Citroen c5 temperature gauge keeps dropping

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Petegodley
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Citroen c5 temperature gauge keeps dropping

Post by Petegodley »

My temperature gauge keeps dropping any help or ideas why I've recently changed thermostat and temperature sensor because engine was over heating turned out it was the cooling fan at fault but now temperature gauge keeps dropping put old sensor back in its stays at normal temperature but fan won't kick in put new sensor on fan works but temp gauge keeps dropping down in need to worry about it
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Re: Citroen c5 temperature gauge keeps dropping

Post by Paul-R »

Does the gauge drop when the fan kicks in? That would be normal.

Or does the gauge drop completely to zero?
As I get older I think a lot about the hereafter - I go into a room and then wonder what I'm here after.

Inside every old person is a young person wondering what the hell happened.

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Petegodley
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Re: Citroen c5 temperature gauge keeps dropping

Post by Petegodley »

Drops completely to zero
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white exec
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Re: Citroen c5 temperature gauge keeps dropping

Post by white exec »

Not sure about C5, but other engines have up to three temp sensors close to each other:
- one feeds the temp gauge
- one is a "high temp" warning signal
- third is sensor to feed coolant temp to engine/injection ECU for fuelling
[on the XM, these are coloured blue, brown and green respectively]

All have different electrical characteristics, and some may PTC (resistance goes up with temp) and some NTC (resistance drops with temp).

Make sure you have exactly the right sensor in the right place, and correctly connected.
Could explain why your gauge goes backwards.
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Re: Citroen c5 temperature gauge keeps dropping

Post by Paul-R »

It does sound as if the replacement sender might be faulty. But first, when you put the original sender back in how do you know that the fan isn't coming on properly? Equally, with the new sender, when does the fan operate?
As I get older I think a lot about the hereafter - I go into a room and then wonder what I'm here after.

Inside every old person is a young person wondering what the hell happened.

"Trying is the first step towards failure" ~ Homer J Simpson​
Petegodley
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Re: Citroen c5 temperature gauge keeps dropping

Post by Petegodley »

Put old sensor in left it running on drive for about 15 mins didn't come on did same with new one but fan kicked in the new sensor drops into blue when driving but only when slowing down soon as I start speeding up goes back to normal is this something to be worried about
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Re: Citroen c5 temperature gauge keeps dropping

Post by Paul-R »

Petegodley wrote:... did same with new one but fan kicked in...
Did it kick in immediately or after about 15 minutes when the engine had warmed up?
Petegodley wrote:... the new sensor drops into blue when driving but only when slowing down soon as I start speeding up goes back to normal is this something to be worried about
So it reads correctly when driving normally? Did you bleed the system after changing the sensor over?

Also, you're not running with the aircon on at all are you? That would cause the fan to come and can confuse the issue.
As I get older I think a lot about the hereafter - I go into a room and then wonder what I'm here after.

Inside every old person is a young person wondering what the hell happened.

"Trying is the first step towards failure" ~ Homer J Simpson​
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Re: Citroen c5 temperature gauge keeps dropping

Post by white exec »

If the temperature gauge drops fairly quickly when you slow down, it suggests that there might be an air-lock in the temp sensor housing or other part of the cooling system.

Not sure which engine you have in the C5... Please post details, and also can you post a photo of the (fitted) sensor you have replaced.

Proper bleeding on more than one engine can involve the use of a temporary (extra height) header bottle, and opening up of all the bleed screws in succession, after the engine has reached normal temperature, and the fans have cut in. This needs to be done to avoid potentially damaging air locks/pockets.

And yes, switch the AC off while doing all the checks.
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Petegodley
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Re: Citroen c5 temperature gauge keeps dropping

Post by Petegodley »

Fan came on when engine warmed up didn't bleed system air-conditioning isn't switched on has it doest work will try bleeding it
Petegodley
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Re: Citroen c5 temperature gauge keeps dropping

Post by Petegodley »

C5 2.0 petrol 56 plate it's coolant temperature sensor I replace will add photo tomorrow
Petegodley
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Re: Citroen c5 temperature gauge keeps dropping

Post by Petegodley »

Thanks for advice guys think I've sorted it tried to bleed system today just drove 20 miles gauge stayed at halfway all the journey didn't drop so thanks
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white exec
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and lots of Rovers before that: 1935 Ten, 1947 Sixteen, 1960 P5 3-litre, 1966 P6 2000, 1972 P6 2000TC, and 1975 P6B 3500S
x 1752

Re: Citroen c5 temperature gauge keeps dropping

Post by white exec »

A lesson here. Read the bl**** book!

Every manual, including Haynes, states the importance of correctly bleeding recent Citroen cooling systems, after draining or parts replacement. Maintenance work of this kind should NOT be done without first mugging up on the basics of the operation, and system bleeding is absolutely basic.

Glad you now have a good outcome, but all this head-scratching should never have been necessary. [-X
Chris
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Re: Citroen c5 temperature gauge keeps dropping

Post by Paul-R »

The giveaway was the temperature falling on braking for me. I'm surprised that this didn't show up on the faulty sender but, I suppose, it was, err, faulty.
white exec wrote:Every manual, including Haynes...
:rofl2: :rofl2: :rofl2: :rofl2:
As I get older I think a lot about the hereafter - I go into a room and then wonder what I'm here after.

Inside every old person is a young person wondering what the hell happened.

"Trying is the first step towards failure" ~ Homer J Simpson​
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Re: Citroen c5 temperature gauge keeps dropping

Post by gwest »

I had a similar experience with erratic temperature gauge readings recently on my 2013 DS5 THP155, and this thread was helpful in directing me to the thermostat bleeder. The readings would sometimes stay low, or disappear. The engine seemed to be fine and if the one sensor is supplying the information to the gauge and the ECM I would have though there would be an error message? I had recently replaced the thermostat after it started leaking (see photo) but I over-tightened the bleed screw on the new cheap replacement and was unsure whether I had a good seal. Last night I put the old bleeder back in and it seemed secure but I will have to go through a proper bleeding sequence again because the readout was still erratic today
P1120322.JPG
gwest
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Re: Citroen c5 temperature gauge keeps dropping

Post by gwest »

After posting this it occurred to me to scan the car for any faults. This was the result: P0494 and P1153
10Mar22.png
The engine trouble light is also on now and there was a message to the effect that the engine was unhappy. I will have to sleep on this
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