2020 M6Di 441 15 and 452 15 codes

[Mazeing5]

I just bought a 2019 MXZ with a M6di that is overheating unless we keep the boat moving after each time we run the boat above 22 mph. It cools with anything over idle, but if you go to idle after wakeboarding, you have to run it at 10 mph around for a few minutes to cool it down or it will throw the stage one manifold alarm. I have checked the strainer and the impeller, and it does have the new Johnson impeller pump on it.

The boat temperature seems to fluctuate between 168 and 175. My old 383 hammerhead I had in my 2009 23 LSV stayed right at 165 to 167. It never fluctuated this much. I would think they would have fixed the service bulletin things if they changed the whole raw water pump, but maybe not.

Where is the Y-pipe located? Is it easy to tell by looking at the relief valve if it has been updated?

[csleaver]

Check all of the hose clamps from the hull inlet shutoff valve to the raw water pump.  It may be worthwhile to check the heat exchanger for old impeller debris as well.  The exhaust y-pipe is at the rear of the engine just behind the cockpit rear bench seat.  Original y-pipe check valves will be painted just like the y-pipe is, but a replacement will not be painted.  A problem with one of the exhaust thermostats may also cause it to overheat.

[Mazeing5]

Thanks, @csleaver, for the fast response. I will check these things when I get back to the lake today.

[Mazeing5]

I checked all hose clamps for leaks and did not see any. I also checked the heat exchanger, and it was clear of any debris. The Y-pipe is painted, so it most likely is the original. We were able to manage the heat by continuing to run the boat after each wakeboard run to cool the engine before we went back to idle. So we did not ever get the alarm, although the temps would reach around 173.

I looked back at the picture I took of the codes the first day I got them, and here is what I had:

B1 HIGH MANIFOLD TEMPERATURE (STAGE 2)

SPN:441 FMI:0

B2 HIGH MANIFOLD TEMPERATURE (STAGE 2)

SPN:442 FMI:0

Y-PIPE HIGH TEMPERATURE (STAGE 1)

SPN:1385 FMI:15

Y-PIPE HIGH TEMPERATURE (STAGE 2)

SPN:1385 FMI:0

 Would it still be possible that it is just one of the 140 degree thermostats?  If it is the thermostat, is there an aftermarket one I can try, or do I need to order from Bakes or Malibu? Also, what temperature range does this engine typically operate in when it is functioning properly?

 

 

[csleaver]

I've only used replacement thermostats from Malibu, so I don't know if there is another source.  I also have never seen both tstats fail at the time, but I guess it is possible.  Most of the exhaust manifold overheat alarms I have seen were caused by a loose water inlet hose or strainer, worn raw pump impeller, or a blockage in the sea water system.  If you can't verify that the Y-pipe check valve has been changed, then I would recommend changing it.

[Mazeing5]

Can you just replace the check valve, or do I need the whole Y-pipe assembly?

 

 

 

[csleaver]

It is just a small inline relief valve, that treads into the Y-pipe and a hose attaches to it.  Malibu PN# E850023.1

[Mazeing5]

I finally got around to taking the relief valve off. It was completely clogged with dirt and rust. I was able to take it all apart and clean all the pieces. It now works but is not a complete seal because the ball in the check valve was rusted and is not a perfect sphere any more. I have not been able to bench test it to see if this has fixed the idle issue. I will get in touch with my dealer and see if I can buy that check valve from them. I will let you know if it is fixed after I go to the lake this weekend. I really appreciate all your help on this.

[Mazeing5]

The cleared relief valve did not fix it, so I completely removed the spring and ball bearing inside of it, and the temperature will still get to 172 unless we put the boat in  gear to increase the water flow of the raw water intake. In addition, I have also added two new 140-degree thermostats, checked the heat exchanger, replaced the impeller, and replaced the Malibu strainer with the Indmar strainer with a garden hose connector. I feel like the problem has gotten better because it seems to cool faster than it did before, but we still have to put it in gear to cool it down.

I was thinking maybe something was blocking one of the water jackets in the manifolds. Can I run the engine with the winterizing plugs out to see if anything flushes out? Also, Is there a 160-degree thermostat somewhere on this engine? If so, where?

Another side note: this M6 engine has the 3077 prop and runs 38 MPH WOT at 5600 RPMs with all tanks empty. Wakeboard at 22 MPH, 4300 RPMs; Surf at 11.5 MPH, 3400 RPMs with all ballast full; and Wedge at 2.

Does that seem correct for this engine to run at those RPMs? I think I may try the ACME 2805 to see if that would bring the RPMs and the strain on the engine down a little.