Mercruiser 5.0 MPI Overheating/Temp gauge issues

[FISHARIZONA33]

Alright, after lots of money spent and myself and my mechanic being stumped, I figured Id ask the pros on here for advice...

I inherited my dads 2007 Sea Ray 215 with a 5.0 MPI/bravo 3 a couple years ago; long story short, because of his health the boat sat for a few years before I got it. Its only got 188 hours on it and looks new, however its overheated every time I take it out; or so I thought.....so....I replaced:

Riser/ manifolds
thermostat/housing/sender
new circulating pump
Impellor
temp gauge

And it STILL reads hot (200 degrees)...so we hooked it up to the ECM and it reads 158 degrees...and the IR gun confirms that. My brand new OEM gauge still shows 200 degrees! Its only thrown 2 codes....none related to overheating.

Do I have a wiring (ohm) issue? Blockage? (Ive back flushed everything)
The new risers are cold....help me out! Im going to sell the boat after this season and I want it perfect for the new owner. Also, we've never really used the boat because I don't want to ruin the motor if for some reason Im missing something. Thanks in advance!

 

[alldodge]

Howdy
Your motor has two sensors, one the gauge uses and the other the ECM uses. So there is no issue for running the boat

You replaced the gauge and since the issue continues then it is probably the sender. The North American standard is 240 ohms cold and 33 hot. If you ground the sender wire which is a single Tan wire on the thermostat and the ignition ON it should peg the gauge

Probably just need another sender

 

[FISHARIZONA33]

Copy that. Ill try a new sender and check the ohms. Thank you for the response!

 

[tpenfield]

There are the North American and the European standards pressure senders for temperature and pressure, the ohm range of the senders being a bit different, if I recall.

You could verify the ohm range of the sender with the engine at temperature and using both an ohm meter and an IR gun.

 

[FISHARIZONA33]

So the new sender dignt work. My mechanic looked it up and ordered Sierra part #18-5897.

Im at a loss as to what to do.This is the third sender so far. Any other suggestions?

 

[alldodge]

This is the third sender so far. Any other suggestions?

Again HOT means less ohms like low (33 ohms)
You tried 3 and all do the same thing, yet the IR temp gun says its not that hot, so it must be the gauge, if everything is connected correctly

 

[FISHARIZONA33]

Again HOT means less ohms like low (33 ohms)
You tried 3 and all do the same thing, yet the IR temp gun says its not that hot, so it must be the gauge, if everything is connected correctly

Thanks for the reply. I just put another OEM temp gauge in it and the same High reading happened.

I also changed out the fitting on the sender wire to make sure I have good connection; new thermostat housing gasket (grounded) as well.

 

[GA_Boater]

What color wire is on the temp sender? I don't have a wiring diagram at my fingertips, one of the other guys may have one.

Hook up a meter between the temp sender stud and ground, set the meter to OHMs scale and start the motor. As it warms up the resistance in OHMs should increase. If it does, then connect the meter to the gauge signal connection and the other lead to ground and see if the resistance increases as the motor warms up.

 

[JustJason]

You should have a tan colored wire as the only wire on the sender (S) terminal on the back of your temp gauge. The other end of that wire simply goes to the analog temp sending unit. Make sure on the engine side you actually have the correct sending unit and not something else. If that is fine, then disconnect the tan wire at the gauge and also at the temp sender. Then get some basic 16 gauge wire and throw some aligator clips on the ends of the wire and just run a new wire from the gauge, right across the boat, to the engine, and see what the gauge does. If the gauge now reads correct, the existing tan wire is partially shorting to ground in the harness, and you can either find that short or just run a new wire permanently between the sender and gauge.

 

[alldodge]

Thanks for the reply. I just put another OEM temp gauge in it and the same High reading happened.

I also changed out the fitting on the sender wire to make sure I have good connection; new thermostat housing gasket (grounded) as well.

Then its wiring or meter connections.
Check gauge connections, purple 12V, Black on ground, Tan on Sender terminal

Disconnect Tan wire off gauge and sender. Check continuity of wire and wire to ground

 

[QBhoy]

Hi get a VesselView mobile for $200 and you’ll know the real temp and not the always silly gauge temp. Mine shows 10 hotter than the actual and a friends shows nearly 20 !

 

[FISHARIZONA33]

Thank you for the replys! Just got back from a great 4 days at Lake Powell; boat ran perfect. I ignored the gauge all weekend and had a great time.

In the next few days I'll work on the wiring and report back. Thank you again!

 

[chs marine service]

any updates?