Overheated Exhaust on Port Side

[seattle2855]

I took my 1989 Bayliner 2855 (OMC 460 King Cobra) out today for a quick spin and 3 minutes at 1800 RPM in I knew something wasn't right. I was hearing these slight popping noises and started to smell burning rubber.

I opened the engine hatch and saw that the rubber exhaust sleeves from the riser and to the Y pipe were smoking a lot on the port side. I immediately turned around and headed back to the slip. I managed to make it in, but the popping and smoked continued.

After cooling down a bit I noticed the lower rubber sleeve to the Y pipe was melted on the port side. The starboard side looked fine and never smoked. I took off the riser and elbow to the Y pipe and noticed the exhaust flapper that should be there was gone (the metal pin it attaches to was still there). There was some remnants of the flapper but it was burned to a crisp. I took off the other riser to examine the flapper on the starboard side. That flapper had dislodged on one side but was still there. However, it did have signs of fresh melting.

The risers an manifolds ports looked open enough for water to come through and the hose from the heat exchanger isn't blocked (I blew threw it). I also replaced the impeller a little over a year ago. Also, the engine temp never got above normal. And if the impeller was the problem, why was the smoke and melting only on the port side.

Is it possible the flapper broke off on the port side and blocked the exhaust causing it to overheat? If it's stuck at the bottom of the Y pipe, how might I get it off (while still in the water). I'm trying to save a towing trip to a dry dock.

Any ideas would be appreciated. I have a new set of manifolds and risers I was about to put on, but I'd like to know the cause of the overheat.

Here's the manifold

and the flappers (port side missing)

Any ideas?

Shawn
1989 2855
OMC 460 King Cobra

 

[HT32BSX115]

Re: Overheated Exhaust on Port Side

Hi Shawn,

Hmmm, where'd you get those new manifolds? (you're lucky to have them!!!)


Well hot burning rubber in an exhaust system is usually due to no water flowing in that riser.

The water MUST flow thru the manifold, riser and hoses/Y-pipe and mix with the exhaust gases there for obvious reasons or the everything will heat up VERY quickly (as you observed)

Now I don't remember exacly how my King Kobra was plumbed but there's hoses from the T-stat housing that go to each side and to the front of each manifold. The water MUST flow thru the manifold and up thru the riser before going out.

If that water was restricted for any reason on one side you wouldn't get enough water to cool the exhaust tube sufficiently.

I don't think a "flapper" would necessasarily cause the exhaust system to heat up if there was enough water flowing there........It might......You do need to retreive the pieces and replace them.

(By the way I do have a complete steering system for that engine/drive to include all the hoses, cooler and pump....It's all I have left of what I pulled out of my Four Winns Liberator and I'm just a stones-throw from you!)


Regards,


Rick

 

[seattle2855]

Re: Overheated Exhaust on Port Side

I found the manifolds and risers on ebay about 2 years ago. Got 'em for $200 total!

I think you might be right that the flapper isn't the cause. It's more likely the result of overheating. Perhaps the port side took the majority of the damage because it's a longer hose from the heat exchanged to that side and/or it's more clogged up than the other side.

My impeller is fairly new, but maybe something else in that area went bad. I guess I'll have to get the boat pulled and take a look out of the water. Since I don't have a trailer and the boat is in a stall, I'll have to have it towed to a dry dock. That doesn't sound like fun

 

[bruceb58]

Re: Overheated Exhaust on Port Side

Either you impellor is bad or something wrapped itself around your drive like a plastic bag(had that happen to me). Did you happen to see what your temp guage said you were running at?

 

[seattle2855]

Re: Overheated Exhaust on Port Side

Either you impellor is bad or something wrapped itself around your drive like a plastic bag(had that happen to me). Did you happen to see what your temp guage said you were running at?

I wasn't overheating per the temp gauge. It stayed normal -- possibly a tad high.

Doesn't seem to be anything on the outdrive either.

 

[user64]

Re: Overheated Exhaust on Port Side

just went thru the same thing where no water went to one riser or manifold..temp gauge never went up because the engine didnt actually overheat...exhaust hose got fried because of no water flow and flapper was crisped. I believe that the burned out flapper is a result of, not the cause of your overheating. Your problem will most likely be found between the thermostat housing and where the water enters the riser (blockage there or in hose?). My case involved a new thermostat housing that was actually blocked on the starboard side from the factory. The heat was intense and wound up replacing the riser, exhaust elbow and manifold..good luck

 

[HT32BSX115]

Re: Overheated Exhaust on Port Side

One thing you could do is remove the manifolds/risers (don't "break" them apart)

set them up on the ground and connect a water hose to each and turn it on and view the water flow out of each riser. You could even put a gage on the supply hose to see if pressure builds up indicating a restriction.

If that's the case either the riser or the manifold has some restriction.

If there's no restriction, then it might be at the thermostat housing or the hose from the t-stat housing....


I would pull the thermostat housing and have a close look at it too.

I'm assuming raw (salt) water cooling?





Regards,


Rick

..

 

[seattle2855]

Re: Overheated Exhaust on Port Side

Thanks for the information.

I took a closer look at the risers today. The water jackets were really blocked up with big rust flakes. I'm thinking (and hoping) that this was causing poor flow through the manifolds/risers. I'm going to replace the manifolds tomorrow and I've cleaned out the risers pretty well. They're on their last legs and I will have to replace them soon too, but I'd like to see if that was the cause.

By the way, the boat is fresh water cooled. The hoses come out of the heat exchanger and go right into manifold. I don't see any thermostat housing in the path of the raw water hoses.

A couple of questions:

1. One of the flappers was missing. How big of a problem is it if it's sitting in the bottom of the Y pipe? Eventually, I remove it, but I'd like to be able to drive the boat to the mechanic. Its i the water, so taking off the drive is not an option until its dry docked.

2. I'd like to confirm that I have good water supply to the manifolds. Can I remove the hose that supplies it, start the engine for a 15 - 30 seconds and measure the supply of raw water coming out of that hose? The impeller is new, but there could be a constriction somewhere else.

3. I'm going to get a heat gun. What temperature should I see on the manifolds, risers, and exhaust pipe?

Thanks

 

[lekmedm]

Re: Overheated Exhaust on Port Side

Subscribe!

Are those manifolds you got on eBay brand new...???

 

[seattle2855]

Re: Overheated Exhaust on Port Side

They are brand new.

I got new risers too, but today I noticed they aren't the same ones that I have.

 

[HT32BSX115]

Re: Overheated Exhaust on Port Side

Hmm,

Your closed cooled system is a "HALF" system.

In a full system, there's engine coolant flowing thru the manifolds. By the looks of the pictures you supplied it appears to be a "HALF" system. I.E. you have salt water running thru your manifolds.


That's not uncommon but since you have manifolds that you want to last as long as humanly possible it might be worth it to get a larger heat exchanger (if one exists) that will support your including the manifolds in the "fresh-water mix." When I had mine I did look briefly at getting closed cooling for mine but I didn't find a full system for it. (there may not be one available) Sorry about that. Raw water manifolds are really running on borrowed time in salt water... especially if they live all the time in salt water......

1. One of the flappers was missing. How big of a problem is it if it's sitting in the bottom of the Y pipe? Eventually, I remove it, but I'd like to be able to drive the boat to the mechanic. Its i the water, so taking off the drive is not an option until its dry docked.

It will restrict the exhaust output but it shouldn't be a big deal if you're not going to run it long or at high power settings.. You might be able to fish it out with a piece of wire.... It might also be down in the exhaust bellows or simply gone.....

2. I'd like to confirm that I have good water supply to the manifolds. Can I remove the hose that supplies it, start the engine for a 15 - 30 seconds and measure the supply of raw water coming out of that hose? The impeller is new, but there could be a constriction somewhere else.

Absolutely.... Since it's raw water you can certainly run it long enough to check flow. run the hose overboard or into a 5 gallon pail. Don't run it for more than a min or so..... (you know what happened to the rubber parts!)

3. I'm going to get a heat gun. What temperature should I see on the manifolds, risers, and exhaust pipe?

If you have good water flow, you should be able to "pat" your hand on the exhaust manifolds or risers and not get burned (maybe 180 degrees or so plus or minus) The whole idea of water jacketed manifolds and risers is that they PREVENT the engine compartment temps from getting very high....


Good luck!


Rick

 

[seattle2855]

Re: Overheated Exhaust on Port Side

thanks Rick. You've been a big help!

 

[offhourrockers]

Re: Overheated Exhaust on Port Side - Me too!!

Re: Overheated Exhaust on Port Side - Me too!!

Wow, same exact thing happened to me today on Starboard side ('88 OMC), including missing flapper valve! It was a little scary, had smoke billowing out and after I hit the engine hard w/ extinguisher heard those popping noises - shut off batterys, dropped anchor and hailed seatow - thk goodnes the admiral wasn't aboard!!

This thread has been very helpful (and comforting in that i'm not alone), pls post your progress.

I will order new mani/riser and thermo tuesday and hopefully tomorrow troubleshoot from impeller to water pump, thermo, and risers. I don't want to haul either so I'm very curious about your findings particualrly w/ respect to the damn missing flapper. I also hope that your diagnosis, that likely not bad impeller (changed mine this season, but also had a soft grounding), b/c it only melted one side is good.

Bob

 

[seattle2855]

Re: Overheated Exhaust on Port Side - Me too!!

Re: Overheated Exhaust on Port Side - Me too!!

Wow, same exact thing happened to me today on Starboard side ('88 OMC), including missing flapper valve! It was a little scary, had smoke billowing out and after I hit the engine hard w/ extinguisher heard those popping noises - shut off batterys, dropped anchor and hailed seatow - thk goodnes the admiral wasn't aboard!!

This thread has been very helpful (and comforting in that i'm not alone), pls post your progress.

I will order new mani/riser and thermo tuesday and hopefully tomorrow troubleshoot from impeller to water pump, thermo, and risers. I don't want to haul either so I'm very curious about your findings particualrly w/ respect to the damn missing flapper. I also hope that your diagnosis, that likely not bad impeller (changed mine this season, but also had a soft grounding), b/c it only melted one side is good.

Bob

I changed out my manifolds yesterday and found that the risers were pretty clogged up with rust scales. I did my best to clean out the rust scales with a couple of screwdrivers to improve water flow. I have a couple of risers on order but they won't be here until next week.

I put it all back together and it's definitely better, but I think the port side is still a little warm. Using an infrared thermometer, the port side riser is running between 160 and 210 degrees. Starboard side riser is running 130 - 175 (fully warmed up and ran at 2000 RPM in the slip).

This is a half closed system where the water comes out the heat exchanger and up through the manifold and out the risers. I've read threads where others have their risers run at 90 degrees, but I don't see how thats possible on a closed system -- the water comes out of the heat exchanger at 120 before it even touches the manifold.

I took off one of the hoses that supplies the manifold and ran the motor for a few minutes. It appeared I have good water flowing to the manifold. I'm going to have the impeller changed anyway. Apparently they can do it in the water without much effort.

My guess is that the port side riser is still constricting flow. I'll put the new risers on when they arrive and it should be working again.

I had no luck removing the missing flapper. I tried to pull it out with a long "grabby" tool, but I didn't feel/find anything. It may have been missing for years. I should have the outdrive removed and have it checked out, but I want to get the boat running right first so I can drive it to a dry dock location.