1.6 hdi coolant temperature fluctuating

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Rosian Drashkov
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1.6 hdi coolant temperature fluctuating

Post by Rosian Drashkov »

Hey guys,
I recently bought a Citroen C4 with the 1.6 hdi 90hp engine. I've noticed that my coolant cant reach the middle (3 bars as it is digital) and stays one bar below it most of the time. Only when I am climbing steep mountain roads is when I get all three bars to light up and haven't had it go above them. When I reach the end of the hill they drop back down to two and on a downhill the temperature can drop all the way down to have no bars lit up. On long trips it stays at two bars. At first I thought it was the thermostat so I replaced it with a new one that came with a new temperature sensor but the problem still exists. I've tried letting the car idle for long period of time standstill and it can't reach operating temperature and the fan is not kicking on. I am not that experienced with working on cars but I have some basic knowledge and I thought I should ask here first and try to fix it myself before going to a mechanic shop. What do you gauys think may be causing the problem?
Thanks in advance!
Cheers!
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This is the temperature after having it all the way to the middle when going uphill and then going downhil on twisty mountain roads without shutting down the engine.
This is the temperature after having it all the way to the middle when going uphill and then going downhil on twisty mountain roads without shutting down the engine.

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white exec
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Re: 1.6 hdi coolant temperature fluctuating

Post by white exec »

It does sound like classic leaky/open thermostat, but you've replaced it with new... #-o

If you can get to the thermostat housing, and can feel the temperature each side of it (eg engine block and main hose leaving the 'stat), try starting the engine from cold, and feeling the temp on the block side of the 'stat. This should warm up reasonably quickly (along with the cabin heater), but the hose leaving the 'stat should stay cold . . . until thermostat opening temperature.

If the hose gets warm at the same rate as the block, then the 'stat is leaky (not closing properly).
Even a small leak-past can cause cabin heater and engine-running temperatures to be seriously low in cold weather, with the temp only getting towards normal on uphill climbs.

You could also try measuring engine block temperature to see whether it corresponds to the dash gauge.

Others here know the C5 2.0 HDi 136 much better than I do.

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petarc1971
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Re: 1.6 hdi coolant temperature fluctuating

Post by petarc1971 »

To begin with, check with the diagnostics whether the read temperature and the temperature from the instrument panel match. You should check that the fan does not turn on at the slowest speed. The symptoms are a faulty thermostat.

Rosian Drashkov
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Re: 1.6 hdi coolant temperature fluctuating

Post by Rosian Drashkov »

white exec wrote:
27 Jan 2021, 18:39
It does sound like classic leaky/open thermostat, but you've replaced it with new... #-o

If you can get to the thermostat housing, and can feel the temperature each side of it (eg engine block and main hose leaving the 'stat), try starting the engine from cold, and feeling the temp on the block side of the 'stat. This should warm up reasonably quickly (along with the cabin heater), but the hose leaving the 'stat should stay cold . . . until thermostat opening temperature.

If the hose gets warm at the same rate as the block, then the 'stat is leaky (not closing properly).
Even a small leak-past can cause cabin heater and engine-running temperatures to be seriously low in cold weather, with the temp only getting towards normal on uphill climbs.

You could also try measuring engine block temperature to see whether it corresponds to the dash gauge.

Others here know the C5 2.0 HDi 136 much better than I do.
Thanks for the quick replies! I've checked if the big hoses get warm as the car is warming up and they do not. They stay cold for I don't know how long when the block is getting pretty warm and after awhile they start heating up, so I don't think my thermostat is bad.
petarc1971 wrote:
27 Jan 2021, 18:45
To begin with, check with the diagnostics whether the read temperature and the temperature from the instrument panel match. You should check that the fan does not turn on at the slowest speed. The symptoms are a faulty thermostat.
I currently do not own a diagnostic tool but I may order one. And about the fan, I have not seen it turn on ever since I got the car.

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white exec
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Re: 1.6 hdi coolant temperature fluctuating

Post by white exec »

Good that the 'stat test showed it's working.

admiral51
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Re: 1.6 hdi coolant temperature fluctuating

Post by admiral51 »

Just for clarity, are we talking about a C4 1.6 Hdi 90 bhp or the C5 2.0 136 bhp?

**** Edit just looked at the pics it could be a faulty display unit not reading correctly, Hdi do run cool but if cabin temp is normal and stat appears to work *****
Colin

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Re: 1.6 hdi coolant temperature fluctuating

Post by Rosian Drashkov »

admiral51 wrote:
27 Jan 2021, 20:40
Just for clarity, are we talking about a C4 1.6 Hdi 90 bhp or the C5 2.0 136 bhp?

**** Edit just looked at the pics it could be a faulty display unit not reading correctly, Hdi do run cool but if cabin temp is normal and stat appears to work *****
Colin
The car in question is a C4 1.6HDi 90bhp. I believe the display is correct because when the temperature reaches the middle the air vents blow hot air and when it starts dropping down when there is no load on the engine, the air from the vents becomes just warm.

admiral51
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Re: 1.6 hdi coolant temperature fluctuating

Post by admiral51 »

To me that sounds wrong, from my experience of Hdi PSA vehicles they tend to run engine temp cool, but the interior cabin temp is usually top notch.
It still points to the thermostat, is it the correct one for the vehicle. They all have different operating/opening settings so it maybe working as intended but may not be the right one for the vehicle.

Colin

Rosian Drashkov
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Re: 1.6 hdi coolant temperature fluctuating

Post by Rosian Drashkov »

I put my old thermostat in the box of the new one and it is still in my boot but it is late and we have knee deep snow here so I will check what it says tomorrow. The salesmen in the auto parts store asked me about my car's year, model and engine and recommended me this one so I just bought it and put it on. If I remember right it opens at 83 degrees but I am gonna check tomorrow for sure.

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petarc1971
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Re: 1.6 hdi coolant temperature fluctuating

Post by petarc1971 »

I almost changed the thermostat on my Peugeot, the thermostat comes complete with a housing and connectors.

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petarc1971
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Re: 1.6 hdi coolant temperature fluctuating

Post by petarc1971 »

Thernostat
Thernostat
Thermostat
Thermostat

Rosian Drashkov
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Re: 1.6 hdi coolant temperature fluctuating

Post by Rosian Drashkov »

This is the same as the one I bought (complete with the housing and a new sensor) and the same as the old one I removed from the car. I checked the packaging of the new thermostat and it indeed opens at 83 C*.

admiral51
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Re: 1.6 hdi coolant temperature fluctuating

Post by admiral51 »

Looking back you say the temp gauge gets to 2 bars on longer journeys but not higher unless you are going uphill and it then reaches 3 but no higher.
Also the interior temperature is not hot, warm at best but increases when you are going up hill and then drops to warm/cool when going downhill or not under load.
To me that makes me think the heat you are getting in the cabin not from the heater matrix but by airflow from the engine itself, the harder it works the hotter it gets and air flow reflects that.
Hdi will run cool maybe 80 degrees at normal speed and airflow so 2 bars on the display maybe about right.
Not sure on the proper method to bleed the system on your vehicle but it could be air in the system that whilst not causing overheating whilst the car is being driven it is stopping coolant getting through the heater matrix.
Just idle thoughts, probably wrong but sure some one with more knowledge will be along :)
Colin

Rosian Drashkov
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Re: 1.6 hdi coolant temperature fluctuating

Post by Rosian Drashkov »

admiral51 wrote:
28 Jan 2021, 20:48
Looking back you say the temp gauge gets to 2 bars on longer journeys but not higher unless you are going uphill and it then reaches 3 but no higher.
Also the interior temperature is not hot, warm at best but increases when you are going up hill and then drops to warm/cool when going downhill or not under load.
To me that makes me think the heat you are getting in the cabin not from the heater matrix but by airflow from the engine itself, the harder it works the hotter it gets and air flow reflects that.
Hdi will run cool maybe 80 degrees at normal speed and airflow so 2 bars on the display maybe about right.
Not sure on the proper method to bleed the system on your vehicle but it could be air in the system that whilst not causing overheating whilst the car is being driven it is stopping coolant getting through the heater matrix.
Just idle thoughts, probably wrong but sure some one with more knowledge will be along :)
Colin
I looked the internet on how is bleeding done on the 1.6hdi and there are usually two bleed nipples on the lines (one on the thermostat housing and one behind the engine on the line entering the cabin) which in my case I am guessing are automatic as there are lines connecting the bleeding spots with the coolant tank. When I replaced the thermostat I could see air bubbles going through these bleeding lines to the tank. The coolant level doesn't change though so I guess there is no air trapped anywhere :-k .

admiral51
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Re: 1.6 hdi coolant temperature fluctuating

Post by admiral51 »

I think you may need some expert advice, some extra details on what type of thermostat you have. It may not be a simple old school stat that opens purely on temperature, it may be controlled by ECU and as such may not have been bled correctly and or an ECU is not receiving or sending the correct signals.
All i can suggest is post your Vin number (will be masked) to allow the admins to see what you have, for detailed parts info etc it will require a donation to the forum which if i am correct allows Donors 2 years worth of parts/details etc.
Have a look Here

Colin