Help !! Volvo 3.0 Exhaust Riser Overheats

[skymech]

First time post, but I have been lurking for quite sometime. I have a 2002 Volvo 3.0 GSP-C s/n 4012058256 that I have owned since new and has only been operated in freshwater. Never have had a impeller failure as the impeller in replaced every other year. I have done all the procedures in the Volvo Penta overheat diagnostic manual. No air bubbles noted in the clear tubing and the pressures are with in spec. The problem only occurs at above 3200 RPM, the engine has been operating flawlessly for the last 3 months until this problem showed up one day. I have narrowed the alarm down to the sensor on the exhaust riser. The engine water temp never goes above 175 *F. I removed the exhaust riser and inspected for blockage, no blockage was noted. I also pressure tested the riser and manifold and no leaks noted. I have performed direct and differential compression tests. Direct cmpression tests ranged from 170 to 180 PSI. The differential pressure (performed at 130 PSI) test showed that no air was leaking into the water jacket around the exhaust manifold (checked using a clear tube filled with water attached to manifold water inlet fitting). I took a 3/4" garden hose and flowed water through the exhaust manifold inlet fitting and the exhaust riser, and found there is absolutely no restrictions. With the boat idling in the lake I took off the hose that goes from the base of the exhaust riser to the exhaust pipe and found that water shoots out of the hose 4-5 inches.( Plenty of water flow). I have also checked the ignition timing and found that to be correct. The two questions that I have are: 1) At what temperature does the exhaust riser temp sensor operate at ? (Can't find any specs in the Volvo manual) 2) According to the Volvo manual the arrow on the rubber coupling should be pointing up, is this correct? As it appears the the rubber coupling may be partially blocking the water passage. Any ideas or comments would greatly be appreciated. Sorry for the long post but I wanted to include as much information as possible. Thank You

 

[jerryjerry05]

Re: Help !! Volvo 3.0 Exhaust Riser Overheats

If the riser's getting hot. Then the flow is blocked somewhere.Or it's not getting enough water.
What drive?
The drive has a rubber hose under the bellows that is connected to the drive.The connector#24 sometimes rot away/corrosion or electrolisis?
The tube in the drive #16?itself,the seals can go bad.

 

[Don S]

Re: Help !! Volvo 3.0 Exhaust Riser Overheats

Have you actually checked the riser temp with an IR temp gun to verify the riser is actually overheating? How do you know it's the riser overheat sensor causing the alarm?

 

[0352Marine]

Re: Help !! Volvo 3.0 Exhaust Riser Overheats

Change your sensor

 

[Don S]

Re: Help !! Volvo 3.0 Exhaust Riser Overheats

Change your sensor

Why change it if it's not broken, or not the problem? Or do you just like the "throw parts at the problem until the problem goes away" method of boat repair?

 

[bruceb58]

Re: Help !! Volvo 3.0 Exhaust Riser Overheats

The drive has a rubber hose under the bellows that is connected to the drive.The connector#24 sometimes rot away/corrosion or electrolisis?
The tube in the drive #16?itself,the seals can go bad.

He doesn't have that type of drive shown in your picture. He has an SX which has a completely different water path.

 

[Thalasso]

Re: Help !! Volvo 3.0 Exhaust Riser Overheats

Check at the Y in the exhaust after the riser and see if the flapper is okay. I don't know if you have one but some that do, the swivel pin that it pivots on gets rusted and wont open far enough for the needed water exit. You can test sensor with a multimeter. Unplug sensor wire and check resistant when cold. # will be higher then when you check it hot. Cold will be around 1700 hot around 900.Put red lead on sensor and black to ground when checking.If sensor has two terminals one lead on one and one on the other. some sensor only have one terminal

 

[bruceb58]

Re: Help !! Volvo 3.0 Exhaust Riser Overheats

Check at the Y in the exhaust after the riser and see if the flapper is okay

On a 3.0?

 

[Thalasso]

Re: Help !! Volvo 3.0 Exhaust Riser Overheats

Yep.
remove the exhaust riser and the flapper might be missing from the top of the exhaust. the burnt flapper valve might be plugging up the exhaust. It is only a safety device to prevent water entering the exhaust during a fast launch.

 

[Don S]

Re: Help !! Volvo 3.0 Exhaust Riser Overheats

Flappers aren't going to cause a riser to overheat, that's impossible.
Besides, Volvo stopped using flappers in those engines in 99.

 

[Thalasso]

Re: Help !! Volvo 3.0 Exhaust Riser Overheats

Why would it be impossiabl for a flapper to cause a riser to overheat? Being that that water must exit through riser to exhaust through lower unit, if exhaust in lower unit is clogged with a flapper it resricts water flow.Having a partially blocked exhaust will cause poor performance and somtimes engine heating, also as the port at the transom is the only exhaust port when stopping the boat, the presure that builds up at the transom is enough to push water up and over risers even with riser extentions added. 3rd, if you find that your flappers are missing you cannot just replace them, you need to be sure that the old ones are not blocking the exhaust at the base of the pipe which is where they end up generally., 4th True volvo no longer makes the valves available but you can use the one from mercuiser but even those will fail at some point. 5th ,the only sure fix (If this is found to be the problem) is to run through the transom exhaust bells with external flappers.

 

[skymech]

Re: Help !! Volvo 3.0 Exhaust Riser Overheats

By process of elimination (disconnecting the thermostat housing temp probe, oil pressure temp probe and the riser temp probe) I determined that the riser temp probe was causing the alarm to go off. I did check the riser temp. with a digital point and shot thermo and it is definitely running hotter than the exhaust manifold and the engine block. The riser was around 200- 210*F. I noted that it was hotter at the outlet side than the inlet side. One thing that I noticed the last time that I had the boat out was that the hose between the thermostat housing and the circulating pump was very hard as in pressurized, even when at idle. That does not seem right to me. The clear hose that I installed between the thermostat housing and the exhaust manifold did not show any bubbles ( at idle or full power) and definitively was not pressurized. So I don't believe that the head gasket is or head is leaking. Also no signs of leaks were noted when the compression checks were done. Any body have any other ideas? Any help is greatly appreciated!

 

[skymech]

Re: Help !! Volvo 3.0 Exhaust Riser Overheats

I should also mention that after the alarm goes off if I let the boat idle for approx. 30-40 seconds the alarm stops. If I run the engine at 1500 rpm just doodling around the lake the exhaust riser is warm but definitely not hot to the touch. I plan on doing some more trouble shooting this weekend. I will let you know if i come up with anything else. Thanks!

 

[Don S]

Re: Help !! Volvo 3.0 Exhaust Riser Overheats

Were the outlets on the riser open?

 

[skymech]

Re: Help !! Volvo 3.0 Exhaust Riser Overheats

Thanks for your help Don. The end of the riser is clear. The one thing that I noted was that the "bulge" on the rubber coupling is not centered over the opening on the riser. It appears that the edge of the "bulge" lines up with the opening in the riser. I installed it per the Volvo manual with the arrow pointing up. I did note that if the coupling is installed with the arrow pointing down that the "bulge" is centered with the riser opening. I may just get another set of riser gaskets and test it that way just to see if it makes a difference. I don't believe this is the problem as the rubber coupling was installed with the arrow pointing up before the problem existed. One other thought I had was to try changing the orientation of the restrictor plate.
It is currently installed with the opening facing the engine block per the manual. What are your thoughts? Thanks

 

[Don S]

Re: Help !! Volvo 3.0 Exhaust Riser Overheats

I am having a problem understanding why only your riser is overheating when all the water goes through the engine, through the manifold and out the exhaust.
What is the manifold temp when you get 210? on the riser?

 

[skymech]

Re: Help !! Volvo 3.0 Exhaust Riser Overheats

If I remember correctly the exhaust manifold was 180* and the engine blocked ranged from 170* to 180* depending on location.

 

[skymech]

Re: Help !! Volvo 3.0 Exhaust Riser Overheats

What is the purpose of the 1/2" ID hose that runs from the base of the riser to exhaust pipe? Is it to help supply extra cooling water to the exhaust pipe? The 1/2" hose has plenty of water flow when I remove it from the exhaust pipe.

 

[Don S]

Re: Help !! Volvo 3.0 Exhaust Riser Overheats

That means you have plenty of water getting to the riser, just not going through it.
The riser is plugged up inside where you can't see it.

 

[skymech]

Re: Help !! Volvo 3.0 Exhaust Riser Overheats

I believe that I found the problem with the exhaust riser overheating. I pulled the Allen plug out of the top of the thermostat housing and found that the bypass hole in the housing was 60-70% blocked with a piece of loose "slag" that appears to have come from the casting process when either the head or the thermostat housing was manufactured. It must have come loose/ broke off and ended up blocking off part of the opening. One other interesting thing that I noticed, while running on muffs, is that the hose between the thermostat housing and the recirculating pump is no longer pressurized, it is firm but not pressurized. It all makes sense now with the symptoms that I was seeing. At low power there was sufficient water supply to keep the manifold and riser cool, but at high power the water supply wasn't adequate. The true test will be on the lake. I am hoping to get out tomorrow and try it out! I will report back with findings, as I find it sometimes frustrating reading through the forums and the OP doesn't post what actually fixed his problem. Thanks for your help everyone, especially Don S.