When you say you top it off, do you try to keep the oil level right at the "full" mark on the dipstick? If so, don't do that. Aim for halfway between "full" and "add", and remember to check with the oil HOT and after the car has been turned off at least 5 minutes.

Oil consumption will often increase when the level is higher than halfway between the marks.

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Steve
'93 400E