New rebuild 454 Gen VI L29 running hot
 

Hey guys,
Still trying to work out a last issue on my rebuild. The motor is running perfectly with 60 psi oil pressure. The issue I'm having is the motor is going between 215 and 210. It's acting like a thermostat is opening at 215 and dropping it to 210. It seems pretty consistent, but I didn't want to run it long at those temps. This is the same on the water or on the hose. I've attached a video below of how it's running on the hose. You can see it's flowing plenty of water. My guess is that there is something up with my new FWC system. It's the Monitor mfh-5374. I bought it through PPT, but they haven't responded to my email yet.
Things I've checked.
- FWC System is new on a newly rebuilt 454 L29 carb'd. Exhaust is all newish and clean. Brand new transom assembly. New raw water impeller.
- Laser Thermometer: Risers, cool to the touch. Thermostat housing, water cross over on intake and heat exchanger all about 207 after I shut it down.
- Pulled the thermostat and tested it on the stove. Seems to be ok. ~165 starts to open. 180 fully open.
- Plenty of A/F. Had to drain some to take the thermostat out.
- Checked the hose routing multiple times.
- L29 heads on an L29 block. Gen 6 head gaskets.

One question on my mind is the factory bypass hose. Supposedly you shouldn't need it, so I replaced the nipples with plugs on the intake and water pump.
Last thing, I believe I'm having carb issues. I can't get up on plane. Runs perfectly with plenty of power up to about 2,800 and then goes flat and loses power until I back off the throttle. Carb was supposed to have been rebuilt, but I don't know any more about it than what the PO said. It's shiny black... I'm thinking I might pull it and rebuild it again myself.

Do you have one of those brass nipples on the thermostat housing (close to the sending unit) that lets you bleed any air out of it ?

Oh , I had carb issues once too and got a supposed 'factory re-built' sent . It was shiny black too and just as foxxed as the original which was still clean and shiny.

No air bleed. Thinking a possible air pocket? Maybe. I wonder if blocking off the factory bypass might have caused an issue. Doesn't seem like it, but I think I'll throw it back on for S&Gs. Redundant, but I can't see where it would hurt. I'll pull the carb and tear into it this weekend. I don't think the two issues are related though.

Any ideas that I could look into?

Lean running is hot running. Your dropoff in power could easily be a lean condition. Hotter combustion = hotter coolant.

Good possibility. The carb is definitely an unknown right now. I'll pull a couple plugs and take a look. It's doing it at idle also. I'm not hearing any detonation, but that doesn't mean it's not happening. Thanks.

Clear tubing (hardware store) between raw water pump and thermostat housing

Would I be looking for solid flow with that? To confirm no air is getting in?

Looking for air
Suggest placing in the water and install tubing. Run and see if air is seen
Hose can only supply so much water, and don't know how your local system is

Sounds good. I had it out on the river also. Same thing as on the hose. I'll add the tubing when I rebuild the carb next week. I just ordered a rebuild kit. Thanks.