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Burnt rubber smell 350 Monsoon 2012 MXZ


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Hello Crew,

I made some modifications to my boat this winter and now I am dealing with a burnt rubber smell while underway.  I decided to build my own surf pipe and built a merge collector (combine exhaust manifolds) so that I only had one exhaust outlet instead of the dual setup similar to the traditional FAE.  I also did a muffler delete during this time.   I re-used one of the long rubber 90 elbows that was original to the boat but it was after the muffler (not connected to the stainless exhaust dump) and I am wondering if this is the source of the issue.  I have measured the outside temperature of the hose at the exhaust dumps and it is about 150 degrees F on the starboard side and 130 degrees F on the Port side.  I also did a cooling system re-plumb as I found out this engine did have an issue with the old plumbing and that seemed to help cool things down a bit, but I still haven't determined the source of the rubber smell.  I wonder if this could be a cooling system blockage or catalytic convertor issue.   I am also thinking to try a silicone hose that has a higher temperature rating instead of the rubber.  Any ideas on where to start?  I know pictures would help so I will try and post some as well.

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I would start by removing the rubber hoses and looking inside them.  It sounds to me like you are getting something too hot, so you may need to reengineer your mods. 

You could easily sink your boat by burning through an exhaust hose. 

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Thanks Gary, lve checked this and I did notice some rubber left on the stainless piping after it was removed.  It was getting much hotter before the cooling replumb, the replumb helped drop the temps.  Ill check it again.  I was also concerned about a lower hose failure sinking the boat so I did install a flapper in the surf pipe for peace of mind.  I have been monitoring the lower hose and its nice and cool.

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Another point to mention is that I just installed a new impeller a month ago.  I did notice that when using the fake a lake water sprays in the bilge so it could be that I am sucking in air if there is a loose connection.  I will investigate this and the transmission cooler for any debris.

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16 minutes ago, Sharpag01 said:

Another point to mention is that I just installed a new impeller a month ago.  I did notice that when using the fake a lake water sprays in the bilge so it could be that I am sucking in air if there is a loose connection.  I will investigate this and the transmission cooler for any debris.

IF water sprays in the bilge there is definitely a loose hose, impeller cover leak or something else bad going on.

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So tonight I went out in the shop and went through most of the cooling system.  I checked the transmission cooler and it was clear, this is on the raw  water pump discharge side.  I began checking all of the suction side hoses and fittings.  So far I have found 3 loose hose clamps and a cracked/broken fitting threaded in the perko flush valve.  This must have been the water spraying into the bilge issue when connected to a garden hose.  I believe I am most certainly sucking in air caused by the above issues.

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Fixed the cracked plastic fitting (replaced with a brass one) and installed new clamps and tightened all the connections on the raw water pump suction side.  Tested the boat on the water this evening and all was good now!  No rubber smell and manifolds were warm to the touch.  Thanks for all the input guys!

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So essentially you tigthened all hoses related to the cooling system and you did not have a burning rubber smell? Last night I was out on my X-30 (Mastercraft) I am having the same issue so I had to jump in here. I started wakeboarding and all the sudden the terrible burning rubber smell came out and a bit of colored smoke that was not exhaust. engine was not overheating.... ran the boat around then I wakeboarded for 20 minutes and it started again. 

 

Hoping mine is fixed with the same fixes here.

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To give you another thing to look at, the belt on my VLX was the source of the burning rubber smell once. My alternator had vibrated loose, loose enough to be enough out of alignment causing the belt to get hot. 

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I checked the entire suction side of the raw water system.  The perko flush valve had a plastic elbow that was cracked, it never leaked becuase it was attached to the flush port on the rear of the boat above the waterline and this is under vaccuum while the engine is running.  I also found some loose hose clamps from winterization at the v drive.  All of the hoses connections on the suction side only had a single clamp so I added a second one for a dual clamp setup.  I also double checked the new impeller.  Seemed to fix my issue.

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Nice thanks man! I am going in to check on all my engine stuff today. I will be looking at the hoses and stuff but my engine was not overheating at all. 


I am also very curious to see if it could be a belt running on a stuck pulley. The other week my new ballast bags like pushed through the wall and it might have touched one of the belts and pulley.

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1 hour ago, Sharpag01 said:

My engine wasn’t overheating either only the wet exhaust system and only knew it because of the smell.

If you smelled burning rubber but the impeller was good, you definitely need to pull and inspect your exhaust hoses.  @Bozboat has a photo of what happens when you bake one.

Your flapper protects you (maybe) from incoming water, but what about the cooling water coming from the engine?  Your raw water pump is rated at 60 GPM at high RPM....

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I got on my boat tonight and I saw there is a leak in one of the mufflers. I didn't notice anything wrong with the hoses. I had to run the boat really hard to get the burning rubber smell.

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2 hours ago, oldbaychay55 said:

I got on my boat tonight and I saw there is a leak in one of the mufflers. I didn't notice anything wrong with the hoses. I had to run the boat really hard to get the burning rubber smell.

The damage is on the inside of the hoses....

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45 minutes ago, oldbaychay55 said:

do you think the leak in the muffler would be the cause of this? 

Anything is possible.  How big is the leak?  If you are talking gallons per minute, then it could be a problem.  If it is a drip or small squirt, then no.  Fix that with a fiberglass patch.

If you have run your boat with a compromised raw water pump, the engine may well have stayed cool enough, but the rubber hose relies on a steady, forceful stream of water to cool the hot exhaust.  The short hoses between the risers and the mufflers would be the first place to look.  The risers inject raw water (already heated to 160*F by the engine) about six inches before the hose, so it takes a constant stream to keep the exhaust temperature low enough to keep the rubber safe.

Since you have a muffler leak anyway, pull the riser hoses and take a look when you inspect and repair your muffler.

 

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thanks for the reply!

The leak was very small. so maybe the impeller is going out... there is deff water moving through but I guess it could be not enough pressure. the exhaust hoses were hot to the touch after I ran the boat yesterday too.

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30 minutes ago, oldbaychay55 said:

thanks for the reply!

The leak was very small. so maybe the impeller is going out... there is deff water moving through but I guess it could be not enough pressure. the exhaust hoses were hot to the touch after I ran the boat yesterday too.

Very carefully inspect the raw water intake system from the hull inlet to the raw water pump (including the pump cover plate).  I'd be willing to bet that you have a leak somewhere.  The problem with a leak in the intake is that it is difficult to find if you only look while the engine is running because it is under suction and pulling in air rather than pushing out water.  Air is a lot easier to move than water, so you can easily end up with a lot of air in your system.

Any small leak is a potentially huge problem.

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13 hours ago, oldbaychay55 said:

thanks for the reply!

The leak was very small. so maybe the impeller is going out... there is deff water moving through but I guess it could be not enough pressure. the exhaust hoses were hot to the touch after I ran the boat yesterday too.

Which engine do you have?  Ilmor 5.3, 6.0, 6.2, 7.4?  Some have a closed cooling system with a heat exchanger and a Thermal Command Center (TCC) and some have raw water cooling.  I would definitely recommend checking your sea strainer, impeller, and heat exchanger (if your engine has one).

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I think the sea strainer is fine. I actually went down to the shop and changed the impeller myself last night because they wont' be able to look at my boat for at least a week. The old impeller was over 2 years old and honestly didn't look that bad (compared to some gnarly ones i've seen online)... but deff was ready for a replacement. I have the 6.0 ilmor.

I wonder if the burnt rubber could simply be the muffler getting so hot from the leak?? It only happens after running the boat really hard.

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1 hour ago, oldbaychay55 said:

I think the sea strainer is fine.

Is this by visual inspection, or an actual pressure test?

1 hour ago, oldbaychay55 said:

I wonder if the burnt rubber could simply be the muffler getting so hot

Once again, your muffler is not made of rubber.  How could the non-rubber muffler smell like burnt rubber?  The burnt rubber smell is a symptom of the problem, but not the actual problem.

One more time, your issue is very likely an air leak in the raw water intake section before or including your raw water pump.  :horse:  Fix that and the burnt rubber smell will stop.  After you get that fixed, replace your rubber exhaust hoses because they are compromised.

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I cleaned the strainer 1.5 months ago and yea visual inspection. You might be right about the air leak... saw some damage to the hose the runs from the strainer and across the front of the engine... but it didn't seem to be causing any leaks. Could check that out more.  thanks!

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