SCANDINAVIAN

When i was out crusing yesterday i suddenly felt the smell of burned rubber. I opened the hatch and found a hole in the stbd exhaust rubber hose. Today i replaced the hose but the same thing happened again at 3000 RPM. The stbd hose were very hot while the hose at the port side were cool. The strange thing is that both risers were cool, ap. same temp. Engine temp. is ok. and visualy the same amount of water comes out of both tail pipes.
I have pulled the riser and checked it out but found nothing that could prevent the waterflow.
Does someone have an idea???

Raylar

Wow, that is really strange! The only thing I can think of is that the top water exit hole in the exit face of the Mercury riser is plugging or something. When you have the riser off, you will notice that there are two water exit holes on the surface just in front of the bell. The top one is triangle shaped and smaller than the bottom water exit hole. It sounds as though maybe the water is not exiting properly from the top hole under pressure on that particular riser. You can hook water up to the riser off the boat and look at the water streams. Other than that, I am stumped, but thats not to hard to do.

Ray @ Raylar

mwdill

Check to make sure that it is a straight shot from the riser to the transom,if it its angled to the left or right or up ,down the exhaust will hit that part of the hose and heat it up to the point it burns thru where it hits it.

SCANDINAVIAN

Thank You both for Your advice!
There is a "straight shot" (as mwdill wrote) from the risers to the transom, no angels at all.

I also hooked up the riser to my garden hose as You suggested Ray and it had a nice water spray from the top hole.

I have now checked the water hoses from the waterpump through both oil coolers and found no objekts that could prevent waterflow.
I wonder what the small "cup" is under the exhaust manifold where the water enters, it looks like a small inline fuel filter. What is that? Can it cause this problem? Is it a valve that prevents the water to flow backwards (i donīt know the english word)?

When I put the riser back I took a short testrun with the same result as before (very hot spot on top of the stbd. exhaust hose).
This time i shut the engine off at 3000 RPM and pulled the plugs, the porcelain were white as they were brand new, they looked the same at both sides. Could this be a sign that the engine is running lean or is it normal for this engine. Even after 15 minutes of idling the plugs still have the same colour.
Is it possible that running lean is causing so much higher exhaust temp. that it burns the hole in the exhaust hose? and if it is possible why only on thr stbd. side??
The plugs are AC Delco 12578277, 41-983 are they right?? This is a new engine, only 10 hours on it so they never have been changed.

Iīm realy lost here, hope someone have some input.


Thanks!

Stefan
Sweden

Mbam

Change the sea water impeller

Tinkerer

Do you have silent choice?
If you do was it closed or open.
If you had it open check to see that both are open.
IF one of them is closed and the other is open the water will all go toward the open side and the closed side will get very hot. ( less backpressure on the open side)

velocity2002

I had this happen to my velocity last year. Check the ball valve under the manifold. It is part of the drain system from what I can tell and it is directly under the center of the maniflod. there is enough water flow/pressure to keep it cool until you get up in the RPM's, than the water bleeds off and exits out the other side. The easyiest way to check is just pull the bleed hose off the bottom of the manifold. Plug both sides and give it a run. If that fixes it than replace the little ball valve thingy.

mark

Raylar

I think the answers here are on the right track. It has to be something with either the water pressure or volumne to that exhaust manifold and riser. the valve you describe I believe is the brass check valve under the manifold where the water from the raw water system enters the exhaust manifold. sounds like may have a bad valve and it is not delivering enough water to that manifold and riser. strange though you should see a manifold overtemp fromthe exhaust manifold water temperature sensor on that side and possibly a beep, fault code fromthe ECM if that were the case. You should probably remove both check valves from both side and check to see if they operate the same. I also think the Merc manual has a troubleshooting guide that covers checking for proper raw water delivery.

Good Luck?

Ray @ Raylar

SCANDINAVIAN

Problem fixed!
I first blocked the vertical "drainhose" under the manifold with no change to the temprature at all.
When i sat there looking at the riser and the exhaust hose thinking of removing the seawater pump to check the impeller, i saw that it was a small vertical angle downwards between the riser and the exhaust hose (mwdill, you were right here).
First i didnīt think that a small angle like that would matter, but after removing the exhaust hose once again and putting a straight piece of wood between the exhaust on the transom and on the riser it was clear that the distance between the exhaust bell and the inside of the exhaust hose was only 5 mm (ap. 1/5" i think). That gap was to little to let enough water pass between the edge of the bell and the rubber hoses inside to cool the exhaust gases.
The easiest way for me to get the gap wider was to flat the bell out a bit. Took my favourite tool ,the hammer , and gave the top of the bell a few punches until i the gap was doubled (10 mm).
Put everything back, went for a testrun and the hose were cool. Went back and made the same operation on the other side, just to be sure.
I still donīt know why the problem was only on the stbd side, but i guess stranger things have happen.

Hope You managed to understand my english!


Thank You all for helping me out!!!

/Stefan
Stockholm, Sweden

d4laseck

What do you mean "exhaust bell"? i have the same issue.