7.4 liter bravo 1 overheat

[wannablast]

I have a 7.4 liter with a bravo 1 that is NOT pulling water to the raw water pump. I always remove the impeller when I winterize and put it back in or a new one if the old one isn't in good shape the following spring. This year it ran for about 15 minutes and then it quit "spitting" water out of the thru hull exhaust for a minute or so and then started spitting again. It then quit spitting and the temp climbed to 200 deg and I shut it down. I pulled the impeller and it was trashed. ( I found all the broken pieces from the impeller.) I replaced it with a new one and it ran fine for about 30 minutes in the driveway with the muffs on. I shut it off and took the boat to the lake the following weekend. I unloaded and as I idled out I looked at the temp gauge and it was climbing above the normal 140-160 deg all the way up to 200 deg and I shut it off and dropped anchor. I took the boat back home and when I pulled the impeller all the vanes had split but didn't separate so they are all accounted for. I removed the engine water pump and pulled the back plate and the vanes look fine on it too. I looked at another bravo drive to make sure I didn't hook the raw water supply hose up wrong and I didn't. I ran water through the raw water supply hose and it pours out of the lower unit. I've done this for about 12 springs with no problems. What next?

Thanks
JT

 

[HT32BSX115]

Re: 7.4 liter bravo 1 overheat

Howdy,


You may have impeller fragments in your oil and/or power steering cooler so tightly packed that they're not allowing water to flow to the t-stat housing.

Follow the hose from your raw pump to the oil coolers and then up to the t-stat housing.

Disconnect the hose from the housing and see how much water flow you have when operating at idle so you can verify that you have flow from the pump.

Do this when the boat is in the water. If you connect a clear piece of hose to the one you disconnect from t-stat housing you can also look for air bubbles too.

You have a sea-water strainer? If you do, you could have a leak that allows air in the system. (although if you do, it should leak if it's below the water line when the engine is off)

If you have good Flow though the oil coolers, you could have blockage in the t-stat housing, block, heads, manifolds, risers, etc.....

 

[wannablast]

Re: 7.4 liter bravo 1 overheat

All impeller vanes have been accounted for. I ran water under pressure back through the oil cooler and it flowed out of the hose from the raw water pump. I put water under pressure into raw water supply hose from lower unit and it flowed out through the holes in the lower unit. I thought I had put the impellers in backwards but I checked rotation of the engine and that was correct also. One of my initial suspicions was that a rodent had nested in a hose over the winter but I don't think that is the case. By the process of elimination I will get it soon. I removed the thermostat and will replace that. I may just go ahead and get an engine circulation pump also. It looks fine though. I hate to was the $ for a marine pump, $120+.