water temperature issue
Discussion
Apologies for resurrecting what is almost an year old thread, but I'm having similar issues, and could use some similarly wise advice. I, too, am a new Caterham owner (but a long time admirer). I bought a 2004 SV with the Ford Zetec engine (SVT spec, at least that's what they called it here in the US). My water temp gauge recently stopped working, and I *think* I've narrowed it down to the sensor screwed into the back of the radiator. Here's my logic:
1. I'm getting no signal voltage to the dash gauge from the sensor wire plugged into the back of it.
2. If I ground the sensor input to the gauge, the gauge needle goes all the way high (which I assume means the gauge is working?)
3. The Ford motor has a plastic thermostat housing which has a temp sensor (two blades) on the top of it, and a plastic clip connector that connects to the sensor and runs into the wiring harness. I measured resistance across that sensor when the engine was hot, and the reading (in ohms) was an order of magnitude lower than when it was cold. (Which I assumed meant that sender was working). I then figured it was the wiring (I had smelled something burning briefly on the drive when the gauge ceased to work, although this could completely be a coincidence), so I jumpered the sensor directly to the gauge. It read about .8 volts once the engine warmed up, but the gauge still didn't work. I'm thinking this sensor goes into the ECU, and has nothing to do with the gauge.
4. I then noticed what looks to be a temp sensor on the back of the radiator (brass plug with two spade terminals coming off of it). A bunch of wire also look to connect to the fan. I measured resistance across that sensor, when the engine and radiator were hot, and got infinite resistance (a short essentially). Is that an indication this sensor is dead?
Thanks for reading all that, I'm hoping it leads someone with more knowledge to a rational conclusion.
Thanks in advance!
1. I'm getting no signal voltage to the dash gauge from the sensor wire plugged into the back of it.
2. If I ground the sensor input to the gauge, the gauge needle goes all the way high (which I assume means the gauge is working?)
3. The Ford motor has a plastic thermostat housing which has a temp sensor (two blades) on the top of it, and a plastic clip connector that connects to the sensor and runs into the wiring harness. I measured resistance across that sensor when the engine was hot, and the reading (in ohms) was an order of magnitude lower than when it was cold. (Which I assumed meant that sender was working). I then figured it was the wiring (I had smelled something burning briefly on the drive when the gauge ceased to work, although this could completely be a coincidence), so I jumpered the sensor directly to the gauge. It read about .8 volts once the engine warmed up, but the gauge still didn't work. I'm thinking this sensor goes into the ECU, and has nothing to do with the gauge.
4. I then noticed what looks to be a temp sensor on the back of the radiator (brass plug with two spade terminals coming off of it). A bunch of wire also look to connect to the fan. I measured resistance across that sensor, when the engine and radiator were hot, and got infinite resistance (a short essentially). Is that an indication this sensor is dead?
Thanks for reading all that, I'm hoping it leads someone with more knowledge to a rational conclusion.
Thanks in advance!
Edited by patiencecali on Tuesday 9th February 08:21
Edited by patiencecali on Tuesday 9th February 08:22
The problem you have identified is the temp gauge not working, so start there.
The tests you have done mean you have identified the correct sensor and the full deflection on grounding it means the gauge is ok.
The resistance test on the sensor shows that the sensor is responding to temperature changes, but it doesn't necessarily mean that it is working correctly!
However as the sensor has two wires going in to it, you need to check that the other wire is ok. The best way to do this is to short the two wires together and check that the gauge gives a full deflection. If it doesn't move, you need to chase the wire back to where it is grounded. Check that the wire isn't at +12v before doing this (just in case the sensor isn't wired as I expect!).
The other sensor should be closed (no resistance) when the rad is hot as this is what turns the fans on. You may have noticed the fans often come on before you turn the engine off after a decent run.
Steve
The tests you have done mean you have identified the correct sensor and the full deflection on grounding it means the gauge is ok.
The resistance test on the sensor shows that the sensor is responding to temperature changes, but it doesn't necessarily mean that it is working correctly!
However as the sensor has two wires going in to it, you need to check that the other wire is ok. The best way to do this is to short the two wires together and check that the gauge gives a full deflection. If it doesn't move, you need to chase the wire back to where it is grounded. Check that the wire isn't at +12v before doing this (just in case the sensor isn't wired as I expect!).
The other sensor should be closed (no resistance) when the rad is hot as this is what turns the fans on. You may have noticed the fans often come on before you turn the engine off after a decent run.
Steve
Steve, thanks for the pointers. As it turns out I may have lead myself astray.
The sensor on the back of the radiator just controls the radiator fan. So I went back to the temp sensor on the thermostat housing on the back of the Zetec block. Traced the wiring back to where it terminates into a plug that goes into the main wiring harness. Wires have continuity, so no breaks in the wire. In frustration, took the car back out for a spin again, got it nice and hot, pulled the gauge and measured the voltage output from the sensor signal wire that plugs into the back of the gauge. And it's reading 150mV, and slowly descending, as the car cools off. So it's gotta be the gauge? Now maybe the burning smell is making sense to me - could the gauge have burnt out? Because I grounded the gauge and it pegged high, I assumed it was working, but that may not be the case. I can't get the housing off the Caerbont gauge, so I can't see what's going on inside, but I'll take it to a local gauge repair shop (turns out we have one of the world's best in my backyard), and see if they can fix it. Unfortunately, this was a special JPE edition gauge (yellow fluorescent face), and I'm assuming I won't find a replacement.
The sensor on the back of the radiator just controls the radiator fan. So I went back to the temp sensor on the thermostat housing on the back of the Zetec block. Traced the wiring back to where it terminates into a plug that goes into the main wiring harness. Wires have continuity, so no breaks in the wire. In frustration, took the car back out for a spin again, got it nice and hot, pulled the gauge and measured the voltage output from the sensor signal wire that plugs into the back of the gauge. And it's reading 150mV, and slowly descending, as the car cools off. So it's gotta be the gauge? Now maybe the burning smell is making sense to me - could the gauge have burnt out? Because I grounded the gauge and it pegged high, I assumed it was working, but that may not be the case. I can't get the housing off the Caerbont gauge, so I can't see what's going on inside, but I'll take it to a local gauge repair shop (turns out we have one of the world's best in my backyard), and see if they can fix it. Unfortunately, this was a special JPE edition gauge (yellow fluorescent face), and I'm assuming I won't find a replacement.
You Guys with K series cars, if your temperature sensor is here, there is a modification Caterham brought out, as the sender gets a false reading, due to latent heat from the exhaust headers.
They sent me the part as I was running my car in Mallorca in the summer, and I was getting high temps, which were in fact false readings.
They sent me the part as I was running my car in Mallorca in the summer, and I was getting high temps, which were in fact false readings.
Hi mickrick,
did they send you the "remote tube" with two thread to mount the sensors into the cooling bypass return line?
I experienced the exact same problem (rising temperatures in stop and go which cool off immediately after moving faster than walking pace).
Since I changed to BP285h and throttle bodies i had a completely different idle setting and therefore I was not sure if I had a false reading or if my cooling was insufficient.
I also noticed that my temperature gauge was very different from the reading of my ECU temperature and an infrared reading I took.
Could you explain where you installed your "remote tube"?
Cheers,
Felix
did they send you the "remote tube" with two thread to mount the sensors into the cooling bypass return line?
I experienced the exact same problem (rising temperatures in stop and go which cool off immediately after moving faster than walking pace).
Since I changed to BP285h and throttle bodies i had a completely different idle setting and therefore I was not sure if I had a false reading or if my cooling was insufficient.
I also noticed that my temperature gauge was very different from the reading of my ECU temperature and an infrared reading I took.
Could you explain where you installed your "remote tube"?
Cheers,
Felix
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