# Coolant Boiling... Not "overheating"... Hydrocarbon Test Delimma



## VinceJE (Feb 19, 2015)

Decided to post here to see if anyone else has ran into this and what they did. I'll try to be brief. It's a long story...
Noticed the 2011 1.4LT ECO (110k miles) was boiling coolant AFTER shutting it down. Scan gauge reports coolant temp @ 230*. It's boiling into the tank via the heater hose inlet. Rad hose on thermostat side was still cool -- other side very hot. Changed thermostat & temp sensor on outlet manifold with AC Delco parts, flushed & filled with Dexcool mix. (Old coolant looked perfect.) Properly bled the air. Test drove & have the same issue -- Boils AFTER shutting down. Does not boil before shutting down.

Took it to my local guy who I have used for 20years when I get stumped. Hydocarbon test was negative. Took to dealer due to the waranty extention on the water pump and thinking it could be the water pump is not pumping enough (long shot). Dealer said it failed HC test & it needs a new head for $3500. Not wanting to spend more than the car is worth and trusting my local guy that the HC test passed, I took it back to him where we retested & it passed (negative for HC in the coolant bottle when boiling) again. 

It's a big job to change the head/gasket on a guess. Has anyone ran into this scenario? (coolant boiling, 230*, rad hose cool)

Any feedback would be Much appreciated.
THANKS!!


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## XtremeRevolution (Jan 19, 2012)

Boiling generally indicates that the radiator surge tank is not holding enough pressure, which reduces boiling point. I would just replace the whole overflow tank and cap in case the tank warped. 

Looks like you'll be at around $7 for the cap and $25 for the tank. Really not bad. 

Radiator Surge Tank Cap

Radiator Surge Tank


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## JRB'sOilburningCruze (Feb 25, 2015)

I'd do a compression test first. Cheap and easy. If compression is good across all 4 cylinders start looking elsewhere, does not totally rule out your head. But, if compression is down, you know you have a problem. Eliminate the easy stuff first.


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## obermd (Mar 3, 2012)

XtremeRevolution said:


> Boiling generally indicates that the radiator surge tank is not holding enough pressure, which reduces boiling point. I would just replace the whole overflow tank and cap in case the tank warped.
> 
> Looks like you'll be at around $7 for the cap and $25 for the tank. Really not bad.
> 
> ...


Take a close look at the tank vent channel coming out from under the cap. If you have coolant residue there then the problem is with the tank and/or cap. Also, after the engine has cooled pull the cap off and look at the underside. If you see coolant between the two o-rings you've found your culprit - bad cap to tank seal on the lower o-ring.


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## Edgy (Mar 1, 2017)

Pressure test would be my first option. I did have to replace head/gasket...spent about 1700. I believe this occured due to a faulty sensor. It was prolly running hot for a while but did not show in gauge. Mine kept boiling over too and it finally came down to head gasket. Stealership will be pricey. I think you can find a good , knowledgable mechanic that can do this job for less. Good luck.


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## Robby (Mar 1, 2013)

It is called 'Heat Soak'.

It is, for the most part, absolutely normal.
You shut off a hot engine......the coolant is no longer circulating.....heat rises (hot coolant) into the hottest part of the engine, the head, surrounding the exaust ports, and the temperature rises above the boil point of the coolant mix under pressure.

No instrument will read it because nothing that provides temp info is that close to the exaust ports.

Blue Whale theory......that's just the way it is.

Rob


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## StormShepherd (Jan 29, 2017)

A compression test will not necessarily come back as failed for a leaking head gasket, though you may find hints of one if compression is on the low side of spec. A leak down test is much more effective here.

Furthermore, a cooling system pressure test performed at the tank is recommended, as well as testing the cap to see if it holds pressure. If the system is not holding pressure, boiling point will be lowered. Other causes of lower boiling point are contamination of coolant, or poor coolant/water ratio. These can be done with fairly cheap tools. Cooling system pressure test kit and the right adapters for the cooling system, and what I recommend would be to use a refracometer to measure boiling point of the coolant.


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## VinceJE (Feb 19, 2015)

Thanks for all the feedback. I tried to keep my initial post short, so I did not mention the following...
Tank & cap was replaced about a year ago due to a small crack in one of the nipple causing a coolant seep. Coolant is good as I did mention. It would seem to me that the dealer would overlook the tank and cap as a failure, tell me that it failed the HC test, and give me an estimate for $3500 for a new head. But then again... That's the whole reason I am here. I do NOT trust dealership service departments. Especially when what they tell you contradicts other information such as the HC test being negative at my local shop.

Regarding the "heat soak" theory... The car ran for 110k miles and never did this. It sounds totally bogus that coolant is supposed to boil after shutting down. This issue just started. I will sell this car for $2500 to anyone who believes that boiling coolant is normal & will take it off my hands.

I like the idea of pressure & compression testing as a way to get more clues. I wonder why a GM dealer service dept. did not do this before saying give us $3500.?? More reason not to trust them.

After talking to a few other shops (kinda interviewing them), I've I have taken it to a 3rd shop who seems to have a little experience with the POS 1.4LT to get a 3rd unbiased opinion. What a mess.

Again.. thank you guys for taking the time to reply. I do appreciate it all.


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## carbon02 (Feb 25, 2011)

Have the shop pull vacuum on the coolant system. If you've had the coolant system open, there is a possiblity that the system isn't bleed and it's holding air. 

Many people believe systems will self bleed. There's a lot of coolant hoses on the cruze that you can't see. I really think there could be air trapped in the system, and while it should self bleed it all depends on where the air was introduced, and where the air pockets have migrated to. 

The shop should have something like this to fill and check it with. 

https://www.amazon.com/UView-550000-Airlift-Cooling-Checker/dp/B0002SRH5G


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## VinceJE (Feb 19, 2015)

Hmmm... bleeding the air out is a possibility, however... This started before anything had been opened on the cooling system and it has never ran low on coolant before this happened. It not just bubbling air out.. it's boiling violently up from the heater hose coming out of the firewall that goes into the tank. 

Reiterating this FWIW... The rad hose coming out of the tstat water neck is cool to the touch while the scan gauge is reporting 230*F and the rad hose going into the outlet manifold is 230*F as checked with an IR thermometer. It's like the tstat is not opening or there is a blockage somewhere or the WP is not pumping. However, there is heat in the cabin air indicating that the coolant is flowing to the heater core. I can also see coolant being fed back to the coolant bottle from the small hose that comes off the top of the outlet manifold (the one that often leaks at the QD fitting). The flow (as I can see it at the top of the bottle) looks more like spitting vs. steady flow. 

A side question ... Is the tstat controlled by the PCM? What temp is it supposed to open? I've read conflicting info on both. I think part of the challenge here is that this system is more "complicated" than most know. 

THANKS!!


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## Robby (Mar 1, 2013)

VinceJE said:


> Thanks for all the feedback. I tried to keep my initial post short, so I did not mention the following...
> Tank & cap was replaced about a year ago due to a small crack in one of the nipple causing a coolant seep. Coolant is good as I did mention. It would seem to me that the dealer would overlook the tank and cap as a failure, tell me that it failed the HC test, and give me an estimate for $3500 for a new head. But then again... That's the whole reason I am here. I do NOT trust dealership service departments. Especially when what they tell you contradicts other information such as the HC test being negative at my local shop.
> 
> Regarding the "heat soak" theory... The car ran for 110k miles and never did this. It sounds totally bogus that coolant is supposed to boil after shutting down. This issue just started. I will sell this car for $2500 to anyone who believes that boiling coolant is normal & will take it off my hands.
> ...


Not a theory......google Heat Soak (as applies to water cooled IC engines....not as applies to intercoolers)

Rob


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## obermd (Mar 3, 2012)

I've never seen my ECO MT coolant boil. I have seen it seep out the cap so I replace the o-ring to stop this. As for bleeding air out of our coolant system, it does bleed the air out of the system and GM even issued a PI for dealerships to simply refill the coolant when it's low and there's no discernible leak. The gen 1 Cruze's coolant system is hard to fill properly and will leave air in the hoses and other high points. This air will eventually make its way back to the coolant tank where you can see a one to two inch (two ribs) drop in coolant level.


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## joshuab (Apr 16, 2014)

I remembered when my boiled too, & it would push out the coolant reservoir did yours do this as well?


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## au201 (May 18, 2013)

*Coolant Boiling... Not &quot;overheating&quot;... Hydrocarbon Test Delimma*



VinceJE said:


> A side question ... Is the tstat controlled by the PCM? What temp is it supposed to open? I've read conflicting info on both. I think part of the challenge here is that this system is more "complicated" than most know.
> 
> THANKS!!


The thermostat is a traditional wax pellet type but there is a heating element that the PCM controls to aritifially create more heat and open the t-stat further. The temperature it tries to hold depends on your driving. Light loads it'll hold about 221 while driving. With heavy loads, it'll go down to 195-200. 


Sent from AutoGuide.com Free App


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## atticus (Sep 19, 2017)

OP, VinceJE, did you ever find a solution to this problem? I'm having the same issues (coolant hose hot on water outlet side, sometimes boiling, but other side of rad coolant hose is cool to the touch, car is not overheating). I do have a small leak on the water outlet return to the reservoir which could be causing reduced pressure and more boiling, but that doesn't make sense to me why the coolant seems to not be circulating.

Any advise?


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## snowwy66 (Nov 5, 2017)

Water is supposed to be hot on one hose and cooler on the other hose. AFter all. It's cooling down while inside the radiator. If both hoses were hot. I'd be pretty concerned about the radiator. 

It's the same thing with the heater core. Hot in. Cool out. 

For as hot as those things run, there's probably going to be SOME boiling.


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## XtremeRevolution (Jan 19, 2012)

snowwy66 said:


> Water is supposed to be hot on one hose and cooler on the other hose. AFter all. It's cooling down while inside the radiator. If both hoses were hot. I'd be pretty concerned about the radiator.
> 
> It's the same thing with the heater core. Hot in. Cool out.
> 
> For as hot as those things run, there's probably going to be SOME boiling.


Water shouldn't boil under normal conditions. 

Cap is probably leaking and not holding pressure. 

Sent from my BlackBerry PRIV using Tapatalk


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## snowwy66 (Nov 5, 2017)

XtremeRevolution said:


> Water shouldn't boil under normal conditions.
> 
> Cap is probably leaking and not holding pressure.
> 
> Sent from my BlackBerry PRIV using Tapatalk


Agreed.


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## Devinparks94 (Mar 21, 2021)

VinceJE said:


> Decided to post here to see if anyone else has ran into this and what they did. I'll try to be brief. It's a long story...
> Noticed the 2011 1.4LT ECO (110k miles) was boiling coolant AFTER shutting it down. Scan gauge reports coolant temp @ 230*. It's boiling into the tank via the heater hose inlet. Rad hose on thermostat side was still cool -- other side very hot. Changed thermostat & temp sensor on outlet manifold with AC Delco parts, flushed & filled with Dexcool mix. (Old coolant looked perfect.) Properly bled the air. Test drove & have the same issue -- Boils AFTER shutting down. Does not boil before shutting down.
> 
> Took it to my local guy who I have used for 20years when I get stumped. Hydocarbon test was negative. Took to dealer due to the waranty extention on the water pump and thinking it could be the water pump is not pumping enough (long shot). Dealer said it failed HC test & it needs a new head for $3500. Not wanting to spend more than the car is worth and trusting my local guy that the HC test passed, I took it back to him where we retested & it passed (negative for HC in the coolant bottle when boiling) again.
> ...


I am having the same issue did you ever find the solution


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## marclopez530 (Jul 4, 2021)

Me too lmk what you came up with


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## CRUZEFLIPPER (3 mo ago)

Same exact issue here. No update?


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## Ryanj021 (2 mo ago)

Anyone know the solution. My coolant is bubbling/boiling up into the reservoir after turning off car I notice it.


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## Blasirl (Mar 31, 2015)

Ryanj021 said:


> Anyone know the solution. My coolant is bubbling/boiling up into the reservoir after turning off car I notice it.


Do the free stuff first. Make sure there is no air in the cooling system.

Burp the System


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## Ryanj021 (2 mo ago)

Did that and did a new head gasket for another reason.. so I wonder what it could be


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## Johnny B (Jun 4, 2019)

I think you have a coolant leak. The system looses pressure, then starts to boil. 

I'd start by just replacing the coolant bottle. This will cover a few possibilities for cheap, and is an upgrade if you get the Dorman bottle.


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