Strange engine temp

[KEN MCDONOUGH]

Hi everybody , I have a strange one I can't figure out , twin 2001 merc 5.0 efi , I changed the impellers over the winter as general maintenance , last season the port engine ran at 170 degrees and the starboard ran at around 175 ,splashed the boat about a month ago and put about 3 hours on it , since the impellers where changes the port engine fluctuates between 170 and 180 and the starboard fluctuates between 170 and 200 the whole time the engine is running either at idle or on plane ( never overheats ) . I used an IR gun and both engines read the same temps no matter where I check , I can hold my hands on top of the risers and I changed the thermostat in the starboard engine just to see if anything changed but it didn't , I would figure if the temp sensor was bad it would either cause full hot or full cold readings but I'm not sure , anyone ever run into this ? Sorry for the long post and thank you for any help

 

[Skybolt]

So last year it ran fine, then you changed the impellers and not your having issues? Sounds like something up with the water channel or the impellers.

If everything was fine until you changed the impellers then it's probably not anything but that, or something to do with what was replaced in disassembly/reassembly.

 

[Scott215]

I have a 5.0 MPI and my boat runs just a tick over 170 all the time with a 160 thermostat and a brand new water pump in the outdrive I don't know what kind of drives you have

 

[scoflaw]

New Impala in a scored pump body will do that

 

[Scott215]

Would that boat have bravo threes or alphas

 

[KEN MCDONOUGH]

Would that boat have bravo threes or alphas

 

[KEN MCDONOUGH]

boat has Bravo twos , when I replaced the impellers I purchased the kit that had the housing, impeller and wear plate and replaced all three pieces

 

[km1125]

... I used an IR gun and both engines read the same temps no matter where I check ....

They read the same temps as what? The other engine? The gauges?

Using the IR gun and measuring near the thermostat (where the engine temp sensor should be) you should verify that the engine gauges are reading the same as the IR gun.

 

[Scott215]

What tenp is at the t stat housing. That's the number

 

[KEN MCDONOUGH]

What tenp is at the t stat housing. That's the number

when I took readings at the thermostat housings both engines where reading between 145 and 150 , I did not shoot the gun right where the sensor goes in and the gun was about 5 inches away and this was after the engines where warmed up and running for about a 1/2 hour

 

[km1125]

when I took readings at the thermostat housings both engines where reading between 145 and 150 , I did not shoot the gun right where the sensor goes in and the gun was about 5 inches away and this was after the engines where warmed up and running for about a 1/2 hour

You just have to make sure you're shooting at the "engine side" of the thermostat rather than the "cooling side" (which could either be raw water or the heat exchanger side). Usually the base of the intake manifold right below the thermostat is the best place (and the temp sensor should be somewhere near there).

 

[KEN MCDONOUGH]

You just have to make sure you're shooting at the "engine side" of the thermostat rather than the "cooling side" (which could either be raw water or the heat exchanger side). Usually the base of the intake manifold right below the thermostat is the best place (and the temp sensor should be somewhere near there).

OK ,when I get back to the boat this weekend I will check again with the IR gun , thank you for the info and help

 

[Scott215]

Your temperature sender should be right on the thermostat housing or right around that

 

[Pirate Lady]

Put black tape over gauge. When alarm screams you have a problem. Stop making yourself crazy with 5 or 10 degrees here or there. Open a cold one. Not Bud Light.

 

[KEN MCDONOUGH]

Put black tape over gauge. When alarm screams you have a problem. Stop making yourself crazy with 5 or 10 degrees here or there. Open a cold one. Not Bud Light.

All the Bud light goes to post #7097 in the bikini thread