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The external coolant leak is not as much of a concern as the internal one. The external leak will merely result in the coolant level dropping slowly; this is compensated for by keeping an eye on the coolant level and adding some as needed.
the internal coolant leak is a different story though. When an intake manifold is leaking coolant internally, the coolant is leaking into the engine oil pan and mixing with the oil. This has 2 effects: the antifreeze and oil mixture does not lubricate sufficiently to prevent engine damage to critical moving parts that depend on an oil film to keep them separated, and the antifreeze chemically attacks some of the metals used in engine bearings. Operating an engine with an internal coolant leak will destroy it from lack of lubrication very quickly. If you have been running the engine with an internal coolant leak, it has already sustained some level of internal damage and has had it's life expectancy shortened; the leak was probably going on long before you noticed any symptoms. Now that the leak is large enough to have to add coolant, the best thing to do is to park the car and not run it untill the leak has been repaired.
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