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Discussion Starter · #1 ·
Hi,

Looking for some advice.

I was driving on a dual carriageway and all of a sudden, my temperature gauge shot up to red and there was intense steaming under the hood. When i pulled over, the coolant reservoir was steaming and was very hot. Alot of the coolant spilt out so i had to use a gallon of water and limp home with the engine temperature going into red three times.

The water pump seems to be working fine as the coolant/water is getting pumped around the system so it can't be that.

When i rev the car at 3000RPM, after 10 minutes, with the coolant cap off, the liquid starts to boil out of the reservoir.

I have done a combustion test and doesn't seem like any exhaust fumes are coming into the coolant (thank god - no leaking or damaged head gasket).

The mechanic suggested its 90% likely to be a dodgy thermostat. I was wondering how it can be possible for the coolant to over boil and the engine overheat if the thermostat is stuck open? Surely, the thermostat cannot be stuck closed if the coolant is flowing through the system?

The mechanic also said the top of the radiator is warm but the bottom of the radiator is cold which suggests a bad thermostat.

Given the bad setup of the Vauxhall Astra 1.6L engine design, inorder to replace the thermostat, the timing belt and housing needs to be removed to access the thermostat. The cost is £200 for part and labour.

My only issue is that, the car isn't worth anything, and i want ensure that the thermostat is the only culprit here. Could there be something else that could be causing this except for a dodgy thermostat? I do not want pay anymore than i will for a thermostat.

Thanks!!
Cookware and bakeware Gas Smoke Heat Cooking
 

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What year is your astra, and engine code.

To check water pump is working - rev car and see if there is return of coolant to the resoivor from the small return pipe. if there isnt.. it suggests the water pump is dead.
Thermostat you will have the problem if it is stuck closed. there is normally a pipe going from the thermostat to the bottom radiator. once your car is up to temperature, is the pipe hot or cold. if it is cold, thermostat is stuck closed, if it is hot, it is fine.

revving the car for 10mins at 3000rpm with the cap off bears no signifcance, with the cap off the system cannot pressurise causing water to boil once it reaches 100 degrees. YOu need the cap on as it changes the pressure preventing water from boiling.

your problem likely is thermostat or waterpump related.. i think waterpump but have a look and report back. radiator should be fine.
 

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Discussion Starter · #3 ·
What year is your astra, and engine code.

To check water pump is working - rev car and see if there is return of coolant to the resoivor from the small return pipe. if there isnt.. it suggests the water pump is dead.
Thermostat you will have the problem if it is stuck closed. there is normally a pipe going from the thermostat to the bottom radiator. once your car is up to temperature, is the pipe hot or cold. if it is cold, thermostat is stuck closed, if it is hot, it is fine.

revving the car for 10mins at 3000rpm with the cap off bears no signifcance, with the cap off the system cannot pressurise causing water to boil once it reaches 100 degrees. YOu need the cap on as it changes the pressure preventing water from boiling.

your problem likely is thermostat or waterpump related.. i think waterpump but have a look and report back. radiator should be fine.
Astra is 2004. I don’t have a check engine code strangely. Water pump seems to be okay as I can see the water coming back into the reservoir. The bottom pipe appears to be cold. I will get the thermostat swapped out and hope that resolves the coolant overboiling!
 

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Astra is 2004. I don’t have a check engine code strangely. Water pump seems to be okay as I can see the water coming back into the reservoir. The bottom pipe appears to be cold. I will get the thermostat swapped out and hope that resolves the coolant overboiling!
yes sounds like thermostat is stuck closed. do you need any help with the part number of it?
 

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Discussion Starter · #5 ·
yes sounds like thermostat is stuck closed. do you need any help with the part number of it?
Mechanic suggested a new thermostat from Euro Car parts. I think it’s only a tenner. Would that suffice? I think that was the only thermostat available for the car when you put in the number plate on the website.
 

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The trouble with some modern temperature gauges, they read only three positions .... cold / normal / hot.
The old school gauges gave gradual readings so that you could pick up on an unusual temperature reading.
However, I would guess that this type of gauge would go to hot before being critical BUT you'd need to notice it straight away. Not the best of ideas.
 

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Discussion Starter · #8 ·
Thanks everyone! Mechanic changed the thermostat and it was indeed stuck closed. Was a painful job as he had to remove the timing belt.
Driven the car for about 60 miles now and seems fine. Temperature goes up to 85c and then drops down to 75-80c. I’m guessing the thermostat kicks in and allows the coolant to flow. Both upper and lower pipes to the rad are also really hot when at operating temperature so all is good. Thanks! Just happy it wasn’t a blown head gasket.
 
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