Mercruiser MPI 4.3

[diver]

I was considering purchasing a 6.2m boat with a 2007 mercruiser MPI 4.3 . I was interested to know about your experience with this engine. What issues have you had, is it reliable, your service costs or do you DIY maintenance so any tips or source of best priced parts.

All I know is the spark plugs cost $33 each, manifolds and risers are around $2000 or $2700 if you have them fitted, apparently these need replacing every six years and the bellow job is worth around $1000 to have done and a lot more if water has got passed the bellows. I believe the bellows need replacing every 5 years rather than wait for them to leak.

[snatchy]

I have one that first went in the water early 2007. Factory fresh water cooled. Now over 650 hours.
problems I have had;
-Alternator siezed a few years ago (~$400)
-Had some rough running issues that eventually was traced to a partially broken spark plug. May have been caused by being dropped when removed and refitted by a mechanic
-idler pulley bolt was wearing out the bush, so ran at an angle and caused edge of belt to shed rubber. new bolt fixed it. ($5?)
I think that is about it for problems

Manifolds on mine have coolant running through them, so they are fine for the whole life of engine in theory
Risers are checked each service and are still OK.
Bellows are still OK apparently

I get a professional to service mine and it costs about $600 each year or 100hrs. I service all my other toys. Looks easy enough to service yourself

I know mercruisers get a bad wrap, but i think these newer ones are generally quite reliable. Every model has it odd failures.

Good luck

[juggernaut]

Not a MPI 4.3 but I run a pair of 2006 8.1 litre 496 ci Mercuriser Horizons (370hp each) with ZF V drives in my recently acquired Sea Ray sports cruiser. The motors are cooled with coolant which is in turn cooled via a raw water cooled heat exchanger. In contrast the manifolds and elbows are raw water cooled and I recently changed the manifolds being 9 years old and salt water use (4 manifolds were $2,600 plus labour) The elbows are the dry joint style and are made of stainless steel and don't need replacing.

I also had one of the cool fuel modules replaced (approx $1,000). The manifolds and cool fuel module were highlighted when the boat was surveyed at the time of purchase. My spark plugs are iridiums and I also had these replaced at the time the manifolds were replaced due to accessibility - nearly $19.00 each. Going by the Mercruiser service manual these plugs are good for 300 hours so that makes the cost somewhat palatable.

Earlier Mercruisers had problems with aluminium exhaust manifolds (raw water cooled), wet joint style elbows and riser heights which lead to many failures with water leaking back into the motor and hydraulicing - and probably leading to Mercruiser having a bad rap.

I like the motors though - start first time every time and are nice and smooth.

Economy is non existent and most on this forum would have a heart attack with the fuel consumption - but it is what it is - it certainly ain't a fishing boat you would travel miles and miles to your favourite fishing ground - unless you were staying for a week or so to make it worthwhile.

I intend to service the motors and v-drives myself.

I've used the boat virtually every weekend since taking ownership in April and so far cannot report any issues at all.

Whilst comparing 2 different motors I believe the later Mercruiser offerings had the bugs sorted and were quite reliable motors. I spoke the the Mercruiser tech at the time of purchase and he said the problems with the motors are due primarily to lack of maintenance by the owners.

[terryc]

Mine is the 4.3 MPI 2003 model, when i purchased 2010 as a precaution i replaced the cast iron manifolds & Risers (were still seviceable) with Hi Tek Stainless steel one piece units cost around $2500 from memory they are still looking brand new, i removed one after 2 years too check on condition and no change still looked brand new, these have a replaceable anode for each side costs $20 to replace these yearly 10 minutes work. I had to replace a sensor under $100 from memory only because my smart gauges showed an error (would not have known otherwise). Just a few months ago i got the leg water pump replaced, new gimbal bearing kit, 2 rear bellows assembly & bushing /seal kit- shaft seal all performed by mercruiser specialist total cost $1,159.50 (the bellows & water pump were precautionary could have left for a few more years). I do the oil changes & filter, plugs myself. Have found the motor to be very reliable smooth and economical. Hope this helps. I thinks whether its Outboards or Inboards it is all dependant on how they are looked after.

[TheRealPoMo]

Not a MPI 4.3 but I run a pair of 2006 8.1 litre 496 ci Mercuriser Horizons (370hp each) with ZF V drives in my recently acquired Sea Ray sports cruiser. The motors are cooled with coolant which is in turn cooled via a raw water cooled heat exchanger. In contrast the manifolds and elbows are raw water cooled and I recently changed the manifolds being 9 years old and salt water use (4 manifolds were $2,600 plus labour) The elbows are the dry joint style and are made of stainless steel and don't need replacing.

I also had one of the cool fuel modules replaced (approx $1,000). The manifolds and cool fuel module were highlighted when the boat was surveyed at the time of purchase. My spark plugs are iridiums and I also had these replaced at the time the manifolds were replaced due to accessibility - nearly $19.00 each. Going by the Mercruiser service manual these plugs are good for 300 hours so that makes the cost somewhat palatable.

Earlier Mercruisers had problems with aluminium exhaust manifolds (raw water cooled), wet joint style elbows and riser heights which lead to many failures with water leaking back into the motor and hydraulicing - and probably leading to Mercruiser having a bad rap.

I like the motors though - start first time every time and are nice and smooth.

Economy is non existent and most on this forum would have a heart attack with the fuel consumption - but it is what it is - it certainly ain't a fishing boat you would travel miles and miles to your favourite fishing ground - unless you were staying for a week or so to make it worthwhile.

I intend to service the motors and v-drives myself.

I've used the boat virtually every weekend since taking ownership in April and so far cannot report any issues at all.

Whilst comparing 2 different motors I believe the later Mercruiser offerings had the bugs sorted and were quite reliable motors. I spoke the the Mercruiser tech at the time of purchase and he said the problems with the motors are due primarily to lack of maintenance by the owners.

First of all Juggernaut, that rig sounds very impressive. It must go like the clappers and sound absolutely horn...
Can the Missus and is come for a spin?

Second, that price for 4 risers and manifolds sounds extremely cheap...and on big blocks too. A guy offered me same for my V6 for similar price.

Anyways, mine had 70 *freshwater* hours on it and I've clocked up 30. I always run that Mac's stuff through it in the hope it actually works.
That'll start another thread I'm sure.

None of that probably helps the OP so I'll get me coat...

[snatchy]

I have one that first went in the water early 2007. Factory fresh water cooled. Now over 650 hours.
problems I have had;
-Alternator siezed a few years ago (~$400)
-Had some rough running issues that eventually was traced to a partially broken spark plug. May have been caused by being dropped when removed and refitted by a mechanic
-idler pulley bolt was wearing out the bush, so ran at an angle and caused edge of belt to shed rubber. new bolt fixed it. ($5?)
I think that is about it for problems

Manifolds on mine have coolant running through them, so they are fine for the whole life of engine in theory
Risers are checked each service and are still OK.
Bellows are still OK apparently

I get a professional to service mine and it costs about $600 each year or 100hrs. I service all my other toys. Looks easy enough to service yourself

I know mercruisers get a bad wrap, but i think these newer ones are generally quite reliable. Every model has it odd failures.

Good luck

I forgot a raw water pressure sensor got blocked or somehow failed. Cost something like $100.

[juggernaut]

First of all Juggernaut, that rig sounds very impressive. It must go like the clappers and sound absolutely horn...
Can the Missus and is come for a spin?

Second, that price for 4 risers and manifolds sounds extremely cheap...and on big blocks too. A guy offered me same for my V6 for similar price.

Anyways, mine had 70 *freshwater* hours on it and I've clocked up 30. I always run that Mac's stuff through it in the hope it actually works.
That'll start another thread I'm sure.

None of that probably helps the OP so I'll get me coat...

Full fuel, water, people, stuff, etc and all up weight is probably over 10 ton, and with a 3.81 metre beam and 21 degrees dead rise its no speed boat but a comfortable cruiser. At 4000 rpm its doing around 24/25 knots (GPS) in favourable offshore conditions. From memory 3500 rpm is around 20 knots in favourable offshore conditions. The day I bought it I ran it flat out offshore and it pulled just over 4600 rpm and just over 29 knots (GPS) but that was with some some tab (rooky mistake) and half tank of fuel - so it might top out at 30 knots (GPS). And yes 16 cylinders do sound nice at any rpm.

In comparison, the previous owner also has a 45 foot Formula offshore boat with these Mercruiser motors and with outdrives and it reportedly does 70 mph! I have heard it run and with straight though exhausts and no mufflers is sounds like a bloody top fueller drag car.

The price I mentioned above was the 4 manifolds only. There are no "risers" as such on these motors as its all integral to the stainless steel elbows which bolt up to the manifolds.

[diver]

Thanks for the reply. Sounds like you are happy with yours and with 650hrs with few issues it is encouraging as apart from the horror inboard stories I did wonder if they were basically a sound engine design. The one I looked at was raw water cooling, seems common I guess it means more frequent manifold and riser changes

[diver]

Terry C I have heard about the stainless replacement manifolds although there are different opinions about as to whether they are better as some feel no rust but can crack. So it sounds like you have had yours for 4 or 5 years without issues from the stainless manifold or the motor. You mention its economical, I was wondering what size boat it is pushing ? I was thinking about 1litre per nautical mile pushing a 6.2 metre boat

[juggernaut]

Diver,

This may be of interest to you.

http://www.ausfish.com.au/vforum/sho...old-and-Risers

[terryc]

Diver,
I listened to all the fears about stainless manifolds/risers, all i can say is all good so far. If i had spent the same money on replacing with Cast iron at the time, i would now be nervously wondering how close they were to needing replacing again. Economy wise i think close to 30 ltr per hr at around 20-22 knots. Last trip was from Bribie Island Marina out through the passage to Flinders reef mostly 15 to 20 knot winds then down to 10 knots on return. Did some running around out there used about 80 litres, didn't make note of the distance sorry, as i had never been there before. The Whittley is 6.6 to 7 metres in length. My average always seems to be in the early 20's l/hr. Whatever motor you end up with economy will always be determined by how much pedal you put to the floor. One other advantage i have felt with the inboard is having the motor inside & low down seem to give the boat a better feel in the water. The MPI motors are so much easier to start than the old Carby's, like chalk & cheese. I still think four stroke outboards are great also, i have had both and each has their merits. Good luck

[diver]

TerryC
Its good that you have had 5 years service from your stainless manifolds and risers. Buying cast ones every 5 or 6 years is unappealing. On the plus side its hard to find a post about them failing but there are good arguments as to why manifolds are cast iron. I must look into it a bit more. The fear of losing a motor, more fear of paying someone to sort it out if water gets into the motor holds me back. I have read that acetone is used to test for cracks by taking the manifold off blanking the water ways and filling with acetone. Supposed to be very thin same as pressure testing with water. I think worth doing this to check for cracks while you have them off.
Yes the motor weight low and forward is supposed to make the boat handle better, hopefully a lower planning speed when things are rough.
I appreciate your response, its good to know with maintenance that these motors appear to be ok

[juggernaut]

FWIW I looked at the Hi-Tek manifolds when replacing mine and found a few issues on the Club Sea Ray site with them cracking, leaking, fitment and cheap gaskets. Perhaps these were early versions as I know some of the members on the CSR site provided feedback to Alan and hopefully this feedback found its way into the latest versions. Since the original cast OEM's lasted 9 years I thought that was a good run - perhaps lucky? I also understand the OEM cast manifolds for my motor (not sure about the MPI 4.3) are also ceramic coated internally but have not personally verified this as I never saw the new replacement manifolds prior to fitment. Perhaps this is why the originals lasted 9 years?

IMO you can test for cracks but they can happen at any time even with the most vigilant of testing.

[Brightsbane]

Some good info here. I've just recently bought a Mustang Clubsport 2200 with a 4.3 MPI. Risers and manifolds replaced before sale. I'm not sure what the fuel economy is like yet but I've heard it's similar to a large 4 stroke outboard. So far so good.

[diver]

Brightsbane,
Whats stopping me buying the boat is the high cost of manifolds and risers which are due for replacement. I cant get the price to reflect this and I figure the next owner if they are informed will expect to see manifolds and risers replaced recently. So I figure I could end up paying for risers going in and when I sell. I figure its appropriate to go halves with the seller if they are due.
I bought a manual and it mentions the 4.3 has cool fuel modules that juggernaut mentions he replaced for $1000 on his 2006 8.1 litre merc. I can see some advantages in 2 stroke outboards for the average light user