Mercruiser 5.0 MPI temperature question for the veteran ...

[Frag]

Hi guys,

Last spring I bought a brand new Starcraft 2119 open deck and I love the boat so far. There is only one thing that I would like to check out with you guys.

The power plant of the boat is a Mercruiser 5.0 MPI with an Alpha One drive. The engine only has 50 hours so far. When cruising at 3000 RPM, the boat temperature gauge shows 190 F all the time. This is a warm summer here, the air is commonly at 94F and the water is at 80F. This is not a digital gauge so I am not sure 100% that the gauge is alright, so I want to validate few things.

Here are my questions.

1. Is 190 F too warm for a 5.0 MPI ? Is it a normal range? I read at few places that 170 F should be the normal operating temperature, but there are many conflicting info about this.


2. I want to validate if the engine run warms or the gauge is wrong. Is there an area on the engine where I can read the temperature with a temperature gun for a precise reading?


3. Any other tricks to have a precise reading? I will change the gauge if I need to, but I would like to confirm that it is wrong first.


4. What should I check out if the engine runs warm?

The engine seems to run alright, but this make me nervous a bit.

Thanks guys!

 

[Bt Doctur]

The gauge reads "ohm`s" so the sender is what sends the ohm`s thru the wire to the gauge. The temp reading corosponds to a specific resistance value.
The lower the ohm`s the higher the needle will read.May just be a sensor problem. Laser the therm housing where the sender screws into for a baseline temp.

 

[Bt Doctur]

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[alldodge]

Have an engine serial number?
Is your temp gauge part of smartcraft or an analog gauge?

Reason for the question is if its smartcraft then the ECM will be reading it from the ECT sender. If its analog then the ohm scale will be 33 to 240 ohms.

Water Temperature Ohms Reading
140? F (60? C) 121-147
194? F (90? C) 47-55
212? F (100? C) 36-41

IMO running at 190 is high and I would start checking the cooling system. Thermostat should be 160 F
When was the impeller change last?
You could get a IR temperature gun and measure the thermostat housing to see what is there.

 

[QBhoy]

Hi
I have the same engine.
At cruising speed or below she runs at around 160. Flat out never above 170.
Previously and after show off rooster tails, the impeller took a little wear (not much to look at) and ran around 170 cruising and below and 180 higher up.
All good now the impeller has been changed.
Moral of the story....no showy off rooster tails !
Cheers and good luck.