No oil pressure for 5 seconds on cold start
Discussion
This sounds a bit long to be a normal "characteristic".
It has started doing it since I changed the oil. I put Mobil 1 15W50 in it (at great expense!), and a Fram PH2821A filter, with the non return flap in it.
The only thing I can think of is that I didnt prefill the filter, as it would all have wee'd out as i inverted it to screw it onto the car.
This makes me think I have a big airlock in the top of the filter, which effectively acts as a pressure accumulator, meaning that the pump has to push about 1/2 a litre of oil through before the trapped air compresses enough to create pressure...
I guess I could prefill it, and noting the non return valve, I'd only have to put a finger over the central outlet to keep the oil in it whilst i locate it on the filter housing stub...
Any thoughts?
Its a little concerning...
Ed.
It has started doing it since I changed the oil. I put Mobil 1 15W50 in it (at great expense!), and a Fram PH2821A filter, with the non return flap in it.
The only thing I can think of is that I didnt prefill the filter, as it would all have wee'd out as i inverted it to screw it onto the car.
This makes me think I have a big airlock in the top of the filter, which effectively acts as a pressure accumulator, meaning that the pump has to push about 1/2 a litre of oil through before the trapped air compresses enough to create pressure...
I guess I could prefill it, and noting the non return valve, I'd only have to put a finger over the central outlet to keep the oil in it whilst i locate it on the filter housing stub...
Any thoughts?
Its a little concerning...
Ed.
Ed, I always pre fill the filter in the manner you are suggesting, you lose very little oil unless you are completley cack handed.
Try taking it off and filling it slowly with the occasional "tap" "tap" on the filter to help the air out, till oil comes up through the holes in the base then fit it.
The flap stops most of the flow just the screw hole dribbles as you say.
Try taking it off and filling it slowly with the occasional "tap" "tap" on the filter to help the air out, till oil comes up through the holes in the base then fit it.
The flap stops most of the flow just the screw hole dribbles as you say.
Thanks for your replies.
I took the filter off, and it was nearly empty. it took about 1/2 to 1 litre of oil, and left index finger over the hole whilst I located it on the threaded spigot.
Primed the pump with my drill and home made tool, the missus reported 30PSI on the gauge. Dizzy back in and the light was out immediately it fired.
Tomorrow morning will be the real proof, once its had a night to sit and cool down.
Ed.
I took the filter off, and it was nearly empty. it took about 1/2 to 1 litre of oil, and left index finger over the hole whilst I located it on the threaded spigot.
Primed the pump with my drill and home made tool, the missus reported 30PSI on the gauge. Dizzy back in and the light was out immediately it fired.
Tomorrow morning will be the real proof, once its had a night to sit and cool down.
Ed.
What about just having a flakey gauge?
Of all the car's I've ever owned the two gauges that have failed
the most are oil and gas.
Next time you change the oil I'd be tempted to screw in a proper oil preasure gauge
where the sending unit is, then take note of that reading and then screw the sending
unit back in and compare it to the reading on your dash.
I'm no mechanic, but it would seem to me that the oil in the filter rises through a
perforated tube, passes through the filtration material then exits through the holes
surrounding the threaded intake tube. Even if there was air at the top of the filter,
the oil if anything should be simply forced not to rise as high and be forced to exit
lower in the filter. And any air in the system should still be preasurised by the oil
pushing on it, thus not taking preasure away? My point is that while air in the filter
could definately effect the efficay of the filter, the preasure should not be at issue
since the air would become compressed to the same PSI as the oil.
Correct me if I'm wrong.
Of all the car's I've ever owned the two gauges that have failed
the most are oil and gas.
Next time you change the oil I'd be tempted to screw in a proper oil preasure gauge
where the sending unit is, then take note of that reading and then screw the sending
unit back in and compare it to the reading on your dash.
I'm no mechanic, but it would seem to me that the oil in the filter rises through a
perforated tube, passes through the filtration material then exits through the holes
surrounding the threaded intake tube. Even if there was air at the top of the filter,
the oil if anything should be simply forced not to rise as high and be forced to exit
lower in the filter. And any air in the system should still be preasurised by the oil
pushing on it, thus not taking preasure away? My point is that while air in the filter
could definately effect the efficay of the filter, the preasure should not be at issue
since the air would become compressed to the same PSI as the oil.
Correct me if I'm wrong.
Edited by brap_brap on Sunday 6th May 15:08
Edited by brap_brap on Sunday 6th May 15:09
You are correct, and during steady state running, there is no problem. I get up to 55PSI.
Problem is during transient periods, i.e. startup. It takes a little time for the oil pump to compress all that air, cos it has a low bulk modulus (i.e. its very cimpressible compared to liquid). Thus, an air pocket in the top of the filter acts much like a capacitor in an electrical circuit: it makes an accumulator out of the oil filter.
Still havent cured it. Thought I had, but it did it again today.
Humph.
Ed.
Problem is during transient periods, i.e. startup. It takes a little time for the oil pump to compress all that air, cos it has a low bulk modulus (i.e. its very cimpressible compared to liquid). Thus, an air pocket in the top of the filter acts much like a capacitor in an electrical circuit: it makes an accumulator out of the oil filter.
Still havent cured it. Thought I had, but it did it again today.
Humph.
Ed.
OK - running pressure sounds too high - and it takes a long time to 'catch' after starting.
Have you checked the pressure relief valve, if it's sticking it could cause both those symptoms.
It's behind one of the large 'nuts' on the oil pump - and there's a spring in there too so be careful when you undo it to catch the spring.
Some people replace the piston style one with a tadpole shaped one - less prone to stick.
Have you checked the pressure relief valve, if it's sticking it could cause both those symptoms.
It's behind one of the large 'nuts' on the oil pump - and there's a spring in there too so be careful when you undo it to catch the spring.
Some people replace the piston style one with a tadpole shaped one - less prone to stick.
Gassing Station | Wedges | Top of Page | What's New | My Stuff