C oil pump losing prime

[Tony S.]

We put a new oil pump in our AC C engine. It makes good
pressure if you prime it, but won't hold overnight. Is there a
check valve in the pickup that's not holding? (We haven't had
the pan back off). Years ago my Dad had the same kind of engine
on a swather. Never had any oil pressure problems.

 

[KL in Wi]

I have an RC that was doing that. Pulled the engine and checked the pump and pick up tube. Couldn't find anything wrong. Messed with it for quite a while. One day I was disconnecting the oil lines from the pump pressure pipe to the filter and head and the pressure pipe coming out of the pump broke off just above the threads. Luckily, the part in the pump came out with an easy out. Installed a new pipe and it's never lost prime since. Must have had a small crank that didn't leak oil but, let air in when not running and let the oil in the pump drain back.

 

[tgrubar]

And RC model that we are working on has no visible oil pressure. We're not even sure where the oil pump is. The previous post have been very informative though.

 

[steve(ill)]

leak back normally occurs when you have an external air leak... look around the filter housing and back toward the pump discharge tube as KL says.