Mag 350 5.7 Still overheating

[Justin Snow]

Hello, I have an 03 Regal 2665 with a 06 350 Mag 5.7 that I rebuilt with some pro help about 6 months ago. The serial number for the motor is 1A041519 . Last month I re-did the exhaust risers, manifolds and elbows after the motor started running hot. Since then it seems to have helped a great deal but recently I got another temp alarm after I got up on a plane (the temp gauge didn't indicate over heating). So I get the temp gun out and start shooting the risers, manifolds ect and see the its running around 170 on the manifolds and MUCH cooler at the elbows... there was a few spots here and there on the manifold that crept up to 195 momentarily but seemed to cool right down if I held the gun there for a few seconds. I ended up unplugging the sensor because the beeping was annoying and started heading in while monitoring with the temp gun. I talked it over with a pro mechanic friend of mine and he says it might be the sensor on the thermostat housing. Has anyone seen this before? Not sure why it runs so hot on those spots on the manifold but when I shoot the thermo housing right after it seemed to be around 150ish if i remember correctly. Is it a bad sensor or is she running too hot somewhere. How can I cool it down if need be?

 

[alldodge]

Thanks for the SN
If the alarm goes off but its not overheating, then its the sensor. The sensor is on the thermostat housing, and the other side is the temp sender for the helm gauge. It doesn't know how hot the mans or risers are

 

[kenny nunez]

Does your boat have a water pressure gauge? If it turns out that the engine is really overheating. And your drive is a Bravo, may have a case of Bravoitis. There probably is a restriction in the water supply line between the intake on the drive and the transom plate. Does the exhaust exit through the drive?
Hopefully it just may be what AD is describing.

 

[Fun Times]

With this design exhaust system 195ish temp readings at the lower sections of the manifolds aren't too unusual to see with a temp gun honestly.

That mentioned I'll bring up that in the past some have brought up running hotter type issues due to sticking check ball valves at the lower side the of the exhaust water hose connections which is item number 10 (8-11) which you ought to have seen in the following parts link, https://www.mercruiserparts.com/bam/subassembly/31751/12840/170

What gauging system seem to be indicating an over heat situation? Smart Craft icon symbol? or?

 

[Justin Snow]

Just had her out and she was running much better. I did get an alarm after running for about 4 hours but no high temp on the dash. I did notice that the oil pressure gauge was reading low.. between 10-0 but I'm pretty sure the gauge is messed up because it sits well below zero when the key is off. the alarm was a constant tone. Not intermittent. As soon as I shifted to neutral it stopped. Temp dropped on the dash to 130ish. Im thinking its a malfunctioning temp sensor but I googled it and Ive heard its possible it could be an oil pressure thing. Maybe the engine bearings? Any tricks to isolate the systems?

 

[Justin Snow]

Does your boat have a water pressure gauge? If it turns out that the engine is really overheating. And your drive is a Bravo, may have a case of Bravoitis. There probably is a restriction in the water supply line between the intake on the drive and the transom plate. Does the exhaust exit through the drive?
Hopefully it just may be what AD is describing.

No it doesn't have a water pressure gauge but I do inspect the leg for proper exhaust water flow at wash down. I get what seems to be really good flow. It doesn't take long to cool the engine raw water down on the hose. I think its either thermo sensors or oil pressure.

 

[alldodge]

Things give you a constant alarm, over heat, low oil pressure and drive lube low, over speed and sea water pressure low.

Over speed happens when the motor thinks its in neutral and rpms exceed 2500. The in-gear switch is on the shift plate

The most common problem is the sea water pressure sensor. Its located on the power steering cooler (item 16). Best way to know if this is causing the issue is with a scanner

https://www.mercruiserparts.com/bam/subassembly/31751/12840/280