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FJR Motorcycle Forums
Technical & Mechanical Problems
Coolant Puke
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<blockquote data-quote="Fred W" data-source="post: 1340344" data-attributes="member: 3828"><p>Radiator caps are always supposed to work like a 1 way pressure valve.</p><p></p><p>They are supposed to remain closed to flow out of the radiator until the internal radiator pressure exceed the cap's pressure rating set by the big spring shown below, and then it allows the expanding coolant to flow to the reservoir.</p><p></p><p>But, they are also <em>supposed</em> <em>to </em>easily allow flow back into the radiator with the least amount of negative pressure (vacuum) when the coolant cools down. This is accomplished with a little poppet valve in the cap, shown as a vacuum valve in the below diagram. It seals under positive pressure, but has a weak spring to be overcome under negative pressure.</p><p></p><p>If that valve gets stuck it may restrict the flow of the coolant back into the radiator and result in the radiator sucking air in from wherever it can Then further thermal cycles would continually pump coolant out into the expansion tank until it overflows.</p><p></p><p><img src="https://www.agcoauto.com/content/images/faq/parts.JPG" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p></blockquote><p></p>
[QUOTE="Fred W, post: 1340344, member: 3828"] Radiator caps are always supposed to work like a 1 way pressure valve. They are supposed to remain closed to flow out of the radiator until the internal radiator pressure exceed the cap's pressure rating set by the big spring shown below, and then it allows the expanding coolant to flow to the reservoir. But, they are also [I]supposed[/I] [I]to [/I]easily allow flow back into the radiator with the least amount of negative pressure (vacuum) when the coolant cools down. This is accomplished with a little poppet valve in the cap, shown as a vacuum valve in the below diagram. It seals under positive pressure, but has a weak spring to be overcome under negative pressure. If that valve gets stuck it may restrict the flow of the coolant back into the radiator and result in the radiator sucking air in from wherever it can Then further thermal cycles would continually pump coolant out into the expansion tank until it overflows. [IMG]https://www.agcoauto.com/content/images/faq/parts.JPG[/IMG] [/QUOTE]
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FJR Motorcycle Forums
Technical & Mechanical Problems
Coolant Puke
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