Emergency Engine Start
- Thread starter FlyingAloha
- Start date
Please note that there is a significant difference between operating an impellor pump dry, and operating it with the input seacock closed. A dry pump has no water in it. The rubber impellor rubs against the metal pump housing generating heat and is soon destroyed.
With the seacock closed, the impellor blades are unable to straighten out as they come off the cam because there is no input water (or air) to fill in behind them. So they freely spin around to the outlet side of the pump where they are squeezed by the cam again. There is still water in the pump to lubricate and cool any rubber to metal contact. Very little damage is done to the pump, and it takes quite a while (10s of minutes) for the engine to get hot enough to cause any damage from lack of cooling water.
With the seacock closed, the impellor blades are unable to straighten out as they come off the cam because there is no input water (or air) to fill in behind them. So they freely spin around to the outlet side of the pump where they are squeezed by the cam again. There is still water in the pump to lubricate and cool any rubber to metal contact. Very little damage is done to the pump, and it takes quite a while (10s of minutes) for the engine to get hot enough to cause any damage from lack of cooling water.
Over 5 decades of 'messin' about on boats of all sorts professionally and for fun, and two, unlimited hp steam/diesel chief engineer's licenses and this is a new one on me. I'm not saying you are wrong, just that this is the first I've heard of this.
So....
Just back from the boat.
ZERO damage to the impeller.
Took off the cap on the heat exchanger. There was 1 semi dirty hole. I really think my problem is that crazy cranked Coolant hose.
Will replace hose tomorrow and see what happens.
But you did change it out, just on principle, since you already had the impeller out, right?
no i did not. inspected it. was a obvious it was recently changed. It looked new. I changed the seal on the exchanger
I've got a 4 cyl Yanmar and attended a 3 day factory diesel training session. Each of our engines were mounted on pallets with the exhaust ported outside. The tech usually had each one running one at a time for up to what seemed to be 10 minutes without any coolant entering/exiting the exchanger. I'm sure they removed the impeller but we were told that diesels don't heat up quickly and it wasn't ruining the engine.
It's important to replace the impeller at least every other year if seasonal like we have in the Northern Great Lakes. Annually if longer than 5 month seasons. Buy a quality OEM impeller and not a cheaper looking one. You get what you pay for and it's not worth taking a chance.
A ruined impeller can cause more problems than just leaving pieces in the exchanger intake. The high temperatures will delaminate the coating in the exhaust hose leaving the engine connecting to the muffler. That delamination will begin internally peeling away a coating and randomly blocking exhaust and water causing engine back pressure and a new strange noise no boater ever wants to hear which is usually scheduled during most difficult navigational adventures. I've experienced all the above adventures and am pleased to share them all with you for your avoidance pleasure.
It's important to replace the impeller at least every other year if seasonal like we have in the Northern Great Lakes. Annually if longer than 5 month seasons. Buy a quality OEM impeller and not a cheaper looking one. You get what you pay for and it's not worth taking a chance.
A ruined impeller can cause more problems than just leaving pieces in the exchanger intake. The high temperatures will delaminate the coating in the exhaust hose leaving the engine connecting to the muffler. That delamination will begin internally peeling away a coating and randomly blocking exhaust and water causing engine back pressure and a new strange noise no boater ever wants to hear which is usually scheduled during most difficult navigational adventures. I've experienced all the above adventures and am pleased to share them all with you for your avoidance pleasure.
on the yans there is an oil cooler feed hose which is pretty fragile and can overheat in a situation such as you describe. to be on the safe side order an extra one of these for your spares kit.. check your parts maual, this is a formed hose, one end is bigger than the other and you cannot gin up a replacement. i had a similar overheat situation on my yan engine where ONE overheat which i caught pretty soon was caused by loss of antifreeze thru the antifreeze lines to the hot water tank leaking. after letting the engine cool, topping up antifreeze and a temporary patch job, everything looked ok . but a week later i noticed drips under the formed hose to the oil cooler.. which hose took a week to get from my yan dealer..