Diesel Stalls at Idle

[jfmid]

Hello all,

My O'day 272LE has a 10 hp inboard Universal Diesel. I had to transport her down from Rhode Island to Barnegat Bay, NJ and did the trip by mostly motoring as there were long stretches with no wind. We ran at about 5 knots and made decent time but it was a long slow trip. There is no RPM guage and just a Temp guage and it was pegged at 185 the whole trip so cooling seemed good. Before the trip we changed all fuel filters and oil filters and new oil so everything was fresh.
At the very end of the third day I got some air into the lines as I allowed her to run out of fuel. DOH!!!! (there is no fuel guage and it used more than I thought it would on the long stretch) I'll be more careful in the future.
I was unable to restart it not knowing that the air in lines prevents proper fuel flow and pattern. Now I know. I got it to a marina where a diesel mechanic bled the lines, replaced filters, and got it running again. Also replaced leaking exhaust water hose and did a tune up adjusting valves, changing impeller, changed oil, and filters. In short checked and tuned up everything.
Bottom line is that on the final leg of the voyage she stalled at a low idle while I was refueling after running for a while. Does the diesel have to be turned off to refuel???
I was able to restart and ran well for about 4 hours until I pulled into the lagoon where we would be docking. Of course just when I needed to go to low idle and maneuver in tight quarters it quit and wouldn't restart. Of note is that prior to going to idle I had to run up a creek for about 15 min at barely above idle as it is a no wake zone. I read on other threads that if a diesel is hot and goes right to idle the thinned oil may not lubricate properly and there is too much friction on the cylinders to move properly. I mention this because it surely must have cooled down over the 15 min crawl up the creek.
Luckily I was able to drift and steer and avoided slamming into other docks and boats and was able to secure to my dock and catch my breath. After a few hours of mental stabilization along with a few cold ones I was puttering around on the boat and restarted the diesel and it idled just fine.
I am concerned now that I cant trust the diesel in a low idle situation. I wonder what steps to take to ensure that it is working well. Is it a factor of being run for a long period of time??? This doesn't make sense to me as diesel trucks run for hours and hours and dont stall as they come up to a stop light but of course small marine diesels are a completely different animal. Do I just increase the idle speed by approx 100rpm? Again no RPM guage so kinda hard to tell what the RPM's are. The mechanic who worked on it will be able to come to my dock and take a look but I want to have an idea of what is going on.
Thanks in advance for any input and suggestions.

 

[zeehag]

did you check the fuel filters after you got to the dock?/ could be something got in there and blocked the flow when the need is for higher flow--as for the idle--if the fuel filter is clogged the idle will be affected. somme diesels use the throttle idling down to turn off the engine properly--mine is likie that on ericson---so low idle is spozed to shut down engine--do you have a cut off switch ?? if not then that is why idle is so low.....if you are able to identify the rpm by ear---then idle her at the sound that you think is closest to a proper idle for your boat. i like the tachometer i had installed into my boat--lol---helps a lot.....

 

[jfmid]

did you check the fuel filters after you got to the dock?/ could be something got in there and blocked the flow when the need is for higher flow--as for the idle--if the fuel filter is clogged the idle will be affected. somme diesels use the throttle idling down to turn off the engine properly--mine is likie that on ericson---so low idle is spozed to shut down engine--do you have a cut off switch ?? if not then that is why idle is so low.....if you are able to identify the rpm by ear---then idle her at the sound that you think is closest to a proper idle for your boat. i like the tachometer i had installed into my boat--lol---helps a lot.....

I didn't check the fuel filters after I got to the dock. Was too flustered by the loss of power in the very tight quarters that I was thankful that I didn't damage anything. I dont want to remove/check filters until I know how to bleed air from lines although what is strange is that we didn't "bleed" lines when we changed all filters up in RI when she was on the hard. The manual says there is an continuous fuel bleeder for this diesel (M-12).
There is a fuel cut off that I pull out to kill the diesel.
I am going to get a tachometer installed (if on this model it's possible) to help me judge what is going on.
Someone on another post I saw when I did a search of this topic mentioned this is a good reason to brush up on close quarter sailing skills. That wouldn't have helped as we were straight into the wind up a very narrow channel/lagoon. No real room to sail.

 

[Steve Dion]

You might consider a laser tach to determine the approx. RPM's. These things are cheap (less than $40).

Typically if a fuel filter is full of crap, it will idle but will not run at higher RPMs. I am guessing that you still have a small leak that is causing your problem. You may want to consider replacing all of your fuel hose if it is marginal. This may be less expensive than having someone trouble shoot your engine.

Be sure that you check all of your connections and the filters too. You could still have a leak there that is sucking air.

 

[Bill Roosa]

engine lub

Hot oil will lub the engine just fine at idle. It is cold oil that will not flow that can cause problems. With that said, the oil pressure is lower at idle and depending on how old the gears are in the oil pump they may not be providing enough pressure. Hot oil is thinner and the pressure naturally drops for all RPMs when the engine is hot.
Do you have an oil pressure gage or low pressure warning lamp/buzzer?

 

[jibes138]

A few suggestions

I have an M25 so not exactly the same engine but probably similar controls. You should have a thumb screw near the front of the engine in the fuel system that you unscrew to bleed the air from the lines. When you unscrew it a turn or so the electric fuel pump will start running very fast letting the fuel flow rapidly through the system and purging the air. Let it run fast for thirty seconds or so and then tighten the screw. You can get a manual for your engine at Torresen, I'd recommend it.
As for idle speed i also experience a slightly reduced idle speed when engine is warm, I just work the throttle a bit to keep the RPM's up, I don't have a tach either. Your transmission should shift OK even with higher than normal RPM's so better to be running a bit fast than to stall. As you pull in to you dock take it out of gear and let the way on the boat provide manueverability, shift into forward if you need a little power, then take it back out of gear. drift into the slip then use reverse as needed to stop her, or use a spring line but better not to stress the gear and dock cleats by using reverse. I shift into reverse while still drifting forward to control forward speed then just give a short burst to final stop where desired.
A modern engine has a computer to controll all kinds of things that hold idle speed dead steady. My new F150 idles at only 500 RPM. Most old engines like our diesels do not control speed that accurately and yes the engine may run a bit differently warm than it does cold. Idle speed when cold should typically be higher as the engine is warming up and for gas engines that might idle at 750 the cold idle might be 1250. You should set your idle speed when the engine is warm at operating temperature and expect the cold idle speed to be higher.

 

[jfmid]

I have an M25 so not exactly the same engine but probably similar controls. You should have a thumb screw near the front of the engine in the fuel system that you unscrew to bleed the air from the lines. When you unscrew it a turn or so the electric fuel pump will start running very fast letting the fuel flow rapidly through the system and purging the air. Let it run fast for thirty seconds or so and then tighten the screw. You can get a manual for your engine at Torresen, I'd recommend it.
As for idle speed i also experience a slightly reduced idle speed when engine is warm, I just work the throttle a bit to keep the RPM's up, I don't have a tach either. Your transmission should shift OK even with higher than normal RPM's so better to be running a bit fast than to stall. As you pull in to you dock take it out of gear and let the way on the boat provide manueverability, shift into forward if you need a little power, then take it back out of gear. drift into the slip then use reverse as needed to stop her, or use a spring line but better not to stress the gear and dock cleats by using reverse. I shift into reverse while still drifting forward to control forward speed then just give a short burst to final stop where desired.
A modern engine has a computer to controll all kinds of things that hold idle speed dead steady. My new F150 idles at only 500 RPM. Most old engines like our diesels do not control speed that accurately and yes the engine may run a bit differently warm than it does cold. Idle speed when cold should typically be higher as the engine is warming up and for gas engines that might idle at 750 the cold idle might be 1250. You should set your idle speed when the engine is warm at operating temperature and expect the cold idle speed to be higher.

I have the manuals from Torreson and it was a little vague about the bleeding screw for the M-12. It also said this model has a continuous bleed so I'm a little confused. I will look more closely tomorrow and see if I can figure it out.
As for controlling speed I was doing exactly what you described on the trip down at the other dockings I did. I guess at the very end of the trip I just got it a little too close to full idle and it quit. Wasn't expecting it but now I'll be ready. It is kind of touchy and I dont have the sense of touch/feel yet. Was surprising it quit after all the maintanence that had been done $$$$$$. The learning curve is quite steep and so are the bills.

There is an oil pressure lamp and it was not on at any time other than at starting. The M-12 is about as basic as you can get with no bells and whistles. The control panel has 2 guages. Amps and Temperature.
I still dont understand how it would start up 3 hours later and purr like a kitten at idle but at the end of a long run it konked out.
How involved is it to clean the fuel tank?? I'm thinking it's a major endeavor.

 

[jibes138]

Follow up

The bleed screw on the M25 is a knorled thumb screw you turn by hand. It should be readily apparent if the M12 is the same. The panel sounds exactly the same, two gauges and a lamp plus a shut off cable.
So step back a bit, what makes a diesel engine run? You need high compression to increase the temperature in the cylinder above the ignition point of the fuel, you need air, and you need fuel injected at precisely the right time so it burns causing a rapid expansion of hte air in the cylinder to force it down . Your mechanic adjusted the valves, you probably have good compression or it wouldn't run cold either. Only thing left is fuel delivery at the right time. A diesel can take quite a while to warm up so if your mechanic adjusted the idle speed when it was cold you may need it adjusted for when it is hot instead. You may need your injectors cleaned could be another source of trouble. As fuel gets sloshed around in your tank you may have some amount of water that the filters don't remove causing a slightly different burn when hot. Let it warm up to full temp at the dock and see if it idles OK when returned to idle. A lot of things change when they are hot, materials expand at different rates so your clearances change, fits change. the engine will definitely run differently hot than cold, so if hot is where you want the sweet spot to be do your adjustments when it is hot. I'm far from a diesel mechanic but a logical approach from a 50,000 foot level should help. Adding a tachometer should be really easy if you want one. My trouble with the engine panel is it is right where you can't see it. The should mount these things on the pedastal they don't put the gauges in your car on the bottom of the driver side door, but in a boat that seems to be the place for engine panels, near your feet and to the left.

 

[Witzend]

Yea, lets put the engine vitals where no one will notice when there is a real problem. My C90W chart plotter has an option to display engine status, but no way to easily interface it.

Another issue with idling is, limit the time you idle!! It's hell on the damperplate, engine mounts, and engine.

 

[druid]

One other out-of-left-field shot: Some engines (including the Universal, I think), has a fuel shutoff hooked to the oil pressure, so if you lose oil pressure the engine shuts down. Maybe at low idle you're not getting enough oil pressure...?

druid

 

[jfmid]

Thanks to all so far. Lots of good clear advice which is why I love this site. I'm a total newbie so it's a bit intimidating but fun all the same. No one here ever implies that one is stupid for not knowing things which is a lot different from my grad school days.
One of my favorite quotes is "You dont know what you dont know". It reminds me to stop and ask a lot of questions. Not sure who said it but it sure is true especially when it comes to sailing.
I will be checking these suggestions/issues out and will post back when I get some answers. It might help someone else down the road.
As for the location of the guages, it too seems to me that common sense left the building when they decided where to put them during design. I understand cost is an issue etc.... but come on if we only needed to look at them when we start up then they could just as well be inside a locker for all the use they get. I will be putting a tach in my binacle area as it will be right in front of my face. Wonder if I could reposition the Temp there too so that I could keep watch on that? Not expecting to do tremendous amounts of motoring now that she's in home waters but you never know when you need to do a long run.
Once this is fixed the next job is to rebed the stanchions as they leak like a collander draining my wife's yummy pasta. I've heard this is common to this model. This may have to wait till the fall when she's out on the hard. We'll see.

 

[jibes138]

Wow - the leaks sound serious

Make sure you check that anything you mount near your compass is non-magnetic or you will mess up your compass big time. My brother mounted a compass on his center console power boat and could never get a proper heading, found out the steering wheel was magnetic. You don't want to make landfall in England when you were heading to Japan.

If the stanchions are leaking that bad the core in those areas is probably a mess. Clean out the rot and epoxy up the holes before remounting the new ones. The stanchions might save your life from falling in some day so make sure they are structurally sound.

 

[J Hunter]

The fact that your motor runs good while powering but stalls at idle for me tells me fuel supply is probably not your issue, most of the fuel is being returned to the tank at idle so small restrictions like filters a little plugged wouldn't show up as idle stalls IMHO. I think you may be low on oil. Your oil pump is off your engine and drops in pressure as RPM drops. If you are stalling at idle speeds the engine normally stayed running at and even when the engine is under power but at slow speeds, I think you are losing compression from lack of adequate lube oil getting winged up onto the cylinder walls. Check your oil and bring it up to the correct level on the dipstick if it's low.

 

[jfmid]

The fact that your motor runs good while powering but stalls at idle for me tells me fuel supply is probably not your issue, most of the fuel is being returned to the tank at idle so small restrictions like filters a little plugged wouldn't show up as idle stalls IMHO. I think you may be low on oil. Your oil pump is off your engine and drops in pressure as RPM drops. If you are stalling at idle speeds the engine normally stayed running at and even when the engine is under power but at slow speeds, I think you are losing compression from lack of adequate lube oil getting winged up onto the cylinder walls. Check your oil and bring it up to the correct level on the dipstick if it's low.

Definitely checked and know that the oil level was good. If the level is good is there another way that the oil wouldn't be getting up onto the cylinder walls??

 

[J Hunter]

That was my best guess, the level being low, I've seen this happen on my Yanmar and your symptoms sounded identical. Otherwise I'd hate to send you on any wild goose chases. My motor has no min. idle detent on the throttle or a min throttle position at the fuel pump, when it starts to stall at low speed I just quickly tap the throttle open a little more until it stays at a constant low rpm - all by ear. Bringing the throttle handle vertical is how I shut off the engine. If there is some min stop on the spring return throttle lever on your fuel pump, maybe the mechanic who did the bleeding and service monkeyed with it. Wild goose chases aside, you still might want to totally eliminate a lack of cyl. lube as a problem by giving the lube oil system another once over- crank the knife edge filter or change the oil filter, change the oil once more and use the good stuff - Rotella T9 Synthetic diesel rated- and fill the crank case a half an inch high just to be sure you have plenty in there. The fact that it happened soon after an oil change and after a solid four hours running means the oil may have been a different grade and was quite warm, that may have been different than the first part of your trip-something is. Make certain you've got good cooling water flow too and your exhaust pipe is running normal temps. For me it's hard to say what those are since I haven't ever worked on an Atomic. Oh, just thought of something - if the stall is caused by a lower volume of fuel getting to the combustion chamber, the motor will lug down (drop RPM and sound like it's struggling to turn over) right before it stalls. If it's a lack of compression it will just die instantly, you won't have time to even grab the throttle.