Do I need to flush the coolant when replacing a cracked radiator?
When a radiator is cracked, people worry that pressurized coolant might mix with the engine oil during a flush or while running the engine. This fear makes it difficult to decide whether to perform a system flush with the old radiator or simply install the new one and let it ride.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
- 1Testing the coolant condition to see if it is still good before decidingDid this help you?
- 2Replacing the radiator and installing fresh coolant without performing a full system flushDid this help you?
- 3Removing the radiator and thermostat to flush the system with a hose before refillingDid this help you?
- 4Skipping the flush unless there is a specific reason to believe the engine has a sludge issue.Did this help you?
- 5Leaving the transmission untouched unless a noticeable problem or failure occursDid this help you?
- 6Relying on multi-point inspections during routine oil changesDid this help you?
- 7Monitoring the dashboard temperature gauge for overheating signsDid this help you?
- 8Posting photos to online forums for adviceDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“I did test it and it is still good it's just I'm afraid of the pressurized coolant mixing with the engine oil through that crack in the radiator.”source ↗
“Last year, I took it to Ed Little's shop in Culver City, Calif. for a brake inspection and transmission flush, especially because I've read about all these issues people have with CVTs.”source ↗
“The mechanic told me that with Nissan's CVT, the best course of action was not to touch it unless you had a problem.”source ↗
“I'd love to get the perspective of some experienced folks around here to verify that this is a sound strategy.”source ↗
“The coolant level has been lower than L for quite a long period(at least it was lower than L for past six months)”source ↗
“During the past engine oil change services(including the recent service done last Monday), They were doing compliment multi-point inspection, and it was always coolant level fine.”source ↗
“So, just a simple question. Is this fine or should i add the proper coolant?”source ↗
“I get that they are separated but I'm concerned it's no longer separated because of the cracks and I'm more worried about that pressurized coolant pushing past a crack if it goes deep enough and mixing with the oil that's going to the engine.”source ↗
Where this came up
People with this problem also raised
- 14Should I reuse an old plumbing drain or replace it?
- 2Why won't coolant flow into the engine and the thermostat open?
- 2Is a water softener actually worth keeping and maintaining?
- 4Why is radiator coolant still green after multiple flushes?
- 10How to fix a coolant leak and sludge in an old car
- 7Is it normal for coolant to be above MAX when warm?