Cummins v8 na 320hp

Yes 23/24 gallons @2300 RPM's,fully loaded with all personal gear, tools,550 gallons of fuel,150 gallons of water.They are really quite economical considering they are pushing about 20tons.Last trip to the Bahamas during winter I did almost the entire trip @ 1350RPM's,which is 8.5 knots and cut my normal cruise fuel burn by 60%. That is taking into consideration that when I got up on the Bahama Bank I hooked up to cruise all the way to Abaco.Another thing that is worth mentioning.The 320's recirculate and burn their crankcase emissions,that in itself makes for a clean engine room and no need for plumbing or Airseps.

They are pretty darned good on fuel for what they are.

Hi,

Can you please enlighten me as to exactly what engines and the application where this problem occurs?

In my case they are pushing a 42' Hatteras sportfish.I don't know of any overheating problem from running them at low RPM's or at high RPM's.I also don't know of any overheating problems from running a CAT a low RPM's either?

Inquiring minds want to know

My mind is just a little bit confused.

First you say they do; then you say they don't.

Knew a girl like that, once.

Could you please be just a little bit clearer, regarding Cats overheating at low rpm.

I don't know of ANY particular model of CAT engines that overheat from running at LOW RPM's,period.

Hi,

Maybe you are.

The two statements were made by two different YF Members.

The first Santelia wrote: Any overheating at low rpm like some Cats have?

The second 42Hatteras wrote: I also don't know of any overheating problems from running a CAT a low RPM's either?

I was curious to know what the engines and the applications were when overheating at low RPM's was referred to by the first poster because like the second poster it is not something I am familiar with and I would like to know if there is a particular issue that is lurking around with an engine type in a particular app that may not be well known.

Hi,

As the speed that supposedly causes Overheating problems there could be a couple of things at play here.

Is the vessel having these problems a dry stack or wet exhaust system?

I am asking this because if dry stack my next bit of writing will have no bearing on the possible cause.

If Wet Exhaust, the engines might not have enough gas flow at those RPM's to clear out the exhaust properly and the back pressure could be elevated causing an increase in heat particularly exhaust temperature.

If not and this could be the problem with either type.

The revs the engine is operating at do not provide enough Salt Water flow to the coolers to get the required heat exchange going.

Either of these type of scenarios can cause similar problems on any engine not just one brand. You will find the old 903's you first asked about can also suffer the same issues but they are not as sensitive to them as a modern engine.

BTW: I have not worked on any marinised 903's but have done a bit on automotive ones 30 yrs ago. They were a great engine in their day sitting in front of a 15 or 16 Speed Gearbox under a big load of logs.

IMO: No relation at all to the 555 POS that carried the same makers label and made it to a number of boats.

The only time I have seen CAT's overheat at lower RPM's like that is if they are in a seriously overloaded situation (load factors 80+) at those RPM's either due to hull design (pushing boat at maximum plow), a dirty bottom, or towing something the vessel wasn't intended to tow, and rarely have I seen it and it usually occurs on a boat that has dirty heat exchangers.

The 903's are especially sensitive to coolant/additive mixture, require a special blend to keep the liner O-rings in condition. If the mix is incorrect, or if straight anti-freeze is run, the liners will pit rapidly, and coolant will mix in the oil.
Test strips are available, but what a PITA!

These motors were designed to be tank motors, built heavy to stand up to radical abuse, but if you talk to some old gray bearded military mechanics, you will find that they weren't that great in that app either.

Sportfishermen around here say the 903 noise or vibration or whatever it is raises big marlin, don't know if that matters to you, but some owners baby these motors along just for that value.

Bottom line, if you are really in love with this boat, make your offer to reflect the need of an almost certain repower.

All of the above is true regarding the PH and condition of the coolant but it also applies to every wet sleeved Cummins and CAT diesel as well.As long as they are using a clean antifreeze /water coolant mixture and the water filter/coolant conditioners are changed once a year in a rec, boat they will last many,many years without any liner issues.

Besides keeping the cylinder packing rings in good shape conditioned coolant also prevents gas bubbles from being suspended in the coolant,thus preventing the cavitation burning or "air hammering" that causes the pin holes in the liners.Actually this was not as bad a problem in the 903's as it was in the NH and NHT series engines,but when Cummins built the N-14 engine they redesigned the block in such a way that no single liner is exposed to direct coolant flow.Consequently protecting the liners.That coolant routing technique is pretty much the same used by all US heavy diesel manufacturers now.

As far as unreliable? Total nonsense........ The 903 Cummins was not designed or built to be a "tank engine" they were in fact built initially to meet specs, to power the entire fleet of New York City garbage trucks! The truck had to be a super heavy duty cab forward,axle back,ten wheel truck,powered by a V-8 diesel of over 300hp. The engine had to fit under the cab and meet certain noise levels. So Cummins built the 903 and Brockway Motor Trucks of Cortland New York built the trucks.They turned out to be really good engines and they responded very well to increased horsepower requirements,but when they couldn't meet the higher EPA emission standards coming in the late 80's the 903 line of engines were only then being sold to the US Government ie: every USCG 41'-UTB and various military apps, including tanks.

Did the 903 have any inherent problems? Yes a couple. They were known to smoke on a pull as their horsepower ratings rose and they broke a crankshaft now and then,but that was almost uniquely a problem only in trucks and it was caused by drivers lugging them down too low before downshifting.

Hi,

Here is one that has had a wee problem in a Tank.

Cummins 903 blew a rod. - YouTube

IFRC, The pure Military Cummins Engines we used to get in NZ from the US were a wee bit different to the genuine Automotive equivalents.

What immediately springs to mind was a 1/8" Bore difference on one of them and a small lump or hollow just under the top edge of the block on the 903's.

It has been a long time and a lot of engines since I had spanners on one so if I have had a brain fart please feel free to correct me.

spanners

"Brain Fart" you sure have, what the h--l are "spanners"

I'd NEVER heard of a boat breaking a crank, until March of this year. I bought my boat in January and ran it home from Boca Raton to Pensacola, Fl, about 500 miles. The first trip out, after running fine for maybe 7-8 hours, the port motor, a VTA903, broke the crankshaft between 1st and 2nd rod journals. parts are available, we found everything needed for a MOH. Also, the USCG is still running alot of 903's, atleast in this area. If they ever de-commission them there'll be tons of surplus parts.

Even if parts were cheap and available, which, in my experience they are not, I still contend that repowering, say with C-series Cummins of a more appropriate horsepower or Cats, or any brand of comparable modern power will save money, time, fuel, and headaches in the long run, and do quite a bit toward keeping our ocean environment healthy.

As mentioned previously, the 903 is a smoky, leaky motor, and leaves an impressively foul carbon footprint.

As old as the motors are, it is doubtful that they have been maintained immaculately for all their life, and hidden issues are certain to be lurking!

Check out the Cummins factory rebuilds, a fantastic savings on motors that are better than when they were new! (no, I am not working for them, just been there, done that, and am happy with the outcome)

The British term for what we call open end wrenches.

Yeah, except the only problem for a lot of people is they can do major overhauls on their existing diesels for 1/3- 1/2 the price of changing them out and re-configuring the entire boat for modern diesels especially when you consider all of the wiring necessary for the electronic controls and gauges.

Hi,

Very well said and to the point.

What do you call the tools with a ring at one end and an open end at the other?

What do you call the tools with rings at both ends?

In NZ and Australia they would be called Ring and Open Ended Spanners and Double Ring Spanners.

In the contiguous 48 I would think the last word would be Wrenches for both.

I believe Yachtjocky was just having a dig as he has no doubt been around long enough to have heard these tools called many things often with a prefix that would be shown here as *******

Before the self proclaimed Language experts chime in, here is an old advert we used to see at home.

Sidchrome TVC - YouTube

I didn't intend to overhaul that engine. I purchased the boat hoping to get a season or two out of the motors, then re-power. When it broke the crank, it looked like we could roll another crank in where it sat, without pulling the motor out of the boat. Once we got the crank out, then we found more damage. In hindsight, I should've bought a running take-out, and I would've been dollars ahead. I WILL be repowering in a year or two, probably QSM11's.