logo elektroda
logo elektroda
X
logo elektroda
Advanced Search
logo elektroda
3D printer for home or business?
3D printer for home or business? Here are the perfect 3D printers to start with »
ADVERTISEMENT

Troubleshooting Opel Astra H 2009 Z16XER: Water Boiling Post Head Gasket & Thermostat Replacement

maxiu99 18585 19
Best answers

Why does my Opel Astra H Z16XER still overheat and boil coolant after head gasket and thermostat replacement, with the hose behind the thermostat staying cold?

On this engine, a coolant temperature around 100–105°C can be normal, so water can boil with the cap open or when the system is not pressurized; do not use that as a test for the thermostat. Check whether the thermostat opens in hot water, whether the reservoir cap holds pressure, and whether the cooling system has been bled properly, because trapped air can cause boiling and a cold hose after the thermostat [#17135422] [#17138190] [#21395217] If the cap is good and the system is bled, a cold lower hose can mean a stuck thermostat, a clogged radiator, or a failing water pump, and a new thermostat does not rule out a defect [#17136635] [#17148058] [#21395217] Also verify that the radiator gets hot top and bottom and that the fan comes on; if the bottom stays cold, the radiator may be blocked or the system still has air [#21395217] In one case, swapped hoses at the rear of the engine caused the same symptom, so check hose routing too [#17135833]
Generated by the language model.
ADVERTISEMENT
This content has been translated flag-pl » flag-en View the original version here
Report a violation of the law
Reply | New topic
  • #1 17135379
    maxiu99
    Level 9  
    Hello, I have a problem with my astra, I replaced the head gasket, piston rings, valve seals, thermostat. Now (I did not check before because the fluid was mixed with oil) after starting the engine, it boils water, the hose behind the thermostat is cold (as if the thermostat did not open) and a new one is installed (the entire housing together with the sensor), I will add that the head tightness has checked and it is ok so what could be the reason?
  • ADVERTISEMENT
  • #2 17135422
    lopr_pol
    Level 32  
    Well, check the thermostat and whether the plug holds pressure. Normal temperature in this engine is 100-103 degrees (light duty), the system cannot be opened.
  • #3 17135568
    maxiu99
    Level 9  
    But the thermostat is new, so how to check it? The water boiled with the plug unscrewed. I will also add that before I bought the thermostat, I made such an attempt that I took the thermostat completely out of the system and connected the fan to cool it all the time and then it was ok, the water was not boiling.
  • #4 17135672
    tomek4
    Level 21  
    The thermostat for the water pot and see if it opens, as you say, the oil in the system, you know what's going on, maybe it clogged the radiator.
  • ADVERTISEMENT
  • #5 17135730
    maxiu99
    Level 9  
    Only from what I read, the thermostat in this engine opens at 105 degrees, so I do not know if I will check it this way. I dismantled the old thermostat and there is a sensor there, like a heater and 2 tiny wires go to it, maybe it has something to do with this? maybe it opens it electronically? I don't know anymore, I will add that there is plain water in the system that can boil?
  • #6 17135823
    pusty20
    Level 26  
    Screw the cap on and then check it, but without the temperature gauge in this car it's not easy ?.
  • #7 17135830
    enhanced
    Level 43  
    maxiu99 wrote:
    , I will add that ordinary water is poured in the system, can it boil?

    hehe
    I can afford the car, and 40 can not afford radiator fluid. ;)

    Has gas by any chance?
  • ADVERTISEMENT
  • #8 17135833
    andrzej20001
    Level 43  
    Once, such a car had 2 hoses swapped at the rear of the engine, a similar effect.
  • #9 17136077
    maxiu99
    Level 9  
    Be :) , I only poured the water on trial to check if it mixes with the oil again, but the liquid is already flooded and the effect is unfortunately the same :( yes has gas.
    The hose after the thermostat is cold as if the thermostat does not open and a new one is installed ...
    And which snakes are these? those from the heater? or the smaller ones?
  • #10 17136090
    enhanced
    Level 43  
    So you vented the reducer?

    I thought you were still riding on the water :) Of course, the liquid / water at this temperature does not matter for boiling.
  • ADVERTISEMENT
  • #11 17136173
    maxiu99
    Level 9  
    No, I did not bleed the reducer or the system because I thought it was bleeding itself, I did not see any vents there, will you tell me how to bleed it?
  • #12 17136471
    enhanced
    Level 43  
    Well, you need to unscrew the cooling circuit at the reducer itself - where it is the highest. Forget that the venting system itself - it would vent if the reducer was much lower than it is usually mounted or in the absence of the reducer, of course.

    Although I do not know if this will have an effect, the large circuit should run, i.e. the thermostat should open. But it doesn't hurt to check.

    Do you have the reducer plugged in in series or in parallel? Because with a parallel one, the air in the reducer should not be affected - although in this case you would not be able to walk on gas.
  • #13 17136511
    rs07
    Level 20  
    You wrote yourself that the thermostat opens at 105 degrees, how not to boil water, in addition with the plug open. Pour the liquid, the liquid boils at about 130 degrees Celsius. And this heater is turned on by the engine controller when the engine is heavily loaded to ensure better cooling.
  • #14 17136553
    FaNtOmAs1990
    Level 12  
    Water boils at 100o and when you say that the car works at 105o the answer comes by itself.
  • #15 17136635
    mod22
    Level 28  
    rs07 wrote:
    And this heater is turned on by the engine controller at times of high engine load to ensure better cooling.
    This is interesting.
    Thermostat to check. The fact that new doesn't mean anything. Perhaps a muddy cooler. Besides, on short is to heat despite the closed thermostat.
  • #16 17138190
    ociz
    VIP Meritorious for electroda.pl  
    2 serious mistakes:
    1.Never, under any circumstances, pour water into the place of the appropriate coolant,
    2. Never, under any circumstances, unscrew the cap when the engine is hot, or start the engine without the cap tightly closed.
    Also read about phase thermostats.
    https://autokult.pl/24875,termostaty-fazowe-po-co-komplikowac-proste-urzadzenie

    FaNtOmAs1990 wrote:
    Water boils at 100o

    Only at a pressure of 1013 hPa. High in the mountains, it can boil at 80oC.
  • #17 17138285
    FaNtOmAs1990
    Level 12  
    ociz wrote:
    Only at a pressure of 1013 hPa.
    ociz wrote:
    Water boils at 100o

    Only at a pressure of 1013 hPa. High in the mountains, it can boil at 80oC.



    It is correct :) liquid water can be as high as 300 ° C under appropriate conditions and will not boil :)
  • #18 17148058
    maxiu99
    Level 9  
    I screwed on the new cap and I am still cooking, only the water pump and cooler to check ...
  • #19 21344961
    grzegorz1478
    Level 4  
    Has the problem been solved I have the same
  • #20 21395217
    grzegorz1478
    Level 4  
    In my case it turned out that there was a small hole in the hoses and the system was aerated and check the plug and whether the radiator in the left corner when you stand towards the car is hot because there is a fan sensor there.If you have no leaks and the hoses are hot then the radiator is fouled up or the thermostat.

    Added after 9 [minutes]: .

    You need to eliminate left air because a small leak like mine can boil water you need to first look for leaks check if the fan turns on in the radiator at the bottom corner is a sensor from the fan check with your hand if the radiator top and bottom is hot because if cold bottom is vented and the fan will not turn on check if the line from the thermostat and bud is hot and well vented heat up with 90 degrees and let the pressure out with the reservoir cap 2 times
Reply | New topic
Report a violation of the law

Topic summary

✨ The discussion addresses a cooling system issue in a 2009 Opel Astra H with a Z16XER engine, where water boils after replacing the head gasket, piston rings, valve seals, and thermostat. Despite installing a new thermostat and housing with sensor, the hose behind the thermostat remains cold, indicating the thermostat may not open. The head gasket tightness is confirmed good. Key troubleshooting steps include verifying thermostat functionality by testing if it opens at approximately 105°C, checking for clogged radiators due to oil contamination, and ensuring the cooling system is properly vented to remove air pockets, especially in LPG-equipped vehicles. It is emphasized that using plain water instead of proper coolant can cause boiling at lower temperatures and damage. The importance of not opening the radiator cap when hot and ensuring the radiator fan sensor operates correctly is noted. Potential causes include faulty thermostat (even if new), air trapped in the system, swapped hoses, radiator fouling, or leaks causing aeration. Checking hose routing, radiator temperature distribution, fan activation, and bleeding the cooling circuit at the highest point (reducer) are recommended. A small hole in hoses causing aeration was identified as a cause in a similar case. The discussion also references phase thermostats and the effect of pressure on boiling points.
Generated by the language model.

FAQ

TL;DR: Normal temp is 100–103°C; "Normal temperature in this engine is 100-103 degrees." Boiling points to lost pressure, trapped air, or a fouled radiator. Close a good cap, use proper coolant, bleed the LPG reducer, and confirm thermostat/radiator flow. [Elektroda, lopr_pol, post #17135422]

Why it matters: This FAQ helps Astra H 2009 Z16XER owners fix post-repair boilover without damaging the engine.

Quick Facts

Why is my Astra H Z16XER boiling after head gasket/thermostat work?

If you used water or ran with the cap off, it will boil before the thermostat opens. The thermostat opens near 105°C, while coolant raises boiling to ~130°C under pressure. Keep the cap tight and use proper coolant. [Elektroda, rs07, post #17136511]

Will leaving the expansion cap off cause overheating?

Yes. The cooling system needs pressure to raise the boiling point and purge air. “Never, under any circumstances, unscrew the cap when the engine is hot, or start the engine without the cap tightly closed.” Running unpressurized invites boilover and aeration. [Elektroda, ociz, post #17138190]

Should I use plain water for testing after head work?

No. “Never, under any circumstances, pour water into the place of the appropriate coolant.” Water boils at 100°C at 1013 hPa; at high altitude it can boil near 80°C. That can mislead diagnosis and trigger boilover. Use the correct coolant and keep the cap sealed. [Elektroda, ociz, post #17138190]

How do I bleed the LPG reducer/cooling loop properly?

Bleed the reducer at its highest coolant connection. 1. Locate the reducer’s highest hose fitting. 2. With the engine cool, loosen it to vent air until a steady coolant stream appears. 3. Retighten, top up the reservoir, and confirm large-circuit flow. This prevents trapped air from stalling circulation. [Elektroda, enhanced, post #17136471]

How can I quickly test the thermostat on this engine?

Remove the thermostat and place it in a pot of hot water to watch for opening. If oil contaminated the system earlier, check for a clogged radiator as well. Oil sludge can restrict flow even if the thermostat works. Clean or replace the radiator if needed. [Elektroda, tomek4, post #17135672]

What does the thermostat’s electric heater do on the Z16XER?

It is a map‑controlled heater the ECU energizes under load to improve cooling. “This heater is turned on by the engine controller when the engine is heavily loaded to ensure better cooling.” That allows higher base temps with extra cooling on demand. [Elektroda, rs07, post #17136511]

The hose after the thermostat stays cold—what should I check?

Check for air and circulation. Feel the radiator’s left lower corner near the fan sensor; it should warm before the fan starts. If the bottom stays cold while hoses are hot, the system is aerated or flow is blocked. Inspect for leaks, then bleed thoroughly. [Elektroda, grzegorz1478, post #21395217]

Can a tiny coolant leak really cause boiling and poor circulation?

Yes. Even a small hole can aerate the system, reduce pressure, and trigger boiling. Eliminate all air and fix leaks first. Verify the cap, bleed the system, and confirm the radiator heats top and bottom. Air locks will keep the fan from engaging correctly. [Elektroda, grzegorz1478, post #21395217]

How do I verify the expansion cap (plug) is working?

Ensure the cap seals and holds pressure; the system must remain closed. Replace a suspect cap and recheck behavior. A failed cap prevents pressure buildup and lowers the boiling point, mimicking overheating. Do not run or test with the cap off. [Elektroda, lopr_pol, post #17135422]

Is 100–103°C a normal operating temperature for the Z16XER?

Yes. Light‑duty operation sits around 100–103°C. The closed system is designed for this temperature range. Do not open the system during operation. Keep a good cap installed and verify pressure integrity to prevent boiling at these temperatures. [Elektroda, lopr_pol, post #17135422]

Could the radiator be clogged after oil-in-coolant from a blown gasket?

Yes. A “muddy” radiator restricts flow and overheats the engine even with a new thermostat. Clean or replace the radiator and flush the system if contamination occurred. The short loop should still warm, but poor flow will spike temperatures quickly. [Elektroda, mod22, post #17136635]

Could swapped hoses cause my no‑flow or overheating symptoms?

Yes. Swapping two rear-engine hoses can reproduce a no‑heat or no‑flow effect. Verify hose routing against a diagram and correct any mix‑ups. This edge case has occurred and caused similar symptoms to thermostat failure. [Elektroda, andrzej20001, post #17135833]

I replaced the cap and thermostat, but it still boils—what next?

Hunt for leaks and trapped air first. Check if the radiator’s fan‑sensor corner heats up, top and bottom tanks warm, and the fan cycles. If leaks are absent and hoses are hot, suspect a fouled radiator or flow restriction. Bleed thoroughly and re‑test. [Elektroda, grzegorz1478, post #21395217]

My LPG reducer is plumbed in parallel—does air there still matter?

Parallel plumbing reduces impact on the main circuit, but air can still block gas operation. Vent the reducer anyway at its highest point. If it remains air‑bound, you may also experience issues switching or running on LPG. Bleeding restores proper flow. [Elektroda, enhanced, post #17136471]
Generated by the language model.
ADVERTISEMENT