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Old 01-25-2016, 08:12 AM   #1
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Cummins engine questions

My twin Cummins 6B 330 series have performed flawlessly for the last 2 years. A little history. The port engine was replaced with a Cummins certified reman in November 2013. Part of the reason was both engines were over-propped for the first 1300 hrs of their lives. So the port engine reman has 500 hrs properly propped its entire life and the starboard engine has 1850 hrs with the first 1300 hrs over-propped.


I run the boat 75% of the time at 1400 rpm at displacement speed, the rest is at 2400 rpm on plane. Coolant temps on the port reman engine is 180 at 1400 rpm and 190 at 2400 rpm. Coolant temps on the starboard engine is 180 at 1400 rpm and slightly above – 182 at 2400 rpm. Boost pressures at 2400 rpm are 8.5psi for the reman and 10 psi for the starboard engine. When Cummins certified the reman their test data showed a boost of 11.8 psi on the reman. I recorded the boost shown on the gauge at certification and it was 8.5, so my gauge is probably off or I’m getting leakage somewhere in the tube or connection. The important thing here is that the boost has not deteriorated since the install.

This data shows an interesting point. The original starboard engine seems to perform better than the port reman. Coolant temps are lower and boost is higher.

I installed SBMar’s envirovent crankcase ventilation system when I purchased the boat at 1000 hrs on the original engines. This system collects blow-by in a “puke bottle” rather than re-introduce it back into the crank case like the Walker air sep system, which I removed when I bought the boat. The reman engine has no blow-by but the original starboard engine produces about ˝ qt of blow-by when run at 2400 rpm after about 15-20 hrs. It produces an insignificant about of blow-by at 1400 rpm.

If you’ve read this far I have a couple of questions. It’s been 500 hrs and 2 years since the aftercoolers have been serviced. Being back in Tampa after our 2 year cruise to the Chesapeake, I removed both aftercoolers and have disassembled the port reman. It looks very clean for 500 hrs of use with a little gunk that’s easy to remove. All the zincs were in good shape.

I will disassemble the starboard original aftercooler this morning. The air cleaner on this engine has a lot of blow-by gunking up the bottom of the air filter. This would be normal since the suction to remove the blow-by is created by the turbo.

1. The reman runs 10 deg hotter at planning speeds, should I also remove the heat exchanger and inspect? There was nothing blocking raw water flow in the aftercooler or tranny cooler. New impellers were installed 200 hrs ago and when they were replaced the old ones looked new. I don’t think the heat exchanger in terms of time needs to be cleaned. Does the fact that is runs 190 deg at planning speed something to be concerned about?

2. The original starboard engine has blow-by. Is ˝ qt in 15-20 hrs at 2400 rpm excessive? Almost none at 1400 rpm. And if so is there anything I can do about it?

3. The original engine has 900 hrs since the heat-exchanger was serviced. Should I remove and clean? Coolant temps on this engine are good.

Lastly WOT at time of reman certification was 2950 on both engines 2 years ago. Last time I checked, 10 engine hours ago I got port reman – 2900 rpm, starboard original engine – 2800 rpm. The boat was heavy with 8 months of accumulated junk from living on it.
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Old 01-25-2016, 09:01 AM   #2
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The blow-by seems high. Not sure I would do anything about it though. Not sure there are any simple inexpensive options.

One of the bad things about 2 engines is that you are always comparing one against the other. With only one, you tend to accept what you see. That being said, there are all kinds of things that can be a culprit for higher temperature. Could be a thermostat or a sending unit. My recommendation is preventative maintenance. Doing the impellers is good. Pulling the heat exchanger end caps and inspecting the tubes would be a good idea also. Making sure the gear cooler and after cooler are clean is also a good idea. I would much rather do routine preventative inspections / maintenance than repairs. How old are the coolant and thermostats. Not sure on the 330, but on both my Cummins the thermostats aren't expensive or hard to change.

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Old 01-25-2016, 09:10 AM   #3
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First thing to do is verify the readings gauges are subject to lots of variation. I wish the specs were in a table because it is hard to understand when scattered in text nevertheless the first thing that came to mind was having the props scanned to be sure they are correct and equal. general prop in Bradenton is my go to shop. No charge for scan. Seawater coolant systems should be opened and inspected every few years IMO even if just so you can sleep well. Higher boost if true would add to blow buy.
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Old 01-25-2016, 09:24 AM   #4
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The differences in temps and boost could be due to a number of benign things; gauge calibration- check with an IR gun and differences in transmission ratio port to starboard putting more load on one engine.


Oil consumption is a little high, but is probably due to the prior overloading. Just live with it. Sbmar's Envirovent will help keep the gunk out of the air cooler.


Tony recommends servicing the air coolers every three years unless fresh water flushed after each use, then five years.


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Old 01-25-2016, 10:06 AM   #5
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Port Reman Starboard
coolant temp @ 1400 rpm 182 180
@ 2400 rpm 190 182
Boost @ 2400 rpm 8.5 psi 10 psi
WOT 2900 2800

The engines are fresh water flushed so will forgo heat exchanger mx. After coolers will be cleaned and installed. I'll swap the coolant gauges and see what I get. Where do I "shoot" the engine with an IR gun to get accurate coolant temps? At the sender?
The props are 500 hrs old and were purchased for the sole purpose of getting proper WOT.
Trannys are original with 1.96:1 ratio. Both same ZF Hurth HSW800 A2-2.0
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Old 01-25-2016, 10:13 AM   #6
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Tim:


Shoot the top of the thermostat housing. Calibrate your IR gun first by shooting the side of a dark pot of boiling water, right after turning the burner off so it doesn't interfere.


Some transmissions, and I haven't a clue if yours is one, specify the forward ratio, but for twins, the transmission is used in reverse for one engine and has a slightly different ratio. Check the data sheet for that transmission to know and check prop shaft rotation. If it is backwards for port engine then likely.


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Old 01-25-2016, 10:18 AM   #7
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A question about the after-cooler o rings? I have used locally purchased O rings from a hydraulic shop, Part # FS 568-248V with a cross section dia of .14" all 4 for a couple of bucks. Cummins sells them for a couple of hundrend $'s and SBMar sells them for $35/pair. Tony on his web site even mentions buying them from a hydraulic shop.

Have I been lucky in using these cheap O rings. I know how important the seal is but are the Cummins or SBMar ones any different?
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Old 01-25-2016, 10:30 AM   #8
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Thanks David, the starboard shaft rotates CW viewed from aft and the port CCW. I will have to do some research to determine actual ratio if different than I stated above.
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Old 01-25-2016, 10:36 AM   #9
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Tim, I think my Cummins dealer supplied me with stock Hydraulic o rings when I did the C450 two years ago. If your changing them every few years, I don't think it would make a difference in that application, as long as they are the right size.

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Old 01-25-2016, 10:42 AM   #10
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Thanks Ted, I've had good luck with the ones mentioned above. They've been on for 2 yrs and 500 hrs without issues. I have a hard time paying big bucks for a part that says Cummins on the package when the exact same part can be bought for much less w/o the Cummins name.
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Old 01-25-2016, 10:43 AM   #11
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I have seen questions like these a few times and have a few questions myself which may help with the answers....


Do you have pyros on the boat?
If yes what do they read?
Are your tachs known accurate?
How do you set engine loads at higher cruise? (rpm?)
Are your trans ratios equal pt and stb (A & B)?
Have your props been balanced side to side so that they are near equal?


I have always suggested that the engine be propped so that they can achieve rated WOT rpm + 3-5% as a brief test in gear on a fully loaded boat when hot a humid. I believe your engines are rated at 2,800 so you would want to see 2,885-2,940 for that test.
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Old 01-25-2016, 11:03 AM   #12
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I read on yahoo that Cummins was in some kind of trouble in a financial way. Was a world market sort of statement. Is that true?
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Old 01-25-2016, 11:04 AM   #13
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Also, blowby is how much combustion gas ends up in the crankcase. It is measured as a gaseous or volumetric flow rate. Sounds like the complaint is the amount of oil ending up in the puke bottle. Two different things, could be related, or not.

To check on blowby, there is a quick test to actually measure it. Whole threads on Boatdiesel give the details.

The two engines being 100rpm off is a concern. Stbd running higher boost at 2400 sounds like it is loaded more.
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Old 01-25-2016, 11:14 AM   #14
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Yes I forgot to ask if you have verified tachs.


there seems to be several different size O rings used. I have always trusted Tony to give me the correct parts even the Cummins dealer has messed up. Yes I agree moat O rings are probably from just a few makers and bearing shops usually have them.
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Old 01-25-2016, 11:17 AM   #15
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yes higher boost and lower rpm indicates more load. I know the props were done before your trip by if it were I would have them rescanned before doing much more. You are doing tests now not two yers ago and need to start with some known baseline data, Guessing about props isn't it.
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Old 01-25-2016, 11:25 AM   #16
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FWIW - on your engines and at that speed and loads boost if very sensitive and can be 'out' by 1.5 psi side to side by many things including but not limited to these:
- props out of balance
- engine rpm out side to side by about 20 rpm
- a dozen or so moderate barnacles on the higher boost prop
- about 5' of 1/4 nylon line wrapped around the lower boost prop (lobster pots)
- a prop which has a small 'ding' in it


Just a few possibilities , the pyro readings would help the diagnosis , coolant temp readings will not typically say much about combustion or overloading other than what the cooling system status may be.
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Old 01-25-2016, 12:20 PM   #17
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Strangely, Tim, I am battling the same overtemp issue you are on the port engine. I still do not have it licked. I have inspected/changed impeller. Aftercooler recently serviced. Coolant recently flushed and changed. The weird thing with mine is that the overtemp is variable and random. Sometimes it does not run hot. Others, like yesterday, it went straight to 195 before I saw the thermostat open and the temp reduced. Anyway, a thermostat is rarely the issue in these cases as your local Cummins dealer will tell you he sells a shitload of them because that is the first thing people suspect. But in my case, I am thinking it might be the Tstat and it will be changed this week. I have even had Cummins people ride along/sea trial with me. Of course, it ran perfectly fine when they were aboard.
As far as IR gun goes. I shoot the outlet "pipe" coming out of the thermostat right after the hose ends. This seems to be the most uniform consistent area to get the gun on. And I would assume since the coolant is coming out of the block right there that it should be a good measure of what is going on in there. Strangely, when we did the seatrial, although my gauge was reading 188...the IR reading was 180 on the nose. And while the starboard side was reading about 182ish, the IR gun shot on that side was 188!!! ALmost reverse of what was being indicated. Anyway, I was borrowing IR guns before this and just purchased my own. Had I not had 8 people on the boat with me yesterday I would have gone down there to get some readings as it was indicating the hottest I have ever seen. I have a thread on here somewhere that I will link you to when I find it.

As far as your old engine "performing better"(my words not yours), the NASCAR guys always say that an engine always runs best right before she gives up!!!!....Sorry amigo....just messing with you and trying to bring levity...although not sure that is the way!!!
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Old 01-25-2016, 12:23 PM   #18
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Here ya go:

Cummins Thermostat location.

Also, as you will read on there some people mention tranny/oil cooler as a remedy/cause for overtemp. That will be my next action if this does not fix it. They are "relatively" cheap and look easy to replace.
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Old 01-25-2016, 02:03 PM   #19
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Curse of the twin engine boat. They never are identical. Differences cause folks to sniff around looking for problems where there might be none.

A good test is to ask yourself if each engine was in a separate boat, would you be worried with what the engine was doing?

That's why I went single!!

One customer named his engines. Girl names, of course. That way when they did something wierd, he could blame it on their personalities. Having a female personality can explain away a lot of wierd.
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Old 01-25-2016, 02:45 PM   #20
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Yes it could be a lot of things and I could spend a ton of money trying to "fix" it.
I do not have pyro's.
The boost I'm really not too worried about. If I increase the port (reman) engine 25 rpm as shown on the tach, the boost for both engines are the same. My sync gauge shows when engines are in sync a difference of 1-2 psi with the reman lagging. But again increasing rpm just 25 rpm brings them together. If I didn't have a boost gauge I would never know there is a difference. So maybe I should sync my engines via boost. Can you calibrate sync gauges?

The coolant temp is more worrisome. But in looking over past data and engine readings the reman has always had a higher temp reading usually by 5 deg. Unfortunately Cummins did not take coolant readings when they certified the engine so I'm going with my own data. But the really stupid IMO coolant gauges are very hard to read. Is the mark above the labeled 180 mark 190 or 200. I think it's 200 and the pointer has pretty much been half way between the two. I was mis reading it for 2 years thinking it was 185, but in reality it was 190 and it's always been there. So I'm going to do what I do best, monitor it.

Final question: With the starboard engine running good and except for the blow-by or as Ski mentioned something else should I dig into the heat exchanger. Temps are good on this engine. It's been 5 yrs since this heat exchanger has seen the light of day.
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