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Ilmor MV8 Thermostat, PRV, and Impeller Change

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  • Ilmor MV8 Thermostat, PRV, and Impeller Change

    First summer in the books with our new-to-us 2014 X30 with the 6.0L Ilmor MV8 – put about 65 hours on it bringing the total to around 270 hours. I experienced the intermittent “sticking” thermostat a couple times this summer, which appears to have been somewhat common on the 2012-2014 MV8’s, and decided to do some diagnosis once it was off the lift and back home in the heated shop. The issue was an occasional sudden jump in engine temperature after sitting idle for an extended period of time which could quickly be resolved by revving the engine forcing the water to circulate and open the thermostat. After researching many threads here on TT (, I bought a new 170 Degree Thermostat (part #: KT1438), Pressure Relief Valve Kit (part #: KT8036), and a new Raw Water Pump Impeller Kit (part #: PV06764).

    Here are a few pictures and general write-up that may be of interest to a few of you this time of year.

    Thermostat Replacement. 1.) remove one electrical plug from the bottom port-side of the intake plenum, 2.) remove the electrical plug from the spark arrestor housing, 3.) remove the hose from the spark arrestor cover, 4.) using a 6mm hex-driver remove the four bolts and pull straight up to remove the plenum (covers intake holes to prevent anything from falling into them), 5.) use a 10mm socket to remove the two bolts holding the top of the thermostat housing in place, 6.) remove old thermostat, gaskets, and clean, 7.) install new thermostat with new gaskets with port hole facing the bow (or back of the engine on a v-drive), 8.) reverse these steps to reassemble.
    Note – I believe part of my intermittent “sticking” thermostat was partly due to the thermostat being oriented 180 degrees off (validated with local MC service tech).
    See - for more detail

    Pressure Relief Value Replacement. 1.) remove one-time use hose clamps, 2.) disassemble the original PRV and remove the old barbed fittings, 3.) assemble the new barbed fittings into the new brass PRV and 4.) reconnect and secure with new hose clamps (not yet completed in pics).
    Note – when disassembling the original PRV it was apparent the old one was broke thus having likely caused part of my intermittent operating temp issue.

    Raw Water Pump Impeller Kit. 1.) remove 4 8mm bolts securing the impeller cover, 2.) take needle-nose plyers and pull old impeller straight out, 3.) lube the new impeller fins and internals making sure the key remains intact, 4.) twist and slide new impeller into housing aligning with the key, and 5.) reassemble the impeller cover and 4 8mm bolts.

    Fairly easy do-it-yourself maintenance items that took about two hours total taking my time on a Sunday afternoon. I plan to pull the boat out and change the fluids next weekend before tucking her away for the winter nap.
    Attached Files
    2014 X30 6.0L

  • #2
    Check the water strainer and ensure the o-ring is there. This will also cause the intermittent overheat at idle.


    • #3
      Thanks for taking the time to post pictures and procedure.

      Curious, have you noticed and improvement in temperature stability? My MV8 seems to oscillate between say 140 and 205 at idle and low rpm. I never need to bump RPMs for it to cycle, Is that what you were experiencing?


      • #4
        For some unknown reason, my boat doesn't have a water strainer. I keep it on Beaver Lake in Arkansas which is a very clean and clear lake.

        As for any improvements, I haven't run it run since replacing these parts but will report back after doing so. Mine would hold temps steady at 160 99% of the time, however if we'd anchor in a cove for a couple hours, it would occasionally jump to 200 while idling out of the cove - give it a little gas and it would come back down.
        2014 X30 6.0L