I've got an interesting issue and...
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04-17-2022 07:11 AM
I've got an interesting issue and hoping someone will have some comments. On my 390 sundancer with twin 496's. I've had some overheating issues that takes a long run but eventually overheats and the engine guardian shuts the engine down. I've been through the complete cooling system with new pumps, new sensors, cleaned the heat exchangers but last year one drive was semi blocked with barnacles. When I pulled the boat over the winter I dropped the lower drives cleaned the inside of the drives with barnacle buster and thoroughly back flushed the water input from the water pump backwords through the drives with barnacle buster. Took it out yesterday and it ran fine as expected with temps in the 168-172 range. On the return trip the temps started to climb as soon as I put the boat on a plane into the 180-190 range. Now, before the engine guardian would shut me down at these temps. So we stopped, reset everything, checked on the engines that certainly didn't seem to be that hot. I didn't have an infrared temp sensor with me. Ran the boat up again and the same thing. The pressures were good and again the engines didn't seem that hot. But the temps climbed up into the 190's so we shut her down and idled into shore. We also noticed both engines temp readings were within a degree of each other and the digital readings were some 20 degrees higher than the analog readings. First, why didn't the engine guardian shut us down? I assumed wherever the guardian resides it is reading the same temp sensors as what is displayed. Also, no alarms were set on the vesselview. If that is correct then there is something wrong with the vesselview. But all the other readings on the vesselview appear normal. I will take the boat out again and try to determine if the engines are really running that hot. If anyone has knowledge on what either the voltage on the temp sensors should be or what thermometer readings should be, that would be very helpful. Also to note that on the whole trip we were in deep water and there should not have been any possibility of clogging the water inlets on the drive. Any comments are appreciated.
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04-17-2022 12:46 PM
If I were tackling this problem I would carefully and properly attach a bunch of calibrated thermocouple probes to all the points of interest and use a thermocouple thermometer to confirm that the temperatures displayed by the boat are accurate.
Another option is to remove all of the temperature probes and confirm the readings while the boat is stationary while the probes are suspended in a boiling water bath and in an elevated temperature bath, w/ the water temperature measured using a thermocouple thermometer.
Not familiar w/ the raw water flow on that setup, is there a hose that may be detached so that the flow to time filling a 5 gallon bucket at idle may be timed for each engine?
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04-17-2022 12:47 PM
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04-17-2022 04:28 PM
Been there. Solution for me was to install 2 thru hulls with strainers which provided more water and strained what was coming in. Something that Br 3s does not do.
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04-18-2022 06:16 AM
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04-24-2022 05:28 AM
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04-24-2022 05:29 AM
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04-24-2022 05:31 AM
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04-24-2022 02:32 PM
Had same issue. Put in through hulls and no more issue, period. Yes it was a bit of an expense – BUT, I will never have to deal with again. IMO, Merc should put in thru hulls in to begin with. And now I can strain what goes into my raw water pump so I don’t have bits of shells and other crap that is sucked in through the OD beating up my impellor and getting into my heat exchanger and the rest of my cooling system. It was a win-win decision for me.
Best of luck.
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04-25-2022 05:42 AM
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05-01-2022 03:36 AM
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05-01-2022 03:54 AM
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05-01-2022 05:33 AM
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05-02-2022 06:08 AM
For someone that is having issues, I want to summarize this post. As I mentioned in my first post, we ran the boat out the first time of this year and it ran great after we had flushed the drives in the winter. We sat at the island and as we returned both engines moved up quickly into the 180-200 range without the engine guardian kicking in. I want to mention this because if you have clogged manifolds, first your water pressure will be high, in the 20's vs the teen's for water pressure and in my case, it would take a 15 mile run before the engines gradually moved up and the guardian kicked in.
But in this latest situation, the engines heated very quickly and the engine guardian didn't kick in. Further investigation showed that the engine got hot but not the manifolds. And I assume that is why the engine guardian did not activate. So this left me with the coolant vs raw water system. I had replaced the coolant water pumps and thermostats in the last few years but lacking anything else I pulled apart the heat exchanger to see if there was any clogging and they looked fine so I thought I would take a look at the thermostats. To my amazement and relief as I stared down at the thermostat, the first was in 3 parts, not good! But now I still had a problem with the other engine acting in the exactly the same way. Again, all I could do was pull the heat exchanger apart and to my total amazement, that thermostat was also in 3 pcs. What had us totally confused was that they both failed at the exact same time. The probability of that is way out there. I did go back and look and they (mercury 8M0076464) were purchased at the same time in 2019, but I knew I had installed them at different times. I am getting two new ones but they unfortunately are the same number and the same design. I just hope Mercury has fixed the manufacturing issue. Sorry for the long narrative but hopefully it will help someone trouble shooting an overheating problem.
I will probably call Mercury, but if anyone knows the electronics on how and where the temp sensor outputs are utilized, I would appreciate the info. I have one on the engine coolant and one on the manifold. Do they both drive the ECU and that is where the engine guardian resides and then out-putted to the vesselview and analog gauges? Also, at what temps do they actually trip the engine guardian?
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05-02-2022 06:26 AM
With respect to the sensors, on my engine, one is more the analog gauge and the other is for the ECU. My analog one is by the thermostat housing. You can pull the wire off to see is if the gauge stops responding. I was just reading on newer engines there maybe a separate sensor on the manifolds. This sounds more like your setup.
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05-03-2022 06:21 AM