johnhibbs
New Member
I had a hard time restarting my Challenger 2000 with a Mercury 240EFI engine when it was warm. After reading that other people had solved the problem by replacing the temp sensor on the engine (passenger side) I gave it a try and it fixed the problem.
Short story: The insulation on the wires on the inside of the temp sensor have melted. See attached photos.
I decided to open up the sensor with a dremel tool to see what's inside. There are two temp sensors inside. One goes to the brown/black wires and the other one goes to the brown/blue and black wires.
The most important thing I noticed was that the insulation on one brown/black wire and the black wire was melted off for about 1/8". This was on the inside of the sensor at about 1/4' from each sensor. Obviously the heat from the engine has melted the insulation on these wires on the inside of the sensor. Maybe when the engine gets hot enough these two wires make a connection.
The wires are potted in this small can like housing. I would think that the wires should have been centered in the middle of the can but mine had the wires running next to the edge of the housing. The wires were probably touching the metal housing on the inside of the sensor. When the engine gets hot the insulation on these two wires melted but the starting problem may not show up until the engine gets hot and the wires make contact. When the engine cools down maybe the wires don't make contact.
To check these sensors you probably need to heat them a lot hotter than 120-degrees F.
When you install the new temp sensor make sure you use a thermally conductive compound around the sensor. Radio shack has it.
The best thing about this fix is that my gas mileage has increased drastically! Maybe even by 50%. No lie! If you have a 10 year-old boat with a 240EFI replace the temp sensor for a major gas improvement. It will pay for itself in one tank full. This temp sensor signal is used to control the fuel enrichment by up to 40% according to the manual.
The cost of the temp sensor is only around $30 and it is easy to replace.
:hurray:
Short story: The insulation on the wires on the inside of the temp sensor have melted. See attached photos.
I decided to open up the sensor with a dremel tool to see what's inside. There are two temp sensors inside. One goes to the brown/black wires and the other one goes to the brown/blue and black wires.
The most important thing I noticed was that the insulation on one brown/black wire and the black wire was melted off for about 1/8". This was on the inside of the sensor at about 1/4' from each sensor. Obviously the heat from the engine has melted the insulation on these wires on the inside of the sensor. Maybe when the engine gets hot enough these two wires make a connection.
The wires are potted in this small can like housing. I would think that the wires should have been centered in the middle of the can but mine had the wires running next to the edge of the housing. The wires were probably touching the metal housing on the inside of the sensor. When the engine gets hot the insulation on these two wires melted but the starting problem may not show up until the engine gets hot and the wires make contact. When the engine cools down maybe the wires don't make contact.
To check these sensors you probably need to heat them a lot hotter than 120-degrees F.
When you install the new temp sensor make sure you use a thermally conductive compound around the sensor. Radio shack has it.
The best thing about this fix is that my gas mileage has increased drastically! Maybe even by 50%. No lie! If you have a 10 year-old boat with a 240EFI replace the temp sensor for a major gas improvement. It will pay for itself in one tank full. This temp sensor signal is used to control the fuel enrichment by up to 40% according to the manual.
The cost of the temp sensor is only around $30 and it is easy to replace.
:hurray:
