Exhaust hose burn thru

[R-and-R]

Burned thru the exhaust hose on the starboard riser, starboard engine today. Pics below. It appears to be an actual burn through, not just age-related failure.

Engine temperature was normal.

Any thoughts on how/what would cause it?

2002 340 Dancer. 8.1s engines. ~ 700 hours

 

[SeadawgVB]

I can only guess or surmise that the cooling water is not flowing thru your starboard manifold or riser. I know on my 8.1 motors the starboard exhaust seems always warmer than the port. I'm guessing how the raw water is routed around the engine.

What do you consider "normal" for your engine temperature?

 

[scoflaw]

Yup, clogged something. Manifold, elbow, hose ?

 

[rcknecht]

You may have a bad impeller. The lack of water flow will cause burn through...

 

[R-and-R]

Hey gents, thanks for the assist!

I did a lot of online reading, talked to some dockmates, and even my mechanic offered some advice. So, here's what I did.

Replaced exhaust hose.
Opened Raw water strainer, mounted my seaflush funnel, filled with water and turned over engine. Pump was definitely drawing water.
Loosened hoses at my dripless and my heat exchanger and turned over the engine again. Pump was pushing water.
At this point I suspected I had a temporary clog from a mud/sand encounter.
Closed everything and then started engine and idled for 10 minutes while monitoring external temperatures with a thermal reader (manifolds, risers, heat exchanger, oil cooler, trans cooler). Everything read about 110-120 degrees. Took her out for a test run, again monitoring external temps with the thermal reader. Nothing over 170 at any of my test points and engine coolant temp gauges stabilized at their normal 170.
Three of my four risers all read within 2-3 degrees of each other. The starboard riser on the other engine (portside) reads 8-10 degrees higher than the others.

So, I think I'm good. I'll continue to occasionally monitor temps with my newly purchased toy (thermal reader).

 

[LG111]

For a point of reference, my twin 8.1S run at 154 degrees esch while at cruise. Never higher.

Are your manifolds aluminium or cast?

 

[R-and-R]

For a point of reference, my twin 8.1S run at 154 degrees esch while at cruise. Never higher.

Are your manifolds aluminium or cast?

Hmm.. Interesting. I hadn't suspected any issue with my operating temps since they've been consistent and steady in the 25 hours that I've operated the boat, and my surveyor didn't remark on it. I know on older car engines you could purchase thermostats with different temperature set points. Could that account for the difference in our boats? I don't recall if there was a specification in the owner's manual as to normal operating temp, will have to check it when I get home later this week.

My manifolds are cast and the risers are stainless. I don't know if that's OEM or if that was a PO modification.

 

[rondds]

Mine run at around 165* according to the engine computers ( temps displayed on the Garmin display). Thermostats are 160* in these engines.

In the spring, when the water is cooler, I run high 150s. On Barnegat Bay at this time of year the water temps are mid 80s and that makes a difference in operating temps.

 

[scoflaw]

Hmm.. Interesting. I hadn't suspected any issue with my operating temps since they've been consistent and steady in the 25 hours that I've operated the boat, and my surveyor didn't remark on it. I know on older car engines you could purchase thermostats with different temperature set points. Could that account for the difference in our boats? I don't recall if there was a specification in the owner's manual as to normal operating temp, will have to check it when I get home later this week.

My manifolds are cast and the risers are stainless. I don't know if that's OEM or if that was a PO modification.

The temp difference is not your problem. You don't have enough water exiting that side

 

[R-and-R]

The temp difference is not your problem. You don't have enough water exiting that side

Agreed. I think I had a clog from an earlier mud/sand encounter. I also think it unclogged itself during my trouble-shooting efforts. When I went on a test run my temperatures were pretty evenly matched across all 4 manifolds, risers, and exhaust hoses.