John Rodgers : we seem to agree, except for what happens under NORMAL operating conditions - IMHO the expansion (overflow) tank is inactive under NORMAL operating conditions and is only used when the system begins to over-heat and the cap "lets go" above its specified setting. I have read today's posts on this topic. What I meant to say was that AFAIK, the Coolant Reservoir cap pressure relief valve is set higher! than the "normal" operating temp of the engine - when warmed up. My experience is that I can drive around all day (even with external temps at 44 deg. C) and the coolant reservoir cap will NOT allow the coolant to flow into the Overflow tank - as long as the van keeps moving! And (just for the record) when the engine cools down it is the pressure that drops and no coolant is sucked from my van's overflow tank - under NORMAL operations. When going up a looooong hill (in 3rd gear), or stuck in traffic, on a HOT day then YES, the fan comes on and if that does not cool things down, then the coolant reservoir cap "lets go" and some of the pressure is relived from the system and, upon cool down, then, yes, coolant is sucked back into the Coolant Reservoir tank from the overflow tank via the coolant res. cap. This "sucking back" may happen while I drive - as the engine temp returns to "normal". So I hope that we agree. Malcolm |
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