an intake and new exhaust......

Alternative route is to find a running take out 496 mag...... IMO this is the best replacement.
 
kghost said:
I would suggest to get a brand new Long block exactly like the one you have now, All accessories can be reused and you will have a fresh engine which may get another 800+ hours.

I would suspect a new Marine 454 HO long block would be in the range of $5000.00-$7000.00 range but that is an estimate.

A brand new Mercruiser complete block would be wel over $10,000 range.........
Click to expand...

That sounds like a great idea. I'm a little bit confused when the mechanic says that the engine is gone. So it's really just the core of the engine that is gone and everything else that I see when I look at the engine can be reused?

So I see the core engine available on this site for $6,500.00. Since the engine is 20 years old shouldn't I replace things such as the belt? How much would it cost roughly in other parts such as the intake if I rebuilt it this way?

https://www.michiganmotorz.com/7-4l-454-ci-base-marine-engine-385-hp-1991-current

Thanks

Scott
 
From the description it sounds as if the engine had a bearing go out. When this happens particles of metal, from microscopic to large, come loose into the oil and circulate throughout the entire oiling system. The whole engine needs to be taken apart, cleaned out, and overhauled. That assumes that there is no structural damage.
This is usually more costly than simply replacing the block with a remanufactured one.
You can reattach the external parts such as the brackets, pumps, alternator, starter, the fuel intake system, and the cooling system, if there is one. The things that you will replace in addition to the engine will be the exhaust manifolds, belts, hoses and clamps, and the engine mounts.
What you end up with is a new engine with zero hours time on it. In order to future proof it, maintain it like a baby. If you don't do it yourself, get it on a program with your mechanic so that you are getting regular checks and winterization.

Also, the engine you linked to is $7499 plus another 300 for shipping. You get $1000 refund when you send them your old engine assuming it can be restored. There will be shipping charge (your cost) to return your dead engine, so just be aware of the actual price.

If there are any marine salvage yards in your area there may be a good used engine that will fit for far far less money. I'd start calling around.
 
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I suggested a NEW long block,
Not Remanufactured.
If you were the one to do the work and had a good background with this type of repair/engines in general, Then a remanufactured Marine engine would be a choice.

If you have to hire someone to do this it is far better to buy new.
 
I would go see your Mercruiser dealer and see what kind of deal you can make on a complete drop-in repower that fits your drive
 
o2batsea said:
From the description it sounds as if the engine had a bearing go out. When this happens particles of metal, from microscopic to large, come loose into the oil and circulate throughout the entire oiling system. The whole engine needs to be taken apart, cleaned out, and overhauled. That assumes that there is no structural damage.
This is usually more costly than simply replacing the block with a remanufactured one.
You can reattach the external parts such as the brackets, pumps, alternator, starter, the fuel intake system, and the cooling system, if there is one. The things that you will replace in addition to the engine will be the exhaust manifolds, belts, hoses and clamps, and the engine mounts.
What you end up with is a new engine with zero hours time on it. In order to future proof it, maintain it like a baby. If you don't do it yourself, get it on a program with your mechanic so that you are getting regular checks and winterization.

Also, the engine you linked to is $7499 plus another 300 for shipping. You get $1000 refund when you send them your old engine assuming it can be restored. There will be shipping charge (your cost) to return your dead engine, so just be aware of the actual price.

If there are any marine salvage yards in your area there may be a good used engine that will fit for far far less money. I'd start calling around.
Click to expand...

Thanks thats very helpful!.
 
o2batsea said:
I would go see your Mercruiser dealer and see what kind of deal you can make on a complete drop-in repower that fits your drive
Click to expand...

I've also heard that the 383 stroker is the Mercruiser recommended replacement for the 7.4 MPI. It seems to have much better fuel economy than my current engine, great performance and a 3 year warranty. It is a small block however but sounds comparable.

https://www.michiganmotorz.com/mercruiser-383-mag-stroker-mpi-with-freshwater-cooling-350-hp

Scott
 
You are misconstruing the info on the 383 stroker.
If you had a different, smaller and lighter boat then yes that choice may be a good one.
In a boat of your size and weight the "economy" would not be realized.

You have a 26 ft heavy boat.
You need torque to move that and a BIG BLOCK is appropriate for that purpose.

If you were to go with the same engine (7.4) with a higher power output then you may see better economy.

Example- lets say your 7.4 is 350 hp and about the same torque (300-325 ftlbs).

If you were to upgrade to 7.4 with 400 hp and 375 ish torque
That would give you better power and allow you to use less fuel to achive the same cruising speeds.

But remember, a boat is not a car.
There is no MPG it is gallons per hour.
 
What Ghost said.
A single small block in your boat would be a joke. A single big block is barely adequate. Twin small blocks, maybe. Twin 6 cylinder turbodiesel yes, very happy. Twin big block, noisy but man what fun. Prolly wouldn't fit tho. Pity.
Your small block won't make max torque until it's way up around 3500 ish RPM. The Big block starts hitting the same torque numbers as the small block way way sooner. That means you get up out of the hole quicker.
 
You are beginning to get to a place where it makes less sense to repower than to put that 25K toward a new boat. I would seriously go see what Mr Mercruiser can do for you tho before making the hard choices.
 
I've done the repower analysis on two of my boats. Both times I increased engine displacement and stayed simple ( No injection).
Both times I got modest top end and cruise improvements but good fuel burn improvements. In one boat I went from 10-12 Gph @ cruise down to a 6 to 7+ gph @ improved cruise. I also found that if you have to pay shop rates on swapping components from one engine to another, you are better off with a new, all up crate engine. Avoiding the "not me!" when trying to get a subsequent problem fixed is worth any extra money.
 
o2batsea said:
What Ghost said.
A single small block in your boat would be a joke. A single big block is barely adequate. Twin small blocks, maybe. Twin 6 cylinder turbodiesel yes, very happy. Twin big block, noisy but man what fun. Prolly wouldn't fit tho. Pity.
Your small block won't make max torque until it's way up around 3500 ish RPM. The Big block starts hitting the same torque numbers as the small block way way sooner. That means you get up out of the hole quicker.
Click to expand...


Thanks guys. You both sound like you know what your talking about but really? The 383 is supposedly what Mercruiser recommends as a replacement for the 7.4 and many people mention that.

It looks like the torque isn't quite a 7.4 but it's about 390 lb versus about 450 or less in the 7.4, is that a huge difference? Boattest tested the same conversion from a 7.4 310 Hp to a 383 350 HP. The test boat was a 29 ft boat weighing 8200 pounds (about 3,000 more than mine). In the video it seems to be really moving and gets to a top speed of 44.7 but it's also much better in fuel economy than the 7.4.

https://www.boattest.com/engine-review/Mercury-Remanufacturing/29500118_383-MAG-Stroker_2015

I also just read a forum post where a guy has a 7500 lb boat with a bravo 3 and gets 35 mph.

I don't want to sacrifice performance but can wait an extra second to get on plane if its more fuel efficient and can still reach great top speeds.

My current 7.4 never reached speeds in the 40s and 50s like it was advertised, top speed was around 38. Do you think that's because it was old?

Thanks

Scott

 
o2batsea said:
You have our opinions. Do what you think is best for you.
Click to expand...

Yes the more I think about it even if the 383 gets to a higher speed I don't want to reduce performance and also if I had a lot of people in the boat it sounds like a 383 would be noticeable. Also if I resell the boat in the future I'm sure a small block would reduce seller value just by perception. Also I've read a few cases of the 383 new completely failing.

Replacing the 7.4 block seems like the most cost effective option and better performance wise however I've had a few issues within the last 3 years. I had a map sensor issue, an overheat issue and an engine coupler issue. Even if they replace the new core with the rest of the parts being old I don't want to run into an issue with something else going bad. When something goes wrong in Rhode Island in the summer it often takes weeks to get a repair.

I think it's time for a new engine and I think that will pay for itself by keeping the engine out of the shop and would have a warranty.

I'm curious what you think of the 8.1 or 8.2 I've heard good things and could that be made compatible with my 7.4 with Bravo 3? This has a 4 year warranty and seacore protection that supposed to minimize corrosion.

https://www.perfprotech.com/engine-...eacore-mercbob-82mag-ho-b-seac/product/336543

Thanks,

Scott
 
o2batsea said:
^^^especially if you like to jam the go lever all the way to 11.
Click to expand...

Alright! Also I am hearing that the 502 is better than the 496. The 496 seems to have more hp at 430 than the 502 which is 380. Is that true should I stick with a 502? If I understand correctly the 496 is 8.1 whereas the 502 is 8.2L.

Thanks,

Scott
 
kghost said:
Re-read Post #3
Click to expand...

Okay I re-read the post but Im sorry I am even more confused because that says the exact opposite of what I had read. Multiple people saying to avoid the 496 that is built for trucks and stick with the 502 that has better internals. I believe they are referring to the non catalyzed versions as the cats are very expensive. The 496 is an 8.1 and the 502 an 8.2 correct?

Thank you,

Scott
 
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o2batsea said:
Don't be confused. The only new engine from Mercruiser is the 8.2 liter in either DTS or Horizon trim.
https://www.mercurymarine.com/en/us/engines/inboard-and-sterndrive/mercruiser/inboards/

Anything else will be a remanufactured unit.
They offer a carbureted 540 as a remanufactured unit, but I would stick with new.
Click to expand...

Okay I think I found the source of the confusion and it has to do with the time frame and the version. From 2010 on Mercruiser offered an 8.2/502 as 380 or 430 HP. These were all new designed by Mercury (not a GM block) and I think that you are clearly referring to the newer ones with cats (those are very expensive). While they may be hard to find there are also non catalyzed versions of the 8.2/502 available like the one I had listed (you can get the non cat if you send back your old engine).

I take it when Docksidemarineservices mentioned the 8.2 being expensive and having cracking manifolds he is talking about the catalyzed version of the 8.2 (the one you linked to) because the issue (if I understand correctly) seemed to be a failure of the new required parts that are very expensive to replace.

Thank you
 
I think you are confusing us by referring to a replacement block as a "new" engine. You are replacing your long block with a remanufactured unit, not new. New implies that which I linked to above. Yes, it is a complete replacement from pulley to flywheel, with everything included.
You, I think, are looking for a more affordable option. This will not be a "new" (as in never installed in a boat before and fresh from the assembly line) but rather rebuilt with new or refurbished innards. The warranty will be reduced, as it is not direct from the factory but a third party supplied unit.
You might look into having your ECU flashed for better performance.
https://www.cpperformance.com/c-1095-efi-upgrade-kits.aspx
You might also consider improved exhaust, camshaft, and even supercharging. You can get a ton of horsepower and torque out of the big block with the right parts.
 
A good used take out 496/8.1L is the best replacement for you..... This is a bullet proof engine... Owners stupidity usually ends their life prematurely.

I have replaced L29's with 496 Mag Ho's in a few boats... The 496's were running take outs from factory go fast boats, the owners wanted to go faster..... I have one at my dock today.... Formula 330ss did the repower with running take outs last in spring of 2020.... $16K for the pair. Boat never ran so good.
 
o2batsea said:
I think you are confusing us by referring to a replacement block as a "new" engine. You are replacing your long block with a remanufactured unit, not new. New implies that which I linked to above. Yes, it is a complete replacement from pulley to flywheel, with everything included.
You, I think, are looking for a more affordable option. This will not be a "new" (as in never installed in a boat before and fresh from the assembly line) but rather rebuilt with new or refurbished innards. The warranty will be reduced, as it is not direct from the factory but a third party supplied unit.
You might look into having your ECU flashed for better performance.
https://www.cpperformance.com/c-1095-efi-upgrade-kits.aspx
You might also consider improved exhaust, camshaft, and even supercharging. You can get a ton of horsepower and torque out of the big block with the right parts.
Click to expand...

Sorry o2batsea I have been going back and forth between both options since I'm 50/50 on whether to replace the block or get a new engine. Just replacing the block seems like the most practical and cost effective route however I have only had the boat three years and have had a few issues and in Rhode Island having a boat issue in the summer means weeks out of the season (just waiting for a mechanic).

Don't get me wrong the engine only had 450 hours, compression test and oil analysis was excellent when I had it done originally and oil analysis each year was good. I think it was taken care of by the previous owners however the last owner did have a water leak and there was some corrosion in the lower elements.

The first year that I had it I had an issue with the map sensor where the boat was slowing down. It took 2 seasons and 2 mechanics and 2 map sensors to figure out whats going on and fix it. What was happening is there was corrosion around the intake where the map sensor threads in so it was causing the map sensor (even after a new one was put in) to fail.

Second I had an issue with overheating this season what turned out to be a simple impeller was made worse by mechanics error. They put the impeller house on incorrectly and the issue persisted. Im not sure if overheating actually damaged the engine because there's no guardian mode on the 7.4 so not sure if it would shut off but was getting overheating alarms.

Finally after getting the overheating issue resolved the engine coupler went. I was told this was caused by tubing (taking off too quickly). That seems strange to me because many people take off quickly (I usually don't).

So given these issues combined with the fact that the engine is still 20 years old I'd hate to see something else go on it after spending thousands of dollars. When you add the costs of the new block plus all the other parts needed (maybe the manifolds and risers are good because they were changed out) but sounds like intake and perhaps more engine parts would need replacing. When you start to add those up plus the extra labor costs (it will probably take longer than a new engine) I wonder what that would add up versus a new engine. Also having a three to four year warranty sounds nice given the problems that I've had.

Scott
 
If you do your own wrenching, buy just the block and move all the old bolt-on components over to the new. If you don't do your own wrenching buy a new engine and have it installed.
 
o2batsea said:
If you do your own wrenching, buy just the block and move all the old bolt-on components over to the new. If you don't do your own wrenching buy a new engine and have it installed.
Click to expand...

No I certainly do not, I wouldn't know where to begin so perhaps getting a new one and having it installed is best.

Thank you!

Scott
 
o2batsea said:
If you do your own wrenching, buy just the block and move all the old bolt-on components over to the new. If you don't do your own wrenching buy a new engine and have it installed.
Click to expand...

Hi it turns out that new non catalyzed engines like the one I had listed aren't available anymore (at least through that site and can't find any). I was able to find a used 2004 496 Ho (430 Hp) through a private seller that has only 250 hours.

I was wondering if there would be any possible major issues going from a 7.4 454 MPI to a 496 Ho.

Thanks,

Scott
 
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