2005 Mercruiser 4.2 ES 320 Diesel

Pavila

Pavila

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Hello dear forum! An engine question on New Year's Day: I'm about to buy a Formula 370 SS with two 4.2 Mercruiser diesels from 2005. Has anyone here experience with the quality, reliability, durability and weaknesses of these machines? Thank you for many answers!
 
Having worked with Mercruiser and Volvo for the past 25 yrs I know that I have had more problems with Volvos, but like any motor in a boat it needs correct maintainance. If they have been serviced properly and they run and sound fine then they are a good motor, they start on the button and idle smoothly and don’t smoke. The heat exchangers may need a clean if they haven’t been done, the easiest way is with Rydlyme. The only common fault I have found is the small metal pipe from the inlet manifold to the turbo wastegate can fracture so you don’t have boost control, its a cheap part and 5 mins to change. I guess it has sterndrives in which case check the service history, the bellows need doing every 5 yrs and I do the gear wire bellows at the same time while the drive is off. Also look at the back of the engines with a flashlight and see if there is water or salt stains running down the inside of the transom from under the steering arm, this is a known problem and if not repaired can at worst need a whole new transom shield as the aluminium holding the seal where the pivot shaft comes out gets eaten away and there is nothing to hold a new seal in place.
 
Thank you very much for your helpful reply, Spannerman! We already found the problem with the steering arm. If I buy the boat we will put the engines out and fix it. If we have them out anyway, do you have other suggestions what to do precautionary? The engine is 2005, 2015 first time in water, now 200 hours.
 
200 hrs is nothing on a diesel engine, once the engines are out I would just go over everything and replace hoses, belts, impellor etc and fix any leaks. Check the fitting where the seawater hose connects to the exhaust bend as they can corrode so there is little holding the hose on. The exhaust bend is no longer available so Mercruiser supply a kit using a later type bend which all works fine. Go over the electrical harness and maybe replace the main battery cables to the engines, its all so much easier when the engines are out. You will have the drives off so check/replace the transom bearing and the short gearwure from the engine to the drive, these get stiff with age so now is the time replace. And check the trim instruments work before you start as if they jump or don’t work this also the time to replace the trim senders.
 
Thank you very much again! One last but never the less nagging question: why are so many people convinced, that Merc Diesels are crap? Are there any major issues, especially on the 4.2 320 ES, like overheating, leaking or similar that I should worry about?
 
I have never had to do a head gasket on one of these engines but done plenty of Volvos, so I don’t believe they have any propensity to overheat, only if there is a problem on the seawater cooling system, impellor, blocked coolers etc, I think there is an element of snob value about having a Volvo, but I can honestly say of the 30 odd boat mechanics I have known over the past 25 yrs none owned a Volvo we mostly drove Mercruisers or Yanmar as they have less issues. I have earned most of my income repairing Volvo engines and drives, I know there are more Volvos out there, but I have never had to rebuild either a 4 cyl or 6 cyl Mercruiser diesel. I think the 320 is a great engine and you are getting 320hp at the prop, whereas Volvo state crankshaft hp so its less at the prop, i.e. KAD 300 is actually 285 at the crank so much less at the prop. Plus Mercruiser have a wastegate so the turbo works from much lower revs so needs no added complication of a supercharger. Volvos aren’t bad engines their market penetration in Europe proves that, but then its the complete opposite in the US, next to no boats are delivered with Volvo engines and I once got offered 3 jobs in 1 hr! in the Miami area as I said I could work on VP as well as Mercruiser. And all Volvos leak sooner or later. So for my money I would rather have a 320 for reliability and ease of maintainance and they seldom leak.
 
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Pavila - about 2 months ago I bought a boat with that same engine in it.

Spannerman gave some absolutely fantastic advice, as above more or less. The engine was running fine although during the sea trial it didn't seem as powerful as a 320hp should when pushing a 25ft fairly light planing boat.
There is a user here, DAKA, who's had these engines for a few years and recommends them.

I've got the engine out at the moment and I'm doing / have done the following:
Remove heat exchanger, clean and paint
Remove aftercooler, clean and paint
Wastegate clean and paint
New turbocharger (around £1100 - old one was beyond repair)
New exhaust elbow - what spannerman described above is happening to me and will eventually crumble away to nothing. €700 for a new stainless one
All belts replaced
Seawater impeller replaced
Engine mounts replaced / new sterndrive mount bolts
New bellows, new steering cable, new steering pin and steering arm, new trim senders (the bolt connecting the bell housing to the gimbal ring doesn't sit in the thread properly, thread has become too big and too loose over time so needs redrilling), gear oil nipple.

I had the rusted steering arm but it was the actual transom assembly that had corroded through, about a pinhole size right above the steering arm retainer nut.

Good luck with it
 
Thank you very much for your reply, Jointventurell! Good to know we are in a similar situation. What build year is your engine and what boat is it? In which country are you located? I will use mine in the Greek Aegean Sea.
 
It's 2007, in a 1968 Bertram 25 Sportfisherman - so it should go quite well once back in, up and running!

I'm in Genoa, Italy. Boat is in the yard looking a bit sorry for herself as she'd not been used for around a year.
 
Had twin mercs since 2000 with only minor probs. While the engines are out check the inboard end of the water intake rubber pipes from the outdrives in the gimble which on checking mine were badly restricted by the plastic inserts. Both makes seem to have their pluses and minus. One advantage with the mercs is the positive pressure oil feed to outdrives from the engine room . I have seen many volvo outdrives found to be low on oil when they are serviced as there is no warning sign if the prop shaft seal is damaged by fishing line.
 
Have 4.2 twins 1998 year ... done all the above Maintenance... and they serve me well ... 600 hours ..
there is a few threads on here that talk about them with great advice ...
give your oil pans a prod just in case
 
As joint venture11 says I have had twin 4.2 Cummins-mercruisers for about 14 years 2x 300 hp which are basically the same as yours and I love them. Very reliable and so easy to maintain. Very little trouble ( touchwood).
Mine are inboards .
Mine were sold directly by Cummins in 2004 who were in the process of joining mercruiser for a short lived partnership , it was long enough for fleetguard to add the filters to their range which makes it easier for parts supply from any commercial vehicle parts stockiest.

Oil filter. Fleetguard LF3443. Diesel filter fleetguard FS19832
 
I thank you all for your very constructive and helpful answers. You made me feel confident to say yes to my new boat, which I did yesterday. It is a real upgrade to my Cranchi CSL 28 that had before and I am looking forward so much to the new season! All the best to you!46CF59A2-57A9-4150-A889-01887D82D197.jpeg
 
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