2003 Merc 5.0 mpi will not warm up

[Talsey]

Ok hopefully someone has had this issue

Port motor will not warm up to operating temperature.  I thought it was the thermostat stuck open so that was replaced.  Fired it up still running at 120 degrees.  Old thermostat was tested in the pot on the stove and was operating fine.

Have swapped everything out with the other motor with no luck (thermostat, temp sensor, housing, gaskets, everything.  Port engine contininues to run at 120.  I checked the temp with an infrared sensor and the gauge is correct.  The hoses all appear to be hooked up the same.

While the engine is running the water coming out of the exhaust is hot to the touch on the right side of the drive and cold on the left...not sure if this is normal or not.   It was a litle chilly today but the exhaust may have been steaming as well.  When i changed the oil there was a little bit of milkyness on the underside of the cap (Oil was fine)

What could be wrong.   Hopefully someone can help.  Usually wouldnt be worried about the engine runing cool but it seems if i try to winterize and the engine is not warming up enough to get the t-stat open i may be asking for trouble.

[Dream 'Inn]

You really have me stumped on this one.  It seems like you have changed everything I would have.  I had read a while back on a forum about a ball that slides in/out somewhere within or around the thermostat housing that can get stuck, but I believe it wasn't on our model (I think it was older).

In worst case, you could remove the thermostat and just winterize.  I also believe some of the water does bypass the thermostat anyhow, thus still winterizing fine.  & if you are staying at 120, you have to have water going thru the engine anyhow.  So, I think either way you are ok to winterize.  But it is something that needs figred out.  Hopefully this is something Al may have seen and can help out, I'm very curious.

[Talsey]

The other thing i was wondering....   

Everytime I take the t-stat housing off there is no water underneath inside the motor.   On the starboard side the water stays all the way up to the underside of the t-stat housing.   

Is it possible that the water circulating pump has failed and the engine is only cooling from the raw water pump and since there is no water traveling through the t-stat housing the temperature is only reading ambient air temp inside, when in fact the motor is overheating.

I dunno...  Just a thought I had while in bed last night.

[alswagg]

I would verify proper reading of the temp with a scan tool.  Note, the thermostat housing has two sending units one for ECM and the other for dash gauge.  Digital vs Anolog.  If you need to winterize, remove the drain plugs and drain all coolant ( sea water ) from engine before flushing with antifreeze.  Any other way is way too risky.  Al

[Talsey]

Thanks al....  

on another note....  Just found a massive tear in the exhaust bellows (Lower flex tube on the outdrive ????)  

Do you think this could cause the problems im describing with the overcooling.   Definetly explains the steam coming from the drive while running.

[alswagg]

No, the exhaust hose will not effect this.  On many models the exhaust hose is only attached on the transom end and the drive is loose.  Many have the exhaust bellows cut directly up the bottom.  Al