New Northern Lights Genny - Problem

[corbinkerr]

Hi All....I had a new M673L3.3G genny installed in the spring. It ran geat for the first 80 hrs, until I picked up a bunch of seaweed that clogged the sea strainer and killed my impeller. Ever since I changed that impeller the genny will run for about 10 mins but then shuts down. I'm suspecting its overheating but there are no gauges or lights to indicate shut down codes. I used the laser thermometer and it seems to be shutting down at about 195F.

I was worried more sea weed might have been trapped between the thru hull and sea strainer so I've snaked that and also from the output side of the sea strainer up to the impeller...Seems all clear. Its difficult for me to judge the actual outflow from the wet exhaust because that thru hull is right at the waterline, but there is a pretty good wake leaving that thru hull so I think the water flow OK.

I did remove all the hose from the impeller up to the heat exchanger and also removed the heat exchanger to remove all the impeller pieces that broke off....Its all clear.

I also flushed the coolant and re-topped it up. Also, did an Oil change just for good measure.

The only remaining thing I can think off is a faulty thermostat but that seems highly unlikely with only 88 hours.

Any other thoughts / suggestions?

tks
Corbin

 

[twistedtree]

There are three safety shutdown switches, and the next step is to figure out which is causing the shutdown. Don't run the engine for any extended time with these switches disabled. Just do it temporarily to figure out which is causing the shutdown. They are:


1) Exhaust over temp. This is in the exhaust elbow coming off the exhaust manifold. Easiest thing to do is feel the exhaust hose right after the elbow to see if it's hot. It shouldn't be. Maybe a touch warm, but that's all. You can also bypass the switch by removing the connector, but monitor the exhaust hose temp carefully running like that.


2) Low oil pressure. This switch is in addition to the pressure sensor for the gauge. I'll assume you have normal oil pressure reported on the gauge. Disconnect the switch wires and see if the unit keeps running. I think it's unlikely that this is the problem.


3) High coolant temp. Like the oil pressure switch, it's in addition to the temp sensor for the gauge. I don't recall the trip point, but 205F sticks in my head. You said the gauge goes up to 195 which is pretty high - probably too high so this is most likely what's tripping. You again could disconnect the switch and see if the unit then continues to run, but watch the temp gauge carefully and be ready to shut down if it's trying to overheat.


My money would be on the coolant temp, mostly because your gauge is also reading high, and because you had an impeller issue. There is probably still something blocking the heat exchanger tubes, probably in the tubes themselves since you already fished out the impeller bits.

 

[ghost]

When you fished out the HE tubes, did you get the end cap back on correctly? It seals in two places on each end, not terribly hard to get the “inner” clamp on wrong in which case you would not actually be cooling anything and visibly it looks fine. The HE tube floats in there until you get the inner clamps on it and can slip so that there is not enough protruding to clamp onto. Also, double check the new impeller to make sure it is still whole.

 

[ksanders]

My thought is to go back to the original problem.

You had a blockage of water that caused your impeller to be water starved, overheat and fail.

I would re-look at everything inline from the seawater pump back first. This includes not only the hoses, also check the 90 degree fittings that are often used to connect to the sea strainer.

I found seaweed blocking the 90 fitting enough times that I changed out my sea strainer for a Raritan unit with a bottom entry out of frustration.

 

[DennisB1]

Try back flowing the inlet line from the pump to the inlet using a connection to your water hose. If you have 40 psi or more at the hose you can verify that the line flows freely. Also when you have access to the heat exchanger run a small dowel thru each tube to verify that they are clear ( from the inlet side to the discharge side) I had a similar problem on a 753 series with collection of broken impeller parts. Still kept cool under load. Good luck

 

[Porgy]

I’d also check the exhaust elbow where the seawater hose connects. There’s a right angle turn into a baffle, then into the exhaust pipe. It can clog fairly easily there if anything got past the heat exchanger. Echo the heat exchanger hose clamps comment. Bob Senter warns to tighten the small clamps first, then the larger.

Our NL M773 runs at a fairly rock steady 189 degrees according to the gauge. 194 is the upper end of normal, shut down is 205.

 

[Ski in NC]

195F on IR gun is pretty hot. Most of these run 160-170F and an IR gun measures surface temp, coolant temp inside is like 5-10F higher than skin temp. And the shutdown switch is usually around 200F, so you are right on the edge.

Two super easy things to check: Get unit started, put hand on impeller cover plate, should be at sea temp. If warm or hot, it is NOT pumping water, for what ever reason. Second, put hand on exhaust hose between genny and muffler. It should be only slightly warmer than sea temp (like 10-20F). If it is super warm or hot, not enough sea water flow.

 

[High Wire]

You did not mention if there was visible water flow out the exhaust. Normal flow?

 

[corbinkerr]

Thanks for all the good advice and I'm continuing to work on the problem. ie. Its not fixed yet

Water flow is difficult to determine because the exit thru-hull is right at the water line. I can tell there is some flow but can't really tell if its sufficient. Also, since this genny is new I don't really have a good baseline from memory to compare it to.

I'm going to start "from the beginning" (the thru-hull) and work my way through the entire system one more time looking for any blockages. If that's unsuccessful (again) then I think I need to conclude its the thermostat.

Corbin
AT34-42
The Donna Lynn

 

[Porgy]

Does it have a water separator in which case you wouldn’t see any water at the exhaust.

 

[corbinkerr]

PROBLEM FIXED....

I finally decided to more carefully go through the entire raw water system (again).....and sure enough I found two impeller fins that were several feet back in the hose between the sea strainer and the impeller. I was able to put the snake through the hose and it appeared like it was clear but there was one "tight spot" so when I worked the snake back and forth several times in that area they finally got dislodged. Reconnected everything and its running like a top again!!!

Thanks everyone for the great advice.

Corbin
AT34-42
The Donna Lynn

 

[ghost]

Super!

 

[High Wire]

Cool! Pun intended.
Whenever you lose impeller vanes, make sure you recover all of the missing vanes. Put the puzzle back together again to be sure. Sometimes you may find pieces from a previous failure.

 

[Jeffk]

Call Northern Lights

With respect, did you think to call them since they are the people who made it? Why look to people who may lead you in the wrong direction. I've phoned them on several occasions and received first hand knowledge as to my situation.

 

[Circumnavigator]

This kind of problem is why I have flow sights such as this on all my diesels:
https://www.mcmaster.com/4195K16/
This one is for the small generator -- those for mains are larger. I put them upstream of the seawater pump so impeller pieces can't get into them.



Jim

 

[bligh]

Cool! Pun intended.
Whenever you lose impeller vanes, make sure you recover all of the missing vanes. Put the puzzle back together again to be sure. Sometimes you may find pieces from a previous failure.

What he said.
Reassemble your old impeller with all the parts so you can be sure you have all the parts. If there is one thing i didn't like about my northern lights, it was that fragile impeller. Change the impeller often , even if you do not use it.