5.0L Injected O/Heat problem - lost need help

[Andrew skier]

Hi all , question from Sydney AU
I have a 2006 bayliner with 5.0L injected mercruiser and Alpha 1 gen 2 leg .
was parked up due to covid and is back on the water today after engine oil change , impeller change and gear lube change .
in the water it comes up to temp and then the temp climbs and climbs - till temp alarm at 200 degrees and even limp mode
Let it sit and cool down etc finally back to dock and onto trailer
Normally temp sits at 175 and hardly moves

Start motor on trailer with leg in huge bucket so it has to draw water itself ( no hose / earmuffs pressure )
pumps heaps of water out transom plate holes and still temp climbs and climbs ....
suspect thermostat playing up
Remove and chuck in pot on stove - opens well before water boils , closes when out , reopens in hot water again
suspect i have put impeller in ass about ..
Drop bottom off leg and check impeller , all good right way in -
speak to local dealer ...
Remove rest of leg and just leave transom plate on so can start engine ( ive split leg so gear oil is out )
Jam hose directly into transom plate to eliminate any leg / impeller issues
thermostat back in - temp still climbs
thermostat out - temp still climbs
thermostat housing feels very hot - and as temp alarm and temp guage are on different senders trust they are reading correctly
Still lots of flow of water through engine and out transom plate
remove engine circulation pump and check - all good no cracks , busted vanes etc
Exhaust manifolds and risers done 3 years ago
No rust etc on impeller housing when removed - so no indication of flaking stuff etc
when running engine there is hot water flowing out of the two smaller outlets of the thermostat housing
Have removed bottom hose where water feeds up to engine water pump (from steering oil cooler etc ) water flows freely from transom plate to water pump inlet
Not sure where to head from here ....
all the Merc guys i have spoken to are lost as well
It seems to me that the water is not getting out of the engine quickly enough .... ????
Any help appreciated

Thanks
Andrew

 

[Scott Danforth]

first, welcome aboard

second, you killed your new impeller

you can not draw water from a bucket. you need to either have your boat in a bucket large enough the whole outdrive is submerged (as in the whole boat fits in it), or you need to use muffs.

you have lack of flow in your system either incoming or outgoing. lack of flow is what causes overheating. start at the thermostat housing and work your way to the leg. you will find debris thru the system, the first place it collects is the PS cooler.

also, if your boat is a salt water boat (should be if you are in Sidney), inspect your manifolds and elbows. being a 2006 you should be due for the second set of manifolds and elbows. the excessive rusting of the channels will cause the water to exit slowly. not to mention you run the risk of engine damage from hydrolocking when the exhaust manifolds fail.

 

[Andrew skier]

Hi , thanks for the reply
but no the whole leg was in a large tub so the impeller is all good and was not run dry ( think big rectangular tub )
Will check power steer cooler in morning for debris but have good flow from transom to engine water pump in both directions
I would not have thought that manifolds and risers would need to be done again as it has been only 3 years (9 months parked up as well )and the boat is flushed and out of the water the majority of the time
Thanks

 

[Bt Doctur]

unless the water level is 4 inches above the cavitation plate,you destroyed the impeller or you missed something putting the lower back on the upper

 

[Andrew skier]

Yes , the water was well above all the inlets for the leg - its not hard to do
the impeller was inspected after running it in the giant tub and its in new condition still
Regardless of that - with the leg removed it takes all impeller , water pipe , housing wear plates etc out of the equation
the overheating issue is present in the motor not the supply from the leg

 

[Bt Doctur]

NO, not above the inlet holes ABOVE the cavitation plate

 

[Bt Doctur]

 

[Andrew skier]

Please excuse the niavity but why must it be above the Cav plate ?

 

[Bt Doctur]

because thats where the impeller is and the impeller does not really suck water, it moves water

 

[Andrew skier]

Fair call , still it managed to compensate and pumped heaps of water
Would appear that the problem looks like the bottom of the exhaust manifolds is full of crud - watert from the thermostat is simply not able to get out of the engine ( on one side at least so far )

 

[Scott Danforth]

you still toasted your impeller.