Raw Water overheat warning

timjet · Aug 16, 2014

Looking for advise. Cruising the ICW in S.C. at 1400 rpm I got a raw water temp overheat. The engine is a Cummins 6BT 330 M3 reman with 180 hours. The overheat sensor is a Borel strap type that monitors raw water temp about 1 ft downstream of where the exhaust is mixed with the cooling raw water. Coolant temp indication was normal

I immediately shutdown the engine upon receiving the O/H warning and verified the overtemp with a heat gun. The overheat warning lasted about 5 minutes after the engine was shutdown. I checked the raw water intake strainer for debris but it was clear. About 10 days prior to this leg I had the bottom cleaned and the diver said the engine intakes were so clogged with barnacles he was surprised the engines didn’t overheat. He cleaned them and changed several zincs. Subsequently we have run the engines 15 hours since the intakes were cleaned and this incident. Prior to this cleaning the boat bottom had not been cleaned since May.

After verifying the strainer was clear I jumped into the water to attempt to verify the intake was clear but due to the tannin in the water and the very swift current I couldn’t locate the intakes. While in the water with both engines running in neutral at idle and then at 1500 rpm, I checked both engines raw water flow out the exhaust and they seemed to be the same.

I continued our cruise with both engines running at 1400 rpm and verified with a heat gun the port engine exhaust hose at the location of the overheat sensor was again starting to rise. I increased rpm to 2300 rpm for about 5 minutes and got no overheat warning. I monitored coolant temp carefully and it was normal. After 5 minutes I reduced rpm to 1400 and checked the exhaust tube at the sensor location. Heat gun read 100 deg. Pretty much the same as the other engine.

We continued on to our destination that day at 1400 rpm, another 5 hours, with no issues and no additional overheat warning.

So what to do.

The black band on the blue tube is the overheat sensor.

Ski in NC · Aug 16, 2014

Rotate the band and sensor a bit. The top of the hose often gets hot at low power due to the water mostly being at the bottom of the hose. Not enough water/exhaust velocity to get things to mix very well. A common issue on this type of exhaust. As long as hose does not get hot enough to degrade, it should be ok. At high power, everything should mix fine and hot spot diminish.

psneeld · Aug 16, 2014

Ski in NC said:
Rotate the band and sensor a bit. The top of the hose often gets hot at low power due to the water mostly being at the bottom of the hose. Not enough water/exhaust velocity to get things to mix very well. A common issue on this type of exhaust. As long as hose does not get hot enough to degrade, it should be ok. At high power, everything should mix fine and hot spot diminish.

could also pull the hose and check the mixing hole(s), whole mixer for issues/debris.

Some elbows have a large opening...some tiny holes...not sure of yours.

ranger58sb · Aug 16, 2014

Failed raw water pump impeller? Broken vanes impeding raw flow downstream from the pump? Sometimes discharge can look OK, especially at idle, when in fact it's not...

-Chris

timjet · Aug 16, 2014

Thanks Ski, currently the sensor is at the 3 o'clock position. I'll rotate it lower on the hose. I did notice when taking temp readings during the O/H the temp just before the sensor was 170+ and just after the sensor it dropped to 125.

Psneeld; will consider that if the issue continues and all other possibilities are illuminated.

Chris, I had thought of that. The impeller and pump are Tony's Anthens units and have 180 hrs on them. They should be OK, but if the issue continues and I verify the inlet hole is clear, that will be the next step. My guess is though SKI is right since the temps went way down when I increased rpm. Broken impeller and the problem should have gotten worse.
And during this episode the coolant temp never changed, 185 degrees.

bligh · Aug 16, 2014

ranger42c said:
Failed raw water pump impeller? Broken vanes impeding raw flow downstream from the pump? Sometimes discharge can look OK, especially at idle, when in fact it's not...

-Chris

x2
cummins are hard to overheat at idle with or without raw water.
check your impeller.

bayview · Aug 16, 2014

Sounds like something is blocking the flow from time to time. Junk or old impeller pieces may block flow then settle down with shut down only to plug up sometime later. Look at the first thing downstream from the pump, trans oil cooler? Then the after cooler then heat exchanger.

Also worth checking the seacock hose for growth if the above easy stuff is not the problem.

sunchaser · Aug 16, 2014

Tim, to be clear, your coolant is not over heating but a hot spot showing up on the exhaust hose? Summer water temps can cause this for me in the PNW mind you I see 150 in the summer vs 130 F in the winter on the one side of a Centek.

But, if your diver saw some buildup underwater, the top holes on elbow may be building up also. Is this a new development?

timjet · Aug 16, 2014

bayview said:
Sounds like something is blocking the flow from time to time. Junk or old impeller pieces may block flow then settle down with shut down only to plug up sometime later. Look at the first thing downstream from the pump, trans oil cooler? Then the after cooler then heat exchanger.

Also worth checking the seacock hose for growth if the above easy stuff is not the problem.

It's relatively easy to check the trans cooler for impeller bits, I'll do that.

sunchaser said:
Tim, to be clear, your coolant is not over heating but a hot spot showing up on the exhaust hose? Summer water temps can cause this for me in the PNW mind you I see 150 in the summer vs 130 F in the winter on the one side of a Centek.

But, if your diver saw some buildup underwater, the top holes on elbow may be building up also. Is this a new development?

Yes a new development. It could be the warmer water but I've operated the engine the last 130 hrs in warmer temps than current with no issues.

And yes the coolant temps have never changed.

I think you're both saying the same thing and that is to check the hose from the sea cock to the raw water pump for clogging. That will require removing the hose, something I probably can't do. I will however stuff a long rod up into the sea cock and see if anything loosens up when the current abates a bit.

Capt.Bill11 · Aug 16, 2014

You could also open each strainer and see if the incoming flow appears the same for each unit.

It may just be time to boil out your coolers to get full water flow back. You can do this without removing the coolers.

hollywood8118 · Aug 16, 2014

timjet said:
Looking for advise. Cruising the ICW in S.C. at 1400 rpm I got a raw water temp overheat. The engine is a Cummins 6BT 330 M3 reman with 180 hours. The overheat sensor is a Borel strap type that monitors raw water temp about 1 ft downstream of where the exhaust is mixed with the cooling raw water. Coolant temp indication was normal

I immediately shutdown the engine upon receiving the O/H warning and verified the overtemp with a heat gun. The overheat warning lasted about 5 minutes after the engine was shutdown. I checked the raw water intake strainer for debris but it was clear. About 10 days prior to this leg I had the bottom cleaned and the diver said the engine intakes were so clogged with barnacles he was surprised the engines didn’t overheat. He cleaned them and changed several zincs. Subsequently we have run the engines 15 hours since the intakes were cleaned and this incident. Prior to this cleaning the boat bottom had not been cleaned since May.

After verifying the strainer was clear I jumped into the water to attempt to verify the intake was clear but due to the tannin in the water and the very swift current I couldn’t locate the intakes. While in the water with both engines running in neutral at idle and then at 1500 rpm, I checked both engines raw water flow out the exhaust and they seemed to be the same.

I continued our cruise with both engines running at 1400 rpm and verified with a heat gun the port engine exhaust hose at the location of the overheat sensor was again starting to rise. I increased rpm to 2300 rpm for about 5 minutes and got no overheat warning. I monitored coolant temp carefully and it was normal. After 5 minutes I reduced rpm to 1400 and checked the exhaust tube at the sensor location. Heat gun read 100 deg. Pretty much the same as the other engine.

We continued on to our destination that day at 1400 rpm, another 5 hours, with no issues and no additional overheat warning.

So what to do.

The black band on the blue tube is the overheat sensor.

A couple things...

Shouldn't the sensor be on the S.S. piping before the silicone (blue) hose? .. the silicone is some what of a insulator and the temp will not be as accurate.

You may have build up inside the hose after the thru hull if the thru hull was as bad as the diver said. Might be time to flush the entire system from the hose at the thru hull through the exchangers with Barnacle Barrier.
I had a similar situation and it was a combo of all the exchangers and the turbo inter-cooler that slowed water flow down enough to cause a overheat at high rpm.
Good Luck
HOLLYWOOD

psneeld · Aug 16, 2014

I'll let Timjet confirm...but I have read where a company that sells an alarm kit say OK to placing on the rubber (why I have no clue having burnt many a hose on the towboat and know that setup intimately)...I think I also remember reading here someone said they had it on the rubber as OKed buy their company.

The OP said the engine temp never changed (at least that's what I thought) so many suggestions would probably result in an engine overheat...not just an exhaust high temp....no harm in checking though.

timjet · Aug 17, 2014

Thanks guys for all your help. I checked the tranny cooler and there was no debris there, so I'm going to assume the impeller is OK.

I think SKI's explanation is correct. A hot spot occurred at low water flow and disappeared with increased rpm. The engine never overheated. The coolant temp never changed throughout this incident.

The engine is a reman installed less than a year ago now with 180 hours on it. It's unlikely the cooling system is in need of cleaning and remember the coolant temp is normal according to the gauge.

As far as I know the location of the sensor on the rubber exhaust hose is OK.

SKI's knowledge of the Cummins engines is highly regarded on another forum, so I take his recommendations with great weight. I adjusted the raw water temp sensor lower on the exhaust hose and will monitor it closely. I don't want to chase problems that don't exist.

Thanks again guys, hopefully no more problems.

Capt.Bill11 · Aug 17, 2014

You are probably right. But just because the op temp is good does not necessarily mean your getting full water volume flow. Sometimes the last thing in the line of the water flow is the first place the lack of volume will show up.

Raw Water overheat warning

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