Engine overheating

[Roc]

Vaseline is petroleum based, so cooking oil is better.

[Steve W10]

Good insights guys, here's Steve's 2 cents...

When I first start my engine, likely as most do, I check two things, oil pressure and that I've got water coming out the exhaust.  As you know, if no water, the water intake valve is either off or clogged or the impeller is toast.  I lost 2 old-stock impellers this year; they were spares that were more than a few years old so I'm sure they were too stiff.  One spun on the shaft and on the other, the fingers all broke off.
If there is water coming out of the exhaust I think Stu is bang-on, burping is required (or you are very, very low on coolant).

After replacing both the temperature gauge and thermostat this year (when I added my over-temp warning system) I noticed that the two gauges read differently and I don't think that is unusual.  I believe it was a 10-15 degree difference with the new one likely closest as I compared the readings with each thermostat (a 160 and a 180 degree).  I don't rely on the gauge to be 100% accurate, because everything is relative anyway.  My point is merely that if you change anything in the system, calibration may be slightly different.

Fins on the impeller. Since I got my boat I've struggled with this.  I've always made a point to put them in correctly (I drew an arrow on my crankcase pulley for rotation direction and agree totally with Ron in reply #10).  90% of the time when I pull the cover off my Sherwood, one or more fins are bass-ackward.  Steve's conclusion... as I shut down the engine, it comes to a stop with at least one cylinder approaching TDC of its compression stroke and the engine slips backward just a bit thereby pushing fins against the eccentric piece and bending them in the wrong direction.  ??? who knows for sure and as long as it works I've decided to not lose any more sleep over it.
I also do very much like in Reply #6+, only I use Vaseline, put it in a zip lock bag, and take it home.

[Kyle Ewing]

Another thing to check is the wiring.  In my case tightening the connections at the terminal strip by the engine (strip courtesy of the wiring harness upgrade 9+ years ago when I purchased Donnybrook) fixed my "overheating" problem.

Symptoms:  My engine normally runs at 160-165 degrees.  I noticed it would slowly creep up to 175, then 180.  I looked at everything in the cooling system described here but couldn't find a problem.  Finally out of desperation I tightened the screws on the strip--some were pretty loose--and immediately the temperature stabilized at 160-165.  I theorize that there was slight resistance by the bad connection which increased as the engine compartment heated up.

[Ken Juul]

Those of you with Oberdorfer pumps can see for yourself if the vanes self align.  Stuff the impeller into the housing anyway you can. Before you put on the face plate, hand turn the engine watching the impeller.  The vanes should self align during the first revolution of the pump.

[Ron Hill]

Steve : What you want to do with your impellers is to spray them with silicone to keep them nimble. 

I take the spares, spray them silicone and put them in a ziplock bag until they are needed. 
At the end of the year I remove the impeller and inspect each blade by bending it.  If I see a crack at the hub "it's toast".  If all is OK I'll reverse it on the shaft and give it another year. 

Maybe it's luck, but in 25 seasons I've only lost 1 impeller.