4.3 Mercruiser not warming up

[Goosegt]

My 2003 4.3 mercruiser is not warming up. Last spring I thought the sensor and/or temp gauge was faulty, but last night I verified they do function. The temp gauge needle moves the slightest amount when disconnected while running......so maybe it's registering 90 degrees? What should I do, just remove some hoses and look for blockages? Would a stuck OPEN tstat make it run that cool? Any help is appreciated. Thanks

 

[ThomW]

When your motor is running, are the exhaust manifolds getting warm? Have you felt them with your hands? Looking for blockage in hoses would normally be a cure for an overheating motor where water wasn't circulating properly.

 

[Scott06]

A stuck open thermostat would make it run cool,

Would try to measure the temp at the thermostat /intake water crossing with an IR gun to see if its low or sender/gauge is the issue. Do this when the engine has been idling for like 5-10 minutes so it should be warm. If you don't have a IR thermometer you can use a calibrated hand... up to about 120 you can keep your hand on it (hot tap water is like 115-125), if its too warm to keep you hand on it long its running ok and check the sender and gauge .

If its cool thermostat is first place to check .

You can test the thermostat by putting it in a pot of water on the stove and using a common kitchen thermometer to see when it opens. This may be more for verification of the issue as I wouldn't reinstall as used thermostat once I had it out...

 

[Goosegt]

The exhaust is getting hot. On muffs I need to jack one side of the trailer up a bit to get both sides to balance out a little......on my driveway one side is HOT while the other cold. After leveling it both seem to be fairly cool while running. The tstat housing isn't getting warm.......I had it running yesterday and it's cool. The engine runs OK but it bogs out of the hole, I have to ease into throttle while pulling the kids on a tube. There is 70 hours on the boat/engine.

Last spring when I first got it out and ran it the gauge worked at first.......it stopped working after maybe 10 or so minutes and hasn't worked since. I thought it was wiring....checked and checked and checked and everything was OK. This year I started over checking wiring.....so I changed the sender AGAIN and it still didn't register. I boiled some water and dropped the "old" sender in and it read about 180 so the sender and gauge are working......so that's why I'm trying to figure out what is making the tstat housing not warm up.