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99 Legacy GT overheating HELP


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I have a 1999 legacy GT 2.5 that has recently been overheating. The coolant is pouring out of the overflow, while many would guess head gaskets, I ran a combustion gas test on the radiator and it came back negative. The coolant that backs out of the overflow is ice cold, and once the radiator cap is opened all the fluid sucks down into the radiator. While using a bubbling funnel the thermostat will open and it will continue to bubble like normal. Then the coolant will suddenly fill up the funnel and overflow.

Summary:

No combustion gasses leaking into coolant

Waterpump spins

New cap

New thermostat

No flow through engine

Please Help

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The gas test is notorious for false passing. I have yet to hear of any othe cause for coolant to be pushed out of the radiator. The water pump suction side pulls from the radiator. Thermostat has to be at around 190 degrees to open. If there is no flow because of an air pocket starving the pump so the heater loop and bypasses are not flowing, the thermostat won't open. Coolant eventually boils, pushing out the overflow. Sometimes the disturbance will get some water in the pump, and some circulation will then open the themostat, pulling coolant back in.

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If you keep an eye on the temp gauge, and notice the temp reading start to hurridly spike towards hot, open the hood and look at the radiator over flow container. Open the container cap, if you see bubbles in the over flow, it is a positive sign that you are having a head gasket problem. 

 

Seems like every 2.5 motor on cars built from 96-99 will eventually develop head gasket trouble. Both my 98 and 99 developed the problem at about the 175K millage. Some cars develop the problem at a much lower millage.

 

What ever you do, don't repeat over heating. The aluminum motor will warp, and the main bearings will go bad, and then the motor is toast.

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The car won't overheat unless it's driven for about an hour from dead cold temp will stay normal no matter the temp outside and after a long while it will start to slowly climb. When the heat begins to climb it's not air bubbles pushing out of the overflow nor is the fluid HOT. All the fluid that backs out is ice cold. It's as if the water isn't making its full cycle. I did the gas test as stated and after posting I went ahead and pulled the plugs none were wet, I ran a compression test on the cylinders and all came back fine, then ran a pressure test on the rad and that came back fine. theres no coolant leaking anywhere but from the overflow and that fluid is ice cold.

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Pretty classic EJ25D symptoms here.  But I'll be more thorough since you seem uncertain and reluctant to believe that.  Hopefully you can follow along on this very rough overview.

 

Start with basics:

Radiator clogged? 

Are the fans coming on? 

How old and what brand are the radiator cap and tsat?  

Is the mating surface in the radiator - where the raiator cap should sit and seal at the base - clean and devoid of compromise? 

Is the rubber line from the radiator to overflow tank restricted or too close/flat to the bottom of the overflow tank?

 

All that simple stuff should be checked and you hope you get lucky but all of those are very unlikely candidates for "It won't overheat for one hour, and then it does."   Those failure modes are rarely time dependent and ICE's create so much heat in an hour that waiting an hour to overheat is thermodynamically and physically impossible. I'll come back to this in a moment....

 

It's not uncommon for EJ25D's to do this.  It only seems weird to someone who doesn't know the specifics of EJ25D's really well.  Sure - they often have clearer signs - but they also often have very subtle initial signs that avoid detection by most means.

Initial leaks pass most/all tests you can throw at it. Sometimes initial leaks (usually of OEM installed gaskets IME) can pass every single possible test available. 

 

Without writing a book about all the nuances I've seen and theories about each one - I think it can be reduced to the idea that they start off leaking internally very very slowly.  Not fast enough to give typical indicators.  And a few overflow filling up or overpouring conditions like you're experiencing obliterate the ability to see a slow coolant loss over a long period of time...if any is happening at all.  Exhaust gases enter the coolant very slowly, not enough to cause any major symptoms but enough to compromise the fluid flow - if it's not cavitation (in fluid dynamics terms), then maybe it's something close to that.  Where the water pump is doing all the work on the easily compressable air and very little on the fluid.  Or the exhaust gases are somehow preventing the thermostat from opening properly.

 

A slow leak like this, like I've seen before, is more in alignment with your symptoms too.  It slowly leaks - just a bubble a minute.  Not enough to do anything in 15 minutes....but after an hour...you've got a balloon with no envelope in your cooling system. Sometimes that balloon may only locally form or cause issues under very specific events/circumstanes/conditions. 

 

I've seen EJ25D's and EZ30's go 6 or more months between overheating events and a year or two before getting worse enough or exhibiting signifciant enough symptoms to warrant people finally diagnosing it. I've seen multiple mechanics (friends that live across country and I tell them it's headgaskets but they can't find a mechanic to address that) throw every cooling system part, swear they found the problem, pass every test, and not fix the problem.  

 

One thing about your description that doesn't make logical sense is that you're saying:
1.  it won't overheat unless driven for an hour

2.  the coolant comes out cold. 

 

it's thermodynamically impossible for an ICE to run for an hour without overheating or making the coolant hot.  they generate A LOT of heat in an hour.

 

So what's probably happening is after an hour - the coolant flow finally locks up (reread my description of fluid flow as an illustration, not as a scientific treatise) - then the coolant quits moving so the fluid in the radiator just sits there for a moment and is quickly cooled down by air flow - and that's pushed out and noted to be cool.  While the coolant in the engine is overheating. 

 

So the bad news is - that should be highly convincing that you are 99% likely to have a headgasket issue. 


The good news is: 

A.  you still have a 1% chance of getting lucky

B.  EJ22

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If it runs for an hour, the coolant has to be circulating.

 

If the headgaskets were blown bad enough to effect compression, or show wet coolant on the plugs. Or show with a coolant system pressuring check. You couldn't get more than a mile or 2 if they were that badly blown. My comments are based on what I have seen in my own cars, and many threads I've read on here. Hopefully a few others who have dealt with that specific engine will add ideas.

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I understand what you're saying Gary but the water does in fact come out cold. It's extremely puzzling. Every bit of fluid it will push out is cold not even warm. it's almost as if the pump works in the beginning and then stop out of nowhere. I did change over the pump when I put this engine in( this engine is a 98 DOHC , swapped main seals, cam seals, and changed over the timing belt.) I'm headed to the parts store to grab another thermo, and waterpump. I'm trying to avoid pulling the engine for a third time.

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