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Technicaldan, Technician
Category: Chrysler
Satisfied Customers: 101
Experience:  Accredited
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The car is not overheating but the coolant boils out of the

Customer Question

the car is not overheating but the coolant boils out of the reservoir. have changed out thermastat and lower radiator hose. the engine still has coolant when thermostat came off so asssume coolant was from the reservoir. refilled with coolanr and the reservoir lost it again without overheating engine. probably ran for 20 minutes before loosing coolant and engine temp was normal.
JA: Have you checked the coolant? Have you checked for a leak in the cooling system?
Customer: i see no leaks in the system and the coolant was what came with the car . been driving it for 3 years before loosing coolant the first. refilled with 50/50 and lost it from the reservoir the second time.
JA: What is the model/year of your Chrysler?
Customer: 2006 300 v6 3.5
JA: What year is your Chrysler?
Customer: 2006
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: changed thermostat
JA: Anything else you think the mechanic should know?
Customer: no
Submitted: 2 months ago.
Category: Chrysler
Expert:  Technicaldan replied 2 months ago.

From what you have described, it sounds to me like the pressurised coolant cap has failed and needs replacement.

This is simply the cap on the reservoir, if you remove it and look at the underside you may be able to see the internals.

The device function is essentially to maintain pressure to stop the coolant boiling, similar to a pressure cooker, to release excess pressure, and to allow air back in during the 'cool down' to release the vacuum.

Please try a replacement cap, as long as the information you have provided me is correct, I would think this will resolve your problem.