Mercruiser MPI 4.3

[Brightsbane]

I can only express the importance of a pre-purchase inspection by a reputable marine mechanic. I did this and it was found that the manifolds and risers were due (although not in desperate need of replacement) and the seller agreed to cover this cost. I wouldn't but unless this was a condition of sale. FYI mine is a 2003 model however it was always dry stacked which likely had given it some extra time. Offer to pay the extra for SS and you shouldn't have any issues with resale.

[terryc]

When i removed my cast iron manifolds & risers they were original & 7 years old with still life in them, so i would think on a well maintained trailer boat, they could easily last 9 years. My decision in going down the stainless route was that i didn't like the idea of the passages in the cast ones gradually closing up as they aged. I won't live in fear of cracking as i can only trust the product until i find otherwise. We all take a risk no matter what we buy whether its inboards, four strokes or old technology 2 strokes. I trembled at moving into the mercruiser, however i have learned to respect the setup as being pretty good. I still think 4 stroke outboards are still the best, however some of the corrosion issues in some of them can be pretty scary. Of course not all boats come with outboards, many have been almost solely designed around the inboards.

[juggernaut]

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

The cool fuel module I replaced was due to corrosion on the ali housing where the water inlet/outlets bolt up to the housing. There is probably a cheaper alternative to full replacement - i.e. drill and tap a larger water fittings with adapter. It probably could have also been prevented by the use of with a decent sealant on the fittings. I kept the old module for spares as the module holds the low and high pressure fuel pumps, etc. Its probably something you could replace yourself if you are handy with a spanner. Apart from corrosion there was no problem with the cool fuel module and manifolds as I initially ran the boat with the originals until I could get them replaced - but nevertheless replaced them to prevent future issues.

Another thing to look out for is whether the heat exchanger(s) have been replaced as these have raw seawater running through them and can be prone to leaking over time. I'm not sure with your setup but I have heat exchangers on the motors and transmissions. I have not been able to find anything that is fatal if they do go but tell tail signs are loss of engine coolant and loss of transmission fluid. I guess pressure testing would at least verify these are currently OK.

Also have the motor compression tested.

As other have said, have a survey/PPI done to find out what the issues are (if any). Then negotiate on price at the time of purchase on the basis of those issues.

Good luck.

[diver]

Thanks TerryC for the reply. My understanding with the cast dry joint manifolds is they are best replaced early around 6 years because there is a risk of some scale causing a restriction, Apparently what happens is that the manifold where the restriction forms will , can crack and allow water to drip into the cylinders. I am told while the manifolds can last longer that is the risk you under take for the extra potential life.
I agree 4 stroke outboards are best, the 4.3 mercruiser I think is ok at a price that reflects the maintenance due. buying a used boat can be a bit frustrating if you are looking for a decent 5 to 6m glass boat with a small cab.

[diver]

Brightsbane, yes I intend to get a pre purchase inspection. I have established the manifolds and risers probably need replacement based on age. At least you have confirmed what I thought that when I try to sell it if the manifolds have not been changed recently then the buyer will want to factor it in to the price so I need to factor it in when I buy. Naturally sellers are anchored to what they paid for the boat. Its interesting how many people are focused on low hours eg its only done 120 hours like new they think where as I think the motor will last 4 thousand hours or 20 years whatever comes first so it might have done 120 hours but it is 8 years old so I done think of it as good as new. I will look into stainless a bit more as some people have had success with them.