What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Transient oil pressure spike

rv6n6r

Well Known Member
Patron
A few times in the last 20 hours, during taxi out on the first flight of the day, my oil pressure has spiked briefly over redline. If I pull the throttle all the way back it goes below redline and if I wait a few minutes all will be fine again including runup and throughout the flight.

Troubleshooting guides point to wrong grade of oil for the temps or a stuck vernatherm. This has happened with OATs in the mid 40s to low 60s. Oil is Aeroshell W-100, with Camguard added so it shouldn't be that. I pulled the vernatherm and all looks clean, the ball and seat are smooth. I put a copper wire down the oil channel to the sump, there didn't seem to be any obstructions, comes out clean with no gunk on it. Last oil change I checked the sump screen which was clean, as was the oil filter.

The only oddity I can find is that the vernatherm spring has a flat worn on one coil, see picture. Also looking into the body of the Vernatherm, there does seem to be some wear in a spring coil pattern.

My questions are, could that flat and coil wear be indicative? Seems like that wouldn't do it but what do I know. Also if my oil pressure spiked that much (143PSI) for a short period could it cause damage I don't know about? I've had the cowl off since and there are no blown seals or anything as far as I can tell. Other than this it continues to run like a top. This is a Lycoming O-360-A1A with C/S prop.
 

Attachments

  • oil_pressure.jpg
    oil_pressure.jpg
    53.9 KB · Views: 241
  • vernatherm_spring.jpg
    vernatherm_spring.jpg
    690 KB · Views: 242
  • vernatherm_ball.jpg
    vernatherm_ball.jpg
    511.6 KB · Views: 202
  • vernatherm.jpg
    vernatherm.jpg
    394.1 KB · Views: 215
Last edited:
Looks like the oil pressure relief valve is sticking on start-up. Until it get warm and loosens up. The ball might be sticking in the housing.
 
Well, I'm no expert, but when pressures or temps change that suddenly and seem to spike a lot, my first suspicion is electrical. Either the connections, including the ground connections, or the sender itself.

And another recommendation is to temporarily add a mechanical pressure gage into the system for troubleshooting.
 
What I see from your graph is pretty much what I would expect running 100 weight oil at 40 degrees. Even Lycoming says it should ONLY be used over 60*. The spike you see is just a delay in the pressure building up after start up. It takes a bit for the system to bleed itself and build pressure. Running 100 weight oil at 40 degrees is a bad idea and I feel you are seeing the results of that. You need to move to 20W50.
 
Last edited:
Aeroshell w-100 is a 50 weight oil.

Yes, I know. HOwever many folks don't know that, so I used what I thought would be most universally understood. Those that know better, like you, also understand my meaning.
 
Last edited:
Definitely don’t want to be running 50 wt. single vis oil at those OATs. 20 wt 50 is multi vis and is ok. I suggest you familiarize yourself with your Lyc operator’s manual for more details on both pressure and appropriate oil weight.
 
A few times in the last 20 hours, during taxi out on the first flight of the day, my oil pressure has spiked briefly over redline. If I pull the throttle all the way back it goes below redline and if I wait a few minutes all will be fine again including runup and throughout the flight.

Troubleshooting guides point to wrong grade of oil for the temps or a stuck vernatherm. This has happened with OATs in the mid 40s to low 60s. Oil is Aeroshell W-100, with Camguard added so it shouldn't be that. I pulled the vernatherm and all looks clean, the ball and seat are smooth. I put a copper wire down the oil channel to the sump, there didn't seem to be any obstructions, comes out clean with no gunk on it. Last oil change I checked the sump screen which was clean, as was the oil filter.

The only oddity I can find is that the vernatherm spring has a flat worn on one coil, see picture. Also looking into the body of the Vernatherm, there does seem to be some wear in a spring coil pattern.

My questions are, could that flat and coil wear be indicative? Seems like that wouldn't do it but what do I know. Also if my oil pressure spiked that much (143PSI) for a short period could it cause damage I don't know about? I've had the cowl off since and there are no blown seals or anything as far as I can tell. Other than this it continues to run like a top. This is a Lycoming O-360-A1A with C/S prop.

Before you waste any more of your time chasing a potential indication problem install a direct reading gage to verify actual pressure. I have worked many oil related problems over the last 50 years as an A&P mechanic and very rarely is it actually an oil pressure issue. It would be hard for your oil pressure to actually spike like what you described on it's own even if the oil pressure regulator malfunctioned.

I had a very similar issue in my RV9A and it was the cheap oil sending unit. I am installing a direct reading oil pressure and fuel gage in the cockpit currently. I have a full glass panel and feel it is good to have some mechanical gages that don't depend on electricity.
george
 
oil pressure

The red line is 100 but 115 is allowed for "short durations" as revised by Lycoming many years ago.
 
More Info?

What oil filter adaptor are you using, are you using a remote filter, what filter are you using? Recently I blew out my oil filter gasket right after start ( ran about 5-10 sec) on a 35F day, oil was at 74F, 100 Plus oil Lost about 2 qts
 
Thanks for all the replies. Clearly I'm putting my ignorance on display for all to see, sigh. Yes I called the oil pressure relief valve a vernatherm, my mistake.

But whether the valve would be the cause or not, my carelessness in keeping "summer" SAE50 in there is certainly something I should deal with so thanks y'all for diplomatically pointing that out (or to put it more succinctly, d'oh!) I'll make sure I'm not running that 50 weight into the cooler months and see if that makes a difference. And check that sender.
 
Pretty sure this is solved. I removed the sender and hose and cleaned out the hose, replaced the sender with a new one and changed the oil, now running SAE40 which I should have been anyway this time of year. I'm pretty sure it was the sender but in any case, several flights now and no spiking OP.

Thanks for all the responses, I'm sure you've all been on the edge of your seats wondering how this would turn out ;)
 
Back
Top