I'm hoping someone can shed some light on this problem. I have a 1946 Ercoupe 415-C, with a C-85. I have had a loss-of-prime problem with the oil pump for all of the 37 years I have owned this airplane. So, you can appreciate that my frustration is absolutely complete.
Oil pressuure is consistently at 33 to 35 lbs at cruise, and not less than 20 lbs at hot idle. If the airplane sits for a week or longer, however, the oil pump loses its prime. I prime it by disconnecting the oil pressure gauge line and pumping oil through it with a small hand-pump oil can. Once primed, oil pressure comes up to 35 lbs less than 3 seconds after engine start. The engine was field-overhauled in 2000, and the oil pump gears and pump cover plate were replaced at that time. The accessory case was magnafluxed also. We recently checked the oil pickup tube for cracks and found none. The tube was properly attached and safetied. I am inclined to think the accessory case is worn internally, in the pocket where the oil pump gears are located, as the problem has gotten worse over time. That is to say, in past years it could go a month or more without losing prime, but now prime is lost in a week or so. What do you all think? Might it be time for a new accessory case? Thanks. WCT
