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YOUR RESEARCHNo oil pressure after a change
Leading reported evidence
Fill filter housing as usual
Performed · outcome unconfirmed
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Leading evidence: 'Fill filter housing as usual' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, the most frequently mentioned possible cause is 'pressure sending unit though, as they are nutoriously unreliable' (1 discussions; 0 report identifying it and 1 suggest it). The most frequently discussed action is 'Check sender out' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Performed · outcome unconfirmed
Just done an oil and filter service on the 996 C4S and pre filled the filter housing no problems at all on startup.
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Performed · outcome unconfirmed · Original poster
I’ve done a dry crank (fuel pump fuse removed - I always do this, just as typically I’ve always pre-filled the filter, albeit on my 997), and the pressure gauge has shown some life.
pressure sending unit though, as they are nutoriously unreliable
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Suspected cause
Likely the pressure sending unit though, as they are nutoriously unreliable.
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Suggestion
Have read of a similar situation happening on V8 Rover engines during an oil change, where filling the new filter with oil can overcome the issue, not practical on a Porsche unfortunately.
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Performed · outcome unconfirmed · Original poster
I’ve done a dry crank (fuel pump fuse removed - I always do this, just as typically I’ve always pre-filled the filter, albeit on my 997), and the pressure gauge has shown some life.
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Suggestion
As I understand it it seems possible that the oil drains past the oil pump and into the sump over time, and dependant on the length of time it seems possible that the advised way to re-commission the engine is to drain the sump and re-fill the oil tank.
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911uk: 1 discussions
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Car been off road for the winter. Just done an oil change. Pre filled the filter housing as usual.
No oil pressure on cranking.
Anyone had this? Stuck relief valve perhaps?
First port of call are as 911UK suggests is the oil pressure switch, and it`s connections.
I think that the modern 911`s oil pump may be immersed in the oil held in the sump..? If so the following may be of little use..
Sorry to read of your issue hermes...Never suffered that on a Porsche though have done on the first car engine I rebuilt even though I (fortunately ) applied loads of lube when assembling it. Cut a long story short, in my case the oil filter was new, thus empty, and thus the oil pump required primed before it could suck the oil up from the sump, I managed that process by pressurising the lubrication system by removing the pressure releif valve and using a lever type oil can to force oil into the galleries, and the pump, on replacing the releif valve and firing the engine up, it was a great relief to see the gauge needle rise...(-:
Have read of a similar situation happening on V8 Rover engines during an oil change, where filling the new filter with oil can overcome the issue, not practical on a Porsche unfortunately.
Hope you get it sorted and might have time to let us know how you get on..
Here's the plan:
Drop the oil
Remove and refit the filter
Stick a new sender on (why not, it's probably 20 years old)
Fit the 'upgraded' 997 relief piston, with a new spring.
Stick oil back in
I'm hoping the car is just cross I sorned it for the winter.
I am no expert, as best I understand it, for the oil pressure relief valve to be unseated, it would have to have been subjected to oil pressure beyond it`s blow off point, so what are the chances of that...? Pull the electrical connections on the oil pressure switch and check they are clean if not clean them.. There will be a way to check the sender out with a meter.. dependant on how handy you might be..? Got to be some info on the www..?
Just in case anyone was holding out for an update.....there isn't one!
I had to order the 19mm crows foot for the pressure sender, which has yet to arrive.
...interesting this because; I never fill the filter case and I always get immediate oil pressure on the initial start up? And I've just completed the start of spring and therefore beginning to think of using it & again good oil pressure?
So should one fill the filter housing? Is this the accepted procedures ? Ta...
Jeez, sorry I missed your question... As I understand it it seems possible that the oil drains past the oil pump and into the sump over time, and dependant on the length of time it seems possible that the advised way to re-commission the engine is to drain the sump and re-fill the oil tank. Given the location of the oil filter it seems perhaps difficult if not impossible to introduce oil to a new filter then fit it without creating a mess, so perhaps not an ideal plan..
I guess my hope is that you may have resolved the issue by now... fingers crossed.
I’ve read a couple of articles/posts by engine rebuilders to NOT pre-fill filters on these cars as it “can” create some sort of airlock. It is a remote chance this is what has happened. I’d remove the filter, empty it and reinstall (yes you can remove it without draining all the oil). You will loose what is in the filter housing but that’s all.
The other thing is the technique a number of builders use on new engines to build oil pressure. That is to crank until first hint of fire, then shut off, then do same a couple of times. This boosts oil pressure with minimal actual rotation of parts. I’ve done it after doing invasive bore scoring inspection. Maybe hokum, but can’t hurt.
Likely the pressure sending unit though, as they are nutoriously unreliable. Normally they act odd first though, with needle jumping around, but not always. First time mine failed was months after getting my car. Needle plummeted to zero, CEL, warning on dash...after a change of underwear, I did some searching to find this was my issue.
The relief valve is another possibility, but I “think” they usually fail in the closed position, so to create high oil pressures, but haven’t actually had one fail. Replacing it is easy, as I did it as a preventative maintenance item a few years back.
Seeing as I may have built in some suspense here….
After over 2 weeks of waiting, my delayed eBay crowsfoot (insufficient postage), and the second eBay crowsfoot both arrived within a day or two of each other.
I changed the oil pressure sender, the relief piston, and emptied the filter housing of oil.
The oil pressure sender took a breaker bar to undo, and was from 2021, so it would be surprising if that was the issue.
I’ve done a dry crank (fuel pump fuse removed - I always do this, just as typically I’ve always pre-filled the filter, albeit on my 997), and the pressure gauge has shown some life.
But, I’ve not done a normal start yet. This weekend, hopefully….
Wheels are back on the wagon.
I'm going to assume the most likely suspect was the filter prefill. After that, the sender.
So next time I won't prefill the filter!
Can get it off the lift now, and get the Elise oil change done......
I always pre fill the filter housing on all my cars that I have serviced, I've never had a problem. Just done an oil and filter service on the 996 C4S and pre filled the filter housing no problems at all on startup. My thoughts are the sender unit.
