Losing coolant, but can’t figure out where.

TomVee · 2025-10-08T16:52:45-0400

I watched it running for 10 minutes and there were no drips. There is nothing visibly spurting or bubbling under the hood. And I don’t hear any hissing or gurgling like I would expect if steam were leaking.

I have a few shops around me that can pressure test the cooling system, but I don’t want to pay for that if I don’t have to.

I am a little suspicious of the coolant reservoir cap. Maybe when it gets under load it is releasing pressure at a too low psi. Is there way to test those?

SE, 2.0, manual transmission

alpinegreenneon · 2025-10-08T18:21:26-0400

Some auto parts stores rent tools like a coolant pressure tester. They will have you pay for the tool but then return your payment when you return it. If you want to keep the tool that's ok with them since you paid for it. Pretty sure Harbor Freight has one for a reasonable cost. A good tester will also be able to test the cap.

TomVee · 2025-10-09T22:09:46-0400

Thanks for the tip. I've never used one before. Assuming I can get my hands on a pressure test kit, do I just drain the coolant, pressurize the system with air, and listen for the leak? Actually, I don't know why I am bothering you with this. There is probably a Youtube video.

alpinegreenneon · 2025-10-09T22:45:00-0400

Don't drain the cooling system. Use the correct adapter and pump up to the correct psi that is on the radiator cap. Look for any sign of hissing or drips. Watch the gauge on the pump for any pressure drop. A drop indicates a leak either externally or internally in the engine. The kit should also contain a cap tester. The kit should come with instructions and I'm sure there are you tube videos.

Losing coolant, but can’t figure out where.

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