Volvo Penta 5.0 GXI Exhaust riser won't come up to temp

[SeaTroll]

I'm hoping someone has seen this as I'm pulling hair out. I have a 2011 Regal 2000 with Volvo Penta multi port injection and catalyst manifolds. Everyone has overheating issues but not me. My manifolds run 115-120 on the hose. My port riser runs 105-110. Starboard runs 85-91 so I keep getting o2 bank 2 sensor 2 voltage low. All o2 sensors read 1244 millivolt when first starting but then start reading normal when the temp sensors sees engine has warmed, all except bank 2 sensor 2. Each exhaust manifold has a seperate thermostat (22643083) controlling flow, installed new one but no change. Also changed engine thermostat even though gauge runs 175 pretty consistent. I have confirmed the temp with ir gun. If you run it and shut it down the temp comes up to same temp as manifold. Start engine and it immediately starts dropping. You can hold your hand on the riser and feel it getting cold as water pump circulates. I thought the manifold thermostat was stuck open and changing it would fix it but no change.

 

[Bondo]

My manifolds run 115-120 on the hose.

Ayuh,......... Welcome Aboard,...... So what does it do, running with a load, on the water,..??..??

 

[SeaTroll]

Ayuh,......... Welcome Aboard,...... So what does it do, running with a load, on the water,..??..??

Thank you. The temps do all come up about 10-12 degrees at the lake under load and come back down when off load like normal. The one riser is still below normal operating temp and will set code, single beep audible alarm at about 2 min constant run under load. It does the same thing with Rinda TechMate on the o2 sensor test. Right at 2 min it codes.

 

[ESGWheel]

Just a thought: it’s possible (but not probable) that even a new t-stat is bad (in your case opening too soon). You could swap them and see if the issue follows the new t-stat. If not at least that is ruled out and back to what the heck!

 

[Thalasso]

Could be the sensors on the risers. Any codes?
Have you tried ohming out the sensors for comparison.
There is a upgraded one.

This look like yours. (borrowed from another person diff site)

 

[SeaTroll]

Just a thought: it’s possible (but not probable) that even a new t-stat is bad (in your case opening too soon). You could swap them and see if the issue follows the new t-stat. If not at least that is ruled out and back to what the heck!

Could be the sensors on the risers. Any codes?
Have you tried ohming out the sensors for comparison.
There is a upgraded one.

This look like yours. (borrowed from another person diff site)

Yes I ohmed the sensors, they all read the same when engine is cold. Changed sensor with the other side. Sensors are reading correct as the Rindo reads same as thermal temp gun. Code is SPN=3266 exhaust 2, o2 sensor 2 voltage low/below normal operating voltage.