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Old 04-17-2014, 07:14 PM   #1
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6BTA operating temps

What are the safe operating temperatures of a cummins 6bta?
I'm running at 160 unless at about 1500 rpm. Above that , the temp goes up pretty dramatically.. almost to 200. I know I have to clean the heat exchangers, but what are the safe temps for this motor?
Thanks
Scott
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Old 04-17-2014, 08:36 PM   #2
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Around 200 degrees is the norm. 160 is too cold, you might want to replace your thermostat.
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Old 04-17-2014, 08:39 PM   #3
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What is a high temperature? What is too hot?
Thanks!
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Old 04-17-2014, 09:19 PM   #4
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Most of the b-motors I'm around run in the 170's at low load, and 180-190F under heavy load. Above 190 the thermostat is full open so that is a sign to clean coolers. If it is a 6BTA with sea water aftercooler, plan on cleaning all three: Aftercooler, gear cooler, coolant HX.

When running these things, if it gets to 200, I pull back.

Running 160 is too low, as per above.

Get a IR heat gun, even the cheap ones work reasonably well. Shoot cylinder head top fwd right corner over tstat. Add about 5F to reading and that is close to coolant temp. Keep gun on the boat as lots of temp gauges are flaky
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Old 04-17-2014, 09:26 PM   #5
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https://marine.cummins.com/attachmen...6b/fr90437.pdf
180-203 per manufacturer specs. Here in tropical waters 200 is about average for them, even at trolling revs for marlin fishing.
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Old 04-17-2014, 10:04 PM   #6
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Stand corrected. 203 it is. But the ones I run seem to stay below 200 unless coolers are getting fouled.
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Old 04-17-2014, 10:30 PM   #7
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Very much a reflection of the water temperatures here (30 deg celcius) but still generally speaking it is preferable to run the engine at the upper end of its heat range provided you have confidence in your cooling system. IE less margin for error at 200 than at 180
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Old 04-17-2014, 10:47 PM   #8
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Bligh

Unless done at survey, this is a good time to verify full rated RPM can be achieved under load. Verify with photo tach. On an NT, if full RPM cannot be achieved you'll be chasing high temperature gremlins round and round.
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Old 04-18-2014, 01:52 AM   #9
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Quote:
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Bligh

Unless done at survey, this is a good time to verify full rated RPM can be achieved under load. Verify with photo tach. On an NT, if full RPM cannot be achieved you'll be chasing high temperature gremlins round and round.
I'm not sure i understand what you are saying. Are you saying i can't achieve full rpm or i can't achieve full rpm without overheating? I'm sure the heat exchangers need to be cleaned on this engine before i try to operate it at full rpm for any amount of time. I'm not even sure what full rpm is. I'm guessing about 2600 rpm. The engine manual is not very helpful in these regards. As far as the cooling system is concerned it does not seem that complicated from what i can see in the manual and on the engine. Please elaborate as i must be missing something.
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Old 04-18-2014, 07:16 AM   #10
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You are aware your heat exchangers need cleaning and you are seeing temps rise rapidly above 1500rpm....what's stopping you just cleaning the heat exchangers?? Simple, inexpensive job on 6BTA's
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Old 04-18-2014, 07:17 AM   #11
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Many engines suffer from over cooling as heat exchangers are designed for worst case , tropical waters Big throttle.

The solution is a bypass thermostat installed at the heat exchanger.

These will usually have a thermostat that will keep the water returning to the engine at about 20deg F below the engines desired operating temp.

The bypass could be done with a valve , but a real thermostat is far less work to live with. Seamless once installed.
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Old 04-18-2014, 07:43 AM   #12
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My 330 6BT's run at 180-185 coolant temp (as read on the gauge) at all rpm's.
I fresh water flush my engines and have never had a cooling problem.
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Old 04-18-2014, 10:14 AM   #13
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When I had my 6BTA 270 it ran at 165-170 at low rpm, and 175-190 under heavy load or WOT. Those are temps verified with an IR gun.
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Old 04-18-2014, 01:20 PM   #14
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You are aware your heat exchangers need cleaning and you are seeing temps rise rapidly above 1500rpm....what's stopping you just cleaning the heat exchangers?? Simple, inexpensive job on 6BTA's
Well nothing is stopping me other than my job and my kids. LOL. I'm going to do it. Maybe this weekend. I'm not keen on the acid flush as I'm sure it is the original HX and I'm not sure how many times it has been acid flushed already. Maybe I can soak it in vinegar all week and reinstall it next weekend.
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Old 04-18-2014, 02:44 PM   #15
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Try BarnacleBuster or RydLyme....you don't have to use acid
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Old 04-18-2014, 03:17 PM   #16
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Quote:
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I'm not sure i understand what you are saying. Are you saying i can't achieve full rpm or i can't achieve full rpm without overheating? I'm sure the heat exchangers need to be cleaned on this engine before i try to operate it at full rpm for any amount of time. I'm not even sure what full rpm is. I'm guessing about 2600 rpm. The engine manual is not very helpful in these regards. As far as the cooling system is concerned it does not seem that complicated from what i can see in the manual and on the engine. Please elaborate as i must be missing something.
Here are the steps to consider:
  1. Insure engine HX is cleaned - remove and ultrasonic is best.
  2. If your TX cooler is older than 7-8 years pitch and get a new one.
  3. Insure after cooler has been serviced. Go to boatdiesel and you will find lots of info on how to do this properly on your engine. That is the Cummins go to place.
  4. Verify tachs and temperature gauge are correct with photo tach and IR gun
  5. Verify full rated RPM plus 50 RPM can be achieved in neutral and when under load.
  6. If full rated RPM cannot be achieved under load and without overheating you likely are over propped. This should have been verified at survey. On this issue, boatdiesel again is the place to post and learn.
A planing design hull like yours needs the right sized props to assure full rated RPM. Ski posts on this site as well as boatdiesel, a PM exchange with him would be insightful on these issues.
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Old 04-19-2014, 07:01 PM   #17
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Our 6BTA5.9 280HPO runs consistently at 185 degrees, pretty much independent of RPM once warmed up. The only time is did not (appeared to run cool) it turned out the electrical connector to the temp. read was loose.
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Old 04-21-2014, 01:17 PM   #18
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Quote:
Originally Posted by sunchaser View Post
Here are the steps to consider:
  1. Insure engine HX is cleaned - remove and ultrasonic is best.
  2. If your TX cooler is older than 7-8 years pitch and get a new one.
  3. Insure after cooler has been serviced. Go to boatdiesel and you will find lots of info on how to do this properly on your engine. That is the Cummins go to place.
  4. Verify tachs and temperature gauge are correct with photo tach and IR gun
  5. Verify full rated RPM plus 50 RPM can be achieved in neutral and when under load.
  6. If full rated RPM cannot be achieved under load and without overheating you likely are over propped. This should have been verified at survey. On this issue, boatdiesel again is the place to post and learn.
A planing design hull like yours needs the right sized props to assure full rated RPM. Ski posts on this site as well as boatdiesel, a PM exchange with him would be insightful on these issues.
Sun, thanks for the info!
Whilst in the engine room, I was able to inspect the cooling system more carefully this weekend. I also read the engine manual instructions regarding the cooling system maintenance.
At this point, I think I'll just replace the transmission cooler due to its age. I imagine the OEM coolers are adequate , but over priced. Can you recommend a better aftermarket manufacturer for a transmission cooler that won't blow my budget? (Something American made preferably?)

As far as the main heat exchanger is concerned, I'm going to clean it for now and see how it does and plan to replace it later in the season with a new cooler. I'm hoping to get everything together to service the entire cooling system this weekend so I only have to drain the coolant once.

Below is a picture of the current heat exchanger.
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Old 04-21-2014, 07:06 PM   #19
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I tend to run my 6BTA at 1300-1400 RPM and the temperature is always between 180 and 185, with both IR gun and temp gauge.

Cruising at 2200 RPM I'm right around 185. WOT (2850 rpm fully loaded) is 190.

This is with a new heat exchanger and recent service on all other cooling system components.
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Old 04-21-2014, 09:29 PM   #20
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You might want to get a price on a replacement transmission oil cooler from Marine Gear / Transmission Oil Coolers for Cummins Marine Diesel Engines. Your HX shouldn't need replacing: just clean it in situ unless when removing the end-caps, the tubes appear very badly clogged...in which case remove the whole thing and take to a radiator shop for cleaning and pressure testing. You can get new end-cap gaskets and O-rings for the end-cap bolts (note these go on the INSIDE of the cap, between the cap and the full gasket) from seaboard marine above. If the end-caps are over-tightened (easy to do) they distort...in which case you can even get new end-caps from seaboard if necessary.
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