The International Cessna^® 170 Association

On startup today, I had no oil pressure. I opened the line at the oil pressure gauge, and no oil came out. I opened the line at the engine case, and no oil came out. I ran the engine about 30 seconds each time.
48 hours ago, I flew with normal oil pressure indications.
Is it time to pull the accessory case and rebuild the pump, or could there be a simpler answer?
Dave

Well Dave i don't really have an answer for you at least any that you might want to hear. Having just rebuilt my engine I'm very familiar with the oil pump and accessory case that it rides in. it is a pretty simple pump. Just 2 gears that ride meshed in a close fitting housing. They do wear and you would get a loss of oil pressure over time but there really is nothing that would fail that quickly. At least if it did the loss of oil pressure would only be one of your problems the other being big metal parts floating around inside your engine.

Another way you could lose oil pressure quickly is if you spun a bearing. You would most likely know this by the loud banging your engine would be making on the 30 second runs you have made. BTW was it really 30 seconds by the clock or did it seem like 30 seconds. Whe you are seeing no oil pressure 10 seconds can seem like 30.

If everything was fine with no hint ever of oil pressure loss then I'd think it would be something very simple.

Not to be smart but do you HAVE oil in the engine? Sumps do rot and have been known to spring a leak just sitting there. Perhaps yours did and the oil has drained into the ground that you didn't notice.

You mentioned pulling the oil pressure line at the engine but did you take out the nipple in the engine where the oil line connects. This nipple has a very small hole by design. Perhaps something has clogged it.

Good luck.

The old A-65 and even the C-85's were known to at times loose their prime in the oil pump. I had a Champ that did that if left sitting for a long time. The pump can be primed by using a squirt can of oil going into the pressure gauge line in some manner of your choosing. If the fitting on the case is restricted as it should be it takes a while.

After doing a complete OH on my O-300A a few years ago I was startled to say the least when during the first hour flight my oil pressure dropped to near zero. Sure that I had just fried my $11K investment I began to trouble shoot and found particles in the oil pressure bypass hole located on the cylinder inside the pressure relief spring. The particles were walnut shells from when the case was cleaned. Anyway cleaning this small hole produce tons-o-pressure HOWEVER it happened again on the next 2 flights. Each time I had to clean crud out of this hole and each time I got normal pressure after. The engine was never starved of oil just the gage (though I did repeated comp checks to see what if anything had happened). Also as in others posts I have now had my C-145-2 lose it's pressure prime after sitting w/o oil for a few weeks. The previously described priming procedure was messy and took MUCH longer than I would have thought but eventually worked and like you I ran the engine for 30 sec each time sweating a no-pressure indication.
My 2 cents.

I had pretty much the same experience as bently with the O-200 in my old C-150. Some debris was keeping the bypass from closing,resulting in a "zero" indication on the oil pressure gage. The good part is that the debris was easily removed. The bad news is that the debris was from the needle bearings in the (key-start) starter clutch, it had self-destructed & came apart inside the accessory case. But it still worked.
Drained the oil,removed the oil sump,flushed,& reinstalled. More debris in the bypass,so I got to do it a second time. The key-start starter-clutch turns all the time,unlime our pull-start clutches, so the TBO on them is less than on the engine.
Check for debris at the bypass (page 16,item 32 in the C-145 parts book-"cap,oil pressure relief valve") on the lower RH side of the accesory case, if you have some there eyeball it real good. You might want to check the starter-clutch if there is some metal debris,it's easy to do. I think the starter-clutch is often neglected at overhaul time--"ah,it still works so I'll justy put it back in & save a couple hundred bucks." False economy, when they fail it can be a disaster.
Mine worked OK but I decided to replace it at overhaul time, after installing the new clutch I realized that the old one had been making a funny (read: potentially expensive) noise.

Eric

Good words about the starter clutch, Eric.
An excellent way to prime the oil pump is to use a NEW or CLEAN grease-gun filled with engine oil. Fix up a fitting on the grease gun hose that will match up to the oil line fitting and pump 'er up!

I have oil pressure again. The only thing that looked like an obvious contributing factor was the AN900 washer on the intake screen. It was missing. It had been teflon taped.
Curious, though, that it would have allowed the pump to suck air, but not leak. I put about 150 hours on the engine in the year that I have owned it.