Low oil pressure on start up

[gav2612]

I Have been having a bit of trouble with my 97 500 the last couple of times I have been out. On startup, the oil pressure takes two or three seconds to come up to the normal 25-30psi and the oil warning light flickers for the same amount of time. After that everything is as normal and pressure remains within normal limits. The oil and filter were changed less than 300 miles ago and all levels seem to be fine. I am getting a little worried about doing long term damage. Any Advice?

[SimonV8ster]

Is that the only time the oil light flickers ?? Or does it do it at other times like when you give it some beans ??

[Slacey]

If the light flickers for short while it could be the pressure sender on it's way out. It's easy enough to change and a cheap part at around a tenner. If you are confident that your oil levels are consistent it's worth swapping it out as a first try fix.

[gav2612]

On start up seeems to be the only time it flickers. The pressure gauge stays at zero for these few seconds or so as well, before getting back up to its 30psi or so at cold idle. This would seem to indicate it isnt just a faulty pressure warning light. I cant recall the car doing this up until the last week or so, and am getting a bit worried that the engine is turning over for the first few seconds with virtually no oil circulating.

[The AJP Griff]

Going by your profile you have a serp engine.The oil pressure does take time to reach its correct place after cranking,and this is worse on a cold winters day.As long as pressures are good under normal operating conditions i wouldn't worry,it might just be a bad connection at the sender,or a faulty sender that is causing the light to flicker,as previously mentioned

[That Daddy]

Quinny said:

The fact that both the light and the guage, stay low would worry me

The light gets it's info from a pressure switch, and the guage from a pressure sender, I think it would be unlikely that both these components would fail and give false info at the same time.

Does the car rattle a bit on start up? indicating low pressure to the followers??

The fact that it shows normal pressure after a short time and holds that pressure when the oil is warm, and hence thinner, would indicate to me that the pump is ok

If it were my car, I'd start by having a look at the pressure relief valve, as a starting point.

Edited by Quinny on Sunday 12th August 15:53

Or a collapsed oil filter internally,the pressure does strange things if this happens

[spend]

Errrm, it goes sump - pickup - pump - galleries (switch / gauge / spares / filter middle) - filter - around engine.... If the filter was restricted wouldn't the pressure go up???

If anything I would have thought crap filter allowing drain back so pump is having to prime every start? Are there any leaks around the unions?

Dave

[That Daddy]

No Dave,pressure goes down not up,think about iti dont know why i bother

[spend]

Cant see that Simon.... If you restrict a pipe at will cause pressure to rise at the pump side, and all instruments are on the pump side. Engine side will see reduced flow, and we are not approaching conditions where the pressure relief would have any effect.

Dave

[That Daddy]

spend said:

Cant see that Simon.... If you restrict a pipe at will cause pressure to rise at the pump side, and all instruments are on the pump side. Engine side will see reduced flow, and we are not approaching conditions where the pressure relief would have any effect.

Dave

Spend wrong,the filter element gets the pressure/flow 1st from the pump direct,so if it as collapsed it restricts the flow to the oil galleries pressure switch etcthink about it remember suction/inlet 1,pump 2,filter 3,galleries 4.

[spend]

I thought the pump blew oil down the middle of the filter - that orifice is directly connected to the galleries for the switch/sender/spare on both preserp oil pumps I have. I have not checked the serp covers - just assumed they were the same.

Dave

[That Daddy]

spend said:

I thought the pump blew oil down the middle of the filter - that orifice is directly connected to the galleries for the switch/sender/spare on both preserp oil pumps I have. I have not checked the serp covers - just assumed they were the same.

Dave

Dave,the oil is blown round the outer part of the filter(larger surface area)then flows thru the element then pushed up thru the threaded hole and into the gallery,end of lesson

[spend]

OK, so how does the squeezing oil up the central hole manage to prime the oil pump on a preserp then?

Dave

[Pasco]

:Popcornsmile:

[GreenV8S]

spend said:

I thought the pump blew oil down the middle of the filter - that orifice is directly connected to the galleries for the switch/sender/spare on both preserp oil pumps I have.

I don't have one in my hand to confirm it, but from memory on mine the oil pump feeds oil down the outside of the filter and the return to the engine comes out the middle.

[gav2612]

Sorry everyone,
been on holiday for the last fornight.
I am now thinking, this problem has only become evident since last service. Indy specialist that did the service put 20W- 50 oil in it. This oil is definately thicker than the oil in in before. Could this be the problem? or possibly due to the new filter internally colapsing as previously mentioned?

Many thanks for the replies

[spend]

Quinny said:

20w-50 shouldn't cause a problem

I really don't believe that the gradings on the labels relate to oil pressure on the gauge... Know theoretically they should, but....

Dave

[spend]

Quinny said:

So you don't think that a heavier weight oil say 20w-50 would be harder to pump around than say a 10w-40??

I would certainly expect to see a difference, especially when the oil is cold.

What I said was that not all brands were comparable by weight (making a nonsense of the weighting on the label IMHO). Viscosity at barometric pressure over a range of temps may not equate to viscosity at same temps when being squeezed (torn apart) inside the engine, is my best interpretation on empirical observation. Hence the reason many of us are so anal about preferred brands, I guess - it works out pretty expensive to try several (particularly the cheap ones which end up being ditched post haste!).

Dave

[Ribol]

spend said:

OK, so how does the squeezing oil up the central hole manage to prime the oil pump on a preserp then?

Dave

It stops you forcing air in and causing an air lock by having oil in it to start with.

[spend]

Ribol said:

spend said:

OK, so how does the squeezing oil up the central hole manage to prime the oil pump on a preserp then?

Dave

It stops you forcing air in and causing an air lock by having oil in it to start with.

Cant visualize that at all... if that is all you are filling (effectively other side of filter - which we all prefill anyway) then the pump would be self priming????? Normal packing with vaseline seems logical, as would squirting in oil after pulling out the pressure relief plunger.

Dave