New Engine Overheating (Strange situation)

IRDaleBracey

IRDaleBracey

New Member
Sep 20, 2020
27
San Antonio, TX
Boat Info
280 Sundancer 2005, Twin Mercruiser 305
Engines
Twin Mercruiser 305
Howdy... My friend Phil is usually the one posting here, but here I am with all the details.
We finally finished dropping in the two new engines (previous owner didn't winterize before the big freeze). A bit perplexed at the simplest of things...

Here's the scene...
2003 Sundancer with dual 305 Mercruiser TBI Bravo
Boat been sitting for three years. Had some stabilizer. Fuel not pumped out; used this fuel.

Port engine fired right up and flows water with muffs just fine. So, we can determine the fuel is ok and not too far gone. (Stabilizer did its job?)

Starboard engine was at first struggling to start. Replaced water separator and pre-filled it with new fuel and some stabilizer/cleaner. Still rough to start, but eventually it fired up. Muffs were on and flowing water into sterndrive. ENGINE STARTED TO GET HOT and hit the alert beep. Shut it off, and checked things after it cooled off. Took seawater pump apart; rubber impeller was TRASHED. Missing pieces and cracked. Dry as a bone too. So, obviously, it didn't get any water to cool/lubricate it. Hmmm... Bought a new impeller and installed with some soapy water to pre-lube; noting to twist the flaps for clockwise rotation with the crank. Fired her up again... overheated again. Pull pump apart again; same deal. Dry and shredded.

Now... here's the weird bits. I 3D printed an adapter to shoot water and air pressure into the lines to try and blow things out...
  • Shot from seawater pump inlet hose out the outboard inlets (water flowed)
  • Shot from before check valve, through fuel cooler, through hydraulic cooler, and out the seawater pump outlet hose into the bilge (water flowed)
  • Shot water through both exhaust riders and out the rear (water flowed)
Things replaced
  • circulation pump replaced
  • seawater pump impeller replaced (twice)
  • thermostat replace (with 160F same)
The thing still wants to overheat and it doesn't appear to be flowing up to the thermostat housing while running. (Disconnected hose before thermostat housing to see if seawater pump was pushing up there; nothing/dry.
Completely at a loss... it's such a simple system, and we've blown backward everywhere to make sure there is nothing in there. And yes, we did initially find bits of rubber in the check valve; that was removed too.

Anyone ever experience this? Have any strange thoughts on things to check, that I may be overlooking?

Most appreciated.
 
Are the hoses new? May be collapsing under suction?
 
Golfman25 said:
Are the hoses new? May be collapsing under suction?
Click to expand...
Hmmm... nope, Old. Good point. I assume the only hose that could get suction is the one between stern and pump inlet. All others would be positive pressure lines?
"Good thing" this is the hose under all the power steering hardware and is "so easy to access" now that the engine is back in. ;)

It's a wire reinforced hose though... guessing the inside can still collapse.
 
Disconnect the raw water pump inlet hose. Set up the muffs and flow water. Report back with results.
 
On the first start you said "Muffs were on and flowing water into sterndrive. ENGINE STARTED TO GET HOT " but was water/exhaust flowing back out? If No I am curious why you did not shut it down then.

If you have confirmed water is coming into the engine mounted raw water pump but water is not coming out, I'd replace the pump at this point.
 
mrsrobinson said:
On the first start you said "Muffs were on and flowing water into sterndrive. ENGINE STARTED TO GET HOT " but was water/exhaust flowing back out? If No I am curious why you did not shut it down then.

If you have confirmed water is coming into the engine mounted raw water pump but water is not coming out, I'd replace the pump at this point.
Click to expand...
Lapse in judgement and focused on everything else. It wasn't something we were looking for at first. The getting hot is what started us tracking all this down. THEN we noticed no water.
 
IRDaleBracey said:
Lapse in judgement and focused on everything else. It wasn't something we were looking for at first. The getting hot is what started us tracking all this down. THEN we noticed no water.
Click to expand...
Right but if I understand you correctly you did it again a second time. Just trying to figure out what I'm missing.
 
Definitely put on the muffs turn on the hose see if water is getting to the pump
 
IRDaleBracey said:
Hmmm... nope, Old. Good point. I assume the only hose that could get suction is the one between stern and pump inlet. All others would be positive pressure lines?
"Good thing" this is the hose under all the power steering hardware and is "so easy to access" now that the engine is back in. ;)

It's a wire reinforced hose though... guessing the inside can still collapse.
Click to expand...
Yes, the inside has been reported to collapse. Everything looks normal from the outside. If you're not getting water to the pump (and thus burning up impellers), and everything else checks out I'd replace the hose.
 
Golfman25 said:
Yes, the inside has been reported to collapse. Everything looks normal from the outside. If you're not getting water to the pump (and thus burning up impellers), and everything else checks out I'd replace the hose.
Click to expand...
Pulled hose just now... looks normal inside and out... maybe it is still weak enough to collapse under vac I guess... going to weasel my arms back in there and try again with the new hose. Thanks.
 
scoflaw said:
Volume matters check for bravoitis
Click to expand...
Mine looked like this… As other mentioned if it were me I would try the garden hose into the pump infeed hose. You should see water in seconds coming out the transom. I would time it so I run the motor and hose at the same time.
58060841727__22A746F8-7C0C-4FB3-B5AA-1C071A3E76F3.jpeg
 
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