6BTA overheating

[Robert Epsten]

Good morning,

I have an issue with one of my 5.9 6BTA 370 hp. motors.

If I go to cruise speed, my port engine wants to overheat to about 200 degrees for 5 to 10 secs, then come right back to 185 to 190. The alarm starts to chirp but then goes off. No problem for the rest of the day. Here is what I have done to try and figure it out.

1-belched the system twice at full temp, a few bubbles not much . Also bleed it through the petcock.
2- changed the tstat twice (OEM 180 degrees), the sender once no help
3-checked the tstat housing with an IR gun and seems to correlate with the gauge
4-bench tested the tstat, begins to open at 185, doesn’t fully open until 195 to 198.

Also, the coolers have been serviced within the last two years. The expansion tank cap replaced 3-4 years ago, fresh water pump changed 4 years and spins freely by hand.

I know by going to the 160 degree tstats I can probably solve the problem and plan on doing it in the next week or two. I am just perplexed on why it’s happening. I just want to be sure that the problem isn’t in another part of the motor that may cause another issue later on.

Thanks, RME

1 user thanked author for this post.

Richard Geczi

Topic

[Tony Athens]

Based on your operation, no, I would stay with what you have..

Tony

[John]

Tony,

I generally cruise at about 1600 RPM (Nordic Tug 34). Will run at higher RPM (+- 2000 RPM) only to run from weather, or to push through some section of fast running water. I’ll also periodically run WOT for 15-20 seconds when coming back from a long cruise to “blow out” whatever. To your comment, if thermostat is sticking, when it comes time to replace, would you recommend the 160 degree t-stat on this engine ?

[Tony Athens]

Likes to runs hot ??? 100% out of context and that was referring to EGT, not coolant temp………

AS to the rest–your thermostat is sticking and needs about 10F higher to open it.. Does it hurt? Not really.. What would I do if had a “B” that cruises above 2000 RPM?————– Give yourself some safety margin..

Tony

[John]

I’m a little confused by what may be a normal process. I’ve got a 270HP 6BTA JWAC, CPL 2956. For 13 seasons, I’ve had this same process described. I start engine and will take off at relatively slow speed, say 1000 RPM. Over the course of time, depending on water temp and RPM, I watch the temp rise from zero up to about 195-200 degrees, then immediately fall back to its normal running temp between 182-185 degrees, and will maintain that “normal” operating temp throughout the day. I will only increase operating RPM once I see the temp fall back to normal operating range. Temp will increase to a max of 200 degrees as I move towards WOT (2600 RPM). According to my CPL 2956 Cummins spec, the original t-stat has an operating range of 181 to 203 degrees. I periodically acid flush the engine, and have replaced the factory Sherwood 1730 with the Seamax pump. I believe what we’re seeing is the normal operation of the standard thermostat opening up at somewhere around 195 degrees, then allowing cooling raw water to flush through the engine. Some have suggested replacing the t-stat with a 160 degree unit. This may be appropriate in warmer waters, but up here in New England, the factory t-stat seems to be working fine. According to Tony A, this CPL 2956 engine likes to run a little hot. What am I missing?

[Rob Schepis]

Tony Donetz wrote:

Overheat fixed. Worn out raw water pump!

Thanks for the follow-up post … it adds a lot of value when these threads run start to finish.

[Tony Donetz]

Overheat fixed. Worn out raw water pump!

[Robert Epsten]

Now that the after-cooler is no longer a potential issue, it seems your salt water side from the through hull to the heat-exchanger has been addressed and functioning properly. If you have an IR gun shoot the sender housing and see if it correlates with the gauge.

[Tony Donetz]

still ovheating

I replaced the RW impellers, replaced the Thermostat, replaced the aftercooler, replaced a coolant line from the exhaust mainfold to the coolant reservoir and again R&R the heat exchanger and cleared all tubes. Flushed the FW side….Still overheating

[Robert Epsten]

Hi Tony,

I’m not familiar with that model after-cooler, but I am sure it works on the same in principle as the newer 6BTA’s. Regardless, even if your current problem is not an after-cooler issue, your way past due for service. If your gear cooler and heat exchanger are original to the motor, best to replace them before you get water into the gear oil or loose coolant out the heat exchanger or even worse get water into the motor from a worn out after-cooler. A good radiator shop should be able to advise you on this issue. Also, don’t ignore the exhaust elbow especially if its from the 90’s.
The fix may not be cheap, but you may of lucked out by finding the problem before it finds you.

Regards, RME

[Tony Donetz]

I purged the system today from a petcock on top of the aftercooler.

I cannot recall the last time the aftercooler was cleaned / serviced – definitely greater than 6 yrs. This is an older engine – 1990. Aftercooler is on top of the block, My service manual does not provide service information. Looking for some advice – I can probably service on Monday.

[Robert Epsten]

Tony, the other circuit you may want to check is the fresh water pump. In my experience they leak before failing. You need to remove the belt (take a pic first of the belt in place because it can mess with your mind putting it back on) then spin the pump and it should spin with little resistance.

Good luck, RME

[Robert Epsten]

Hi Tony,

I am not a Cummins mechanic but feel like one after spending considerable time and $$ looking for a overheating issue on my Cummins 6BTA. In your case I would suggest the following.

1-be sure there’s no restriction from the thru hull to the the salt water pump including hoses and valves

2-you didn’t mention the after-cooler, has it been serviced or flushed in the past 3 years??

3-did you replace the tstat or at least check it to be sure its fully opening in boiling water at the correct temp?

4- are you sure the coolant system was properly purged upon filling?

Also look to see if the hose between the salt water pump and the fuel cooler, and the hose between the fuel cooler and after cooler are bulging under load. If so, the problem is in the after-cooler, oil cooler, heat exchanger, exhaust elbow or all the above.

I use the salt water acidic flush between servicing my after-coolers, oil coolers and heat exchangers but always pull off and have them professionally cleaned and tested every 3 years.

Lastly you can get an IR gun and shoot the motor at the thermostat to see if its a gauge or wiring issue. In my experience its the motor and not the wiring.

Good luck, RME

[Robert Epsten]

6BTA overhgeating

Been awhile since I checked in about my overheating problem. I installed the 160 tstats and all’s well. I would still bet the problem is in the new design of the cummins tstat and not in the remainder of the coolant circuit.

RME

[Tony Donetz]

I have similar issue

I can run at 1800 – 2K – temp remains at 190. Over 2K and the temp rises and then goes over 200. Back down and the temp goes down.
Replaced the impellers, citric flushed the heat exchanger raw water side, flushed the fresh water side and replace antifreeze. checked tranny cooler for obstructions – none.

Swapped gauges. about to change out the temp sensor

Any other suggestions???

Tony

[Robert Epsten]

Thanks for all the input. I will update you when I finish the 160 stat install.

RME

[Rob Schepis]

Rob Schepis wrote:

My 330B’s sit right at 160 at all rpms.

[glenn111]

Had a similar condition with my 330’s. Especially on the Port engine. Removed all zincs and replace with “blanks”, rigged up a brass attachment to fit the lower Aft Cooler zinc port to a clear tube, ran Heat X ger output to a bucket filled with Barnacle Buster. Attached all to bilge pump in the bucket and ran for several hrs in one direction (normal flow) and then back flow (BTW, several good articles on this at this site). Perhaps also hook up a vacuum cleaner to the bottom zinc port of the Aft Cooler to suck out any left over impeller pieces (point of first contact). Problem solved. Just a note, also installed the 160 tstats.

[Rob Schepis]

Is your question what the temps will run with the 160’s ?
My 330B’s sit right at 160 at all rpms. But they also sat right at 180 with the OEM tstats…

[Robert Epsten]

Thanks for the reply. I’ll change it out.
In your experience what engine temp would I be looking at 2400 RPMS if im currently at 185 to 190 degrees with the 160 tstat in place??

RME

[Tony Athens]

If he has rattle pins, he has the factory stats or a copy………………The Hi-flow 160’s work on a different principle as to “bleeding/preventing air-locks”, and 99+% of the time solve the issue as described..

Of course, I am assuming the seawater flow circuit of the engine is clean and working/pumping water as it should.

Tony

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