Overheat issue…maybe
 

I switched from OMC to Bravo over the winter & now seem to have an overheating issue. With the OMC, the motor would rarely see 135 degrees. After the first run this season with the bravo it ran about that for most of the day but then progressively got hotter & hotter…pegging the needle @ 240. You can put your hand on the exhaust & it feels cool. The motor is hotter but I wouldn’t say its anywhere near 240. I thought it was the thermostat so I drilled some holes in it. No difference. I then replaced the thermostat & then the sender too. The motor now will run @ 160 but will climb up to 200 when tubing or running hard. If I let it idle the temp will come back down to 160 & stay. Last night I checked the impellor, its flexible & fine. I also back flushed the oil cooler & power steering cooler & I didn’t notice any sediment. I haven’t run the motor yet but don’t feel like I’ve solved this? Should I drill 4ea holes in the new thermostat? I’m not running a cross over. Any suggestion?

You sure you have the correct hose on the intake of the sea water pump?

The intake hose is not factory merc hose but is a high quality fiber wrapped suction hose so it shouldn’t be collapsing.

Partially plugged intake ports or low water pick-ups? Is it ok the blow compressed air into them?

Now worried about the hose collasaping just want to make sure the intake side is the intake so its not backwards,

The intake is on top of the sea water pump. Wouldn't it not pump any water if it was reversed? Yesterday the temp would climb to 240 @ idle & then drop back to 160 when running hard. Completely opposite of what it was doing the other day?

I'm now thinking it may be a ground issue. The horn, blower & beilge pump don't work. These things do work when I bypass the wire harness. The fuses are fine & there is power to the switches. I'll look for lose ground wires unless I'm off base on this thought?

Check to make sure the temp gauge is grounded to a good ground. A weak or loss of ground to the gauge can cause high temp readings.

Looks like most of this is a weak ground issue but the temp does climb still @ idle. The guage will peg @ 240 but the thermometer gun says its closer to 190. The temp will drop back to 160 once under way.

I'm now second guessing the intake hose thinking it may be too big? Its a clear 1.1/8" fiber reinforced hose. Is the factory hose 1" with flaired ends? If you hold the hose @ idle there doesn't seem to be a lot of volume going through it.

The bravo pulls through a 1 1/4 inch hose that goes to the transom, then pulls through about a 3/4 ID hose to the drive. It creates alot of suction pressure in that system. Not sure where you got that hose, or what type it is, but it sounds like hose you can get at the hardware store that is really meant for pressure, not suction. I'd think it isn't able to handle the suction, but maybe I'm not understanding the hose you have. Mine has a hardwall hose with wire reinforcement. You can't collapse it with your hand. Even with large pliers would be tough.

The othe possibility is a curse of bravos - corrosion collapses the ends of the hose between the drive & transom, resulting in low flow. I've heard it called Bravo fever.

I know you checked the impeller, but did you confirm oil and water flow?


Russ

The OMC power steering & oil cooler are bigger than the single merc combo cooler off the 330hp motors so I'm still using the OMC coolers so the oil flow hasn't changed. I also replaced the impellor & housing just to rule it out... no change. I have the intake hose from the transom going to the top port on the sea pump & the lower port connected to the coolers/engine. This is a v belt drive sea pump so I believe this is the correct flow? Wouldn't it not cool the motor @ all if it was hooked up backwards?

Do I need to remove the drive to check for the "Bravo Fever" mentioned? Can someone walk me through how to check this.

If it hit 240 as many times as you said it did it would not be still running . I would put a 140 stat in it and start looking for a ground problem . just my .02 worth

Try flshing water from the inlet hose of the raw water pump out the drive. If you can't get good flow, then yes, you'll need to statr working on the drive portion. It can corrode & collapse at the transom or the belhousing connection.

The other possibility is that the hose between the transom & bellhousing is collapsing under suction. I've heard about that one.

But, before I started disassembling anything, I'd fix the electrical issue to make sure I knew what the temp was at all times.

What i was trying to say was check the incoming water volume coming into the cooler (apollard basically said it too) so I would dump it in a 5 gallon bucket and see how long it takes to fill up and garden hose or otherwise cool the system while you're testing. Those pumps should easily hit 20 gals per min. They're designed for 27 if my memory serves.

Russ

Still chasing this problem. Spliced into the wire harness & installed another jumper from the ground wire directly to the battery….no difference. The temp sender does have a sealent on the threads. Should I clean that stuff off & try it without any. Maybe that’s not allowing it to ground properly.

I ran water from the intake back out the transom / drive & the flow seems normal. I haven’t tried filling the 5 gallon bucket yet. I did have a inline hose adapter in that intake hose & wonder if its leaking & allowing loss of suction. I ordered a merc intake hose & will leave that adapter out & try it again.

The seapump is used primarily for cooling when the boat is idling or moving slow. At planing speeds water is forced throught the system by the movement of the boat. It sounds like a bad seapump to me.

That fricken hose adapter was causing the higher temps @ idle. Removed the swival for the hose & installed a plug, problem solved.