Mercruiser Exhaust System

[Bernie 1977]

Hi all, just looking for a little advise. I have come accross a 22' sea ray with a 4.3 ltr inboard petrol mercuiser engine with an alpha one stern drive and an open loop cooling system. It was wintered badly and the outlet manifolds cracked during a particularly cold night. I have repaired the manifolds and the cooling system seems to be running ok, engine temp maintaining when connected to an external supply, and the engine is running well and reving out beautifully on dry ground. I brought it into the water last weekend however and it wouldnt run well at all, and i ended up getting towed back to shore(embarrasing) i put the boat back on the trailer and of course it started perfectly which leads me to think its a problem with the exhaust system. i have checked the exhaust flaps and they seem to be ok but one seems a little worn, however when i was doing this i realised the extractor fan on the engine bay wasnt working. i have fixed this and i am now wondering if that was all that was wrong i.e. were the exhaust gases comming bak into the engine bay while it was idiling and then contaminating the combustion air. any advise would be grateful, and an explanation on the exhaust gas path when the engine is idling in the water would be great as i understand it has an alternative path to when the engine is at power and the exhaust gases go out under water.

many thanks

Bernie

 

[Scott Danforth]

Re: Mercruiser Exhaust System

usually if the manifolds are cracked from freeze damage, the block and intake are taken out as well. did you verify that the engine does not have another temperature declination induced material breach?

another item. all engines run well without load on the muffs. when under load is when ignition, fuel and other issues show themselves. when the engine is in water vs on land, there is a slight increase in exhaust back pressure.

 

[HT32BSX115]

Re: Mercruiser Exhaust System

were the exhaust gases comming bak into the engine bay while it was idiling and then contaminating the combustion air. any advise would be grateful, and an explanation on the exhaust gas path when the engine is idling in the water would be great as i understand it has an alternative path to when the engine is at power and the exhaust gases go out under water.

many thanks

Bernie

Howdy,

Welcome aboard!

No. it's VERY unlikely that exhaust gases are coming back into the engine compartment. All the exhaust gases exit through the Y-pipe and the transom area thru either the relief ports and/or the exhaust bellows and thru the prop.

You have other either mechanical or tuning problems with that engine. assuming it is running on all 6 cyl, you may have leaky valves, ignition, carburetion or timing problems.

I have repaired the manifolds and the cooling system seems to be running ok

If your "repair" did not involve replacement, you may end up with a destroyed engine. There's no real way to safely "repair" cracked manifolds.

If you didn't do a cooling system pressure check, it should be on your list. Any discussion of freeze cracked components almost ALWAYS includes a cracked block. It may start leaking (internally) at any time.

I have come across a 22' sea ray

If that means you didn't buy it.......... before you make an offer, make your decision on the possibility that it needs a complete engine replacement (including manifolds and risers)

If the drive wasn't removed recently or the owner (or previous owner) cannot tell when drive service was done, the drive should be removed, the bellows' and gimbal bearing inspected, alignment checked/adjusted and the raw water pump replaced.

The adult stickies above in the main Mercruiser thread list have all sorts of DIY info there.


Regards,


Rick

 

[Bondo]

Re: Mercruiser Exhaust System

Hi all, just looking for a little advise. I have come accross a 22' sea ray with a 4.3 ltr inboard petrol mercuiser engine with an alpha one stern drive and an open loop cooling system. It was wintered badly and the outlet manifolds cracked during a particularly cold night. I have repaired the manifolds and the cooling system seems to be running ok, engine temp maintaining when connected to an external supply, and the engine is running well and reving out beautifully on dry ground. I brought it into the water last weekend however and it wouldnt run well at all, and i ended up getting towed back to shore(embarrasing) i put the boat back on the trailer and of course it started perfectly which leads me to think its a problem with the exhaust system. i have checked the exhaust flaps and they seem to be ok but one seems a little worn, however when i was doing this i realised the extractor fan on the engine bay wasnt working. i have fixed this and i am now wondering if that was all that was wrong i.e. were the exhaust gases comming bak into the engine bay while it was idiling and then contaminating the combustion air. any advise would be grateful, and an explanation on the exhaust gas path when the engine is idling in the water would be great as i understand it has an alternative path to when the engine is at power and the exhaust gases go out under water.

many thanks

Bernie

Ayuh,.... Welcome Aboard,.... Yer takin' an awful risk runnin' patched up manifolds,...

They leak inside, 'n yer buyin' a new motor....

No,... The bilge blower ain't yer problem,...

Did ya give it a Tune Up,..?? how 'bout a Compression test,..??

Did ya change the fuel Filter,..?? how much crud was in the old 1,..??

How old is the gas in the tank,..?? was it stabilized,..??

Could ya use a few paragraphs, so's it's easier to read what yer writin',..??

 

[Bernie 1977]

Re: Mercruiser Exhaust System

Thank you all for all the advice and assistance, to answer a couple of your points and put some perspective on the advice I'm looking for; I have not purchased the boat, it was a friends and he has offered me the use of the boat if i can get it going and i want to see what the extent of the dmage/cost is going to be before i spend alot of money on a full service of the boat and engine.

I agree there could be alot of issues with the block, the head, the compression, the drive etc. and i may find further down the road that it may not be even worth bothering with but when i turned over the engine on the trailer it starts immeadietly, runs well so I thought it strange that immeadietly on putting it in the water it would not run, this could as mentioned in all the advice be the timing, tuning or mechanical problem but again it was before the engine was put under any pressure. Again i accept the back pressure on the exhaust could be just showing an underlying problem but i was under the impression that the exhaust relief valve should allow the engine to idle in the water in the same way as it would idle on the trailer, hence the reason for asking about the exhaust relief and path of the gases. I dont see any obivious exhaust relief hole on the stern of the boat. I was wondering how the relief on these models work, as i mentioned it is a Sea Ray 220, 4.3ltr mercruiser petrol with an Alpha Gen 2 drive constructed approx 1995 i believe.

thanks again for all the help