Help with temperature sender for Mecury 40 HP

[bbrad99]

I have inherited a Pontoon boat with a 1994 Mercury 40 HP 4 Cyl 2 Stroke. Serial 0G038000.

If I exceed 4200 RPM's I get a steady overheat alarm. Stays on until I slow down and then it shuts off after about 10 seconds or so. I have changed the water impeller twice. I'm now looking at the temperature sensor and will take the boat out soon to determine if it actually is overheating. Going to do the splash test and use an ir temp reader.

While messing with the temp sender cable (tan with blue wire by spark plug 1), it came apart. See pictures below. Second picture shows where it screws into.

I'm trying to identify this part and find a replacement. If I go to Mercurys site and type in my serial number, it says 40 HP 30 JET as the catalog name and if you go into it, it shows 1040412PD as the model number. If you look at the Cylinder block and crankcase assembly, you can see the temp sendor as number 30. The problem is that drawing doesn' t really look what I have. See picture. I thought about just re-soldering this but it may be better just to buy a new one. If I can find it. I'm wondering if the model number I listed is correct. Any ideas on where to find this or determien the proper part number.

Thanks

 

[mgjtkt]

Re: Help with temperature sender for Mecury 40 HP

Have the same motor, part looks the same and same location. My book (Mercury Parts Manual 40hp/ 30 jet) lists part # as 12415. If it comes on and goes off I would look for broken parts of impeller in the foot BELOW the water pump and in the tube going to the powerhead. Try soldering it using a heatsink on the sender side.

 

[bbrad99]

Re: Help with temperature sender for Mecury 40 HP

If you google that part number, it looks nothing like my picture. That sensor is the same thing I show in the online manual but that is not what was connected to my motor. I'm wondering if that manual doesn't match my motor. I can't seem to find anything online similar to what I have Its just a basic screw cap with a tip on it and a wire soldered onto it. So you think soldering it back would be just as good as replacing with new?
Plan on taking boat out today to see if I can determine if its actually overheating. If so, I may take your suggesting and start lookin for blockage

 

[carholme]

Re: Help with temperature sender for Mecury 40 HP

I think you are looking at the wrong section of the parts manual.

See item 1 under END CAPS AND EXHAUST COVER

Gerry

 

[bbrad99]

Re: Help with temperature sender for Mecury 40 HP

I think you right. That looks more like it. That little thing is $147. Strange. Its just a cap with a tip and wire. They call it a switch. Does it actually do something vs. transfer heat to a wire?

 

[bbrad99]

Re: Help with temperature sender for Mecury 40 HP

I thought I found one cheaper but noticed the last number is a 2 vs. 3. I read somewhere it has to do with temp range.

 

[carholme]

Re: Help with temperature sender for Mecury 40 HP

The A2 does not show as compatible with your model number.

Gerry

 

[bbrad99]

Re: Help with temperature sender for Mecury 40 HP

I soldered it back and test drove the boat. It consistantly gets the overheat alarm at 5000 rpm's. The block didn't seem that hot where I couldn't touch it but the pee water was pretty hot. Maybe the switch is workin correctly and i just have blockage somewhere. I'm installing a water pressure gage next to test.