I've got an interesting issue and...

[cbruck]

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.

[wingless]

Why not start w/ confirming that the indicated temperatures are accurate?

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?

[wingless]

BTW, an IR thermometer is handy, but the readings are affected by the surface emissivity, so even though I've used that instrument, I prefer a thermocouple thermometer.

[Korkie]

What is your PSI Gauge for your raw water system reading? If you have ruled out heat exchanger,( by properly cleaning and flushing it, impellor (by replacing it), manifolds (by interior inspection) As you mentioned you have drives, I assume Br 3s, I would strongly suggest bravoitis. Even if you have back flushed the tubes in the drives, you need to check where the drive tube comes through transom. The tube gets blocked and even though you can flow water thought it, it will not supply the engines needs. As your rpm's get higher, the pumps attempt to draw more water and the tubes collapse starving the pump of water. If your raw water PSI is low, this is exactly your issue.
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.

[cbruck]

Thanks for the comments. I do agree with your comment on the thermocouplers vs the IR. I am headed down that path. As you said, I have to confirm whether or not the engines are getting that hot.

[gregk]

Another thing to check is for air bubbles entering the cooling path. You need to install a clear tube

[gregk]

prior to the raw water pump. I happen to have a clear Perko engine flush where I can see. This was my issue.

[gregk]

Another option is to try using an existing thru hull to see if this helps. I was able to use my existing one from the head.

[Korkie]

Take the connection at the transom that the raw water hose goes to and check for constriction. The slightest constriction will cause you to over heat. Our 496s require all the water the OD can give them, which when brand new is enough. That hose gets weak and the engine drawing through it will collapse it, therefore less flow.



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.

[cbruck]

Thanks for the comments.

[gregk]

FYI: On my 350MAG there are two separate temperature sensors, one for the analog guage and a second one for the vessel view/engine. The guardian system doesn't use the analog one.

[gregk]

Another thought, are you running antifreeze in your closed system? If so, do you have the antifreeze diluted? Straight antifreeze will not transfer heat quickly and exhibit the symptoms you are seeing,

[tomd]

Had a similar issue last year with my 280SDA. Changed all the temp and pressure sensors but that didn't resolve the issue. Turned out one of exhaust manifolds had a block in the water flow channel. New manifolds resolved the problem.

[cbruck]

Again, thanks as these are all good comments and may help out someone that is reading this post. I had eliminated most of these issues with new manifolds/risers, new water pumps etc in the last two years. But last year I did have barnacle buildup in the drives that I resolved over the winter by removing the drives and backwards flushing from the pump through the drives with Barnicle Buster. Which I will give them a plug, works extremely well. The inside of my drives looked new after flushing them. I'm adding that to my list of must-have chemicals to maintain these boats.
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?

[gregk]

Glad you were able to resolve the issue, and thanks for posting the resolution. I have a raw water cooled motor in salt water, thermostat was almost 15 years old before I replaced it to be on the safe side. It was still working and looked good.

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.

[cbruck]

Just wanted to add a picture of the mercury 8M0076464 thermostats which were purchased in 2019. And the new one are of the same design.