The Cessna 120-140 Association Forum

When I start the engine the oil pressure to the gauge is delayed by 45seconds or so, even with the oil warm from having the heat pad on the sump plugged in. Once I have oil pressure it stays 40 - 45 psi through out the flight. The last couple of starts I left my headset off and I think I can hear a difference in the sound of the engine when the pressure comes up on the gauge.
Anybody have any experience with this. Search turned up “loss of prime” issues mostly.
Thanks,
Brent

The oil pressure sensor is the last item in the system route so important components are getting oil before the gauge comes up, however 45 seconds is very long time (the flight manual limit is 30 seconds). Is it 45 seconds to get full stabilized pressure or to get any pressure registering at all?
Si

Check your gauge and associated plumbing. Rubber hoses have been known to start failing internally requiring greater pressure for initial reading . Somewhat a witch hunt situation, never happened to me on an a/c but happened to me on a Mercedes auto years ago!

However, the sound you are hearing maybe the valves due to slow pressure rising. How long has it been happening? Do you have an oil filter, if so, change filter and cut open and examine contents. Possibly system operating with bypass valve operating inside filter. I wouldn't continue operating/flying until resolved. Just thinking out loud!!

Hopefully, the gurus will have better info.

Is this something new or has it always done it since you have owned it?
If it is has an oil tube that goes to the gauge, you may need to bleed the air out of the line.

Rick

Brent,if you haven't already read it, take a look at Neal Wright's excellent/detailed related piece on this (hopefully this link will work...if not, it's accessible on the website: viewtopic.php?f=10&t=139

Some (most) of "us" seem to get by decades of owning/flying behind these small Continentals without "slow to pressure or loss of prime" issues. Some don't . A related newsletter article a few issues back suggests the problem can develop from excessively worn oil pump cavity, gears, and/or gear shaft bores...also, from the oil pump cover being "hydraulically warped" at start-ups with thick oil in the pump (Ken Morris explains it much better in the article). In any event, it can be frustrating to chase as already mentioned. There's related experience to be shared here and you'll likely see more. Meanwhile, keep us posted and feel free to PM me if I can share some of my own experience in more detail.
Mac

8209 wrote: ↑Sun Nov 06, 2022 10:14 pm When I start the engine the oil pressure to the gauge is delayed by 45seconds or so, even with the oil warm from having the heat pad on the sump plugged in. Once I have oil pressure it stays 40 - 45 psi through out the flight. The last couple of starts I left my headset off and I think I can hear a difference in the sound of the engine when the pressure comes up on the gauge.
Anybody have any experience with this. Search turned up “loss of prime” issues mostly.
Thanks,
Brent

Seems a little slower than my slow-to-rise gage. Usually about 10-20 seconds to show a rise at say 35F, more like 10 seconds above 60F. I did once have loss of prime in cooler weather, which I associated with the one time I used the Victory oil with the Lycoming additive. Back to X/C standard and never another issue with loss of prime from very cold to very hot temps with delays between flights of between 5 and 30 days.

Thank you for all the good suggestions guys.
The problem started a couple of months ago. The idea that there may be some obstruction in the line or the gauge would be best case scenario I’m thinking.
Annual is due this month, so we will get everything apart, oil filter cut and inspected and oil line and gauge cleaned out good and see if we need to go deeper.
I haven’t ever lost prime so I’m hoping nothing is wrong with the oil pump, but preparing for that as well.
I will report back on what we find, if we find anything.
Brent

The new filter may cure the problem. My guess is it takes about 45 seconds to refill the filter.

Brent,

I battled the same problem for a few years. None of the oil prime suggesdtions worked. The answer was a new accessory case. Expensive but i've not had a hint of problem since. If it is the case, and depending on how bad the wear, DivCo might be able to repair it. Mine was not repairable. Before you do that, you might want to hook-up a temporary oil pressure gauge. If you're getting good, quick pressure, try draining the small diameter oil pressure line between the engine and gauge and refilling with a very thin oil. I used 3 in 1. It made the gauge much more responsive.

Dave wrote: "...battled the same problem for a few years"

Yep -- same here. Having put up with the occasional loss of prime for years, when majoring the engine we sent the original magnesium acc'y case to DIVCO for "reconditioning" & they were able to rebush the pump gear shaft holes & "certify". There was "legend" of another Tulsa shop that could/would weld, build up and "overhaul" the pump cavity but actually locating ANYone who could/would tackle the magnesium proved fruitless (We could find those who "knew a guy who knew a guy who'd weld magnesium"...but we could never find that guy ). The reconditioned case did OK for a few hours and, then, the frustrating loss of prime returned if engine not run for a couple of weeks. Once "manually" primed and "up", oil pressure at idle & at cruise & at all temps was never a problem. With a LOT of effort I was able to locate a serviceable acc'y case & installed with new pump gears and cover -- it's functioned flawlessly for 100+ hours now. I was going to opt for a new (aluminum$$$$!) acc'y case but, unfortunately, TCM had experienced some sort of foundry incident that resulted in a world-wide shortage of new cases at that time. If I were experiencing the issue again, I'd certainly opt for the new case if available.
Mac