Hot riser temp

[Knottyd]

I'm new to the forum so please bear with me. I have a 2000, 5.0GL Volvo Penta. I'm diligent about maintainence with my boat so for PM purposes I replaced exhaust manifolds and risers, it was about 7 years since it was done. New raw water pump last year but replaced impeller this year due to my problem. I replaced thermostats, checked thermostat housing for restrictions. Pulled intake hoses off and checked those. I pulled out drive off and back flushed hole system. Water flow seemed fine. I ran engine on muffs and in the water. The temperature at the bottom of the riser runs about 115-120, front of riser a little higher, but at top back part of the riser runs about 150-165. This seems way too hot. The engine temp is normal. I checked all this with a laser. I don't know what else to try. A marine mechanic said it it's just how it's going to run?? Sorry this was so long, just wanted to tell all details.
I would appreciate any input.

 

[Scott Danforth]

Pull riser and check for rust flakes

 

[bruceb58]

Those temps seem normal.

You run in salt water?

 

[Knottyd]

I talked with tech service at Sierra and they sent me out a set of new risers and gaskets. Nice people to deal with. I replaced the risers again with the same results.
There was no rust flakes anywhere. The whole system has been flushed out several times.
I do run it in salt water but flush after each use. Thanks

 

[bruceb58]

Have a picture looking down onto the manifolds by chance when you had the risers off?

BTW...I installed the Volvo NeutraSalt system on my boat. I use it even if I am going to flush the motor. I run the system before I take it out of the water and after I flush so that the neutrasalt solution stays in the block and manifolds.

 

[Knottyd]

I'm sorry I don't. But the risers and manifolds are brand new. Second set was put in yesterday.

 

[bruceb58]

I think you are fine. The back part of the riser is where the exhaust and the water mix and is going to be the hottest part of the exhaust.

 

[Knottyd]

I will try it tomorrow, thanks