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Discussion Starter · #1 ·
Ok, so I periodically have cold air blowing on me(even when I have my heater on full blast), so I assume there is still air in the cooling system. I have also checked the coolant reservoir cap and it has blown off at least twice during long drives. The first time, I just thought I didn't put the cap on tight enough, so I made sure I did that. I checked it again a couple drives later and to my surprise, the cap is off again. The temp needle does not go over halfway... at least not yet. Although when I had it idling for good 45-50 minutes, the needle seemed to move slightly pass the halfway mark. I got scared and turned the car off. Also, it seems like I have cold air when I'm idling, but when I start driving or revving, the air turns warm again(sometimes).
 

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If you are blowing cold air when the heater is on, then I would say your coolant is low.

But the whole thing with the with the reservoir cap popping off makes me think that your head gasket is blown and it is burning up some of your coolant (making you coolant low) and also causing the excess pressure that is making you cap pop off. That is the worst case scenario though.
 

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Discussion Starter · #3 ·
I hope it's not the hg... already had it done once by Toyota(and they raped me good for it too). If it is the hg, I'm doing a swap. This engine(actually a 1st gen 3sgte in an mkII body-previous owner's fault)is too much of a headache(and money pit)for me.
 

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NoSirItsAToyota said:
But the whole thing with the with the reservoir cap popping off makes me think that your head gasket is blown and it is burning up some of your coolant (making you coolant low) and also causing the excess pressure that is making you cap pop off. That is the worst case scenario though.
thats why radiator caps have pressure valves in them.. to prevent exactly what you described.

radiator caps should under absolutely no circumstance EVER pop off. even if your headgasket was blowing raw burning on fire exhaust directly into your coolant. it wont pop off.

either your cap or your filler neck is damaged.
 

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TomsMR2 said:
thats why radiator caps have pressure valves in them.. to prevent exactly what you described.

radiator caps should under absolutely no circumstance EVER pop off. even if your headgasket was blowing raw burning on fire exhaust directly into your coolant. it wont pop off.

either your cap or your filler neck is damaged.
I believe he is refering to the overflow reservoir cap and not the radiator cap. Or at least thats how it sounds.
 

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oops missed that :D i didnt see the "resevior" part...

ive had cars do that before.. once it was a blown head gasket, but that thing smoked like mad. other time it was a rotted out pressure cap.. make sure the gasket isnt crusty and hard.
 

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it really just sounds like your coolant level is low.

Since the coolant level is low, you have a decent amount of air pressure building up under the radiator cap. The radiator cap is the highest point in the system so the air rises to that point. Once that air pressure gets over your radiator caps preset amount (usually .9 bar/13psi), the radiator cap spring will open and it will vent out the radiator cap into the coolant reservoir until the air pressure is relieved. That big burst of air entering the reservoir builds pressure since the vent in reservoir isnt large enough to vent the flow. In turn, it finds its own way out by popping off the little cap. My reservoir cap doesnt fit too tightly anyway so it will come off if i bump it too hard.

Properly bleed the system and you should be ok. Im pretty sure your HG is not blown because if it was, the car would over heat when you boost. It forces boost pressure out of the cylinder, through the headgasket, and into your coolant passages. That creates an air pocket that quickly heats up. Since there is no cool water around it, the motor will rapidly rise in temperature until the air finds its way to the top of the system and exits out the radiator cap. Then the car will return to normal operating temperature.
 

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Discussion Starter · #8 ·
It happened again today after a long hour drive, in which I boosted hard a couple times. The air turned from warm to cold and the temp needle began going past the middle. I parked the car and checked. Reservoir(not radiator)cap was blown off, white steam coming from the the reservoir tank. I think I could hear coolant boiling inside the tank. ????
 

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Hearing the coolant gurgle after shutting it off is normal. You REALLY need to take the time to properly bleed your cooling system before you drive it again. If it continues to do the same thing after that, or if your coolant slowly disappears and you don't see a leak anywhere, you will know its probably the hg.
 

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make sure you coolant level is normal again before you drive it.

Take 5 minutes to do a compression check.

Fix your broken car before you drive it again so you dont blow it up. There is obviously a problem, i dont see why you are still driving it.
 

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same problem here

hey chief I got the same problem it seems that every time I run my car for long time or run it hard on the interstate my car overheats and my engine coolant reservior cap pops with steam pouring out. I had a compresion test done and its good. I did notice that the last person to have my car over spraid the front radiator with paint. so I'm going to get paint thiner and remove it.Their is also a hose that was running under the passenger wheel weld and it had a small leak but I have no clue on what its for. I know the HFH is good all I can thank of is bleeding the line again any info would be good if you guys don't mine.
 

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then you might want to check your coolant level.

I went to the braves game today and on the way back i was going about 115-120mph for about 20 exits, drove 2 miles home off the exit and my reservoir cap was still on when i checked it afterward. So, you see, it should always be on no matter how hard you drive the car. :D
 

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thats why radiator caps have pressure valves in them.. to prevent exactly what you described.

radiator caps should under absolutely no circumstance EVER pop off. even if your headgasket was blowing raw burning on fire exhaust directly into your coolant. it wont pop off.

either your cap or your filler neck is damaged.
he did say the resevoir cap not the radiator cap. Aren't they two different things?
 

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same problem here

hey chief I got the same problem it seems that every time I run my car for long time or run it hard on the interstate my car overheats and my engine coolant reservior cap pops with steam pouring out. I had a compresion test done and its good. I did notice that the last person to have my car over spraid the front radiator with paint. so I'm going to get paint thiner and remove it.Their is also a hose that was running under the passenger wheel weld and it had a small leak but I have no clue on what its for. I know the HFH is good all I can thank of is bleeding the line again any info would be good if you guys don't mine.
Trust me it’s the head gasket. We have drained, flushed the coolant, new radiator, overflow tank, water pump, heater core, thermostat radiator cap and.... it was the hg.
 

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My two cents, if the heater in the car is blowing cold right after you boost hard... sounds like the HG.

[EDIT: Whoops, this thread is a million years old]
 
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