Overheating - 5.7 EFI Mercruiser w/Bravo 3

[kfm]

I have a 2000 Chaparral 230SSI with a 5.7L EFI and Bravo 3 stern drive. The first time in the water this year, it overheated and the alarm sounded while idling at the dock. I stopped the engine and took it out of the water and did the following:

- Impeller in the sea water pump had 2 of the "paddles" broken off, but they were lodged in the sea water pump housing. I replaced the impeller and got as much of the smaller pieces out of the hoses that I could find.

- After starting the engine with the new impeller, I noticed that the circulating pump was leaking through the weep-hole. Also, the temperature gauge would move steadily from approx 160 degrees to approximately 200 degrees, and then move steadily back to approximately 160 degrees. This cycle was continuous. I replaced the circulating pump and thermostat. (The thermostat is in the proper position.)

Now when I take the boat out, the engine does not overheat to the point that the alarm sounds, but the temperature gauge still constantly cycles between approximately 160 and 200 degrees. The gauge moves steadily from 160 to 200, and then quickly comes back down after reaching 200, and the cycle continues.

Has anyone had this problem, or are there suggestions as to what I could try next?

 

[TilliamWe]

Re: Overheating - 5.7 EFI Mercruiser w/Bravo 3

Never had that, no. i susp[ect you didn't get all the pieces of the old impeller out of the system. When my B3 in a 5.7EFI puked, I found one whole vane in the thrmostat housing itself! You have to backflush the ENTIRE system from the thermostat housing all the way to the raw water pump.

Are you sure the thermostat is in right? That plastic collar thing seems backwards to me, and you HAVE TO get it right or you have trouble.

 

[kfm]

Re: Overheating - 5.7 EFI Mercruiser w/Bravo 3

I was very careful to get the thermostat back in correctly. I don't like the design with the plastic sleeve, but they didn't ask me. I put a new sleeve in as well.

I did not backflush the system... I just loosened the hose clamps and drained the water at each juncture. I checked the manual and didn't see anything about backflushing. Any tips on how to do this? Is there an attachment or kit to use for this, or do you just spray water through the hoses?

 

[TilliamWe]

Re: Overheating - 5.7 EFI Mercruiser w/Bravo 3

Spray lots of water, at a good hard pressure through the hoses.