oil pressure

[mickl]

Hello all, I have finally registered my 75 Berlina 2000A but there are still a few issues to resolve here or there. On starting up the oil pressure gauge reads about 35 but within a couple of minutes of driving it slowly falls back to a zeo reading. What is wrong and is it a worry?
Thanks in advance, Mickl

[AikenDrum105]

I think the 105 series oil pressure gauges and senders can be a bit nebulous at times.. 

Not unusual for the pressure to be high when the car is cold,  then drop when hot (but not right to zero).  Typically when revving the engine over 2k you will see the pressure increase a little, and then drop low again when idling (hot). The older the engine, with greater clearance in the bearings and wear in the pump - the lower it will sit at idle.         If you get the car hot,  turn it off then restart it immediately - does the pressure run high again for a minute or two - or stay zero while the car is hot ?

A dropped crankshaft plug can cause this too.

More of a worry that you can't differentiate between a low hot pressure and zero hot pressure

Possibly the best option would be to ask your local tame mechanic to check the pressure with a handheld gauge screwed into the oil pressure sender hole - pretty quick to check.   

Perhaps a quick test would be to measure the voltage between the sender and earth with the ignition on but engine off,  then check it with the engine running and cold,  and again when hot.    If there's a significant difference between hot running and engine off   then there's some pressure there but the gauge or wiring is out of sorts.     If there's no difference but obviously oil pressure - the sender is possibly hosed.

You could also check the resistance of the sender wire - disconnect it from the sender and the back of the gauge and measure the ohms across it with a multimeter - or even just run a temporary wire from the sender in the engine bay, through the window and up to the back of the gauge to see if that gives a different reading on the pressure gauge - I've done that a few times to find dodgy wiring.

The sender is on the drivers side rear of the engine - usually a brassy coloured tin can (coated in gunk by now) with an electric terminal sticking out the back.  If you look down between the rear carburettor and the firewall you'll see it there above the starter.     It's a 14mm nut holding it on I think - if you get under the carbs with a spanner to get it off - disconnect the battery,  the starter +12 is hanging around down there and loves spanners and petrol fumes.

if you had to take a stab in the dark I'd start with the sender. - I think they'd standardised a bit by the 2000 berlina stage - earlier differences between years and manufacturer (jaeger / veglia)  have them all over the show in terms of voltage output of the sender / sensitivity of the gauge - make sure you get the right one 

Hope that gives some options anyway

Cheers,

[colcol]

But take more notice of your 'idiot light', when you lose oil pressure you want a red light telling you, not looking at an oil pressure gauge, watch the road, i have found the Alfa idiot light senders can be a bit dodgy at times, luckily they normaly leak before they fail, so you replace it before it gives trouble, just make sure its on before you start the car and it lights up when you switch the engine off, when it fails to, fling it for a new one for piece of mind, Colin.

[aggie57]

I'd only be seriously worried if it was 0 when cold.  Oil pressure on these can be like a a new born baby crying.  It's fed, it's clean and it's burped but it still cries!  It just wants your love......

[Anthony Miller]

My 88 model 75 does the same thing and so did all three of my joolies, so it's not just 105s or older ones. Always check your oil levels regularly and you should be alright, unless of course your oil pump is rooted but you should be able to hear that, remember zero oil = zero oil pressure. I saw at Bruno's what a lack of oil does to a JTS, a hole big enough to put your fist through.

[mickl]

Thanks all for the responses which have helped and are reassuring.
The pressure does come back up after turning the hot engine off for a minute, and then starts to drop again after a little while. It improves marginally after revving a bit in neutral. AikenDrum, I will be checking the various electrical tests once I get the car back from the brake specialists......the right rear caliper has once again leaked fluid out bypassing the piston seals with a small puddle on the floor when I looked this morning!! I suspect I still have a way to go to get these damn brakes working properly.
The warning light for low oil pressure on the left bottom part of the tacho is not coming on at any time so a new one will be installed soon.
Aggie, this car is no newborn....it`s a grumpy mother-in-law. Not sure if I will ever love it after all the problems I have encountered/am still encountering.
Have some vibration issue too so new post on this topic on its way.
Thanks again,    Mickl

[colcol]

Hey Anthony, the JTS you saw at Maranello Pursang Motors was due to the owner not checking their oil level every week, when the oil level drops down enough for the idiot light low oil pressure to show, it means you are up for a new engine, in a Sud or 33, its a bit more forgiving, oil light flickers on when you pull up at lights, better check oil level this weekend, thats why every Alfa Romeo should have a fully functioning low oil pressure light, i think my sensor was about $20 at Repco, Colin.

[Anthony Miller]

Too right mate, when I first got into these cars(alfas that is) a very wise man(Richard Anderson) said to me that pretty much all alfas use about 1ml of oil per km which equates to 1l per 1000km and from what Ive read here and on other fora the newer engines are not that different either.

[colcol]

The newer engines, particulary the JTS's use a bit more oil as they use thinner oil to keep the fuel consumption down, for the older engines you would use a thick mineral oil, where the new engines have to have a 10-60 fully synthetic oil, that finds its way past the rings quite easily, Colin.

[mickl]

The low oil pressure warning light does not come on after turning the key before starting so I checked the globe behind the tacho and it was blown. New bulb installed but still no light coming on. I then tried to find the sender and could not find one. Is it mounted directly opposite the one which sends to the veglia guage but on the left side of the engine?? If so, it looks like a previous owner may have removed it and put a very close fitting screwed bung in the engine casing. There is also a short length of grey wire going no-where about 300mm away.
Would you rec trying to remove the bung and putting a new sender in?....the bung may need to be drilled somehow and an easy out used to remove it.
mickl

[colcol]

Now that you have the globe going, try shorting out the stray bit of wire to earth, the engine is a good place, to short out, and see if the oil light comes on, then presto, you have found your wire, then remove bung and see what sort of thread it has, and if there is any oil around it, now get a low oil pressure idiot light sender for your particular car and see if it goes in, the idiot light senders are about $20 from Repco, they are quite well priced, its the oil pressure gauge senders that cost big $$$, Colin.

[mickl]

Thanks Col, the wire does indeed light up the globe on the tacho, but it is not going to be easy to remove the bung on the block. I have thought out a couple of alternatives which I would be grateful if anyone can recommend the best solution:
1) Remove bung and buy new elec sender for warning light as per Col`s post...Cons: difficult to remove bung and still have an elec gauge which is not very reliable
2) Remove the elec pressure gauge sender and replace it with a T piece which can then have both the elec warning light sender and elec pressure gauge sender attached......Cons: removes need to drill and remove bung, bit more expensive, unreliable elec gauge remains.
3)Remove elec pressure sender and its gauge and replace them with a mechanical gauge which I can mount in the old elec gauge hole in the dash and which will only cost about $40...Cons: is the top of the block the best place to fit a mechanical oil pressure pipe?
I have not yet actually checked the hot oil pressure but intend asking the mechanic to do this for me in a few weeks when the car goes in for head retightening.
Thanks again everyone.
Mickl

[colcol]

If you have an oil PRESSURE sensor currently, you could replace it with a combined oil pressure sender and combined low oil pressure light, i know VDO make them, but don't know about Veglia, you could try and find out, Colin.

[AikenDrum105]

I've seen plenty of earlier cars with a low pressure switch teed in exactly as you describe off the existing Oil pressure sensor port.   I'd go that route if the bung is too fiddly to get out.    Benefit is you can take your existing sender with you to buy the T piece / low pressure switch etc - to make sure all the threads match

I'd been meaning to fit an idiot light exactly like this to my Super for ages - but doing the TwinSpark convo now - that engine has sensors all over it already for that stuff - even a low oil level which is nice ... (if it works...)

Cheers,

[mickl]

Thanks for the posts. I will take a picture later in Feb once I have installed the T piece and had the hot oil pressure checked by the mechanic.
Mickl