Radiator cap hissing sound

Old 06-22-18, 07:22 PM
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Radiator cap hissing sound

Hi all,
have a 2002 pt cruiser. I noticed today when i shut car off after driving about 8 miles that there was a faint hissing sound. Opened hood a it apeared to be coming from radiator cap. The sound went away after about a minute. The temperature guage was in the normal region whete it always is after it warms up. The cap appeared to be pretty hot when touched. Check after cooled and the cap eas tight. Any thoughts. New radiator was put in about 10 months ago. Thx
Old 06-22-18, 10:20 PM
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If it was actually hissing, that would indicate it was relieving pressure. You got a new radiator...did you get a new cap of the correct pressure rating? And are you sure the sound was at the cap or possibly a nearby hose? What is the condition of the rubber seals(s) on the cap. If it's not maintaining the pressure, your boil point is decreased. You temperature might not change in normal driving, but in abnormal conditions you could have an issue.

Hissing would also allow minute quantities of coolant to escape over time.
Old 06-23-18, 05:46 AM
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Are you losing coolant?
Is the coolant reservoir within the normal range? Is the radiator full when cold?
When the engine gets hot it moves coolant to the reservoir - when it cools off it draws the coolant back into the radiator.
You could hear coolant being released/returned through the radiator cap as designed.
You don't want coolant being released into the atmosphere by the cap.
Check your reservoir level - if it's good , you're good
Old 06-23-18, 05:21 PM
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I agree. Keep in mind that the coolant is at its hottest shortly after shutting off the engine (no coolant flow/no air through radiator) so during that short span of time the coolant will expand slightly above where it was during operation and the excess will be vented to the recovery tank. As it cools, the system will draw it back in as 2grand talks about.
Old 06-23-18, 07:05 PM
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Oh duh...I agree with the others...could be completely normal and probably is.

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