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Overheating Issue


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Happy holidays, folks.  I'm a newbie to this board and to Malibu boats and would very much appreciate some advice on an overheating issue.  I have a 2014 LSV 247 with an Indmar Monsoon 6.0L engine and a v-drive.


I had a bad impeller and the boat overheated.  I shut it down when the alarm went off, but it got hot enough to bubble the finish in a spot on the exhaust manifold.   I replaced the impeller, which wasn't too bad.  All of the fins were there with no big chunks missing, though the end were tattered.  But upon starting it, the temp shot up.  I then took a bucket filled with water that has a clear hose connected to the bottom and connected the hose to the raw water intake hose.  When I ran it, it sucked up water from the bucket, so the impeller is working.  I double checked all of the water system hose connections and drain valves and they are all in place and secure.  I figure the problem must be either 1) the thermostat is stuck closed, 2) the water circulating pump is fried, or 3) bits of the old impeller are creating a blockage in the system.  #3 seems unlikely given the shape the old impeller was in.


Left to my onw devices, I'd pull the thermostat and test it in boiling water.  Then I'd check for blockages.  Lastly, if none of that worked, I'd replace the water circulating pump.  Is there a way to test the thermostat without removing it?  I there any way to test the water circulating pump without removing it or at all? Could it be a different cause all together?  If anyone has any experience with this and can help me shortcut this diagnostic, I'd greatly appreciate it.


Thank you,



Edited by BWilliams
more info.
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remove the hose from the inlet side of the transmission cooler and check for obstructions.  it's built such that it accumulates crap.

be careful removing the hose from the trans cooler as it's a soft metal.

also don't overtighten clamp else you can damage the trans cooler.

the trans cooler is roughly cylindrical, and is located on the front of the engine on a dd.

it has two smallish hoses routed to the transmission and two larger water hoses.


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To test the thermostat in the block: start the  engine cold, fast idle it for a few minutes with water from a hose or lake, keep hand on thermostat hosing, when the thermostat opens your hand will quickly from warm to hot. Check the temperature gauge when you feel the heat on your hand.

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@BWilliams -  on start after impeller change, did you prime (burp the throttle) as a procedure to ensure water flow?  Also, did you get the housing re assembled so there is no chance of sucking air rather than water, are all the hoses hooked up correctly and air tight (inlet to inlet on raw water pump).  Your comment suggests all good based on sucking water but worth a check.  You noted impeller change although your comment on condition might imply it was not that bad,  what was the detective work you did to decide to change?  Inlet debris in trans cooler a typical issue for many that boat in weedy lakes.  Assume it is a crank driven pump?  Check the key. Good luck.  A handy tool  to have is an infrared temp gun, helps troubleshoot water temp issues.

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You didn't say if it was running hard or at idle...all the above advice sounds good.  Hopefully it's still applicable with your year of engine, but might be worth noting: ·      

  • Verify circulation pump is working.  If overheating at speed vs idle, it may be that pump.  Remove the drive belt and open the top port on the circulation pump and then turn the circulation pump by hand, with water in system you should see movement.  If a broken pump is suspected, remove entire housing and shake: if you hear noises, it is a broken circulation pump.
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@csleaver has a good point.  Here is more from my notes, not sure if it's applicable, but here it is:


  • Verify the vent line to transom is clean. On the transom you’ll see a little metal port about the size of a button. After running the engine and shutting down it will continue to vent water like its peeing for a few minutes. If it isn’t venting water it’s plugged up. There’s a hose that will run to the top of the engine. Take that hose off and blow it out with compressed air.
  • Verify the shaft seal is NOT plumbed into the transmission cooler. On an L96 the transmission cooler is on the vacuum side of the cooling system so if the shaft seal is plumbed into the transmission cooler you’ll suck air. If it is plumbed into the transmission cooler you can get a brass plug to screw into the transmission cooler and a T from your dealer to plumb the shaft seal into the correct place.
  • Check your engine serial number. Indmar published Service Bulletin SB2012-3IN to address a cooling issue with the L96 motor. It affects 2012 and 2013 L96 (6.0) and LS3 (6.2) engines with tube and tube exhaust manifolds and 7-digit serial numbers before serial number 2249300.
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