coolant overflow tank

Jason Mauldin · **Posted:** Wed Sep 10, 2003 12:15 am

Since I'm still waiting on my oil pump to arrive, I've been playing around with my intercooler setup on the mirage.

While doing this, I found that I needed to move my coolant overflow tank. Does this need to be mounted above or level with the radiator cap? Does it matter if it's mounted lower in the engine bay?

Patrick Wellenius · **Posted:** Wed Sep 10, 2003 12:45 pm

the expansion tank should at least be partly above the radiator. the reason being that any air that's in the system will float to the highest point in the system and you would rather that be your tank than the radiator. on my VW, the upper radiator hose has a small offshoot that plugs into the tank near the top. this allows any little air bubbles and some overflow coolant to flow back into the tank.

someone correct me if i'm wrong on this...,but HTH
pat

Charlie Guthrie · **Joined:** Thu Aug 28, 2003 8:14 pm **Posts:** 832

Personal opinion follows: I have done engine swaps where there was no way to have the overflow tank above the engine (even the remote pressure surge tank in my Alpine was below the engine water outlet). This can cause a small amount of air to become trapped in the top of the radiator and/or the line between the pressure cap and the overflow tank. Generally this should not concern you because if the fluid level in the resevoir is kept above the intake hose at the bottom of the tank, no additional air will be sucked into the system. Admittedly, there may be air in the hose, but it will not "multiply" ( as long as there are no leaks in the line).
Also, if you are clever, there are ways to force fluid into the lines as you are sealing the radiator cap. (If the tank is below the radiator pressure cap, pinch the hose just at the overflow tank then over fill the radiator so that fluid fills the hose. there are other ways to skin the cat)
Charlie Guthrie

Patrick Wellenius · **Posted:** Fri Sep 12, 2003 12:16 am

that's completely true. but if the tank's the highest part, it will bleed out most air that's in the lines after re-filling the system. i guess the consensus is, if you can do it such that the tank is highest, do it, if not, it's not gonna ruin anything.

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coolant overflow tank

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