cat 3126 Overload and full consumption

[Almirante]

A maybe stupid question, but I will ask it:
Does an engine that is overloaded use more fuel at for ex. 2000 RPM than another not overloaded engine at the same 2000 RPM?
I would say he needs more, but am I right?

Background is that my starboard engine broke down with a big burst and a lot of white smoke on Saturday for the second time within 30 hours. Last time a valve broke and now it seems that the cylinder head has a big problem.
The engine cylinder head was overhauled from the CAT dealer about 40 hours ago after breaking down the first time.Then after 10 hours the valve break and now again after 30 hours this big problem.
Then the thing with the fuel consumption. Last time when I put on fuel I found that the engine used much more fuel (nearly double) than the port engine...
CAT is again working on the engine, I think tomorrow they can tell me what happened...
So any ideas are welcome.

Greetings, Stefan

 

[HUMPH]

The engines should burn the same amount of fuel if they are at the same RPM. I am not really sure what you referring to when you say one is overloaded. Hopefully fuel is not dumping out your exhaust or something.

 

[480ces]

You are correct that an overloaded or propped engine will demand more fuel at the same RPM.

You should be able to get a graph from Cat that show's RPM vs. Fuel Bun at rated output.

If you are burning more than it's rated for you will be above the max output curve and have HIGH EGTs. This can lead to valve and valve seat problems among other things.

Of course a sticking injector could do the same...

Are your props the same?

 

[Almirante]

Props are the same. All original.
CAT will repair the engine the third time now within 40 hours and provided that CAT does good work, there must be a reason for the breakdown in such a short time which is not known yet.
On the other side: When everything in the system, props, shaft etc. is original and had worked for many years, why should the engine now be overloaded? Makes also not really sense to me...but compared with the port engine which goes with ease up to 2900 RPM the starboard engine which I am talking about needed always much more effort to reach higher RPM, and did not reach 2800 RPM.
So "overload" is one of the possibilities I am thinking about.

 

[fwebster]

If nothing changed in the drive line, then an engine that ran to 2900 last year should do the same this year if t he other engine in the pair still turns 2900.

On the overload question, if an engine rated for 2800 rpm will only turn 2400, and you advance the throttle to WOT then you are dumping in the same amount fuel as you would if the engines turned to 2800, so yes an overloaded engine will use more fuel.

Far be it for me to criticize the mechanics in this; I haven't even seen the boat...... but Cat has some very sophisticated testing procedures and they should be able to fix broken valves and blown head gaskets.

 

[Lazy Daze]

Fuel usage is primarily dependent on your throttle input. The farther you "have your foot into it", the more fuel you are demanding. Assuming that there's no issues with an ECM where it's pulling fuel for some reason, you are in complete control of how much fuel is being used by where you have the throttles positioned, not the actual RPM's. Another way to think about it... If you would run the engine out of the water, you would max your RPM's with VERY little throttle input, but obviously you wouldn't be using much fuel.

 

[HUMPH]

If nothing changed in the drive line, then an engine that ran to 2900 last year should do the same this year if t he other engine in the pair still turns 2900.

On the overload question, if an engine rated for 2800 rpm will only turn 2400, and you advance the throttle to WOT then you are dumping in the same amount fuel as you would if the engines turned to 2800, so yes an overloaded engine will use more fuel.

Far be it for me to criticize the mechanics in this; I haven't even seen the boat...... but Cat has some very sophisticated testing procedures and they should be able to fix broken valves and blown head gaskets.

Frank, so if both engines are running the same RPM there is a chance for one to pull more fuel? I assume you mean if the engine using more fuel can't reach max RPM so it is essentially using max RPM fuel at less than max RPM? (If the question makes sense)

 

[fwebster]

Ken,

If both engines are properly loaded, then the difference in fuel consumption would be a product of differences in pump, governor,or injector timing and settings.

On the 2nd question, yes.

 

[Almirante]

O.k. I remember that I always had to put the starboard throttle lever more to WOT than the port lever at the same RPM´s. So, that means, when I resume, this is the reason for more fuel consumption of the starboard engine (although the same RPM´s like port) and this says to me also, that there is a good chance that the engine is overloaded.
If this is so, my question is why? The propeller is the original, nothing changed in the past.

Stefan

 

[Lazy Daze]

What's the condition of your prop? Maybe it's out of spec? Or as Frank mentioned above in post #8.

My guess... Have a Cat mechanic check it out.

 

[The Bill Collector]

O.k. I remember that I always had to put the starboard throttle lever more to WOT than the port lever at the same RPM´s. So, that means, when I resume, this is the reason for more fuel consumption of the starboard engine (although the same RPM´s like port) and this says to me also, that there is a good chance that the engine is overloaded.
If this is so, my question is why? The propeller is the original, nothing changed in the past.

Stefan

When was the last time the props were off and balanced ?

 

[Almirante]

When was the last time the props were off and balanced ?

I own the boat since last year. Spoke with the old owner, he never checked this. Just when the boat was out of water checked for scratches and damages. So I did before buying...

So this is what CAT told me yesterday evening: Oil analysis which they made first says that this time there is water mixed within the oil. This explains the white smoke we had. Than they said that (again) a valve broke and part of it is fallen into the engine. Today they will find out if this caused further damage so that the engine has to be removed for repairing or that they can repair it with the engine still build in.
The only thing that calms me down is that CAT just informed me that this is all covered by their guarantee...
I will report how things go on...

 

[fwebster]

You might not be aware that Caterpillar had a batch of bad valved supplied by a vendor in the 1996-1999 time period. The hardness of the valve material was no to Cat's spec. NObody knows how or why the bad valves made it thru Cat's normal inspection procedures. The valves found their way into both 3116 and 3126 engines. When they fail, the usual problem is the keeper on the valve stem comes off and the valve drops into the cylinder. Cat had no production records that tied the bad valves to a particular group of engine serial numbers. Cat repaired all the engines involved when the valves failed.

Since Caterpillar has already agreed to repair the engine under warranty, the above is just background information.

 

[Almirante]

You might not be aware that Caterpillar had a batch of bad valved supplied by a vendor in the 1996-1999 time period. The hardness of the valve material was no to Cat's spec. NObody knows how or why the bad valves made it thru Cat's normal inspection procedures. The valves found their way into both 3116 and 3126 engines. When they fail, the usual problem is the keeper on the valve stem comes off and the valve drops into the cylinder. Cat had no production records that tied the bad valves to a particular group of engine serial numbers. Cat repaired all the engines involved when the valves failed.

Since Caterpillar has already agreed to repair the engine under warranty, the above is just background information.

This is exactly I found out in the meantime: The Serial No. is 08NM 1681 this is one of the effected engines. The warranty refers to the repair they did and which I already
paid months ago. After this first repair which cost me around 19k Euro the engine broke after 6 hours of operation (valve broken) and now 32 hours later again with the same problem. And a "whistleblower" told me one other thing. In 2004 the first owner here in Portugal on the island had the same problem...

Thanks for the informations. I did not get news from CAT today, but I will tell if there is something new...

Stefan

 

[moparlvr4406]

SOUNDS LIKE AN INJECTOR ISSUE TO ME
could explain the internal damage also.
but it's been years since I did any diesel work

 

[Almirante]

Short update: Caterpillar decided to change the complete cylinder head and the block. Covered by the warranty. In the next days we put the boat to the dry dock. Then the engine will be removed...Plan is 4 weeks to complete the works. I will remove the shaft and the prop too, to check them.
So things go into the right direction.

 

[Almirante]

Short update: Caterpillar decided to change the complete cylinder head and the block. Covered by the warranty. In the next days we put the boat to the dry dock. Then the engine will be removed...Plan is 4 weeks to complete the works. I will remove the shaft and the prop too, to check them.
So things go into the right direction.

So here we go> Cat replaced the cylinder head and the block. The boat is in the water again since yesterday.
My question now< How do you handle it, most of the engine and especially the moving parts are new, do you run at reduced rpm the first hours.

Thanks,
Stefan

 

[fwebster]

About the only guidelines from Caterpillar techs who do work here are for the first 50 or so hours, to stay away from WOT and to vary the rpms, i.e. avoid long sustained runs at the same rpm's, but to vary the engine speeds. Other than that, use and enjoy the boat.

 

[Almirante]

About the only guidelines from Caterpillar techs who do work here are for the first 50 or so hours, to stay away from WOT and to vary the rpms, i.e. avoid long sustained runs at the same rpm's, but to vary the engine speeds. Other than that, use and enjoy the boat.

Thank you Frank, I could not find something about these things in the maintenance book and I will do like you suggested, vary the rpm and avoid WOT for the next 50 hours. This makes sense to me.

Stefan

 

[ttmott]

Suggest also oil change and analysis at the 50 hours. Normally will see elevated ferrites on break-in but more interested in copper and coolant components. Also suggest saving the oil filter for cut-up and pleat inspection. Your Cat mechanic should direct these as procedure.