Overheating Troubleshooting Guide

[formulaben]

OVERHEATING TROUBLESHOOTING

This free tutorial is compiled from posts from The Malibu Crew forum and their members; please consider being a supporter.

IMPORTANT: do not run engine in overheated condition!

• Verify the raw water intake valve is completely open; if utilizing a flush valve or fresh water intake (a.k.a. fake-a-lake), verify that the water intake is routed from an open port/hose/valve as appropriate.
• If on land, verify good water pressure to water intake. Note that using any type of external coolant system could mask a cooling issue. Avoid using a fake-a-lake if at all possible; permanently installed flush valves are far better and safer. 
• If on water, bump the throttle to “prime” impeller in case of air in system (especially first time out on the lake for the season.)  If you have a “run dry” impeller (such as the Globe 100J) they are known to be prone to priming issues at times; if so, a short 1500-2000 rpm engine rev should prime it.
• Verify the impeller is good; inspect or replace with new if ANY overheating.  Although your impeller may look pristine, there have been failures where the shaft rotates inside the rubber impeller, resulting in no rotation of the impeller.
• Verify the transmission cooler screen (and raw water intake screen) is clean.
• Verify the thermostat is good.  They are inexpensive, replace if in doubt.
• If overheat condition is based solely on an instrument indication, then verify the temp sensor is good. They are inexpensive, test or replace if in doubt.  There are up to 3 temp sensors, depending on engine: 1 sensor for dash, 1 sensor for ECM, and another for light/buzzer (older models.)  See picture below; applicable to many Indmar 5.7 or Chevy small block 350 based engines.
• Any small openings or leaks can allow air to be sucked into system upstream from impeller resulting in no prime or loss of prime.  Verify all hose clamps are tight and hoses are not kinked. Trace from the raw water intake through the entire system.  Check for loose hose clamps along the way and any kinking, especially around the tiller arm area upstream of impeller.  Swing rudder tiller full left and right and verify there is no interaction with cooling hoses.
• Verify circulation pump is working.  If overheating at speed vs idle, it may be the circulation pump (not impeller pump.)  Remove the drive belt and open the top port on the circulation pump and 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.
• If you have a heater, verify the heater circulation pump is running. You will get heat even if it isn’t running so don’t make any assumptions based solely on if you have heat. If it isn’t running first check the fuse for it.

                                                                                               

NON-MONSOON (INDMAR 350) MOTORS ONLY

• Verify the vent line, aka “pee hole” 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.

[formulaben]

Please post any additions or suggestions and we'll edit the guide.

[justgary]

If you have an idle overheat issue, it is likely caused by either a blockage or air as the guide says.  Keep in mind that air is a lot easier to move than water, so even a tiny air leak can pull a lot of air into the system.

If the overheating doesn't go away after removing any blockage and checking the hoses and connections from the hull fitting to the pump, I would recommend that you actually remove each hose and inspect it for blockage, then reinstall it again to make sure that it seats fully without leaking.  Too many people think that since it "looks" good it must be good.  You have to actually take action to change an air leak, though.  Get in there and wrestle with the hoses!

Also make sure that the raw water pump cover plate is sealed properly.  The inlet side of the impeller is creating suction, so it is possible to draw air under the cover plate and yet it will never leak a drop of water.  Do not over tighten the screws, though, because they are usually brass and will twist off fairly easily.

 

[skisky89]

If you can't find any blockages check your transmission cooler ! I had a drippy hose on the transmission cooler, that was rusting out my alternator below. The generous drip was enough to prevent me from priming until I was on plane.