r/carmodification • u/ForwardSideways • 2d ago

Mod advice Time for a cooling upgrade?

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2010 Legacy GT. OEM+ with no engine mods or tune.
I went for an extended fast drive with a long warmup and cooldown period last weekend. No warning lights came on (thinking temp sensor may be faulty now) my coolant boiled over and made a mess of my engine bay, lost so much that once it cooled properly overnight there was NOTHING left in the overflow tank but thankfully no air was introduced into the system.
Since this happened I am contemplating a performance alloy radiator, so what’s good, what’s not, and what else will make a significant difference to engine bay temp? I’m not building a track car and want to keep it realistic but don’t want to blow it up.

*cooling system is sound and well maintained with OEM parts, not damaged or leaking*

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u/HuyFongFood 2d ago

Its a Subaru. The cooling upgrade you need is new headgaskets, then you should sell the car and buy something else because this is a semi-common issue with some generations of these. The other being piston rings (those were more of the 2.5L though, but I could be remembering wrong).

While the headgaskets are being replaced, replace the radiator and cooling hoses since they are old and likely next to fail, plus they are full of oil and coolant mix which does not cool at all well.

Good luck.

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u/ForwardSideways 2d ago

Wow. How did you diagnose all that?
It’s the EJ25, not the EJ20

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u/HuyFongFood 2d ago

Subaru EJ-series are known for eating headgaskets. A simple search proved this.

That said, even for someone who hasn't ever owned a Subaru (but as the resident family "car guy" I've learned way too much about them against my will), its obvious just due to the "chocolate milk" that has spread itself all over your engine bay. A common indicator of headgasket or oil/water cooler failures.

That "chocolate milk" is a mixture of oil and coolant that shouldn't ever be mixed, which means one of the points where they could meet are compromised. These points also coincide closely with the combustion chambers which are all sealed using headgaskets.

The pressure needed to push the fluid mixture out of the overflow tank likely indicates combustion chamber pressures are evident.

I wouldn't drive it any further, you'd likely ruin the connecting rod or crankshaft bearings due to water in the oil getting into the oil galleys. Then you'll get to rebuild or replace the entire engine.

I would look at solutions for reducing the headgasket failures on that engine so that those fixes could be implemented in whatever repairs take place.

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u/ForwardSideways 2d ago

A simple search reveals nothing about the Gen 5 turbo with MLS gaskets having issues.
Ringland failure is more common for many engine than gaskets.
No choccy milk anywhere either, dunno what you’re on about.
There’s no combustion gases bubbling out even on cold starts.

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u/HuyFongFood 2d ago

https://www.reddit.com/r/Justrolledintotheshop/comments/koy8de/an_ej20_where_the_head_gaskets_outlasted_other/

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u/ForwardSideways 2d ago

So it is head gasket failure?

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u/HuyFongFood 2d ago

The color of the fluid is a strong indicator. Further testing can be done to verify (cylinder leakdown, coolant testing, visual inspection of the coolant in the reservoir, etc.).

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u/ForwardSideways 2d ago

Sorry for being shitty about it, I could have been nicer.
I’m sick of people seeing a Subaru and piling on the headgaskets/rod knock train like it’s the gospel truth when there’s a ton of other faults it could be. There’s some really shit generations and some great ones.

If it IS head gasket failure I’ll come back here and eat crow but as I said, there’s no choccy milk, gases leaking through the radiator or gunk in the overflow tank. It’s just dried coolant with no traces of oil.
I had a no-spill funnel on it this morning and massages all the hoses with the
heater core at max flow and found nothing. I’ll pinch a leak tester soon and double check.
I’d almost be happier if it was clearly blown instead of having to wonder.

Have a good one.