# Radiator and Reservoir Cap Pressure Test in Upland > Losing coolant with no drip? Route 66 Auto Repair in Upland pressure tests your radiator or reservoir cap to its rated release point and checks the seal. Source: https://route66autorepairshop.com/cooling-heating-ac-services/cooling-system-radiator-cap-test Updated: 2026-09-17 Business: Route 66 Auto Repair, 1775 W Foothill Blvd, Upland, CA 91786, (909) 608-7699 Hours: Monday to Friday 8 AM–5 PM, Saturday 8 AM–2 PM, Sunday closed **TLDR:** A cap test is quick and specific: it shows whether the cap **holds and releases** at its rating. It pairs with a **system pressure test** for leaks. A radiator cap test puts your cap on a tester with the right adapter and pumps pressure until the valve releases. That tells us whether the cap holds the pressure your system is designed for. Route 66 Auto Repair in Upland runs this test on radiator caps and pressurized reservoir caps, checks the seals by eye, and writes down the result so you know whether the cap stays or goes. ## When should the cap be tested? - Coolant level slowly dropping with no visible leak - Coolant in the reservoir boiling or pushing out the vent - At every coolant service or radiator replacement - When buying a used car with unknown history - After overheating, since heat can weaken the spring ## How does the test work? The cap is fitted to a hand pump tester with an adapter that matches its size and thread. We slowly raise the pressure and watch the gauge. A good cap holds steady up to its rated point and then releases. A weak cap releases too early, and a stuck one does not release at all. We also look at the rubber seal for cracks, flattening or a deposit that stops it from seating. The cap test pairs with a test of the whole system, where the tester pressurizes the radiator neck to check for leaks. That test is covered on [cooling system pressure test](https://route66autorepairshop.com/cooling-heating-ac-services/cooling-system-pressure-test). ## Our cap test process 1. **Cool down:** The cap is only removed with the engine cool, for your safety and ours. 2. **Inspect the seals:** The pressure seal and the small return valve are checked for wear and debris. 3. **Pressure test:** The cap is tested with the correct adapter and compared to its rating. 4. **Record the result:** Pass or fail is written on the repair order, with a replacement quoted only if it fails. ## What's included in a radiator cap test - Visual check of the pressure seal and return valve - Pressure hold and release test with the correct adapter - Filler neck inspection for nicks or corrosion - Written pass or fail result - Replacement cap quote if it fails ## What does a failed cap test mean? **Need now:** - Cap releases well below its rating - Torn or missing seal - Coolant boiling or overheating on the drive **Need later:** - Cap passes but the seal is starting to harden - Light corrosion on the filler neck with a good seal ## How pricing and timing work A cap test is short and is often part of a larger cooling test. If it is the only thing you need, the counter will tell you the fee up front, and it applies to approved related repair. A new cap is a small part. If the neck is damaged, the fix may be different, and the estimate explains that. For cap parts only, see [radiator cap replacement](https://route66autorepairshop.com/cooling-heating-ac-services/radiator-cap-replacement). ## After the test If your cap passed and the coolant still drops, the next step is a deeper leak search. If the cap was replaced, check the reservoir cold for a week. Call [(909) 608-7699](tel:+19096087699) if anything changes. ## Frequently asked questions ### Can I test a radiator cap at home? Not accurately without a tester. Looking at the seal helps, but a cap can look fine and still release early. ### Does a new cap need testing? It is a good habit. Occasionally a new cap is wrong for the vehicle or defective, and testing catches that. ### Why is the cap on my reservoir instead of the radiator? Many newer cars use a pressurized reservoir. Its cap does the same job and is tested the same way with a different adapter. --- Call (909) 608-7699 or visit https://route66autorepairshop.com/contact for a written estimate.