2007 MerCruiser 350 MAG MPI Low Operating Temperature (Sea Water)

[LakeEffect75]

Hello all,

Looking for some pre "dive into the problem" advise on a 2007 MerCruiser 350 MAG MPI that won't reach operating temperature. At start of the season I noticed the engine was not reaching operating temperature on the gauge. Connected Diacom while engine running which showed that the water temperature starting at 65 degrees and stopped at 100 (lake temp is 62). My assumption is that something is jamming the thermostat open. This would by first crack at accessing the thermostat, hoping it's easily accessible since I can't seem to find the location of the thermostat on the engine online (outside of the mercury schematic, boat is 1 hour away). My thought since I'm opening the housing is just to replace it since it's inexpensive.

Side note, early spring I did have to replace the cooling water distribution housing because I was an idiot and stepped on the drain plug which cracked the bottom. I can't imagine that would be related to the temp issue.

Thanks!
Jason

 

[Scott Danforth]

all V8 thermostats are in the front center of the intake manifold there is a casting with two bolts. cant get any more accessible unless it had teeth and would bite you.

make sure you have a thermostat and the prior owner didnt simply remove it.

 

[thumpar]

Make sure you get the gasket with the rivets in it and not an auto version. The one without the rivets can prevent the sensors from grounding. Thermostats are cheap. I would replace it. You will find a plastic spacer in there holding the thermostat in. Don't break it.

 

[tpenfield]

While you have things apart, you could also test the temperature sender with a small pot of hot water and a good cooking thermometer to see if the gauge, the ECM readout and the thermometer are all in general agreement.

On an MPI engine, you do want the temperature readings by the ECM to be correct, else you will run rich, if they are low.