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 ½ 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 ½ 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.

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.

Ted

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.

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.


David

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

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.


David

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?

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.

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.

Ted

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.

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.

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?

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.

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.

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.

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.

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!!!

Here ya go:

http://www.trawlerforum.com/forums/s6/cummins-thermostat-location-23371.html

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.

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.

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.

First check the temps of the thermostat housing with an IR gun to confirm real temperature differences before doing ANYTHING ELSE. Gauges can easily be off 10 degrees.


David

Baker:
I had cummins that had to get to a high temp before the Tstat opened then temp dropped like a stone. When I removed the stats it was obvious that one was rubbing. replaced them and all was well.

timjet said:

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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My original gauges were similarly unhelpful. And come to find out, not even close... although they were at least consistent. The sweep needle suggested running temps approx. 155-160°F and that's not close to our temp specs.

Once I got the new digital gauges set correctly to interact with our particular senders, the engines run P176/S175° right where they should be. During the process, we discovered we had all along a sender-gauge incompatibility mismatch, so no wonder...

As for the heat exchanger... I simply flushed the whole raw water system, in place, with Rydlyme. Made no difference in temps, but also the ejecta during that process wasn't all that bad anyway... so I wasn't much surprised there was no change. But it wasn't all that difficult to do, might be worth considering if other symptoms suggest some blockage.

-Chris

bayview said:

Baker:
I had cummins that had to get to a high temp before the Tstat opened then temp dropped like a stone. When I removed the stats it was obvious that one was rubbing. replaced them and all was well.

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Thanks for the heads up. I will let you know how it turns out.

Also, Tim, I think your gauges have a celsius mark below each English marking(mine are so I am assuming yours are the same as mine). That will help confirm the temp at that mark after 180. It does work out to 200. I thought it was pretty smart as the range from 180-200 takes up about 30% of the gauge....IOW expanding the range we are most concerned about.

Many boats
I don't think Cummins is in any financial difficulty. They have a strong balance sheet. Engine sales to truck manufacturers have dropped a bit; US sales have been strong until very recently. Sales to China and Brazil are way down, no surprise given their economies. Can't give you a break down on marine sales.
Now the stock, which reached about 160, has dropped to about 85; a reflection of concerns that US sales may have stalled and foreign sales remain poor. It trades at about a 9 P/E.

Timjet, I was doing some routine maintenance on my boat and could not find any documentation in the log to determine when the heat exchanger was last cleaned. There were heating issues 5 degrees above the manufactures recommendation. Decided I wanted to have a date the heat exchanger was cleaned. I figured I find some clogged tubes but much to my surprise 25% of the tubes were blocked. The zincs were gone. It will be a while until I can see if the heating issue was fixed because the boat is winterized. Soaked the heat exchanger overnight in vinegar and used a rod to clean the tubes. Worked well. If it did not would have taken to local radiator shop for a acid bath. Inspecting your heat exchanger may not be a bad idea.

I dont think your engines are operating out of spec. I did in fact have a sticking thermostat in my 6bta. There was some debris in it causing it to stick partially closed and partially open at times.
Your engines both seem to be operating according to specs. But maybe you could buy 2 new thermostats and install them both and see what that does.

ranger42c said:

As for the heat exchanger... I simply flushed the whole raw water system, in place, with Rydlyme. Made no difference in temps, but also the ejecta during that process wasn't all that bad anyway... so I wasn't much surprised there was no change. But it wasn't all that difficult to do, might be worth considering if other symptoms suggest some blockage.

-Chris

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Flushing your cooling system with ridlyme is not a definitive way to clean your coolers. Any picture of a clogged cooler will explain why.

bligh said:

Flushing your cooling system with ridlyme is not a definitive way to clean your coolers. Any picture of a clogged cooler will explain why.

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There are two things that inhibit heat transfer in a heat exchanger. The classic gunk that an acid wash can cure(rust,scale/lyme,etc). But there is also the silcate gel that acid or ridlyme will do nothing to help. Silicate gel is usually caused by using incompatible coolants so probably not an issue in this case. But I have heard the symptom is a gradual increase in temp. Anyway, Fleetguard sells Restore which is good on the classic stuff and there is Restore Plus used primarily for the removal of silicate gel. My guy says that the only way to remove silicate gel is ultrasonic/laser treatment by some specialist in our area. But dunno who to believe. My point here is there are two very different things that can retard heat transfer meaning there is no one universal solution to flush with.

Before I deal with this heating issue further I will do as David and others suggested - calibrate the gauge with an IR gun. I cleaned both after coolers yesterday and they will be re-installed later this week and I'll post the results.

Baker said:

Silicate gel is usually caused by using incompatible coolants so probably not an issue in this case. But I have heard the symptom is a gradual increase in temp.

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That's interesting John and I'll bet most of us have never heard of that. On my port engine BEFORE it was replaced with the reman, I had to remove some coolant for some procedure I've since forgot and to replace the lost coolant I went to Walmart and picked up some I believe Prestone. When I got back to the boat and opened the container it was orange in color, not like the green color coolant that was in the engine. I called Tony and he said it was OK to use.

The orange color coolant looks too much like diesel fuel on oil absorbing rags and makes it difficult to diagnose leaks. I don't know how to tell the color of a bottle of coolant without opening it first.