The coolant reservoir, or degas bottle, holds coolant and separates air from the cooling system, and a cracked one or bad cap causes mysterious coolant loss.
What it does
The reservoir stores coolant and, on many diesels, degasses the system by letting trapped air separate out. A pressure cap maintains system pressure, which raises the coolant's boiling point. A cracked bottle or a cap that will not hold pressure causes loss and overheating.
Signs it is failing
- Coolant loss with no obvious leak
- Overheating or coolant boiling
- Cracks or staining on the bottle
- A cap that will not hold pressure
Replacement and what to know
A cracked reservoir or failed cap is inexpensive and straightforward to replace, and it is a smart first check when a truck loses coolant. Use the correct cap rating and inspect for cracks, especially on trucks that run hot.
Frequently asked questions
What does the degas bottle do?
It stores coolant and separates air from the system, while the cap maintains the pressure that raises coolant's boiling point.
Can a bad cap cause overheating?
Yes. A cap that will not hold pressure lowers the boiling point and lets coolant escape, causing loss and overheating.
Is it an easy fix?
Yes. A cracked reservoir or failed cap is inexpensive and a smart first check for unexplained coolant loss.
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