White smoke, reduced RPM, increased fuel consumption

Status
Not open for further replies.

jviss

.
Feb 5, 2004
6,745
Tartan 3800 20 Westport, MA
This year the M25 in my C36 has been smoking under load, white smoke. I had just assumed it was steam, but now that I'm starting to put things together, I'm not so sure.

It won't rev up past about 1800 RPM under load. Prop and shaft are clean.

Fuel consumption seems higher than normal: I used about 1 gallon per hour during a one week cruise, mostly motoring. I recall in previous years about 0.4 gph.

Nigel Calder, in his Marine Diesel Engines book seems to think that if not steam, it's unburnt fuel. It's a bit confusing because he says "one or more cylinders are not firing," but "if the smoke persists" after warm-up, says it may be a defective injector.

The injectors were replaced ten years ago - about 1000 hours of use since.

So, engine experts - care to offer a diagnosis?

Thanks,

jv
 
Jul 1, 2012
155
Catalina C22 Georgetown
Sounds like excess fuel in the combustion. Fuel not completely burned usually results in white smoke, whether it be from a bad injector, bad injection pump or faulty injection timing. Best way to find out is do a cylinder contribution test. Run your engine at about 1200 rpms, then crack open each injection line one at a time. If RPMs don't change on a particular cylinder, then that one will be your culprit. If they all change, then problem more than likely lies in the injection pump.
 
Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
A common problem is the injectors not atomizing the fuel well enough. Instead of a fine mist it is larger drops which don't burn well and end up going out the exhaust as white smoke. It also explains the lack of power as if you can't get enough fuel in to the engine in a state that is actually usable (regardless of how much the injector pump supplies it needs to be able to burn) you can't produce power.
Did this come on suddenly or over time?
Slow mo's contribution test will require lots of rags and I'd note that you are looking for (in a perfect world) a consistent drop in RPM as you take each cylinder's fuel supply away. If one cylinder does not show a drop or shows a smaller drop in RPMs then it was not contributing as much as the others.
 
Jul 1, 2012
155
Catalina C22 Georgetown
I forgot to mention, a quick diagnostic would be to run a quality diesel injector cleaner for a few hours (like Lucas, Amsoil, Seafoam). Sometimes these detergents are enough to knock loose any carbon build up in or or the injector nozzle.
 
Dec 2, 1999
15,184
Hunter Vision-36 Rio Vista, CA.
White smoke is usually an indication of water/coolant in your exhaust (can be a head gasket).

Black smoke is usually unburnt fuel.

Blue/gray smoke is usually oil.
 
May 24, 2004
7,129
CC 30 South Florida
Go with Slow-Mo and run a diesel fuel injector cleaner. The majority of maladies affecting marine diesels are fuel related.
 
Jul 1, 2012
155
Catalina C22 Georgetown
White smoke is usually an indication of water/coolant in your exhaust (can be a head gasket).

Black smoke is usually unburnt fuel.

Blue/gray smoke is usually oil.
Black smoke is fuel not burned completely, usually just heated and turned into carbon.
White smoke can be steam from water or coolant, but will dissipate. But if it doesn't dissipate, or has a fuel smell to it, it is diesel fuel not being burned at all. It is essentially "diesel steam".

Best way to think of it is spraying fuel on a very hot campfire will burn the fuel, but not completely, creating black smoke- lots of heat, and lots of even sprayed fuel.
Dumping fuel on a hot skillet will create white smoke- uncontrolled pattern of lots of fuel, creating a rapid cool down in certain areas of the cylinder, leaving fuel molecules unburned.
Remember, diesel does not ignite from flame, it ignites from heat.
 
Nov 6, 2006
9,885
Hunter 34 Mandeville Louisiana
Diesel steam usually won't make it past the water filled muffler .. without condensing to a little slick..
 
Feb 26, 2004
22,760
Catalina 34 224 Maple Bay, BC, Canada
Go with Slow-Mo and run a diesel fuel injector cleaner. The majority of maladies affecting marine diesels are fuel related.
We use injector cleaner to fill our fuel filters when we replace them.
 
Apr 22, 2011
865
Hunter 27 Pecan Grove, Oriental, NC
Black smoke is fuel not burned completely, usually just heated and turned into carbon.
White smoke can be steam from water or coolant, but will dissipate. But if it doesn't dissipate, or has a fuel smell to it, it is diesel fuel not being burned at all. It is essentially "diesel steam".

Best way to think of it is spraying fuel on a very hot campfire will burn the fuel, but not completely, creating black smoke- lots of heat, and lots of even sprayed fuel.
Dumping fuel on a hot skillet will create white smoke- uncontrolled pattern of lots of fuel, creating a rapid cool down in certain areas of the cylinder, leaving fuel molecules unburned.
Remember, diesel does not ignite from flame, it ignites from heat.
Great explanation! I'll try that out next time I go camping!!!
 

jviss

.
Feb 5, 2004
6,745
Tartan 3800 20 Westport, MA
I have seen white smoke:
  • when there's insufficient raw water flow, and it's steam;
  • from unburnt diesel fuel;
  • when there's a new pope.

I don't think it's a new pope. I don't think it's insufficient raw water flow, as there seems to be enough, or at least the same amount of water coming out the exhaust. Plus, less raw water wouldn't explain the loss of revs or the increased fuel consumption.

I'm praying it's an injector. I might just buy three, swap them all, and see what happens. I don't want to risk injecting fuel into my skin diagnosing it, and I'm really hoping the injection pump is O.K.

Seems injector prices have fallen in 10 years. I found them this time for $55. (new) with a $10 core charge. Haven't decided yet if I'll buy them.
 

jrowan

.
Mar 5, 2011
1,294
O'Day 35 Severn River, Mobjack Bay, Va.
I agree with Steve that in a gasoline engine white smoke is a sign of a cracked head gasket, but a marine diesel is a completely different animal. I have a 5411 that always produces white steam vapor from the exhaust. When I first saw this I thought "cracked head gasket" until I found out that this was normal for this engine. A compression test will also tell you how each cylinder is performing, unless the problem is fuel related. If the injectors are that cheap though, it can't hurt to replace them. Does you engine rev up to full RPM's when its in neutral? If it rev's properly in neutral, but then drops significantly when in gear & under load, then it may be something fouling the prop & running gear, or binding at the stuffing box. Good luck & tell us what fixes the problem.
 
Jul 1, 2012
155
Catalina C22 Georgetown
:cussing:
Great explanation! I'll try that out next time I go camping!!!
You can try, but I wouldn't recommend it. Two things will happen- you'll put out your fire, or if you use a spray bottle and successfully light the diesel, you'll lose a bit of arm and facial hair.
Diesel is what Hollywood uses for big fiery booms...
 
May 27, 2012
1,152
Oday 222 Beaver Lake, Arkansas
White smoke can be steam or oil. Oil wafts away in the breeze and smells like oil. Steam dissipates into thin air. It takes a lot of water for a diesel to make visible steam because of the high combustion temperatures.

Rather than guess whats wrong I generally follow a particular pattern. Experience has shown it most always saves time and money. Pull the injectors, then, before doing anything else, check compression. A broken piston or stuck rings can just as easily be the cause. Compression, then, becomes your fork in the road.

If it passes, you follow up with a full tune up. If it fails, you dig deeper.
 
May 24, 2004
7,129
CC 30 South Florida
Before you start replacing parts on a hunch go ahead and determine which cylinder is not properly burning the fuel. It could be due to a clogged injector, an air leak or low compression. White smoke may be indicative of a lean air fuel mixture caused by a clogged injector or an air leak. Instaliing new parts always carries a risk as they could be defective or something may go afoul with the installation. This could seriously complicate the diagnosis of the ongion problem. The other negative is the cost of replacing perfectly working parts. If you can get your hands on a sensitive temperature measuring devise you may detect a cylinder that is not properly firing as it will run cooler. The other method might be by elimination shutting down and restoring fuel to each cylinder individually until you find your culprit on the one that does not affect the way the engine is running now. You may then remove the injector from that one cylinder and check for compression. If compression is present at this point I would have no qualms about replacing the injector. If none or low compression then check valves, head gasket or piston rings.
 

jviss

.
Feb 5, 2004
6,745
Tartan 3800 20 Westport, MA
Summary of symptoms and remediation plans

Thanks for all the input!

Here's the summary of symptoms:
  • white smoke
  • double the fuel consumption
  • half the RPMs under load

Seems pretty clear to me that I have a fuel induction problem. I'm hoping it's just an injector because of the cost and ease of replacing, compared to the injection pump.

Then again, I guess it could be a valve problem, like a stuck-open intake or exhaust valve. I guess I could do a compression test to figure that out, but I don't have a diesel compression tester; might buy the Harbor Freight one today (on sale, $25). I guess I could take the valve cover off and take a look at the valve stems. Comments?

Meanwhile, I ordered three new injectors, $55 each.

I'll replace my filters first, since I will be bleeding anyway. Then replace the injectors, bleed, and try it out.

The thing about diagnosing it before buying parts it that the boat is 75 miles away, and I'd like to spend a little money and play a hunch to possibly dramatically shorten the time-to-repair.

I'll let you know what happens.

jv
 

weinie

.
Sep 6, 2010
1,297
Jeanneau 349 port washington, ny
Thanks for all the input!

Here's the summary of symptoms:
  • white smoke
  • double the fuel consumption
  • half the RPMs under load

Seems pretty clear to me that I have a fuel induction problem. I'm hoping it's just an injector because of the cost and ease of replacing, compared to the injection pump.

Then again, I guess it could be a valve problem, like a stuck-open intake or exhaust valve. I guess I could do a compression test to figure that out, but I don't have a diesel compression tester; might buy the Harbor Freight one today (on sale, $25). I guess I could take the valve cover off and take a look at the valve stems. Comments?

Meanwhile, I ordered three new injectors, $55 each.

I'll replace my filters first, since I will be bleeding anyway. Then replace the injectors, bleed, and try it out.

The thing about diagnosing it before buying parts it that the boat is 75 miles away, and I'd like to spend a little money and play a hunch to possibly dramatically shorten the time-to-repair.

I'll let you know what happens.

jv
don't forget to google for a 20% harbor freight coupon.

You also need to make sure you have the correct adapter for the injector hole. If you look at the manual on the harbor freight website, it will show you what adapters and sizes it comes with.

I thought I could rig up an adapter up from my old injectors and some brass fittings, but I gave up and bit the bullet and just ordered a kubota adapter from tractorsmart.com for $70.

ETA: the harbor freight kit does have an adapter that will fit the glow plug hole, but there isn't any room to fit your gauge. You would have to remove the intake manifold and the fuel pipes. But even after capping the fuel lines, you still may not have enough room. Your engine may be different. I have the M18.
 

jviss

.
Feb 5, 2004
6,745
Tartan 3800 20 Westport, MA
don't forget to google for a 20% harbor freight coupon.

You also need to make sure you have the correct adapter for the injector hole. If you look at the manual on the harbor freight website, it will show you what adapters and sizes it comes with.

I thought I could rig up an adapter up from my old injectors and some brass fittings, but I gave up and bit the bullet and just ordered a kubota adapter from tractorsmart.com for $70.

ETA: the harbor freight kit does have an adapter that will fit the glow plug hole, but there isn't any room to fit your gauge. You would have to remove the intake manifold and the fuel pipes. But even after capping the fuel lines, you still may not have enough room. Your engine may be different. I have the M18.
Wow, thanks for that! My wife is already picking up the gauge on her way home, so missed out on the coupon thing; but it's on sale today, so not so bad.

I certainly hope I can make it fit. Mine's an M25, same as 5421: Kubota D850.

I have some old injectors, and a lathe and machine shop skills. Maybe I can make an adapter. How did you try to do it?
 

weinie

.
Sep 6, 2010
1,297
Jeanneau 349 port washington, ny
Wow, thanks for that! My wife is already picking up the gauge on her way home, so missed out on the coupon thing; but it's on sale today, so not so bad.

I certainly hope I can make it fit. Mine's an M25, same as 5421: Kubota D850.

I have some old injectors, and a lathe and machine shop skills. Maybe I can make an adapter. How did you try to do it?
I figured after removing the the top half of the old injector I could find some brass fittings and cobble something together with that fits into the lower half of the injector one one end and also attaches with an air compressor type fitting to the compression gauge hose. Of course it would still have to be air tight at 500psi.
 

jviss

.
Feb 5, 2004
6,745
Tartan 3800 20 Westport, MA
I figured after removing the the top half of the old injector I could find some brass fittings and cobble something together with that fits into the lower half of the injector one one end and also attaches with an air compressor type fitting to the compression gauge hose. Of course it would still have to be air tight at 500psi.
Hey there,

Received my new injectors so I figured I'd check the compression tester adapters agains the injector. As you mentioned, there is an adapter that matches - a short, M24x2 threaded piece. Here are pics, the first with it lined up next to one of the original injectors; the second the assembled compression gauge:





Are you saying this gauge assembly wouldn't fit in where you could use it on your engine? I'm hoping it will work on mine. My recollection of the engine configuration says it should.

By the way, this HF compression gauge kit is the deal of the century at $25!!!

One thing, the new injectors didn't come with new crush washers. Off to NAPA!


jv
 
Status
Not open for further replies.