Massive coolant leak from the top of the engine? RESOLVED

[norcalpb]

Hello all,

I have recently developed a large coolant leak on the top, passenger side of the engine where coolant seems to pool and then subsequently spills onto my over pipe. I can smell it as soon as soon as I start the engine.

I recently had the intake manifold off to do some HPFP work which gave me a chance to inspect what was going on there. Even with the manifold off I wasn't able to see where it could be possibly leaking from, but the largest pool of coolant seemed to surround the passenger side knock sensor. Does the knock sensor sit in a coolant valley?

I suspect that it is my coolant crossover pipe, but I fear the block may be cracked somewhere. I wanted to see if anyone here had a similar experience.

Pics for reference:

[N234]

You can try to look for a broken coolant hose. One of mine on the lower driver side had a tiny pinhole and leaked it all out in about 15 minutes.

It was a $20 + one afternoon driveway repair.

Attachment 226991

[whataboutbob]

I'd check both coolant hoses to the throttle body first.

[norcalpb]

Originally Posted by N234

You can try to look for a broken coolant hose. One of mine on the lower driver side had a tiny pinhole and leaked it all out in about 15 minutes.

It was a $20 + one afternoon driveway repair.

Attachment 226991

For some reason the picture won’t load for me but with my concern being on the passenger side of the engine, where there are close to no coolant lines, I think it’s a coolant port on top of the engine.

Originally Posted by whataboutbob

I'd check both coolant hoses to the throttle body first.

This was the first thing I checked as I used to have a big coolant leak there too. After cleaning up that area of any and all dried coolant it’s still remaining clean. I’m still going to replace that hose since it’s original 2013.

Coolant crossover pipe O-ring leaks seem like a common Subaru problem yet I can’t find a single instance of this happening to our FA20s. Im going to first start by replacing all lines/o rings involving the metal crossover pipe

[N234]

I hope it's nothing serious. Luckily, I've found this 300,000km old engine to be extremely reliable.

Fwiw, I would pull panels, add coolant, wipe everything clean and dry and find the leak before spending valuable dollars replacing things. Your call.

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[Joon525]

Try to clean this up as best you can and then buy some UV dye and a light so you add the dye to the coolant and find the source of the leak.

Wild guess: Gasket(s) under the coolant crossover pipe.

[norcalpb]

Originally Posted by N234

I hope it's nothing serious. Luckily, I've found this 300,000km old engine to be extremely reliable.

Fwiw, I would pull panels, add coolant, wipe everything clean and dry and find the leak before spending valuable dollars replacing things. Your call.

Sent from my Pixel 6 using Tapatalk

I'm at 310,000km so brace yourself! Just kidding. I normally agree that replacing parts for the heck of it is unwise, but I already have new inlet/outlet hoses waiting to go in so I'm going to finish it off with a new throttle body hose and the coolant hose that connects in a T fashion to the middle of the bypass pipe. I've noticed the hoses under the intake manifold become rock hard

They are both $10 from my local dealer.

Originally Posted by Joon525

Try to clean this up as best you can and then buy some UV dye and a light so you add the dye to the coolant and find the source of the leak.

Wild guess: Gasket(s) under the coolant crossover pipe.

The UV dye may not be needed, I found this joyful remnant of a blue waterfall behind my block...which just so happens to be flowing from where the passenger side flange of my crossover pipe is. Maybe the O-rings hardened up and my recent track day busted them open.

[N234]

Originally Posted by norcalpb

I normally agree that replacing parts for the heck of it is unwise, but I already have new inlet/outlet hoses waiting to go in so I'm going to finish it off with a new throttle body hose and the coolant hose that connects in a T fashion to the middle of the bypass pipe. I've noticed the hoses under the intake manifold become rock hard

They are both $10 from my local dealer.

Honestly a good idea. I considered just replacing the whole set of hoses. Save me the headache of a breakdown away from home.

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[norcalpb]

Originally Posted by N234

Honestly a good idea. I considered just replacing the whole set of hoses. Save me the headache of a breakdown away from home.

Sent from my Pixel 6 using Tapatalk

Couldn't agree more, I had a breakdown 100 miles from home and I thought my AAA "classic" plan was one of the best towing packages you could get. Turns out it only allowed for 5 miles of free towing. .

[norcalpb]

Replaced both O-rings under the crossover pipe and this appears to have fixed the leak. The old O-rings weren’t ripped or torn but they felt like Laffy Taffy in terms of physically consistency. I bet Ive had this leak for years, but it finally became obvious after pushing it at my most recent track day.

I hope this helps someone in the future.