5.0L MPI running cold

Her Diamond 2

Member
Jan 3, 2010
77
Midland, Ontario, Canada
Boat Info
2004 300 Sundancer
Engines
5.0L MPI - 260HP - Bravo 3
I have twin 5.0L MPI engines. Normally both engines runs at 150 degrees at idle and 160 degrees while running on plane. The port engine is now running cold 120-130 degrees when not on plane. When on plane it very slowly increqdes to 160 and falls quickly when throttles are backed off. The thermostat was changed and the problem persists. The connection into the thermostat housing looks ok. I'm thinking it may be the thermostat sensor. Has anyone else experienced this?
Thanks
 
Sounds like the thermostat might be stuck open to some degree.
 
Sounds like am open/partially open thermostat to me too but I'm no mechanic.

On a different but related question (trying not to hijack thread), if you have smartcraft gauges, can you look and see if both engines run with the same water PSI or if one is half the other? Take a look while idle and also while on plane. Mine run the same, but a friend's run differently. One runs up around 18psi on plane, the other runs around 9, but the temperature stays steady and approximately the same on both engines. The one that runs with lower water pressure is the side with the hot water heater that's heated by engine water exhaust. Wondering if that's the difference or if they should be the same.


Thanks
James
 
Sounds like am open/partially open thermostat to me too but I'm no mechanic.

On a different but related question (trying not to hijack thread), if you have smartcraft gauges, can you look and see if both engines run with the same water PSI or if one is half the other? Take a look while idle and also while on plane. Mine run the same, but a friend's run differently. One runs up around 18psi on plane, the other runs around 9, but the temperature stays steady and approximately the same on both engines. The one that runs with lower water pressure is the side with the hot water heater that's heated by engine water exhaust. Wondering if that's the difference or if they should be the same.


Thanks
James
 
JimFromMD, I do have smart craft gauges and will Check the readings. I'll be out of WiFi and cell range for the balance of the week but will get back to you later in the week.

The thermostat was my first guess. Both were changed a few years ago and the problem persisted intermittently. Maybe once or twice a season. Mechanic told me not to worry about it. Better running cold than hot. Typically the problem would go away after getting back on plane but this time it's not going away. For the price of a thermostat I'll likely change it but it seems like something deeper.
 

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