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How hot can a stock 496 run safely?

Old 06-01-2011, 10:09 PM
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Join Date: Sep 2010
Location: Manasquan, NJ
My Boats: 2002 Formula 370 SS, 1986 Formula 242 LS(sold), 2010 Grady-White Sportsman 180 ( for sale)
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Default How hot can a stock 496 run safely?

I have twin Merc 496/375hp closed cooled engines. The seemed to run around 165 to 170, but the other day I ran into shallow water and the starboard engine started to run hotter and an alrm went off at about 180 degrees. I shut down untill it cooled but would it have been ok to get home with the engine running 180 to ? What is safe? I don't have hydraulic steering without the starboard engine running.
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Old 06-02-2011, 09:00 PM
Join Date: Jan 2004
Location: San Diego, California
Posts: 2,777

You probably sucked up sand or debris and you should check your strainer and clean it and back flush the raw system from the front of the oil cooler back and check afterwards to see if the system is pumping a good flow of water out the exhaust or read the water pressures with a scan tool. If you don't have a raw water strainer-SHAME ON YOU, especially if your going to boat in shallow water areas or debris filled water. The pressures should be 2-5psi min at idle and should climb to 12-15 psi at 2500 rpms or so. If not then you may have wiped out the raw water pump impeller and housing if sand was the problem. The "guardian" alarm generally goes off about 185-187 degrees and its ok to generally idle and low rpm ("guardian" system limited) run until the engine gets to about 195. Beyond that save the engine and go for a tow, its still less expensive that rebuilding an engine or replacing blown head gaskets!

Hope all is minor and easily fixable.

Best Regards,
Ray @ Raylar
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