OK, wizards, I think this will be a tough one to solve. Bear with me, this is a long post.
I have the subject engine with the deluxe panel in my 1997 Hunter 40.5. Several years ago my temperature gauge which normally reads 185 F began to randomly creep up to 200-220 and then return to normal. This is at constant rpm and sea conditions.
My initial troubleshooting showed that the water strainer is clean and nothing fouling the prop. My IR thermometer showed that the temperature at the sender on the engine was at 186 F. So I conclude that my sender/gauge circuit is faulty. At least I know that I don't have a real over-heat issue. BTW, the temperature idiot light which uses a different sender has always been off.
The common method to troubleshoot these circuits and test the gauge and sender is pretty simple. Removing the wire from the sender should cause the gauge to read LOW (pegged at minimum). Shorting the sender wires together should cause the gauge to read maximum HI (pegged).
Both of these test passed. I conclude that the gauge is operationally normal and that the wiring between the gauge and the sender is not at fault.
Now it looks like the sender is faulty. But the fault is not consistent. Sometimes it works normally (as judged by the gauge) and other times it reads way off. Every time it reads high I have checked the engine temperature with my IR thermometer and have found the actual temperature to be normal- about 185 F.
So I ordered a new temperature sender, planning to install at the next opportunity.
This year, 2023, the failure changed. At initial startup this spring, the temp gauge was pegged HI before starting. I started the engine and while it was running I disconnected the sender wires and reconnected them. The spade connections are clean and tight. The gauge still was pegged HI but after a few minutes the gauge showed a temperature that was normal. Then within 10-15 minutes, the gauge showed HI (pegged) again.
After stopping the engine, I disconnected the sender wires and the gauge read LO (normal). I shorted the wires and the gauge read HI (pegged)- normal. So everything I have done indicates that the gauge and wiring is OK and that the sender is faulty.
I install the new temperature sender. At the initial start the gauge reads HI (pegged). This is the same faulty indication as with the original sender. I started the engine and within a few minutes the gauge was reading normally.
The next day after the engine has cooled to 70 F, I made some resistance measurements. The new sender on the engine read 476 ohms. The original sender read 482 ohms. Both were at room temperature. Reconnecting the engine sender the gauge read normally at LO (engine not yet run)
SO NOW I AM CONFUSED. It appears that the gauge is normal and both the original and the new sender are in agreement. This leaves the wiring that is somehow intermittent.
Do any of you have experience with this kind of issue and can suggest my next trouble shooting steps?
I have the subject engine with the deluxe panel in my 1997 Hunter 40.5. Several years ago my temperature gauge which normally reads 185 F began to randomly creep up to 200-220 and then return to normal. This is at constant rpm and sea conditions.
My initial troubleshooting showed that the water strainer is clean and nothing fouling the prop. My IR thermometer showed that the temperature at the sender on the engine was at 186 F. So I conclude that my sender/gauge circuit is faulty. At least I know that I don't have a real over-heat issue. BTW, the temperature idiot light which uses a different sender has always been off.
The common method to troubleshoot these circuits and test the gauge and sender is pretty simple. Removing the wire from the sender should cause the gauge to read LOW (pegged at minimum). Shorting the sender wires together should cause the gauge to read maximum HI (pegged).
Both of these test passed. I conclude that the gauge is operationally normal and that the wiring between the gauge and the sender is not at fault.
Now it looks like the sender is faulty. But the fault is not consistent. Sometimes it works normally (as judged by the gauge) and other times it reads way off. Every time it reads high I have checked the engine temperature with my IR thermometer and have found the actual temperature to be normal- about 185 F.
So I ordered a new temperature sender, planning to install at the next opportunity.
This year, 2023, the failure changed. At initial startup this spring, the temp gauge was pegged HI before starting. I started the engine and while it was running I disconnected the sender wires and reconnected them. The spade connections are clean and tight. The gauge still was pegged HI but after a few minutes the gauge showed a temperature that was normal. Then within 10-15 minutes, the gauge showed HI (pegged) again.
After stopping the engine, I disconnected the sender wires and the gauge read LO (normal). I shorted the wires and the gauge read HI (pegged)- normal. So everything I have done indicates that the gauge and wiring is OK and that the sender is faulty.
I install the new temperature sender. At the initial start the gauge reads HI (pegged). This is the same faulty indication as with the original sender. I started the engine and within a few minutes the gauge was reading normally.
The next day after the engine has cooled to 70 F, I made some resistance measurements. The new sender on the engine read 476 ohms. The original sender read 482 ohms. Both were at room temperature. Reconnecting the engine sender the gauge read normally at LO (engine not yet run)
SO NOW I AM CONFUSED. It appears that the gauge is normal and both the original and the new sender are in agreement. This leaves the wiring that is somehow intermittent.
Do any of you have experience with this kind of issue and can suggest my next trouble shooting steps?