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Old 03-04-2016, 07:15 PM   #1
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120 Lehman exhaust gas temp

So after a 50+ hr run at 2000 RPM (I usually run at 1600), I noticed slight discoloration of paint at elbow from cylinder into exhaust manifold on cylinder 6. Upon further investigating at various RPMs the EGT varies between cylinders but is consistant in the ratio of tempurature variance thru the RPM band. Cylinder 2 is always coolest, cylinder 6 is always hottest, the others fall in between. The concern is that at 1800 RPM (highest tested) #2 is 245 deg F, and #6 is 315 deg F. This is more of a delta T then I would prefer. I assume the jerk injection pump plungers are injecting different amount of fuel per cylinder with the hottest being a richer mixture. I am doubting injector or valve adj., but they are easily checked.

At what temp does the exhaust valve become a concern? Obviously #6 temps are always a concern in this motor anyway. I know these are low tech motors, but still would like to be proactive as we have no back up propulsion and will be leaving Mexico for Pananama in Spring. Those of you not familiar with our blog, should note tis is a Bowmac Reman motor now with 430hrs. So also may still be breaking in...

Thanks,

Scott
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Old 03-04-2016, 07:37 PM   #2
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Keep in mind that #6 has the exhaust from #1 through #5 flowing past it. Completely normal for the aft cylinder ports to run hotter. Also there is some variation in cooling jacket shape that makes some ports cool better than others. Don't fret too much over those readings.

If engine sounds smooth, runs smooth and does not smoke too much, good chance it is happy.
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Old 03-04-2016, 09:27 PM   #3
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you should email bomac with that same data.
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Old 03-04-2016, 10:55 PM   #4
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I assume you have a Lehman 120. I believe there is a kit you can purchase to give #6 additional coolant. Check with ADC.
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Old 03-05-2016, 12:36 AM   #5
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Quote:
Originally Posted by meridian View Post
I assume you have a Lehman 120. I believe there is a kit you can purchase to give #6 additional coolant. Check with ADC.
Do you mean the overflow bottle kit? We fitted Mercruiser kits to our engines.
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Old 03-05-2016, 12:49 AM   #6
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Quote:
Originally Posted by what_barnacles View Post
you should email bomac with that same data.


They have a phone too.
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Old 03-05-2016, 05:40 AM   #7
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No, not the overflow kit. I don't remember the details but doing a web search I got a hit on "diverting Coolant to cylinder #6" at boat diesel.com. You have to be a member to read. I think it's $25/year.


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Old 03-05-2016, 08:10 AM   #8
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I am talking about exhaust gas temp which is directly related to the combustion process. I have measured the water jacket temps on block(part of underway inspection) and am satisfied with those readings. I am very meticulous with heat exchanger, raw water pump, and block flushing due to the #6 issue. I will eventually contact ADC or Bowmac, just wanted to run my theory by someone more knowledgeable then me. Again, I do not believe this is an engine cooling system issue.
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Old 03-05-2016, 08:56 AM   #9
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I was wondering if your starting to have an injector problem?
Found this, although how large is large for temp variation to qualify?
Why Diesel Fuel Injectors Fail - Diesel Power Magazine

Quote:
Large cylinder-to-cylinder exhaust temperature variation
Causes:
Poor nozzle flow balance
Nozzle needle lift incorrect (mixed or missing parts)
Partially plugged nozzle
Wire-brushed nozzles

Prevention:
Keep fuel system clean, change filters, purchase fuel from reliable sources, and avoid filling from portable construction fuel tanks or questionable sources
Reject all fuel system replacement parts that have metallic burrs
Do not use remanufactured or aftermarket components that are not properly designed or manufactured
Ensure injectors are serviced or purchased from a reliable source
Do not clean nozzles with a wire brush
Failure: Incorrect Injection Timing and Duration
Indicators:
Rough running, poor cylinder balance, and knocking
Piston damage
Large cylinder-to-cylinder exhaust temperature variation
Causes:
Ball seat wear
Incorrect injector assembly, parts mixed, or parts missing
Injector needle lift increased to increase output
Prevention:
Replace worn injectors
Ensure injectors are serviced, tested, and purchased from a reliable source
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Old 03-05-2016, 09:43 AM   #10
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Nigel Calder says 20 deg. F delta T, but fIls to state ar what load. I am in that range most likely at idle, increasing Delta T from there. Engine sounds, and performs fine. Not noticing sheen on water at exhaust or black smoke, which was why I was thinking injectors MAY be OK. I can always switch injectors around and see if temp variance follows. But at anchor in MX, would rather not!
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Old 03-05-2016, 09:44 AM   #11
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Sorry for all the typos, iPad is killing me
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Old 03-05-2016, 06:08 PM   #12
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I would also appreciate anyone that could shoot there Exhaust gas temps right on elbow as it leaves the head into exhaust manifold and post or IM for comparison purposes. A FL120 would be best, but any old low tech NA diesel with an inline jerk pump would be interesting. No rotary pumps as I think the metering is same for all cylinders, then distributed.
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Old 03-06-2016, 10:53 AM   #13
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You must be reading egt on outside of pipe, with an infra red meter. Actual egts, should range from 400 to 1200+ depending on load. I would guess that under normal load actual temp should be around 600-700 degrees. Things start to go sour after 1300 degrees.
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Old 03-06-2016, 11:14 AM   #14
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I am using an infra red gun on outside of pipe before water jacketed manifold. I did read similar numbers when researching egt from other sources, but really have no way of checking actual temp on all cylinders. I am hoping for a comparison with someone else using infra red gun, preferably on a FL120.
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Old 03-06-2016, 12:30 PM   #15
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What exactly are you trying to figure out? The temp of the manifold in uncooled areas is going to vary from cylinder to cylinder for many reasons.

It is not a reliable way to check each cylinders EGT.

Nothing wrong with 350F in those areas when running a bit hard. Exhaust gas temp probably in the 800-1000F range, but that is not what you are measuring.
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Old 03-06-2016, 01:34 PM   #16
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#6 is the Achilles heel of the 120. All of the failures that I have heard of, from friends or hearsay say the number 6 failed. I have never heard of any other cylinder having issues. I think it is much more likely to be something to do with coolant (the engine was not designed to be tilted) or more likely something to do with number 6 running lean.
Make sure the cooling jacket is burped and try switching injectors. If they have not been done on your watch, it is worth having them checked/overhauled. Unless there is an obvious change, the injector pump is more likely to cause lean running than an injector.
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Old 03-06-2016, 06:41 PM   #17
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Ski, yea I think I'm over thinking it, probably just anxiety over running some of the long open ocean legs in my future w/o auxillary propulsion. Honduras to Panama, and Panama/Columbia to DR or PR. Thanks for the input
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Old 03-06-2016, 07:04 PM   #18
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Sealife- Understood. Single engine here too, so I'm well aware of keeping the big beast happy.

You ran 50hrs at 2000rpm with no issues. That is a good thing. The Ford apparently has fairly weak cooling flow around cyl #6, so if you did not blow #6, you should be ok in that regard up to 2000. That you have proven.

To be more cautious, while out in the boonies, don't go over 1900 and you will still be in the proven safe operating "envelope".
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