T&T: Generator overheating

[Milt Baker]

Greg,

Since the generator apparently was operating without overheating at full load before 
you blew an impeller,  I suspect Bill is on the money: you probably didn't get find 
and remove all the pieces of the old impeller downstream from the pump.  That's 
where I'd look first.

You mentioned that you have been running the genset a lot this summer and you
also mentioned running it under a battery charging load only, apparently a good bit
of the time.  You're probably aware that gensets--even late model 12kW Northern 
Lights (I have one too!)--should not be run for long periods at less than a 40% load.
Assuming that you're running it at 240 VAC, that means it should be loaded to at
least (40% x 50 amps) 20 amps for good generator health.  If you have been running 
it at less than that for long periods, it's my guess that your water injected elbow is 
carboned up and not allowing enough raw cooling water to pass to cool the engine 
under heavy load.  

How old is the genset and many hours does it have?  Another possibility is rust 
in the water injected elbow.   Rub a clean paper towel under the elbow; if it comes 
away rusty, you have a crack in the elbow.  Even if it's not leaking water now, it 
will be soon!  Although I don't use my 12 kW as much as my smaller genset, the 
original cast iron water injected elbow developed a small crack and required 
replacement at about 3 1/2 years and 800 hours.  (I think the time was more a factor 
than the hours.)  When I removed it, the rust has closed down about 30% of the 
opening, restricting the water flow.  I replaced it with a stainless steel elbow from 
Northern Lights, p/n 27-32003.  Stainless exhaust elbows are available for all late 
model NL gensets and should outlast the original cast elbows by at least two to 
one.

Good luck!

--Milt Baker, Nordhavn 47 Bluewater, Southwest Harbor, ME
 

Greg wrote:

On a Northern Lights 12 KW
I have been running the genset a lot this summer.  Yesterday the unit
backed and stopped suddenly when I turned on the A/C after having run
for hourrs with the battery charger only.  Temp was high and the
safety shutoff saved the day.  After refilling cooling water I pulled
the end caps from the heat exchanger and found a few impellor blades.
There was water flow but evidently not enough to cool under the
increased ;pad I guess

So I changed the raw water impellor and the water flow increased substantially.

So tonight with battery charger only the unit ran fine. I turned on
the A/C and within 2 minutes it overheated and shut down again

I am looking to verification that it must be the thermostat not
opening all the way.  The internal cooling water boiled off so after
refilling, I ran the battery charger only for hours with no problem

Does the thermostat sound like a plausible problem area.
Again the raw water flow is gushing from the exhaust so its getting
enough cooling water.


Bill wrote: 

I had a similar problem.  I thought I had accounted for all the missing
pieces on a blown impeller but about a month later a head-sea must have
dislodged part of a blade that was wedged way up the hose near the
anti-siphon loop.  The piece ended up laying across the hose blocking the
flow.