Volvo Penta 4.3 riser gets HOT

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Apr 14, 2011
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I have a 1998 Volvo Penta 4.3GL with an SX outdrive (I know Don S suggested including engine model numbers but I can decipher them due to fading) in a Regal 2100 LSR that I just bought. I changed the impeller as a precaution since I didn't know the history. Upon using the hose to "bench test" it before hitting the lake, I noticed the left riser was considerably warmer than the right and that the elbow showed previous signs of excessive heat (left being my left when looking back at the motor from inside the boat). The temp guage never indicated any overheat so we hit the lake last night for the maiden voyage. We were running 50-55 mph with no issues. Stopped to see how things were doing and could smell a slight burning. Couldn't find the source of the smell so we headed toward the ramp. Took another break and the smell was stronger so we knew something was going on. A bit further and there was confirmed smoke coming off the left elbow coming off the riser (the riser was hot but not smoking, just the elbow). Needless to say, it was cookin. We let it cool and limped back to the dock. BTW....no high readings on temp guage and the engine was actually running quite well. After sitting for about 20 minutes we experienced a hyrdrolock. Once home I noticed that the rubber boot that connects the riser to the elbow was damaged. It was almost like it was unhooked but it wasn't, similar to being cut right around where the elbow would be inside the boot. I cannot confirm that this was a result of the heat or if it was like this before we headed out and caused the heat due to an air leak.

So....here is my question/s.

1.Can someone explain the anatomy of a riser and how a failure would allow a hydrolock?

2. What would cause the elbow to get so hot (I know lack of water flow....but specifically what type of blockage?)

3. What are the chances that I have caused permanent damage to my engine?

4. Would a bat T-stat cause these symptoms?

5. Would a faulty boot create enough of an air leak to cause the symptoms I've detailed?

I've got plenty of experience with OB's but I'm new to the I/O scene. I've read where riser height is of concern but this is all factory set up and really don't think that's an issue for me. Furthermore, I've read posts that indicate that riser/manifold replacement is part of "routine" maintenance. This is a freshwater boat that has always lived in KS so no saltwater issues to contend with.

Any guidance or tips are certainly welcome.

Thanks
 

Don S

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Re: Volvo Penta 4.3 riser gets HOT

It sounds to me like you have a blocked manifold or riser on the hot side. Remove the riser and see if the water passages are plugged up. During the overheat, the gasket failed and allowed water in the riser to leak into the exhaust manifold when the engine was shut off, and into an open valve (hydrolock).
If it is plugged up with rust and corrosion, you will need to replace both manifolds and both risers. DO NOT just replace one side, or you will then have an overheat on the other side. Water will take the path of least resistance.
Without water flow, the hot exhaust gases burn the rubber hoses.
 
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Re: Volvo Penta 4.3 riser gets HOT

Thanks for the quick reply.

Now...when you say to replace BOTH manifolds and BOTH risers, I trust your judgment but can you elaborate on why I would have to replace the manifolds? Would it be possible to just replace the risers and minimize my costs? I can get new risers and gaskets for around 300 but to add manifolds would certainly double that price. As you can well imagine, I want to keep my costs down but I also don't want to neglect critical engine parts only to have a catastrophic failure later on.

Lastly, what would cause a blocked manifold or riser? Corrosion? If so, is it feasible to clean them?

Pardon my ignorance but this is a whole new learning curve for me compared to the familiar OB's.
 

Don S

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Re: Volvo Penta 4.3 riser gets HOT

I trust your judgment but can you elaborate on why I would have to replace the manifolds?

I answered that in my first reply.


Lastly, what would cause a blocked manifold or riser? Corrosion? If so, is it feasible to clean them?

Rust from the manifolds corroding is what plugs them. It's an early warning system that tells you they need replaced.
Cleaning them usually doesn't work, and can cost you an engine.
 
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Re: Volvo Penta 4.3 riser gets HOT

Thanks Don S.

I'll look into it and with any luck I'll have her up and going in no time flat.

I'll post my results.
 
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Re: Volvo Penta 4.3 riser gets HOT

UPDATE:

I disassembled the riser yesterday and everything appeared to be in fine shape, no corrosion, no build up, nothing. My next step was to remove the hoses and check for a blockage. Yep.....sure enough there was a blade from the impeller that had lodged in the outlet of the T-stat housing leading to the manifold that got hot. It had been in there for some time since the impeller I just replaced as a precaution still had all it's blades. I'm pretty confident that I found the source of my water restriction on that side of the engine and no other parts need replaced, i.e. risers and manifolds. Talk about a lucky break!! The only parts that need replaced are T-stat as a precaution, riser gaskets (both sides) and both exhaust hoses on the one side.. With any luck I'll get out for a 100.00 repair.
 
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Re: Volvo Penta 4.3 riser gets HOT

One other thing I failed to mention.

During the process of trying to start it during the hyrdrolock, I believe I stripped the bendix on the starter. Now all it does is "whirr" when I try to crank it. This should be a relatively easy fix shouldn't it? I've already removed the starter, just haven't had the time yet to look into it a bit deeper.

Just looking for ideas on what the deal is with it before I tear it appart.

Thoughts?
 

Don S

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Re: Volvo Penta 4.3 riser gets HOT

This should be a relatively easy fix shouldn't it?

Maybe not.

Look at the teeth on the flywheel. They may be damaged as well, if they show damage, it will shorten the life of a new bendix as well.
The good news, you can replace only the ring gear, you don't have to replace the whole flywheel.
It's also very possible you bent a rod
 
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Re: Volvo Penta 4.3 riser gets HOT

During the hyrdrolock, the start was engaging the flywheel, just not turning it for obvious reasons. This was prior to diagnosing the hydrolock. The first couple of attempts, the starter was definately engaging with full force. Then on about the third try, the starter was spinning but not engaging the flywheel. I checked the flywheel and the starter as well, no visible damage to the ring gear or the starter gear. This is why I suspect the starter being stripped.

I have no reason to suspect a bent rod at this point. Perhaps when I get the starter repaired and start cranking the engine I will discover other issues but I don't suspect I will as the engine was never running nor turning over during the "lock".
 
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