Air in Racor

[wpc691]

Leaving for a short cruise last Friday, I fired the engines up about 1/2 hr before planned departure. After 5-10 minutes, I walked to the stern to check water flow. Both sides OK, but as I was looking at the port tube, the engine coughed, then quit. Cranked engine, no start. Pulled top off Racor, can half empty (or half full, depending on your outlook on life). Filter looked clean, changed it just because, filled can, primed with manual pump, good flow out of injector pump bleed. Tried to start, cranked for 5 seconds, nothing. Cranked again, advanced throttle quickly to full, fired up, idled smooth. Ran 10 minutes or so, coughed and died. Checked Racor, half empty. Just because it’s easy to do, switched port supply and return over to keel tank. Filled Racor, etc, cranked 5 sec, no start. Cranked and advanced throttle, fired up, ran smooth. Half hour later, still running. Decided to proceed with weekend anchor-out, ran 2 hrs to destination, no issues. On Sunday afternoon, stbd engine started right up, port cranked, no start. Cranked again, advanced throttle, started up, ran smooth, ran about 3 hrs to home with no incident. I’m thinking I have an air leak somewhere between the main tank port side pick-up and the manifold valve, and have no explanation for the new need to advance the throttle to start. First thing I’ll check is the pick-up tube, although I don’t think that’s the problem. I think all the line between the tank and manifold is copper (to be confirmed), so the manifold valve itself might be the most likely culprit. I’ll report back after inspecting the pick-up tube, piping and manifold valve. Meantime, any suggestions or ideas are welcome. TIA

 

[SEVEN]

Could be a weak seal on the cap of the unit. I had a leak from the drain at the bottom of the bowl. No fuel came out but air was being sucked in and you could see the bubbles. Turned out the bowl had a crack at the bottom next to the drain. Good luck.

 

[JuiceClark]

Could be a weak seal on the cap of the unit. I had a leak from the drain at the bottom of the bowl. No fuel came out but air was being sucked in and you could see the bubbles. Turned out the bowl had a crack at the bottom next to the drain. Good luck.

I just changed my Racor filters last weekend and a couple of the gaskets looked a little questionable. Of course, I changed them with the ones which come with a new filter, but a little donk in the top of the housing could have easily caused a leak.

That tiny o-ring looking gasket on the threaded cap screw could be out of place or broken as well.

 

[wpc691]

Yep, that little red o-ring has bitten me before - I think I posted about it a couple of years ago. Since the engine operated fine on the keel tank pulling through the same Racor, I’ve eliminated everything downstream of the manifold. Tried to pull the pick-up tubes this afternoon, but stalled at the elbows that thread into the plate. Surprised, as the fittings on the shutoff valves came right apart. I soaked them in penetrant and left them to marinate for the night.

 

[Pascal]

If you have an electric fuel pump, hook it up and at the racor and run it with a clear hose returning to the tank thru the hole for the gauge and check for air. Or hook it up to suck from the tank thru the racor and back to the pick up tube. That may clear whatever in the pick up tube. You could also turnoff the selector valve which would slightly pressurize the racor and valve and check for leaks.

 

[Captain Ralph]

You did not mention the secondary filter.
If it is restricted, the lift pump may not be able to draw from a further away tank.
Just a thought.

 

[sunset grill]

In similar cases, it has been a leaking Racor, a loose secondary spin-on, or a weak lift pump.

 

[wpc691]

Just an update. Pickup tube was clear. Thinking of Capt Ralph’s suggestion, I decided to do the next easiest thing and change the secondary fuel filter. Couldn’t budge the filter, and instead of warming up the engine, I got a bigger wrench...and snapped off the filter mount. New filter mount arrives at Kelly Tractor on Wed. While playing with the filter, I spun the top off the Racor...and found the can half full, same as the failure condition with the aft tank. Was the engine minutes from failing on the keel tank? Don’t know, but as long as I’ve got the filter mount off, I ordered a new secondary filter-to-pump fuel line as the next most likely restriction - it runs across the top of the engine, so leads a hard life. If that doesn’t do it, the priming pump-to-Racor and Racor-to secondary soft lines are the next candidates.

 

[wpc691]

Replaced the filter base, complicated by Cat having renumbered the part, presumably when the 3208 went out of production. Replaced both Racor o-rings, and installed new secondary filter. Engine started up on aft tank with application of throttle, and ran an hour without a stumble; Racor vacuum was steady at just below 4 mm Hg. Opened the Racor and found fuel level down several inches. Tomorrow I’ll switch Racor tops just to eliminate one more thing. After that, I’ll get a couple of fittings to back pressure the lines and look for leaks.

 

[racclarkson@gmail.com]

How much is several inches? 2-3” down is normal ops.

 

[wpc691]

How much is several inches? 2-3” down is normal ops.

I guess I should actually measure it Robert. I believe the pickup point on the outflow tube in the Racor 900 is 4” down from the edge, and I think I’m close to that. My other Racor is full right to the top of the filter.

 

[wpc691]

Hopefully closing out this thread, the shutdown problem seems to be resolved. I was suspicious of the ancient fuel lines, having read many threads about their contribution to fuel flow problems. So, half a boat buck or so later, I have 3 shiny new soft hoses on each side. Primed the engines, ran for 1/2 hr without a hiccup. Like before, the port Racor is down 3 1/2”, stbd down 1”. At this point, I’m accepting that as “normal” for each engine. I dissected the 2 Aeroquip hoses (unfortunately, discarded the Cat hose earlier) from the port side, and found the ID’s quite a bit smaller than nominal. The -10 (5/8”) hose measured 7/16”, and the -8 (1/2”) measured 3/8”. If my math is correct, that’s a 25% reduction in cross-section, not insignificant. For all I know, that reduction could have occurred in the first week after installation 35 yrs ago, but I’m thinking it’s a gradual phenomenon. My theory in this case is a combination of a near-end-of-life secondary filter, higher than designed pressure drop across those hoses, and the long lift from the aft tank combined to starve the engine. If that’s right, it should be smooth sailing now...until the next time. Thanks for all the responses.