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A radiator has several seals: the gasket between each plastic tank and the core, O-rings on quick-connect hose fittings and drain plugs, and seals at transmission cooler lines. Route 66 Auto Repair in Upland finds which seal has failed and tells you whether it can be renewed on its own or whether the whole radiator is the better fix. You see the wet seam in a photo first.
What are the signs of a leaking radiator seal?
- Coolant beads along the full length of a tank edge
- Wet drain plug or petcock after a coolant service
- Drip at a quick-connect hose fitting on the tank
- Leak at a transmission cooler line on the radiator
- Seep that appears only after the engine is fully hot
Which radiator seals can be renewed?
Drain plug O-rings, petcock seals and quick-connect O-rings are replaceable parts, and fixing them is quick. Transmission cooler line fittings on the radiator can often be resealed too; that overlaps with transmission cooler line repair when the line itself is worn.
The gasket between the plastic tank and the aluminum core is held by crimped tabs. Re-crimping or re-gasketing is possible on some designs, but the plastic around the seal is usually as old as the gasket. We explain the odds honestly and quote a complete radiator repair as the alternative.
Our radiator seal repair process
Step 1: Clean and pressurize
We clean the radiator edges so fresh seepage stands out, then pressure test.
Step 2: Pinpoint the seal
Tank gasket, drain, fitting and cooler line seals are checked one by one.
Step 3: Written options
You get a seal-only repair or a replacement option with photos.
Step 4: Repair and retest
The seal or radiator is replaced and the system is tested hot and cold.
What's included in radiator seal repair
Included on the work order
- 01Radiator cleanup and pressure test
- 02Seal-by-seal leak check with photos
- 03Replacement O-ring, gasket or fitting as quoted
- 04Transmission fluid level check if cooler lines were disturbed
- 05Coolant top-off and air bleed
- 06Hot and cold recheck
Is it a need-now or need-later repair?
Need now: call
- Active drip at any radiator seal
- Transmission fluid mixing with coolant at a cooler fitting
Need later: book
- Dry crust at a tank gasket with a stable level
- Drain plug seal that is aging but dry
How pricing and timing work
A drain or fitting O-ring is a small, quick repair. Tank gasket work takes the radiator out and may not outlast a replacement, which is why we price both. If we are unsure a seal repair will hold, we say so in writing before you decide. AAA members save 10% on parts and labor, up to $75. If the leak turns out to be elsewhere, coolant system leak detection is the next step.
Aftercare
Look at the repaired joint with a flashlight after a hot drive; a dry joint is the goal. Keep checking the level cold. If cooler lines were opened, we recheck the transmission fluid, and you should watch for any red drip for a few days. Questions: call (909) 608-7699.
Frequently asked questions
Why does my radiator only leak when hot?
The plastic tank and aluminum core expand at different rates. An aging gasket can seal cold and open hot. We can test at temperature to confirm.
Is a tank gasket repair worth it?
Sometimes, on radiators that are expensive or hard to find. On common cars a new radiator often costs about the same once labor is counted, and it renews the plastic too.
Can a leaking cooler seal hurt my transmission?
If coolant gets into the transmission fluid, it can damage clutches. Any sign of mixing needs attention right away.