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Has anyone seen a gas engine diesel after shutoff and ingest water from rotating backwards?

V

v8George

New member
Hi All,
I am trying to figure out what caused an engine to die.

Carb'd 454 Mercruiser with an Alpha 1.

The boat is trailered, never stored in water, and flushed after every use, raw water cooled, operated in salt water.
The manifolds and elbows are 2 years old.

The engine was test fired on the trailer on muffs to make sure we could hot launch from a busy ramp.
Got to the ramp, fired right up and out we went. The engine ran great then developed a miss. Pulled the hatch and saw one of the brand new Sierra spark plug wires had fallen off. Replaced it, went out further, same thing, but different wire. Eventually stopped and recrimped all the wires.
Engine was running great then developed a miss due to a wire coming off again, brought the boat off plane and killed the engine. It started to diesel, which it has never done before, and ran-on for a few seconds while the backlash of the wake bounced off the transom.
Fixed the last plug wire and tugged on them all to make sure we had no issues.
Motor wouldn't turn, not even a tiny bit, it felt hydrolocked. Got towed in.
Pulled the plugs when we got home, and water poured out of all the cylinders. Rolled the motor over and it just blew tons of of water out.
Replaced the plugs and it wouldn't start, turned over funny like it had no compression. Checked the timing and it didnt jump.
Pulled the manifolds, they looked good, gaskets looked good, elbows looked good.
This my theory.

When the engine died and dieseled, it counter rotated and sucked water through the flappers, through the exhaust valves, and hydrolocked the motor, bending the connecting rods in the process.

I can't think of any other way a running engine with no signs of water intrusion on the manifolds would go from running to locked.

Does this sound like a feasible explanation?
Any input appreciated as I am being told that marine engines can't counter rotate and suck in water.
 
Have seen that plenty of times, dieseling is from a hot engine, hot spots on the pistons, timing error, lean fuel, turning off the key with forward motion
 
Bt Doctur said:
Have seen that plenty of times, dieseling is from a hot engine, hot spots on the pistons, timing error, lean fuel, turning off the key with forward motion
Click to expand...


We were definitely moving forward when the key was turned off. I am thinking that combined with a cylinder full of unburned fuel vapor caused the dieseling. I just can't seem to find anything to document that it would draw water in.
 
It will absolutely draw water in......Just think of the engine as a pump, spin it in the correct direction air goes in the top exhaust out the bottom....spinning it in the wrong direction.... puts a vacuum in the exhaust and water goes in the bottom and air goes out the top.


Have a professional investigate it and if he can prove the wires caused it Sierra will pay the bill on the repair.
 
Does this sound like a feasible explanation?
Click to expand...

Ayuh,.... It happens quite often,....

If ya understand dieselin', aka: run-on, it makes perfect sense,...

When a motor diesels, have ya noticed that just as it dies, it sounds very different,..??
That's the motor runnin' Backwards,....

That's why, if ya have a motor tryin' to diesel on ya,... ya turn the key back On,... let the motor idle to cool, then try to shut it off again,....
 
I'm sorry to hear that your engine encountered this.
Water against very hot exhaust valves, hot cylinder walls, hot piston decks, etc is not good, and typically causes severe damage.


Gasoline Engine "Run-On" (or what some call "dieseling") is caused by one or several things:

..... as noted... carbon deposits that will hold enough heat to ignite fuel
..... lean fuel/air mixture along with the above
..... higher than need be idle RPM along with the above
..... poor combustion chamber design


When an Engine undergoes "run-on", it will typically continue to rotate in the intended direction due to the normal intake/exhaust cycles.

However, when an Engine undergoes "run-on" that would create suction within an open exhaust port, it will have now changed rotation direction (aka running backwards). Under these conditions, it will typically stop in short order due to the intake/exhaust cycles being interrupted.
When one does run backwards, it is basically turning in that direction via inertia only.
In other words, there is nothing more to combust! (i.e., it's no longer pulling in fuel/air.)


Good luck! I hope that the damage is minimal!





That's why if you have an engine trying to diesel on you,... turn the key back On,... let the engine idle and cool, then try to shut it off again.
Click to expand...

Good point and very true.

Perhaps better yet...... do not shut down an engine under hot conditions!






.
 
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Bt Doctur said:
Have seen that plenty of times, dieseling is from a hot engine, hot spots on the pistons, timing error, lean fuel, turning off the key with forward motion
Click to expand...

and you can add deposits on spark plugs to that list.

Re: turn off key, turn on key and let idle to cool, turn off... Not always work. May have to stall engine by cutting off air flow or fuel valve. Hot spots in chamber (only takes one!) make the spark ignition engine work like glow plug ignition (think model airplane engine).
 
Thanks for the replies. We are basically arguing with an insurance company that is stating that marine engines can't diesel and run backwards.
They are trying to say it was due to a rusted through manifold since that is the only engine failure they won't cover.
There is no way it was a manifold, we pull the elbows every year to inspect them and they are in great shape.
They cut one elbow in half at a machine shop and got back to us and said it wasn;t rusted through.
We then pressure tested the manifolds with 20 psi and got no leakdown.
There is no way it was due to failed manifolds or elbows. The flow through raw water system can't even generate 20 psi. Now they want to pressure test the heads, which show no signs of cracking.
The only feasible explanation for having that much water in the engine that quickly is from counter rotation.
 
...................
v8George said:
Thanks for the replies. We are basically arguing with an insurance company that is stating that marine engines can't diesel and run backwards.
They are correct! Continued reverse operation is very unlikely.
Understand that while the engine may be spinning in the opposite direction, the intake and exhaust systems have exchanged functions. In other words, the exhaust now becomes the intake, and the intake system is now exhausting the gasses that are within the cylinders.
This means that NO combustible fuel/air mixture is being introduced into a cylinder.

However, understand that during the initial "spinning in the opposite direction" (caused by heat-holding carbon deposits and/or by excessively high cylinder temperatures), it is very possible for an engine to kick over in the reverse direction for up to several cylinder cycles ONLY.



They are trying to say it was due to a rusted through manifold since that is the only engine failure they won't cover.
There is no way it was a manifold, we pull the elbows every year to inspect them and they are in great shape.
They cut one elbow in half at a machine shop and got back to us and said it wasn;t rusted through.
We then pressure tested the manifolds with 20 psi and got no leakdown.
There is no way it was due to failed manifolds or elbows. The flow through raw water system can't even generate 20 psi. Now they want to pressure test the heads, which show no signs of cracking.
The only feasible explanation for having that much water in the engine that quickly is from counter rotation.
As you can see, it should be easy enough to prove that the manifolds are OK!

With all that said...... I must ask you what is it that causes you believe makes this an insurance claim?
Click to expand...
 
Short version, the insurance policy covers engine failure but they won't cover it if it is from rusted out manifolds. When I say it ran backwards, it ran for a few seconds dieseling, not actually running on a proper 4 stroke cycle.
 
When the engine died and dieseled, it counter rotated and sucked water through the flappers, through the exhaust valves, and hydrolocked the motor, bending the connecting rods in the process.
Click to expand...
T'aint NFW. I can't explain how you hydrolocked, which has not yet been shown or proven, but you cannot run an engine in reverse.
What CAN happen is that you came off plane as the engine was being shut down. The huge stern wave probably nearly swamped the transom. With the water level higher than the exhaust and virtually no pressure to hold it back the water gushed up into the exhaust manifolds and into the open exhaust ports. Bye, engine!
 
Engine was running great then developed a miss due to a wire coming off again, brought the boat off plane and killed the engine. It started to diesel, which it has never done before, and ran-on for a few seconds while the backlash of the wake bounced off the transom.
Click to expand...
re read this. Yeh, it was coming off plane too fast that killed it. This happens almost instantaneously and the fact that it continued to run at all is amazing. I can understand that you were frustrated because you failed to fully seat the plug wires and you were likely out of patience. When it started to lose power again you jammed the throttle to zero in frustration. The result was water geysering into the exhaust as that stern wave hit. This is, unfortunately an expensive lesson to you in boat handling.
I hope that your insurance covers this kind of loss.
 
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Just a few thoughts...when an engine is dieseling, it is not firing on all cylinders and therefore a lot of unburned fuel is deposited into the exhaust system. When pre-ignition occurs and the engine suddenly spins backwards, the exhaust will be sucked back in. When this fuel rich exhaust is sucked back in it is combustible and will allow the engine to run backward for several revolutions before it finally stops.
 
bobbyc said:
Just a few thoughts...when an engine is dieseling, it is not firing on all cylinders and therefore a lot of unburned fuel is deposited into the exhaust system. When pre-ignition occurs and the engine suddenly spins backwards, the exhaust will be sucked back in. When this fuel rich exhaust is sucked back in it is combustible and will allow the engine to run backward for several revolutions before it finally stops.
Click to expand...
No way. Even if conditions were ideal... The engine cannot run in reverse long enough to pull that much water back up into the exhaust. If by several revolutions you mean maybe three or four? How many revs do you think it could run and how many do you think it takes to hydrolock an engine?
I have serious doubt that any "dieseling" occurred in this case. I think the OP was hearing his engine being killed. The engine was running well and not dieseling just moments before in other shutdowns.
 
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I've heard of NASCAR engines doing that when they spun out and ran backwards (both the car and motor). but not in a boat. Something else is going on here.

Jeff
 
Here is a message Kghost sent me on a problem engine he was working on this past summer that we diagnosed over the phone.....

"So in the end, Bad impeller caused over heating combined with a very rich running condition caused, like you said, the engine to diesel which sucked in the water.....thanks for the advice. All issues resolved!"

A plug wire off and another one coming off will cause a rich condition.....If the engine has carbon in the combustion chamber and the engine is hot when you shut it down it will diesel and pull water back into almost all the cylinders. Considering this is a 7.4 in front of an Alpha drive, it is probably safe to assume the water pump is not 100% considering that new spec for service from Mercruiser is to change the Alpha 1 pump every year if used in salt water and every other year in fresh water.

It is also probably safe to assume that this is in a Formula or similar set up where the height of the exhaust elbow is probably right below the minimum spec and actually needs a spacer.
 
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bobbyc said:
Just a few thoughts...when an engine is dieseling, it is not firing on all cylinders and therefore a lot of unburned fuel is deposited into the exhaust system. When pre-ignition occurs and the engine suddenly spins backwards, the exhaust will be sucked back in. When this fuel rich exhaust is sucked back in it is combustible and will allow the engine to run backward for several revolutions before it finally stops.
Click to expand...

Ayuh,..... This is a Fact,....

As I said above, the last gasp of a dieselin' gas motor, is the motor spinnin' Backwards, just as it finally dies,....
 
Yeh maybe, Chris. The OP didn't mention an overheat issue tho. We also don't know how long it was "dieseling" or what. Perhaps a combination of many factors that created a perfect condition for suckage.
 
o2batsea said:
Yeh maybe, Chris. The OP didn't mention an overheat issue tho. We also don't know how long it was "dieseling" or what. Perhaps a combination of many factors that created a perfect condition for suckage.
Click to expand...

Doesn't have to overheat, just run a little hotter than normal. Alpha/big block was a bad set up without a thru hull and inboard/bravo water pump.
 
OK...... let's look at this as though we're doing some forensic science.




As per Chris in post #19, the 454 engine in front of an A drive. The A drive seawater pump impeller is likely borderline adequate for this engine.
If it is equipped with an additional seawater pump (belt driven or crankshaft style), then this can be eliminated.



Some spark plug cables came loose. Replaced, but came loose again. An engine that is not firing properly on all cylinders, yet is pushing a hull through the water, is most likely operating at higher than normal temperature.



Shutting this engine down quickly most likely caused the "Run-On".



As Bob mentions in post #13, the idea of the un-burned gasses being pulled back in while operating in the reverse direction is plausible. But again, I would suggest for only a few revolutions!



Shutting down abruptly and causing run-on (possibly reverse run-on), along with the wave surge against the transom .... is very likely the cause of the water ingestion.





It sounds as though the insurance company is debating the mechanical aspect, siting that the manifolds were faulty and caused the damage.
I would first have an authorized shop verify this one way or the other.

If they prove to be OK, then that can be removed from the list.


It may also be possible that the insurance policy covers operator error. If so, perhaps that should become the focus.




.
 
I would say the engine dieseled for about 3 seconds before it quit, and from what I remember, the wave backlash coincided with the engine stopping.
The outdrive is a year old. It's a new old stock Mercruiser that we literally took out of the factory box and bolted up at the end of last season. Has very low hours.
The hull is an 87 SeaRay 250. The engine itself is a Mark V replacement engine with low hours and it wasn't running hot, but was definitely loading the dead cylinder with fuel.
Insurance will cover operator error, but not rusted manifolds.
 
Below are two pretty detailed service bulletins from Mercruiser covering these type of symptoms.

https://www.manifoldwarehouse.com/mes/news/Mercruiser_SB_Water_Ingestion.pdf Regards to Gasoline Engines and Water Intrusion

http://www.boatfix.com/merc/bullet/97/97_17.PDF Regards to Engine ‘Dieseling’ or ‘Running-On’

Below are just some general highlights of each bulletin.
Engine Running Conditions that could cause Water Intrusion:
1. Ignition misfire (fouled spark plug).
a. If an engine has a spark plug that is not firing, that cylinder will act like an air compressor and it can draw water backward into the exhaust manifold. Inspect all spark plugs, wires and the ignition system to make sure this was not the cause for water in the engine.
2. Engine run-on (dieseling).
a. An engine that continues to run after shutting the ignition key off can draw water backward into the exhaust manifold. Engine can run in reverse direction when it ‘diesels’. If an engine ‘diesels’ when the key is turned off, turn key back on and increase rpm (in neutral) to 1300 for 40 seconds then return engine to idle rpm. Let engine continue to idle for 60-90 seconds and then turn key off. Refer to Service Bulletin 97-17 for additional information.
3. Bad valves.
a. Valves that are not seating properly can draw water backward into the engine. Take engine compression. If low, grind valves and seats.
4. Sticking exhaust valve.
a. An exhaust valve that sticks in its valve guide can draw water backward. Cylinder will act like an air compressor. Repair cylinder head, as necessary.
Click to expand...

Engine ‘Dieseling’ or ‘Running-On’
Models affected: MCM 4 Cylinder, V6 and V8 with Carburetors.
Situation:
Under certain conditions, carbureted engines may ‘run-on’ when the ignition key is turned off. Normally, it will take a combination of several of the following conditions to make the engine ‘run on’. These conditions include but are not limited to:
1. Type and formulation of gasoline available in the area.
2. Type of boat and its engine compartment ventilation system.
3. Outside air, inside engine compartment air and engine coolant temperatures.
4. How quickly the engine is shut off after running at cruising or higher RPMs.
5. How the boat and engine are operated.
6. Engine idle rpm set too high.
7. Wrong heat range spark plugs or spark plugs with deposits on them.
8. Deposits in combustion chamber.
Carbureted engines, unlike EFI, do not shut off the fuel supply to the engine when the ignition key is turned off. As the engine is coasting to a stop, air is still flowing through the carburetor into the manifold. This air flow can still draw fuel from the carburetor, through the intake manifold and into the combustion chamber. A hot spot in the combustion chamber will cause this fuel/air mixture to burn. The engine now ‘diesels’ or ‘runs on’ although the ignition system is not firing. EFI engines do not have this problem because the injectors do not inject fuel once the ignition key is turned off.
Suggestion to Minimize ‘Run On’
Items number 1 ,2 and 3 can correct or reduce most of these ‘run on’ problems. Letting any engine idle a minute or two before shutting it off is desirable. This helps the engine to normalize at idle rpm before being shut down.
1. Be sure engine idle mixture, idle rpm and ignition timing are correct. On 4 cylinder and V6 or V8 engines with Thunderbolt IV ignition, setting idle rpm as low as possible can help stop ‘run on’.
2. Adjust throttle cable barrel so that the carburetor’s throttle lever returns against the idle speed stop screw every time the remote control throttle lever is returned to neutral, idle.
3. Idle engine 1 to 1-1/2 minutes before turning key off after running at cruise or higher engine rpm.
4. Try a different brand of regular fuel or try some premium fuel.
5. Increase idle mixture by 1/8 turn ‘richer’.
6. Go to next colder heat range spark plugs.
7. V6 and V8 only: Install a 140 °F(60 °C) thermostat.
Click to expand...
 
v8George said:
I would say the engine dieseled for about 3 seconds before it quit, and from what I remember, the wave backlash coincided with the engine stopping.
The outdrive is a year old. It's a new old stock Mercruiser that we literally took out of the factory box and bolted up at the end of last season. Has very low hours.
The hull is an 87 SeaRay 250. The engine itself is a Mark V replacement engine with low hours and it wasn't running hot, but was definitely loading the dead cylinder with fuel.
Insurance will cover operator error, but not rusted manifolds.
Click to expand...

What is the drive ratio? I think the 454/alpha had a drive ratio of 1.32:1. This ratio helped with pumping more water. Higher shaft speed.

How long was your NOS drive sitting in the box before it was installed. If the pump is a few years old it needs to be changed.
 
There is no way---no way!-- the engine cold have run backwards long enough to fill the motor with water like that.

Something else is going on here.

Jeff
 
The insurance company is trying to build a case that points to bad exhaust components as being the cause........... Yes/no?

The OP suggests that the exhaust components are good and are not the cause............. Yes/no?

If so, why not take the exhaust components to an authorized shop and have them tested and assessed?
Then turn the findings over the insurance agent while you simultaneously file your claim.

At least that part of the battle will have been settled, and you can begin fighting the next one.



.
 
Docksidemarineservices said:
What is the drive ratio? I think the 454/alpha had a drive ratio of 1.32:1. This ratio helped with pumping more water. Higher shaft speed.

How long was your NOS drive sitting in the box before it was installed. If the pump is a few years old it needs to be changed.
Click to expand...


It is a 1.32.1, I have no idea how long the drive sat, but the engine runs at 165* max and was running at 165* when it died.
 
RicardoMarine said:
The insurance company is trying to build a case that points to bad exhaust components as being the cause........... Yes/no?

The OP suggests that the exhaust components are good and are not the cause............. Yes/no?

If so, why not take the exhaust components to an authorized shop and have them tested and assessed?
Then turn the findings over the insurance agent while you simultaneously file your claim.

At least that part of the battle will have been settled, and you can begin fighting the next one.



.
Click to expand...


Yes, and yes. They initially blamed a bad elbow and took it to test, claiming it was the rustiest part. They cut it in half with a bandsaw and it was fine. Now the adjuster wants to inspect everything. The adjuster picked up the manifolds and heads today to pressure test. I already tested both manifolds with block off plates and they are tight up to 20 psi. Mercruiser recommends not going higher than that.
The heads looked fine. Even if they had hairline cracks, I can't see how a cylinder head can dump that much water that fast.
 
Just to share a story about dieseing....During a high school auto shop class, We ran out of gasoline in one of our shop cars (a pre-emissions Chevy v8) and substituted Coleman fuel. The engine ran fine at idle, knocked badly when the throttle was suddenly opened, and dieseled continuously when the ignition was shut off. As I remember, we needed to put it in gear to stop the dieseling. This was the most extreme dieseling I have ever witnessed. Obviously due to the low octane rating of the Coleman fuel. This is only a related story and is not directly related to this thread but I thought it may be interesting to fellow motor heads.
 
At idle speed the water in the Y pipe is almost up to the rubber coupling where the shutter should be. A sudden slow down or sudden stop with and backwash and it goes up the pipe into a cylinder or two, no dieseling required.
With the correct conditions a backwards flip of the motor will fill a few cylinders and lock the motor a lot quicker.
Look at the firing order of a running motor,now imagine all that air sucking thru a straw (Y pipe) during a dieseling condition from whatever cause . Water cannot compress and will lock the motor.

A BBC running at 3200 rpm and losing a valve face and driving the face into the head rupturing the A/F section of the head caused the A/F to enter the intake runner and #4 rod bent, #3 piston broke, and #6 rod exited the oil pan.
 
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