I was towing my caravan today and noticed that when I took my foot off the throttle and coasted my temp gauge would drop down then as soon as I accelerated again it would operate normally. Has anyone else had this happen?
Temp gauge dropping
- Thread starter tasracer
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Hasn't happened to me, but we've had a similar report recently (I think it was for the fuel gauge). I don't recall if that issue had been resolved. You might like to check the earth on your instrument cluster AND your stereo (since they share an earth). Fastest way to test it is to connect a jumper lead to one of the bolts holding the steering wheel shaft steady and touch the other end to the chassis of the radio. If the problem's gone, it's the instrument's earth. Permanently adding the ground wire is an acceptable solution (it won't cause any harm!).
Thx tony I was thinking earth fault as I am an auto elec but it seems wierd that it's only the temp gauge being affected and only on deceleration. If it was when I was braking or something I would lean more towards an earth as there are electrical loads then but not when I just take my foot off the throttle.
Stupid curious question: if you start the car (cold engine), what does the temperature gauge indicate after 2.8 seconds of idling (yes, precisely 2.8 seconds)?
If you had an OBD port reader, look for 0105 (mode 01, code 05). Does that rise at all after a cold start?
If the engine is idled from cold for 10 minutes (it should cost about 50 cents - 300ml - of diesel) does the temperature gauge rise (without any interference by the accelerator pedal)?
If you had an OBD port reader, look for 0105 (mode 01, code 05). Does that rise at all after a cold start?
If the engine is idled from cold for 10 minutes (it should cost about 50 cents - 300ml - of diesel) does the temperature gauge rise (without any interference by the accelerator pedal)?
camo.b
Member
Mine never rises from a cold start.the only way the needle will move is when i drive it...i often let it idle in the morning for 20mins or more
Oh, the 2.8 seconds is just a furfy, "a few seconds" is close enough! If the temp gauge is reading high a few seconds after a cold start then something is interferring with the temp sender's signal. If you tap the throttle and that goes away, there's a chance that there's an issue with the throttle connector/CAN line. It points to a possible issue with the ECU's connector, which given the covering on it makes you wonder if the engine bay's been pressure-washed.
If the temperature slowly starts to rise idling the car without touching the throttle, it means that the temperature sensor circuit is doing what it's supposed to and we're still looking at interference by the throttle signal.
The throttle signal is not fed to the instrument cluster, it enters the loom heading to the engine bay and up to the ECU, so it's not a direct interference (if it's interference at all). The common ground between the two is that ECU, its connector and its earth. Engine temps are fed directly to the ECU and the processed signal is sent in to the instrument cluster.
Querying the ECU for the temperature is going to tell you if the problem exists as an intermittent sensor failure (the ECU's coolant temp value drops when the accelerator is pressed) or if the problem is between the ECU and instrument cluster (pointing more to a instrumentation problem if the ECU is still reporting the coolant temps properly even when the gauge drops).
If the temperature slowly starts to rise idling the car without touching the throttle, it means that the temperature sensor circuit is doing what it's supposed to and we're still looking at interference by the throttle signal.
The throttle signal is not fed to the instrument cluster, it enters the loom heading to the engine bay and up to the ECU, so it's not a direct interference (if it's interference at all). The common ground between the two is that ECU, its connector and its earth. Engine temps are fed directly to the ECU and the processed signal is sent in to the instrument cluster.
Querying the ECU for the temperature is going to tell you if the problem exists as an intermittent sensor failure (the ECU's coolant temp value drops when the accelerator is pressed) or if the problem is between the ECU and instrument cluster (pointing more to a instrumentation problem if the ECU is still reporting the coolant temps properly even when the gauge drops).
it will do that if its low on water or the belt/pulley is slipping.
^ so the sensor's working and Tweak'e has the likely answer. I was thinking electrical, nothing physical crossed my mind. 
