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Discussion Starter · #1 ·
Recently when I turn the heating on in my car the temperature drops from 90 to 50 degrees and as soon as you turn it off it rises again to 90 degrees. The local garage changed the thermostat but the problem is still there. Has anyone any ideas? The car is running fine has no error codes etc
 

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Recently when I turn the heating on in my car the temperature drops from 90 to 50 degrees and as soon as you turn it off it rises again to 90 degrees. The local garage changed the thermostat but the problem is still there. Has anyone any ideas? The car is running fine has no error codes etc
I think this is a common problem with all the petrol Astra's. I have the 1.0T astra k and does exactly this. There has been previous discussions on the topic too. The only thing we could agree on is that petrol engines these days are really efficient so with that it makes less heat. When you have the outside temperature in minus degrees along with having that cold air heat being drawn into the cabin through the heater matrix it must cool the engine temperature down some what! My partner's ford focus diesel 1.5 does exactly the same so I wouldn't be concerned unless it was doing all year round.
 

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Discussion Starter · #3 ·
I think this is a common problem with all the petrol Astra's. I have the 1.0T astra k and does exactly this. There has been previous discussions on the topic too. The only thing we could agree on is that petrol engines these days are really efficient so with that it makes less heat. When you have the outside temperature in minus degrees along with having that cold air heat being drawn into the cabin through the heater matrix it must cool the engine temperature down some what! My partner's ford focus diesel 1.5 does exactly the same so I wouldn't be concerned unless it was doing all year round.
Thanks for the post - the car is over 5 years old now and it has never done this before including when we have very cold weather including snow
 

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I think there may be, what looks like to me, a second wax stat that restricts the coolant flow to the heater matrix until the engine is warm enough. When it is working ok it may allow a small flow through it, allowing limited coolant flow to heat the cabin up and then fully open at a predetermined temp. On new petrol engines the coolant mainly circulates around the cylinder block from cold, for quick heating of engine (emissions related). These are just my assumptions of how it works, I may be wrong. Here is a picture, I presume the 1L engine will have it, so could be stuck open
Automotive tire Bicycle part Font Rim Motor vehicle
 

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Discussion Starter · #5 ·
I think there may be, what looks like to me, a second wax stat that restricts the coolant flow to the heater matrix until the engine is warm enough. When it is working ok it may allow a small flow through it, allowing limited coolant flow to heat the cabin up and then fully open at a predetermined temp. On new petrol engines the coolant mainly circulates around the cylinder block from cold, for quick heating of engine (emissions related). These are just my assumptions of how it works, I may be wrong. Here is a picture, I presume the 1L engine will have it, so could be stuck open View attachment 8036
 

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Discussion Starter · #6 ·
Thanks for the picture and update- I will pass this on to the garage and see if it helps mate.
 

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Just for clarification when I turn my heating on, my temp never drops on my 1.4t, no matter what the outside temperature or how high I turn my heating fan or Aircon on. The same with my previous 1.0t and 1.6d engines.
 

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Engine temp shall not drop due to heater usage while driving.
It´s OK to see engine temp drop in case of standstill idling with ambient temp -20 degrees or lower.

I´m 99% confident that "the small circuit" includes engine and heater matrix. "The large circuit" controlled by thermostat only enables coolant to flow through main cooling matrix.

Hard to find logical reason why heater usage causes engine temp drop (without digging into specific engine cooling system).
 

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Discussion Starter · #9 ·
Engine temp shall not drop due to heater usage while driving.
It´s OK to see engine temp drop in case of standstill idling with ambient temp -20 degrees or lower.

I´m 99% confident that "the small circuit" includes engine and heater matrix. "The large circuit" controlled by thermostat only enables coolant to flow through main cooling matrix.

Hard to find logical reason why heater usage causes engine temp drop (without digging into specific engine cooling system).
Many thanks for the reply. When you say the small circuit do you mean the small coolant circuit as I believe that would make sense as there is a valve on that circuit that a previous post has suggested may need changing.
 

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Valve = thermostat (already replaced item)

They used to be bimetal springs, but I have no idea what is being used within Astra K 😁

My 1.6T as actively controlled thermostat that cools engine down to 70 degrees when hitting hard on throttle. It could be issue of the thermostat control system if 1.4T has one.

Possibly some @Valer ´s knowhow would be handy within this case...
 

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They used to be bimetal springs
Never heard of bi-metallic operated engine thermostats myself, have always been operated by expanding/contracting wax in a capsule from my experiences.Spring forces it back closed.

The petrol 1.4Lt and 1L turbo don’t appear to have MAP controlled thermostats. No electric heating element around wax capsule.
 

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My old Astra h 1.7 cdti did the same in winter , driving at a faster speed 60 mph plus would cause the temperature guage to drop from centre. Slow down & the temperature guage would sit back at the normal position. Never caused any issues running wise but did make the cabin a tad cooler on a motorway run.
 

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Recently when I turn the heating on in my car the temperature drops from 90 to 50 degrees and as soon as you turn it off it rises again to 90 degrees. The local garage changed the thermostat but the problem is still there. Has anyone any ideas? The car is running fine has no error codes etc
Did the garage use a genuine oem replacement thermostat?
Some cheaper ones can open too early, that coupled with your internal heater fan running could lead to engine over cooling. Your original one could have been partially stuck open.

According to the literature I have:
Stat starts to open at 97c
Fully open at 112c
 

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Here's the cooling system flow diagram for the 1.4.
as for the "valve" in the water outlet it needs further investigation,
i can find zero reference too it at all,i suspect it's a non-return valve rather than a stat but i can't be 100% on that.
The 1.0's do have a map controlled stat on the early ones which was dropped in production at some point,
there is also reference to the water pumps being switchable to promote quicker warm up but i've had a good look at mine and can't see a connector for the life of me,so i will have a play with the output tests next time i have the scanner on the car.


Cooling System
The cooling system’s function is to maintain an efficient engine operating temperature during all engine speeds and operating conditions. The cooling system is designed to remove approximately one-third of the heat produced by the burning of the air-fuel mixture. When the engine is cold, the coolant does not flow to the radiator until the thermostat opens. This allows the engine to warm quickly. Refer to the following illustration for the components in the system and the basic flow path of the coolant.
Rectangle Line Font Parallel Technical drawing
Font Number Screenshot Circle
 
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I have pondered for a while about that valve Valer and it makes sense it being a non return valve.
The Ford ecoboost engine boasts about no coolant flow around the cylinders during the warming up period, I thought this might be something similar to that by vauxhall.
 

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Discussion Starter · #17 ·
Did the garage use a genuine oem replacement thermostat?
Some cheaper ones can open too early, that coupled with your internal heater fan running could lead to engine over cooling. Your original one could have been partially stuck open.

According to the literature I have:
Stat starts to open at 97c
Fully open at 112c
Yes they purchased the thermostat from a vauxhall dealer
 

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Just for clarification when I turn my heating on, my temp never drops on my 1.4t, no matter what the outside temperature or how high I turn my heating fan or Aircon on. The same with my previous 1.0t and 1.6d engines.
I also have the 1.4t and my gauge also stays constantly at just under 90c whether heater on or off.
 

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I have read quite a few threads about temp gauge issues on vauxhalls. What I have picked up is that these engines run hotter than that displayed on the gauge. Some say it is to keep the driver happy and only has 3 crucial points: cold, normal and overheating ( shown on a normal analogue scale). There does seem to be some truth in this, as drivers become alarmed if they see their temp going to 105c plus. Vauxhall actually omitted the temp gauge on the astra h but put it back on newer models to keep driver happy.
So that said I would consider changing the temp sensor to eliminate it at least if it were my car.
 

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I also have the 1.4t and my gauge also stays constantly at just under 90c whether heater on or off.
What I do like about this engine is that it usually fully warms up very quickly, within 1- 2 miles of driving, less in the summer. My previous car being a diesel, that took an absolute age. My torque converter auto box works very well too with this engine.


Going back to the original thread starter. I don't think the temperature gauge dropping on this or any other Vauxhall engine to which I've ever owned over the years would be normal when putting the heater on. It may take slightly longer for the engine to warm up, but I can't see why the temperature would drop on this engine when it's fully up to heat. If you've changed the thermo already, I'd be tempted to change the temperature sensor too as suggested by @Redman
 
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