Overheating without thermostat

[upwindskipper]

My 2002 3cyl. 50HP is overheating. I did a full water pump rebuild about 10 hours ago, albeit last year. I just replaced the thermostat with the prescribed 110 degree unit. Telltale stream is strong, seems to be better than last year. Today decided to remove the thermostat and try it. I ran about a mile at slow speed and the overheat alarm went off. .A few questions: if the telltale stream is strong, could I still need a new impellor? If not the impellor and not the thermostat, what else could it be? thanks in advance for your thoughts.

 

[ondarvr]

The first thing to determine is if it's actually overheating or if the alarm is going off because it's faulty.

You can test the sensor by putting it in hot water, I'm not sure at what temp it should make contact on that motor so you'll need to look that up.

The block could be plugged up, or if this motor has a head gasket it could be leaking.

 

[upwindskipper]

Thanks ondarvr. I have not checked the alarm. I have overheated three times: once with an old thermostat that later tested bad, once with the new thermostat and today, with no thermostat. Each time the alarm came on after about 5 minutes of running. If there's a blockage in the cooling loop, how do I clear it? Would a blockage affect the telltale stream?

I did check compression and it was uniform, not sure if that rules out the head gasket. I have a temp gun - will do some testing tomorrow on the cylinder heads and report back.

 

[Faztbullet]

Make sure sleeve is not cracked that t-stat sets in...

 

[upwindskipper]

So today I started and idled at the dock (getting tired of paddling back in with an overheat), with no thermostat and powerful telltale stream. Cylinder head temps were (top to bottom) 137, 132 and 125. I then obstructed the telltale with a wire-tie in the hose, reduced that flow, and the temps dropped by about 5 degrees. I then opened the empty thermostat housing and it looked slightly damp, definitely not wet. I never got an overheat alarm but never applied a load either.

Seems like a blockage somewhere. any suggestions as to how to clear it are welcome.:

.

 

[1nebel0]

Drop the lower unit and blow air down the thermostat housing...something is blocking the passage possibly...you can blow up the water tube as well...Just fixed my buddy's evenrude that was overheating yet pumping good water out the pisser....he had blockage that we freed...lucky his overheat alarm worked....quick way to have to buy a new outboard....