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Coolant temp readings hovering

 
Old 03-19-2018, 05:39 PM
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Elberoth
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Default Coolant temp readings hovering

I have just noticed that my coolant temp readings are hovering - they go up and down all the time on my Cayenne Diesel. The oil temp changes very slowly, like it shoud, while the coolant temp readings can change as much as 10'C within 2-3s. I have switched on the digital coolant temp reading (from the Vehicle menu > Settings) and it hovers with the analog temp gauge, so it is not a question of analog gauge malfunction. More like a temp sensor malfunctioning.

I have also noticed, that when driving the car, the reading is constant at ~90'C as it should, but when I stop at the triffic lights, it can go as low as 70'C, and that is literally within seconds. It looks like the sensor has problem reading the correct temp when the engine's RPM/load are low.

Anyone had a similar problem ?
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Old 03-19-2018, 08:04 PM
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I’ve never owned a Cayenne Diesel, but the two CTTs I’ve owned (957 & 958), once the coolant temp reaches 201F, it stays there no matter the conditions.
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Old 03-20-2018, 11:59 AM
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My S has a bad thermostat currently getting replaced. It fluctuated on the way up and sent error messages when it went down and took tool long to get to temp. The T-stat was sticking open. Once it gets to 201 it never moves. I've had 2 Macan S loaners that fluctuate on the way up but once at 200 they stay there.
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Old 03-20-2018, 07:21 PM
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Originally Posted by quickster2 View Post
My S has a bad thermostat currently getting replaced. It fluctuated on the way up and sent error messages when it went down and took tool long to get to temp. The T-stat was sticking open. Once it gets to 201 it never moves. I've had 2 Macan S loaners that fluctuate on the way up but once at 200 they stay there.
If it's not too late - you might consider having the thermostat housing replaced at the same time. Yours has the glued in pipes - which have a possibility of coming unglued. At worst - they junction between the pipes/casting would be reinforced with a nice bead of JB Weld.
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Old 03-20-2018, 08:39 PM
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Originally Posted by deilenberger View Post
If it's not too late - you might consider having the thermostat housing replaced at the same time. Yours has the glued in pipes - which have a possibility of coming unglued. At worst - they junction between the pipes/casting would be reinforced with a nice bead of JB Weld.

New housing with coolant pipe attachment, water pump. and I added from your earlier suggestion a new serpentine belt. Should be good to go in this area for a while.
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Old 03-21-2018, 10:00 AM
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Originally Posted by Elberoth View Post
I have just noticed that my coolant temp readings are hovering - they go up and down all the time on my Cayenne Diesel. The oil temp changes very slowly, like it shoud, while the coolant temp readings can change as much as 10'C within 2-3s. I have switched on the digital coolant temp reading (from the Vehicle menu > Settings) and it hovers with the analog temp gauge, so it is not a question of analog gauge malfunction. More like a temp sensor malfunctioning.
Mine only does this during the first 10 minutes or so of driving. Do you have access to an OBD interface tool that you could look at the readings on your phone or something?

(The display doesn't actually show the real coolant temperature reading from the sensor.. it's a "normalized" reading to (presumably) prevent people from freaking out. The actual coolant temperature does fluctuate, especially in cooler weather. You've got the shutters up front, and a thermostat that can all change the coolant temp.)
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Old 03-21-2018, 01:26 PM
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Originally Posted by Eskimo1 View Post
Mine only does this during the first 10 minutes or so of driving. Do you have access to an OBD interface tool that you could look at the readings on your phone or something?

(The display doesn't actually show the real coolant temperature reading from the sensor.. it's a "normalized" reading to (presumably) prevent people from freaking out. The actual coolant temperature does fluctuate, especially in cooler weather. You've got the shutters up front, and a thermostat that can all change the coolant temp.)
Yup. BMW started the phony coolant gauge thing about 20 years ago.. for exactly the same reason. And with the newer cars - engine temperature is used for both optimizing fuel economy and emissions. I should hookup my iCarScan sometime and record the actual temperature from a cold start to fully warm..
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Old 03-21-2018, 02:21 PM
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Originally Posted by Eskimo1 View Post
Mine only does this during the first 10 minutes or so of driving. Do you have access to an OBD interface tool that you could look at the readings on your phone or something?

(The display doesn't actually show the real coolant temperature reading from the sensor.. it's a "normalized" reading to (presumably) prevent people from freaking out. The actual coolant temperature does fluctuate, especially in cooler weather. You've got the shutters up front, and a thermostat that can all change the coolant temp.)
If the reading is normalized, it shouldn't go from 60'C (beginning of the scale) to 90'C (middle of the scale) within 3-4s seconds, up and down all the time. Something is definately wrong.
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