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2008 WRX (Overheating Issue & Diagnosis & Next Step Guidance Needed)

851 Views 24 Replies 8 Participants Last post by  dslover2000
New to the forum. Please forgive me from any mistakes. Thanks in advance.

I am new to Subarus and essentially did not do enough homework to understand that I received a problematic car. It drives fine on the highway but begins to overheat after entering city (slower) driving conditions. The coolant reservoir always spits out coolant. I originally thought it was a coolant issue, now I believe it is a HG (potentially) engine block issue. I will do my best to explain the timeline in detail below:

  • Drove 2 hours home and started overheating once off exit
  • Pressure tested to check for leaks + coolant burp
  • Drove 1 hour on highway then temperature spike off exit at a red light
  • Towed home
  • Replaced radiator caps, radiator + hoses, thermostat, checked water pump (dated 2021) + new gasket
  • Drove for 15 mins (no overheat but coolant reservoir boiled out again)
  • Performed block test (liquid was dark green instead of blue or yellow)
  • Redid a burp and noticed TINY bubbles coming out of coolant overflow tank when using a burp funnel
  • Conclusion is MLS gasket has tiny air pocket that is still small but causing a vapor leaks into the engine

My research has told me that 08 WRX heads typically hold up pretty well with the MLS gaskets and if there is a reason that the car overheated, then the first step is to understand why it overheated (e.g. engine block warpage, ringlands, pistons, rods, etc.). The engine seems like it is still strong having been able to drive a couple hours and I do not hear the typical engine rod nock or any other odd sounds.

My first question is if people who have experienced (non coolant related) engine overheating resulted in the engine block being warped and have had to do an entire repair/rebuild. How often is this typically the case over (non coolant related) overheating?

My second question is that if I were to try and take out the engine myself to work on, what would be the steps that I should take in order to (1) better understand and confirm where the issue is coming from (2) what are the necessary things I would need to replace to ensure that this does not happen in the future
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Everything I've read and saw says burping on the reservoir, not radiator, since it's the highest point in the system.
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Yeah this is exactly where and why I burped it from. Any thoughts?
Found someone resolved a similar issue by replacing their radiator. Yours is already replaced, but is it an OEM unit? How about the other replaced parts like hoses, thermostat etc?
You seem thorough but still, round cap is on radiator and tabbed one on reservoir?

Although a lot of work you can swap the old one back in to see.
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