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

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[Rob Schepis]

So you’re staying with the 180 tstat or have you switched out to the SMX 160?

[Robert Epsten]

Hi Rob, i am back.

Since we last chatted I have replaced the heat exchanger and oil cooler. I also swapped out the gauges port for starboard. I placed the thermostat with the rattle pins in the 12 and 6 o’clock position. I did a slow fill, a purge or two but still have the same problem. I also checked the spitters and they are open.

At this point I feel I may just need to live with it. If I let the motor fully warm up no problem. I havent looked at the impeller but it was changed last year and I have no heating issue at a load.

My only other thoughts that maybe the new design housing design could have something to do with it?? I wish I had my original tstat.

RME

[Rob Schepis]

You shouldn’t have to modify the tstat. As to the physical design differences of the SMX 160 vs OEM supplied tstats maybe Tony will chime in with something as he was behind the SMX design. Here is what I removed from my current B engines and I never had an isse with the OEM’s just changed them out to go with the 160’s. Mine was a prior part number to what you are using, here are the part numbers. There was also a technical bulletin along the way, here it is. Sure, why not test it, can’t hurt and if you don’t you might always wonder…

[Robert Epsten]

Thanks, Rob I will give it a try in the next week or two and get back to you. My last questions;

1- I noticed on Seaboards site the 160 tstats have a single drilled out hole maybe 3/16 of an inch at the base of the tstat flange. The Cummins OEM tstats have 2 tiny holes with a brass insert in the flange, I am assuming to get trapped air out? Should I remove one of the brass insert and drill a larger hole like 3/16 of an inch??

2-any value in testing another thermostat to see if the old and new open at the same temp?

Again, thanks for the helpful advice,

RME

[Rob Schepis]

Yes a very slow fill on the coolant refill. And leave the coolant level well below the base of the neck in the expansion tank. Cap loose on light to med load run to get her up to tstat opening temp on two full cold to hot cycles.

[Robert Epsten]

1-to belch the system I use the petcock when filling. I do squeeze the hose between the heat exchanger and the stat housing.

2-I then take the expansion cap off, bring the motor to temp to allow it to vent. Recently did it twice. I removed coolant as it heated up so it wouldn’t spill into the bilge. I do have reservoir tanks

3- I would say 30% of the time I’m at cruise, otherwise trolling

4-the motors are usually about at 160 when I go to cruise. If the motor is shut off while still warm, I don’t believe the overheat occurs.

I’m thinking about getting another 160 stat and comparing the old with the new in hot water to see if they open at the same temp. Possibly if the stat fully opens at say 185 degrees it wouldn’t overheat. Maybe.
When I replaced the coolant, fill a little slower and do the radiator cap belch under a load.

[Rob Schepis]

Part number of tstat is good.

Really need to be 110% sure an air-lock is not the culprit here. What exactly was your “belching” procedure?

Also, when you bring the rpm’s up are you going from idle to full cruise load or are you bringing her up to light load (say 1,200 or so) until thermostat opening temperature and then going full cruise load?

No issues using the 160 tstats if you like to run on plane, but not for those that just putt-putt around all day at no wake speed.

Seaboard sells low setpoint alarm switches to compliment the lower temp tstats to be used with a redundant coolant temp alarm

https://www.sbmar.com/product/smx-deluxe-temperature-alarm-switch/

[Robert Epsten]

Thanks, sorry for the power flush confusion,

The part number on the thermostat is 5292738 – 180F – 54mm
Motor serial number if it helps is 46181279

I have not spent a lot of time looking at the 160 tstats. Do they interfere with performance or cause more smoking?? I would imagine it would be a good idea to get a sender that maybe alarms earlier like 190? Is this available from cummins or Seaboard??

Thanks, RME

[Rob Schepis]

I was not referring to a pressure test, just a pressurized flush like with a garden hose but it sounds like the coolant passages should be all clear based on your #1 and #2 replies. As to seawater issue I was thinking perhaps she was getting air bound on the seawater side momentarily when being pushed to higher rpm and getting on plane. Unlikely, yes, just trying to be outside the box in thinking through this as you have covered a lot already.. The 160 tstats are never recommended to be used to correct overheating issues but yours does sound tstat related if the coolant passages are all clean and clear. Have pics and part numbers of what you installed?

[Robert Epsten]

Thanks Rob,
1- yes the coolant easily drains out of the small fitting on the heat exchanger tube
2-it’s clean blue being the 50/50 Cummins mix
3- i haven’t pressure tested it since I’m not loosing coolant
4- the strainers are clean, the raw water pump isn’t leaking, new 3 years ago and impeller was changed last year;hull strainer removed and cleaned last spring

I would think if it was a salt water issue the engine would always run hot.Also if it was a heat exchanger issue wouldn’t it run warm all the time? The way the needle on the temp gauge goes from about 200 back to 185 so quickly sounds like a sticking thermostat. It’s been changed twice so getting a defective one twice is unlikely. On the bench it doesn’t fully open to about 195 but I bet that’s normal.

Thanks,RME

[Rob Schepis]

Have you fully drained the coolant? Is it a nice clean green or ?? Did it drain as soon as the drain plug was removed or did you have to clear sediment from the drain plug port? Have you pressure flushed the coolant loop? How about the hull pickup strainer, engine room strainer and seawater pump – what can you tell us about those?

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