3.0 liter OMC exhaust riser hose

way2buzy

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Mar 5, 2012
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6
I have a 1988 Four Winns 160 Freedom with the 3.0 liter OMC engine. I have twice now replaced the exhaust hose connected to the manifold riser. It has blown out both times. Seems like it just gets hot and melted a hole in the hose. Any ideas on how to fix this? Thanks
 

HT32BSX115

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Dec 8, 2005
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10,083
Re: 3.0 liter OMC exhaust riser hose

I have a 1988 Four Winns 160 Freedom with the 3.0 liter OMC engine. I have twice now replaced the exhaust hose connected to the manifold riser. It has blown out both times. Seems like it just gets hot and melted a hole in the hose. Any ideas on how to fix this? Thanks

Howdy,

Welcome Aboard!

Your exhaust hose is getting hot because there is insufficient cooling water flow through it from the engine.

All the cooling water from the raw water pump goes through the exhaust manifold and exits through the riser.

If there is a restriction anyplace in the circuit, water flow will be reduced. If it's reduced enough the exhaust system will run much hotter than it should (and the engine itself may not get hot)

Start by checking how much water flow you have from the pump to the thermostat housing.

Put the boat in the water, disconnect the hose from the transom mount to the t-stat and run the engine at idle briefly and see how much water comes out of the hose. It should be a pretty good stream and should increase if you rev the engine

If you have good flow, you could either have a restriction at the t-stat, exhaust manifold or riser. If you don't, you might have a restriction in the hose or piping in the transom mount or even a defective raw water pump.

A lot of the cooling water actually bypasses the engine (only a small amount is actually allowed into the engine, controlled by the thermostat as needed to control engine temp) Most of it goes directly to the manifold and riser and mixes with the exhaust.

If there isn't enough water making it out of the riser or manifold (because they're clogged with rust) the manifold riser and any components downstream will get hot. In some cases VERY hot!

Regards,


Rick
 

way2buzy

Cadet
Joined
Mar 5, 2012
Messages
6
Re: 3.0 liter OMC exhaust riser hose

Howdy,

Welcome Aboard!

Your exhaust hose is getting hot because there is insufficient cooling water flow through it from the engine.

All the cooling water from the raw water pump goes through the exhaust manifold and exits through the riser.

If there is a restriction anyplace in the circuit, water flow will be reduced. If it's reduced enough the exhaust system will run much hotter than it should (and the engine itself may not get hot)

Start by checking how much water flow you have from the pump to the thermostat housing.

Put the boat in the water, disconnect the hose from the transom mount to the t-stat and run the engine at idle briefly and see how much water comes out of the hose. It should be a pretty good stream and should increase if you rev the engine

If you have good flow, you could either have a restriction at the t-stat, exhaust manifold or riser. If you don't, you might have a restriction in the hose or piping in the transom mount or even a defective raw water pump.

A lot of the cooling water actually bypasses the engine (only a small amount is actually allowed into the engine, controlled by the thermostat as needed to control engine temp) Most of it goes directly to the manifold and riser and mixes with the exhaust.

If there isn't enough water making it out of the riser or manifold (because they're clogged with rust) the manifold riser and any components downstream will get hot. In some cases VERY hot!

Regards,


Rick

Can I perform this test with the muffs on the lower unit or must it be IN the water?
 

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
Re: 3.0 liter OMC exhaust riser hose

Can I perform this test with the muffs on the lower unit or must it be IN the water?

Not really.


If your raw water pump impeller is faulty, the water pressure from running it with "muffs" will mask the problem.

If the exhaust manifold or riser is clogged it won't make a difference though.

Also, if you have not removed your manifold and riser in the last couple of years, or you have NEVER removed it and replaced the gasket or inspected either the riser or manifold, now would be a good time to do it.

With cooling problems, in general, you should start at the impeller.

Do you operate in salt water? If you do and the manifold and riser hasn't been replaced in more than 5 years or so, you may need to start looking for replacements.
 

way2buzy

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Joined
Mar 5, 2012
Messages
6
Re: 3.0 liter OMC exhaust riser hose

Not really.


If your raw water is faulty, the water pressure from running it with "muffs" will mask the problem.

If the exhaust manifold or riser is clogged it won't make a difference though.

Also, if you have not removed your manifold and riser in the last couple of years, or you have NEVER removed it and replaced the gasket or inspected either the riser or manifold, now would be a good time to do it.

With cooling problems, in general, you should start at the impeller.

Do you operate in salt water? If you do and the manifold and riser hasn't been replaced in more than 5 years or so, you may need to start looking for replacements.


It has only been run in freshwater.

I checked the impeller and one of the blades was torn off and others were a little melted on the ends AND the housing had a hole melted in it.

Also pulled the riser and found the flap in the exhaust pipe had also melted which made me then think to remove the t-stat housing only to find some rust and a very rusty t-stat.

I have ordered all new replacement parts and appropriate gaskets.

The only question I am left with is, the pieces of the flapper that either burned or melted off, where are they. Did they burn out and expell or are they stuck, and if they are stuck, how do I remove them. The wife's vacuum hose wouldn't go deep enough.


Thanks for the info!!
 

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
Re: 3.0 liter OMC exhaust riser hose

It has only been run in freshwater.

I checked the impeller and one of the blades was torn off and others were a little melted on the ends AND the housing had a hole melted in it.

Also pulled the riser and found the flap in the exhaust pipe had also melted which made me then think to remove the t-stat housing only to find some rust and a very rusty t-stat.

I have ordered all new replacement parts and appropriate gaskets.

The only question I am left with is, the pieces of the flapper that either burned or melted off, where are they. Did they burn out and expell or are they stuck, and if they are stuck, how do I remove them. The wife's vacuum hose wouldn't go deep enough.


Thanks for the info!!

Hmm,

Looks like you may have found some (or all) of the problems!

The "Flapper"or Exhaust Seal (fragment(s) ) is(are) either in the bottom of the exhaust pipe where it exits through the transom or it all went overboard or into the drive exhaust. I seem to remember the exhaust seal being metal so it probably is sitting at the bottom of the exhaust

You might want to pull the drive and see if you can look into the exhaust area or try to "fish" it out that way. (if you haven't pulled the drive to inspect, lubricate and check the alignment in the last couple of years, now would be a good time to do it. (Mercury suggests every year)

You DO want to ensure that you get it all out of there. It could restrict exhaust flow.

You also might want to ensure that there aren't impeller fragments in the raw water supply hose from the transom to the t-stat housing.
Small fragments can get stuck in the hose.
 

wire2

Lieutenant Commander
Joined
Jun 25, 2007
Messages
1,584
Re: 3.0 liter OMC exhaust riser hose

One indication of a partially blocked exhaust is reduced top speed. How does it compare with when you first got the boat?
 

way2buzy

Cadet
Joined
Mar 5, 2012
Messages
6
Re: 3.0 liter OMC exhaust riser hose

One indication of a partially blocked exhaust is reduced top speed. How does it compare with when you first got the boat?

The max it ever reached was 25 mph on the gauge. I just figured it was because we had 7 on the boat. It is rated for 8 and 1000lbs. which we were under.
 
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