Manifolds, risers, valves

BahamasBlair

BahamasBlair

New Member
Mar 15, 2009
93
Freeport, Bahamas
Boat Info
340 Sundancer 2005
Engines
8.1L Horizons
Well, this is a lousy start to the season. Just had my port engine lockup due to water getting in through the aluminum exhaust manifolds. What a mess. I only have 410 hours on these 8.1S engines. When we opened the head, there was 1/2 inch of salt water sitting on top of the pistons. Holes right through the inside of the manifolds.
WHY DID MERCRUISER EVER MAKE THESE OUT OF ALUMINUM I WILL NEVER UNDERSTAND.
Has anyone else had similiar problems. Hope we are getting it repaired properly. Can't afford it to happen again.
:smt013
 
Go search. Frank W posted about this problem a year or two ago so that you guys with these engines could be proactive before it became a problem.
 
fc3 said:
Go search. Frank W posted about this problem a year or two ago so that you guys with these engines could be proactive before it became a problem.
Click to expand...
All, I just read Frank W's thread from 12-9-07 and it scared the sh!t out of me. When I purchased the 380 last July with 350 hours on it MM told me that the boat had been docked, wintered and maintained by them at their Lindenhurst LI facility since new. However they would not give me the service records so I dont know if this replacement has been done or not. Is there anyway to tell by visually inspecting if they are originals or replacements ?
 
Hey,
Apparently Merc made the 8.1S from 2002 to 2005 with aluminum exhaust manifolds and aluminum risers. Totally ridiculous. This is costing me north of $6,000 for parts and labor. Thank God I caught it before the engines blew! Over here in The Bahamas we have 35% duty on the parts !
Ouch!
 
Nope. They are cooled with sea water. The manifold sucks in sea water to cool down the manifolds. The seawater has it's own circuit in the casting. What happens is the aluminum corrodes very quickly and the seawater infiltrates into the hot exhaust chambers, flows down hill onto the valves and into the cylinders. Ugly...very ugly.
 
If you go thru a Sea Ray/Mercruiser dealer for the repairs, you can usually get some help with the repair cost. This is a known problem but one Mercruiser is not recalling since there is no issue with the 8.1's run in freshwater. Our dealer is quite familiar with the corrosion issue with both the manifolds and the KoolFuel fuel cooler and I've seen them get Mercruiser to do everything from furnish parts only to paying for the full repair to replacing a complete engine that hydrolocked.

Search for the other "Heads Up" thread on these engines..........covers the fuel cooler. If you have the KoolFuel 3, you are only part way home......its next.
 
Frank, is there a way to visually tell if the aluminum risers and manifolds have been replaced ? As I stated MM will not give me the service records from the previous owner.
 
The replacements should be cast iron, not aluminum.

This is not a regular replacement maintenance item like the risers and manifiolds on the 7.4, etc. It is a design defect, or just plain stupid engineering- take your pick. If you still have aluminum manifolds on your engines and you are in a salt water location then get to your Sea Ray dealer and ask that they have Mercruiser replace them immediately.....you are on borrowed time. Remember, it isn't the dealer's fault, not is it Sea Ray's, but they are the guys who are going to make it possible for you to get a resolution, so don't shoot the messenger if you get some bad news. Just be firm and persistant even to the point of going to Sea Ray customer service with the "I trusted Sea Ray because of your reputation for quality.......I am very dissapointed with the fact that you expected me to do free product testing and now I'm stuck with a $7500 time bomb" card.
 
Frank, Great post and info. Do you know how long a fresh water cast iron manifold and riser system should last? Hours/years? My tug is 76 and I believe the manifolds have been replaced once already. I don't believe there are many hours on the boat but I can't confirm this. No water ingestion yet but I want to change out the manifolds next winter and add transom exhaust. Do you have any opinion on the header style stainless steel log exhaust manifolds. Look cool but what's the point other than performance increase (if any)as it's all under cover.
 
is there a way to visually tell if the aluminum risers and manifolds have been replaced
Click to expand...

Refrigerator magnet.
 
rondds said:
Refrigerator magnet.
Click to expand...
Ron, the manifolds check out to be iron, are the originals solid aluminum or aluminum lined ? the elbows are non ferrous, either aluminum or stainless I guess. This is the confusing part.
 
Yikes,
Can you elaborate on the Kool Fuel issue? I am itching to know what else can go wrong with these Mercruisers......
Very disappointed with the whole enchilada!
 
The Koolfuel is a fuel cooler that is a cast aluminum assembly that is sea water cooled. They don't perforate like the manifolds, but the passages get blocked with corrosion and they cannot be cleaned, they must be replaced..........I think they are about $1200 ea.

Don't ask me why Mercruiser decided on this design..........the industry has had bronze fuel coolers for many many years yet the Experts at Merc chose to try to re-invent the wheel...........


The 188 Mercruiser is a Ford 302/352. To my knowledge they have never been known for corrosion problems, but it is a simple thing to pull off the riser/elbows and look inside to see what's in there. All it costs is a couple of gaskets and an hour's time. I don't much like to fix stuff that isn't broke. If the OEM manifolds have served you this long, why change? Any performance increase is going marginal and will be at RPM's you almost never run anyway, unless you use thru hull exhausts. Are you sure you really want to listen to an unmuffled 302 all day at the lake?
 
I don't get it.
Replacing cast iron with aluminum in what has to be the worst place for corrosion (extreme temps and saltwater) on an engine. If they wanted to go with aluminum to save weight, why not include them on the closed side of the cooling system?
 
Frank, Thanks for the reply. I will continue to run them as they appear to be in good shape so far. Nothing inside to make my suspicious and the thing has never seen salt. Do you think they will flow enough exhaust if I go to a 4 barrel carb? The ports look big enough to handle it. I'll deep six the through the transoms exhaust. Don't want the admiral upset as she tries to read while I'm tooling around with open exhaust blasting in her ears.
 
This goes back 30 some-odd years so my memory may be off some, but I think there was a 228 hp version of the same basic drive system that was a 351/4bbl engine.
 
tobnpr said:
I don't get it.
Replacing cast iron with aluminum in what has to be the worst place for corrosion (extreme temps and saltwater) on an engine. If they wanted to go with aluminum to save weight, why not include them on the closed side of the cooling system?
Click to expand...

You don't get it.............Mike?

Welcome to the club! There are a lot of saltwater owners of '03-'05 (?) 8.1's asking the same question.....not to mention all the rest of us who have had all the Mercruiser "pulling them green - let the customer do the R&D" fun we care to. Personally, I'll stick with old proven technology (like my mechanical Cat diesels) even though I'm called a dinosaur.
 
I'm called a dinosaur.
Click to expand...
Same here - well, at least with regards to my Gen IV 7.4s with carbs and engine mounted mechanical fuel pump. Simple to work with/on/around and parts are easy to get!
 
You must log in or register to reply here.

Forum statistics

Threads
113,241
Messages
1,429,111
Members
61,122
Latest member
DddAae
Back
Top