exhaust ? please help

[deves3000gt]

hello I have a 78 slickcraft with a 250 gm motor thrue hull exhaust. Question is my right hand side port spits out plenty of warter all through the RPM range, but my left side will start out with good flow at but if you let it sit at idale the water goes away. As you rev it up it will steam then start flowing again. the riser does get a bit hotter then the other but you can still keep your hand on it for a bit. I would assume there is a block but i dont understand why it comes and goes. Oh, btw i am running the boat on muffs in the yeard. If you keep the RPM's up even a little like 1500 the water is fine. I thankyou guys in advance.

steve

 

[deves3000gt]

Re: exhaust ? please help

Sorry one more thing I thought i should add. I removed the three hoses from the maniflod and riser to make sure they were clear and they were.

 

[Howard Sterndrive]

Re: exhaust ? please help

If you drive the trailer up onto a block of wood on the side where water is mostly coming out at idle. Your "problem" will move to the other side.

What you see is normal.
Unless the boat is sitting 100% plumb level, the water is going to want to flow out whichever riser is a fraction of an inch lower.

 

[deves3000gt]

Re: exhaust ? please help

THANKYOU SO MUCH!!! That makes sence. and some to think about it the boat is tilted that way. MAN you just made my day.

 

[havasuboatman]

Re: exhaust ? please help

The reason for this is simple physics. Lower RPM's = less water volume. The water flows into the right hand side of the block first so the right side exhaust has more water pressure.
How long has it been since you replaced the impeller? As they get older, they get less efficient, and that's an indicater that failier is near.

 

[Zackman]

Re: exhaust ? please help

Had a very similar experience a few years ago. Just to make sure we're facing the same direction, I'll reference everything as either port (left side of boat facing bow) and starboard.​

I've got the captains call with thru transom exhaust. On the muffs, with full water pressure, I would always get an even flow of water out the thru hull exhaust when they are closed. With most of the water exiting out the exhaust tube.​

Once, after reading that you should never apply full water pressure, I only supplied about 1/2 flow to the muffs. I noticed that the port side had water comming out the thru hull but not the starboard side.​

Concerned, I went to the local hardware store and bought two, two foot lengths of the high temperature clear plastic hose. I hooked these up from the thermostat housing to the underside of each manifold.​

With only about 1/2 water flow to the muffs I ran the engine again. I noticed that the water flow to the port side was noticeably more than the starboard side. That seemed odd, because the water flows into the thermostat housing on the port side heading to the starboard side. I believe what happens, particularly at low flow conditions, is that the water entering the housing gets diverted towards the port side inside the thermostat housing and flows easier towards the port exhaust manifold. I think this is why the starboard riser is normally hotter than the port side.​

Anyway, to make a long story short, I decieded to fully open the water hose to the muffs (like I always did in the past) and sure enough even flow out each thru hull exhaust pipe.​

I believe you have to be careful depending on the type of muff you use if you're going to use full water pressure. Mine allows excess water to come out the sides until the engine starts and the pump begins to pull water then they seal pretty tight.​

Anyway, if you're not getting water out the starboard side try having someone open the water supply to the muffs after you start her up. Or take the boat to the water and run it and see what happens.​