Thread: temp. for 1992 Mariner 150 Magnum II
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Old 09-27-2009, 08:10 PM
Blue_Heron Blue_Heron is offline
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Default Re: temp. for 1992 Mariner 150 Magnum II
I have a 1991 Merc 150 XR4. Your Magnum II is the gray version of the same motor. My engine temp stays constant around 160 after initial warm up regardless of load.

My XR4 experienced the same problem you describe after the powerhead was rebuilt a couple years ago. Turned out the poppet valve was reinstalled incorrectly. If you have a water pressure gauge, it should read between 10-15 PSI at cruise. If the pressure is way up at cruise, and your temp gauge swings back and forth between 180 at cruise and 120 at idle, I would say it's probably the poppet.
Dave
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