It can cause a no start if it is bad enough. It can leave white looking smoke trailing behind. Try to do a compression test and see what kind of numbers you get. On a healthy engine all six cylinders will be 400+ psi BUT they will start/run down to 200 psi, although they will be harder to start. If it is a head/head gasket issue you will see one or more cylinders significantly lower than the others which is not a good thing.

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Jim