454 Magnum thermostat question

[Trips]

Hi, I have a Mercruiser 454 Magnum/Bravo I (0F352752)and it was starting to run hot so instead of pulling it out of the water, I had my marina take a look and they replaced the thermostat and raw water impeller/housing. Ran great for a couple hours with perfect operating temp. I went back to the boat a few days later and took it out and it immediately began to run hot at higher RPMs and when I went to 3,000, the temp spiked and the alarm came on. Dropped back to idle, temp came back down and I limped home. My water pump hose out of the thermostat was very hot, the fresh waster hose was cool as well as the manifold hoses. Sure looked like a thermostat issue so I bought a new one and replaced it. The one I took out that the marina put in was a 140, and I believe that Magnum uses a 160. I installed a 160 and took the boat out and the temp is proper again. My question, is this just a case of a defective thermostat stuck closed? Was the 140 damage somehow by the 454 Magnum that is designed to use a 160? Is there a potential lurking issue that might cause my 160 to fail quickly?

 

[tpenfield]

Could be marine growth getting clogged in the oil cooler which is in line between the sea water pump and the thermostat. Every time you open up the cooling system it has the chance to back flush a little. You can always test the thermostats to be sure they are opening, etc.

 

[Tail_Gunner]

Could be marine growth getting clogged in the oil cooler which is in line between the sea water pump and the thermostat. Every time you open up the cooling system it has the chance to back flush a little. You can always test the thermostats to be sure they are opening, etc.

Your cooling is not working properly.....A 140 degree thermostat is needed ......water hose coming thru the transom assembly starts to collapse from corrosion know condtion for bravo's.....Bravos pumps are also known to go easy...check the oil cooler's for debris.

This is rather important in a 454 it keeps down the oil temp, remember it may run 400 hp but the tourqe it produce is huge there not like a 350 and under

 

[Trips]

Update: Confirmed that 160 thermostat is correct for Gen V 454 Magnum. Block as well as intake hose had been back-flushed by marina but I did again just for fun. Ran up to operating temp at dock and temp gauge hovered around 160 at around 3k RPM's. Checked fresh water hose at thermostat housing and started to remove-great pressure/flow. Went out to sea trial and ran hard, temp never spiked.