1989 OMC Cobra 4.3l exhaust coupler burnt

[Jalysogo]

Hey guys,

So I just bought a boat with the 4.3 OMC Cobra motor and it send to have been fixed with parts that weren't intended for Marine use. There it's a 3" to 4" coupler that connects the exhaust manifold to another pipe and it burnt a hole in the coupler after only a couple hours of use. I replaced it with an identical part and it did the same thing again but this time two holes. I got to looking up a part diagram and it shows that it was not the right coupler. But they replaced both of these with the wrong part and both times only the one has burnt up. My question is does you think if I replaced the couplers with the stock part that it would fix the issue or do you think that there is another issue that needs to be addressed due to only one side burning through the couplers? Thanks for any help.

- Joe -

 

[Scott Danforth]

You have a cooling water issue. Specifically no water flow on that side.

Start with replacing the raw water impeller, and then pull your manifolds and check for rust

 

[Jalysogo]

Is the raw water impeller the same thing as the water pump assembly or something different? Fairly new to boat motors and I am having difficulty determining which part to purchase/replace.

You can use this link to see the diagrams of my motor. If you can just let me know the part number I would be eternally grateful.

http://www.crowleymarine.com/johnson-evinrude/834.cfm?mdl=ZFVP8M

Thanks,
- Joe -

 

[Lou C]

Even if they used different couplers, the rubber hoses definitely should not burn up. Is the engine overheating? (normal is 160-175*F). If the engine is not overheating but you are still burning up exhaust couplers, then you need to check the flow out of the thermostat housing, the 2 nipples on the left and right side feed raw water directly to the exhaust manifolds. Make sure that these ports are open and not clogged with rust. The Cobra impeller (raw water pump in the rear of the upper gear housing, not the automotive style pump on the front of the engine) can move a lot of water but they also wear out and should be changed every 3 seasons or so. A good test is to put the boat in the water. Then disconnect the raw water intake hose (larger than the manifold hoses, it comes up from the transom mount alongside of the engine on the starboard side). Hold the hose up while someone starts the engine (very briefly!!) you should see a stream of water 2-4" tall. If not then you need to replace the impeller, wear plate, and make sure there are no old impeller parts stuck in the P/S cooler on the rear of the engine.

​If you burned up those couplers, I bet you burned up the exhaust flappers too.

 

[Lou C]

http://www.crowleymarine.com/johnson-evinrude/parts/55625.cfm?mdl=ZFVP8M
impeller is part #12

http://www.crowleymarine.com/johnson-evinrude/parts/55612.cfm?mdl=ZFVP8M
​flapper is part # 22

 

[Jalysogo]

So status update. I replaced the impeller and all related parts. I replaced the coupler that burnt up. I checked to make sure there was no clogged ports or lines and made sure there isn't excessive rust inside the manifolds. But while taking apart the pipe for the exhaust I noticed that neither side has the flappers currently. Is there any chance that this could cause the issue that I am having or is that unlikely? Also, would it be wise to replace my thermostat even though the boat does not seem to be overheating? And since the flappers are gone do I need to take apart anything to get the old flappers out of the exhaust?

 

[Scott Danforth]

Yes. You need yo pull it all apart to look for the remnants of the flappers

You burned up the rubber flappers, leaving the metal bits to fall into the y-pipe

 

[Lou C]

Yep and yep. Probably have to pull the drive and rig up a grabber tool of some sort to get the burnt up flappers out of the exhaust opening.