DD 6-71 ti air in fuel system

[Spike]

I have Covington Marine DD 6/71 ti's. Last summer I had a fuel/gear oil cooler fail and ordered 2 since I figured the other one would be close to failing also. During winter storage I had the yard replace the other cooler as PM. The only other engine service I had done was to pull and clean both HE's. After launch last week while running both engines up to temp the port engine (the cooler they changed) started surging and stalled after about 20 minutes. I found the Racor about half empty so I changed the filter and gaskets, ran the prime pump and started the engine. After 20 minutes, same thing surge then stall. checking the filter again it was almost empty. Over the long weekend I checked hoses and clamps, restarted the engine with the same results. We have 2 fuel tanks for each side and tried both tanks with the same results.

Obviously air is getting into the system somewhere and I'm leaning toward a loose connection on the cooler which I was unable to check for tightness due to access and my tool availability. The tech will be coming back this morning to begin tracking down the leak. I'm looking for suggestions from the brain trust here of what I'm possibility overlooking. These are simple engines and there should be a simple fix. Since everything was fine last fall I'm inclined to think it's something they worked on versus something else failing while simply sitting in a heated barn over the winter.

Thanks,

 

[twistedtree]

The fuel cooler is on the return, right? Could there be an obstruction fo some sort that is preventing normal fuel flow through the whole system? Maybe something as simple as a return valve that was closed while replacing the, cooler, and never re-opened?

 

[Spike]

The manifold is set up so whatever tank is selected the fuel returns to the same tank. I guess it's a KISS system. I've thought about a bad hose or obstruction in a hose but I can't figure out how that would introduce air into the system. Yes, restricted flow would cause the same surge symptoms but not the air pocket, correct? I've thought about switching the hoses from port to starboard racor and see if the problem is the same but don't want to get ahead of the tech and his thoughts.

Thanks for the thoughts and keep the ideas coming while I (patiently) wait for the tech.

 

[jhall767]

The air leak would be at or prior to the racor from the tank. Did they change any fittings or hoses prior to the racor? Unlikely to have anything to do with the fuel cooler as that is normally on the engine and after the fuel pump. You need more than a tiny air leak to starve a 671. I've seen this where debris clogged the pickup tube. How much suction is showing at the racor?

 

[Spike]

So it was something simple and not related to the repair. The racor lid had some flaking paint which I didn't think much about. Attached is a picture of the lid after being cleaned up. Apparently between the paint and the pitting it was enough to not get a good seal on the T handle O ring. Even looking at the cleaned lid I wouldn't have thought it was enough to allow an air leak.

We cleaned and re-assembled both lids and the engines ran at idle for almost an hour with no issues. It is showing a bit less than 10# on both vacuum needles but this is about normal from what I remember. Hopefully we'll be underway tomorrow with no issues. Thanks for the help