Oil pressure (to much of a good thing).

[Scarpia]

Dear sirs,
when the engine is cold, the pressure is off the gauge and remains there for the first 10 minutes at least.It will sag to the upper limit of "normal" when warm and not under acceleration but under acceleration will always move to the max again.Is this influenced by the release valve sticking? If I remove the engine filler cap whilst running there is some degree of pressure blowing out of the engine and whilst there are no visible problems the car seems rather more fumey than is entirely pleasant.Are the two things related and is this entirely normal?.

distressed of northern belgium

[inthedark]

Is it an electric gauge or pipe fed from engine ??

[chugga boom]

No expert on aprillia's but my dad has similar problems on his astura, problem being the oil pressure gauge feeds off the cylender head, because of a certain amount of wear the oil pressure drops off alarmingly as the engine warms up.
To settle his nerves my dad rigged up a separate oil gauge off the auto clean which is crankshaft oil pressure and this reads well above normal oil pressure, the car has covered well over 10,000 miles like this trouble free, also both of our augustas are very similar but with no ill affect, it may be worth checking the crank oil pressure 1st

[JohnMillham]

   It sounds like your present pressure relief valve isn't opening properly. You could try putting a slightly weaker spring in it and see what happens. However, I would rather have too much oil pressure than to little.
   It is best to avoid too many fumes in the engine of an Aprilia, as the oil filler cap has been known to dent the bonnet when it blows off as the fumes ignite. A rocker cover breather might be the answer.

[fay66]

   It sounds like your present pressure relief valve isn't opening properly. You could try putting a slightly weaker spring in it and see what happens. However, I would rather have too much oil pressure than to little.
   It is best to avoid too many fumes in the engine of an Aprilia, as the oil filler cap has been known to dent the bonnet when it blows off as the fumes ignite. A rocker cover breather might be the answer.
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good heavens John ::)That conjures up a Brockbank Cartoon!
Not that well up on Aprilia but is there any percentage in removing the pressure relief valve and having a clean up of any? deposits.

Brian
8227

[JohnMillham]

Possibly Brian, but any muck in that area is more likely to prevent the relief valve closing, rather than opening. People have been known to put stronger springs in to try to improve the oil pressure when it's low.

[Scarpia]

thanks for the ideas.
In my car there is not a ball bearing (which is always described) but a sort of tiny version of an engine valve which is held in place by the spring.The engine is recently rebuilt. What causes the crankcase pressure in an engine and why does it have such a flammable content?Is this "ignition charge leakage past the piston rings?I already blew the oil filler cap against the garage roof on a previous occasion by removing a plug lead with the engine running....
Geoff, the pressure gauge is fed by a pipe from the engine, not electric. 

[fay66]

Hi William,
Certainly sounds like blow by past the piston rings, if the engine has recently been rebuilt did they get the gapping of the rings correct, gaps staggered and not in line with the gudgeon pins


Brian
8227

[Scarpia]

next time I rebuild we will know the answer to that one....

I am going to see if I can test the oil pressure at the release valve somehow.

[davidwheeler]

As the iron lady said "rejoice, rejoice!"  My Aprilia engine is rebuilt but not yet in the car so I can't compare, but my Lambdas always start with the pressure off the gauge and then relax a little as they warm up. The Aprilia did always start a good way across the gauge as I remember and the big ends were rattling happily so I suspect that the pressure relief valves are a little inadequate.   What oil are you using?  I have converted the Lambdas to modern filters and get along very well with 10/40 full synthetic.  Using a 20/50 will give a high pressure with no great benefit to the engine.

[Scarpia]

shell helix 15-40.Cannot imagine there is much wrong with that.I am interested to hear you run synthetic.I always thought there could be no real benefit to be honest.?

[davidwheeler]

It's fit and forget basically.  Full synthetic does not break down with heat as do mineral oils and can be left in the sump longer.  My wife's Skoda, on ordinary oil has a 10,000 mile change but on full synthetic it's 30,000 miles.  I'm probably overdoing it but the price differential (using oil form the motor factor, not Castrol) is minimal so why not?  The Lambda is bored out to within a millimitre of its life so anything that can reduce wear is worth trying.

[Scarpia]

The best product to prevent wear I have ever come across is ZX1.I don't know if its still available but i found its performance quite astonishing.I'm not normally an additive fan but this can save an engine .I saw a demonstration were the oil was drained from an engine and then allowed to run on without problems.A noisy engine will literally quieten down in seconds as you add this.

I used to run my thema turbo with it and it made a big difference to the economy also.It is actually a small oil molecule that clings into the tiny irregularites in the metal surface which the ordinary oil then acts against which reduces friction very much more than a normal lubricant alone.It doesn't clog like ptfe based products.I haven't seen it for 10 years.

I went for a long run yesterday and have decided my oil pressure is ok.Its on the high side but that's no bad state of affairs.
I do seem to have a lot of back pressure when I remove the filler cap with the engine running.Not smokey exactly but a good steady blast against your hand and its smelling of unburnt fuel slightly.

The plugs are all a nice colour,no sign of a blown head gasket in the water or oil so I'm scratching my head a bit. Brian suggested the rings might be put on with the gaps in the wrong position but I think this unlikely and cannot easily check of course. I think a faulty or sticking (inlet) valve would be noticable with the engine running so I'm stuck for ideas.The pressure is sufficient to give a slight leakage from the plug extension covers for those that know an aprilia engine.Can I attach a quicktime film on here then everybody could see .......?    

[inthedark]

Take out all the plugs and do a cylinder compression test( with throttle fully open ), If that's ok,  check breather system,
on a lot of engines  Ford, Vauxhall etc  it's quite common to have pressure in the rocker box, after all if the piston is going
up and down there will always be pressure of some sort .

Geoff

[Scarpia]

all is well.

compression and oil pressure are "tip top"

I suspect I'm being just too fussy.The fumes are also improved since I replaced some small gaskets that seal the joint of the spark plug extensions.These are a bayonet fit in the cam cover and a couple were a fairly loose fit due to ageing of the spring clips that retain them.This wasn't helping a think.   

Another line of thought is possible also.
The car tends to run very cool .If I fully open the shutters when warm , under normal driving, the water temperature will drop back down to 30-40 degrees (c) which  much lower than desirable.I have an excellent book from the 40's which suggests the ideal operating temperature  (of the water jacket) to be quite narrow at between 70-80 degrees.Once falling much below 70 degrees there is a tendency for the fuel charge to condense partially on the cylinder walls and wash past the rings by breaking down the oil seal at the rings themselves.This can lead to fuel vapour in the crankcase and of course serious wear in the bores.This accelerated  wear is the reason most manufacturers were more worried about cold running modification, such as radiator blinds than possible hot running problems.
I kept the blinds partly shut yesterday and an half eye on the temperature to keep it "in the zone" and had noticably less fumes..(but I had also just fitted the new plug gaskets so it's hard to say which made the real difference of course!)