Maxum 3700 scr exhaust system??????

[F5MANN]

Can anyone validate that the Exhaust system on the 2000 3700 SCR was factory defective? I am advised that my 454 7.1L MPI engines have water backing up into the motors because there is insufficient down angle to keep the engines from ingesting water.

HELP!

[William Ferrell]

I heard that and what I understood was that the angle was so that as the engines were cooling condensation would form and run back down into the engines. I repowered my 1998 3700 SCR right after I got it and ask that question prior to the install and my marinera checked to see if that was the case and if so did I need a spacer to raise the manafolds. Merc said no and I have never had a problem

[F5MANN]

This is a direct quote from diagnosing technician from MarineMax Cocoa, Florida
"MAXUM boat exhaust system is engineered to not have enough drop to keep the engines from ingesting water. Replace the boat exhaust system with Vernalift mufflers and fabricate flywood mounting plates for the mufflers."
The technicians diagnosis also called for a long block replacement
I called MarineMax here in Cocoa Florida to diagnose why the port engine would not start. Compression check of 2 cylinders was 0 and 70 PSI, plugs were water fouled.
Now I realize that MarineMax is a 500 lb SeaRay dealer in the US, and both SeaRay and Maxum boats were built by the Brunswick Corp. But the more I did into the 15K$ repair estimate I get very suspicious. So as possibly a last resort I posted to Maxum owners.
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Possibly with out much trouble on your part you may have a source to verify or disregard MarineMax suggestions relative to the exhaust systems. Both risers and manifolds were replaced (NEW) 10 months ago.
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[shrew]

The engine and exhaust are Mercruiser, which is also a Brunswick product. You'd think all of the million or so Mercruiser 454's that have installed in a wide variety of boat lines beyond Maxum over many many years would have this problem.

Does your current setup have a spacer between the manifold and riser? My old 454 and now my 496 both use a 6 inch spacer. Are you sure that isn't all you really need to resolve this issue?

[F5MANN]

Thanks Shrew,

I will verify the presence or absence of spacers when I am stateside next week.

Thanks,
MM

[dronthelake]

We have had no issues with our 1998 3700 with original 7.4s and exhaust. I pulled the elbows and risers off last from for inspection and everything was fine.

[pascavone]

there are two possibles for wet spark plugs: (other then a blow head gasket)

the 7.4 sits low in the boat below the water line, and has 6" spacer blocks that are under those elbow you step on to walk in the engine compartment.

The vertical 6" spaces, elbows, and manifolds are ALWAYS full of raw water in the outer chamber of the manifolds. This is like a toilet tank holding water above your exhaust valves.

1. the raw sea water is pumped into your exhaust manifolds on purpose as the manifolds have an inner and outer cavity, inner is for exhaust gasses to escape, and the outer is the raw water cooling cavity that keeps the manifolds cool, and is dumped out the back of the boat along with the exhaust gases.

If you have a leak in the manifolds between the inner and outer chamber, then water will end up in the cylinders, and into the engine oil.

Usually, you will start with a miss in the engine, and then the engine will dry out the spark plug from the heat, the and boat will run fine again. Also, the running boat exhaust gases will push exhaust gas into the raw water cavity.

But, when your turn off the boat, then the water stored in the manifolds, will drip into the exhaust inner cavity and end up in your engine again.

Some water in the engine will not hurt anything, as it steams off as soon as your run the motor.

Its when you leave the boat over the winter and the raw water hydro-locks the rings to the cylinder walls.

2. The sea water can push back up thru the exhaust pipe into the manifolds, but there are little one-way flapper valves like a butterfly that prevent this backflow, along with the exhaust gas pressure blowing out from the running engine, so this is usually not a problem.
So, the engine is not defective if maintained. The veranlift will not help if your manifolds are shot.

Solution, is to user that money to replace your manifolds every 5 years......

(I got new gaskets but it still leaked...., two bent push rods....)

[mmwjr]

For the most part I agree with what pas has said, however it may just be the gaskets between the spacer and manifold or spacer and riser and has failed and allowing water to leak into the exhaust passage then back into the engine. These gasket fail over time and almost always if the engine is overheated even though it may not be appearant right away.
Also buring water raises the exhaust tempature and over time may result in a burnt exhaust valve to valve seat.

[F5MANN]

I have burned many hours of telephone and email time finding the root cause of the issue. The issue is reported and the Issue was released by the Brunswick Corp as a TA (technical advisory) to Sea Ray dealers -That in itself was strange to me. Anyway for what it is worth here is the issue and the item that prevents the water intrusion. BTW. If you power your 454's down from idle throttle, and you do not have the designated resonators or proper down angle on the exhausts water will intrude. I have read the TA and Brunswick states NEVER power off the 454's at idle. Always power off at 1200 RPM. This provides sufficient back pressure to expel any water from the exhausts

[h=2]Mercruiser Exhaust Systems and Accessories[/h]
THROUGH THE TRANSOM OR HULL EXHAUST
[TABLE]
[TR]
[TD]

NOTICE

[/TD]
[/TR]
[TR]
[TD]

Refer to Exhaust Resonators in this SECTION for additional information on 454 and502 cid (7.4 L and 8.2 L) engine exhaust requirements.

[/TD]
[/TR]
[/TABLE]
When designing and installing an exhaust system, in addition to other model specific requirements, Mercury MerCruiser requires the following to be observed:

• Exhaust fittings (flanges and outlets) must be of proper size to accommodate 4 in.(102 mm) inner diameter exhaust hoses.
• Exhaust fittings must be equipped with internal water shutters.•An exhaust flapper must be used over each outlet.
• Exhaust outlet must be slightly above the water line with boat at rest in the water and a full load aboard.
• Exhaust hoses, collectors and pipes must not be higher than exhaust elbows at any point.•The drop in the exhaust system must be continuously sloping so that a low spot does not exist at any point in the exhaust hose or pipe.
• The exhaust system on Mercury MerCruiser engines must have a minimum of 6°downward slope between the exhaust elbow outlet and the exhaust outlet of the boat.•The exhaust system on Mercury MerCruiser engines must have a minimum of 4 in.(102 mm) of vertical drop between the exhaust elbow outlet and the exhaust outlet of the boat.

EXHAUST RESONATOR
The exhaust resonators (provided with the engine package or available separately) aredesigned to provide increased resistance to water ingestion due to the tuning effects of the exhaust system. Quicksilver resonators are designed to break up the exhaust pulses.
[TABLE]
[TR]
[TD]

CAUTION!

[/TD]
[/TR]
[TR]
[TD]Avoid severe engine damage. Water ingestion by the 454 and 502 cid (7.4Land 8.2L) engines may occur in some instances without the use of speciallydesigned exhaust resonators. Install exhaust resonators in the exhaust system when specified.[/TD]
[/TR]
[/TABLE]
IMPORTANT: Exhaust resonators must be installed on 7.4L MPI, 454 Mag MPI and 502Mag MPI Models of sterndrive engines with through the transom (or through the hull) exhaust
On 454 and 502 cid (7.4 and 8.2L) sterndrive engines using through the transom or hullexhaust systems, special care must be exercised in system design and construction toprevent an adverse tuning effect on engine exhaust output.
Exhaust system tuning can be affected by various factors that are beyond the control ofMercury MerCruiser. Following are several factors that can affect exhaust system tuning:

• Type and configuration of exhaust outlet.
• Length of exhaust hose.
• Amount of back-pressure in exhaust system.

Exhaust Resonator Kit use on Sterndrive Models:
[TABLE]
[TR]
[TD]CAN Be Used With[/TD]
[TD]CANNOT Be Used With[/TD]
[/TR]
[TR]
[TD]1. Transom mounted muffler tips.
2. Waterlift mufflers or other mufflers that are mounted outboard of exhaust elbows.
3. Open exhaust.
[/TD]
[TD]1. Silent Choice Exhaust System.
2. Below swim platform exhaust.
3. Mufflers that mount between exhaust elbow and exhaust tip.
[/TD]
[/TR]
[/TABLE]
INSTALLATION
The resonator is installed in exhaust hose with open end toward exhaust elbow. Resonatoris positioned so that inside flat surface is approximately 17 in. (432 mm) from front edgeof exhaust hose, but no closer than 2 in. (51 mm) to exhaust outlet on sterndrive. The17 in. (432 mm) dimension can be reduced, if necessary, to a minimum of no less than13 in. (330 mm).
A clamp is then installed and tightened around the hose so that it clamps around center ofresonator. This position is 1 in. (25 mm) less than the position of the resonator as discussedin the previous paragraph.

454 AND 502 MAG BRAVO MODEL EXHAUST RECOMMENDATION
IMPORTANT: To get maximum performance from Magnum Bravo Models, through the transom or hull exhaust is required.
NOTE: If noise regulations do not allow the use of through the transom or hull exhaust, an exhaust pipe kit (Quicksilver Part Number 44266A6) must be installed for through the prop exhaust. This kit also contains an exhaust tube that is used in place of the exhaust bellows.
IMPORTANT: It is recommended that the exhaust bellows on the transom assembly be removed. This is necessary to avoid creating a vacuum at the exhaust outlet in the propeller at higher boat speeds. This vacuum could degrade propeller performance on some boats.

HTH

[khendra]

Did the installation of the resonator solve the ingestion problem? I just had my 502's re built from the block up and the mechanic installed resonators and turbulators to prevent ingestion and ten months later he's finding that they are still ingesting water. I called a local Sea Ray dealer and spoke to someone in service who suggested replacing the long blocks, as if they may be cracked, but I dont' see how this has anything to do with water coming back in from the exhaust. I'm at a loss of what to do after spending a small fortune to rebuild the engines. Mine is a 1998 3700 SCR, and the engines hadn't been rebuilt until last April, so how is it that there wasn't an apparent problem for about 15 years and now twice in two years there is water ingestion? Can you post the actual TA?
Thanks
Kevin

[mmwjr]

khendra welcome aboard

This is a 2 year old thread and the OP has not posted since then. You will be better served starting a new thread with your issue.