Technical Loss of Oil Pressure

[Pete145]

Hi everyone,

As some of you may know, earlier this year I upgraded my 500L to essentially a 595SS spec, and installed VDO oil pressure and temperature gauges as part of that process.

Watching the oil pressure gauge for the last few months has been a really interesting exercise.

From installation it's followed the same pattern. Upon start up the gauge immediately bounces nicely to the expected 3-4 bar. So far so good, but as the engine warms up the pressure gauge drops down proportionally to the oil temperature rising, eventually settling (after 15-20 mins or so) to around 1 bar when the temperature settles at 75 deg, and sometime it falls just below 1 bar.

The sender is mounted close to the sports exhaust, could the heat from the exhaust be interfering with the sender and giving a false reading?

Assuming not, and the reading is correct, I know 1 bar is too low for an operating oil pressure. What should I be looking at to correct it?

 

[AndrewHarvey]

Hi Pete
Where have you mounted the pressure sender?
When my engine was built - the oil pressure at the tapping for the oil pressure switch only indicated 1 bar
When we measured it in the pipework for the oil cooler it showed 7 bar
The oil pressure switch, switches at 2 psi - so measuring from this tapping is not ideal and is measuring the return pressure as it re-enters the pump.

 

[stevehg]

IIRC I get a constant ~4 bar, with no noticeable drop when hot. I used existing outlet, with switch and sender mounted on the rear bulkhead. Here's a pic of when I first installed engine...

cheers, Steve

 

[the hobbler]

Hi Peter;
At what stage is the pressure going down to only 1 bar? According to the 'book of words', when the engine is idling HOT, the low pressure light may come on. It is designed to come on at between 0.8bar and 1.0bar. The light should go out immediately the engine is revved above 1,000rpm. The normal (again, HOT) oil pressure should be between 2.5bar and 3.0bar (35psi and 43psi) when running above 1,000rpm.
Andrew's 7bar at the oil cooler sounds exceedingly high--probably too high; to the point that you risk blowing cooler/filter seals out. Have you carried the required modification to the DRIVING gear in the oil-pump Andrew?

 

[AndrewHarvey]

Hi Tom
Could you describe the oil pump mod please.........?

 

[AndrewHarvey]

My bad!!! Reviewed info 5.5 bar ......got a bit carried away!

 

[Bleeding Knuckles]

Greetings, I also have a remote dual sensor tapping off from the standard switch location. With my set up the pressure will rise to approx 4/5 bar and the slowly reduce to some 2/3 bar when hot. I have had some extreme temperatures recently prior to getting the heads and gaskets sorted, but even when at 95 deg c and maybe more the pressure has never dropped below 2 bar at tickover and no low pressure light either.

Ian.

 

[Pete145]

Hi Pete
Where have you mounted the pressure sender?

Hi Andrew, it's mounted on the side of the crank case, in the same position that the original sender was.

Quite close to the re-routed sports exhaust, and I did have issues with the original sender as well.

 

[Pete145]

Hi Peter;
At what stage is the pressure going down to only 1 bar?

Hi Tom, the only pattern and proportional relationship seems to be with the temperature. So, it's hits 4 bar on start up, and slowly sinks as the temperature rises and settles at just below 1bar. Stopping at traffic lights or foot down, it sticks at just below 1bar once at running temperature.

 

[Pete145]

IIRC I get a constant ~4 bar, with no noticeable drop when hot. I used existing outlet, with switch and sender mounted on the rear bulkhead. Here's a pic of when I first installed engine...

Looks like a neat set-up Steve. I might relocate the switch and sender away from the heat of the exhaust and see if that makes a difference.

 

[AndrewHarvey]

What oil are you running?
A nice thick mineral or a fancy modern synthetic ?

 

[Pete145]

What oil are you running?
A nice thick mineral or a fancy modern synthetic ?

I'm running the Castrol Classic, 20W-50. Mineral with some additives according to the website!

 

[AndrewHarvey]

When I bought my oil external filter / cooler from the leading UK supplier I was perturbed to see that the oil pump fitted was second hand - I was told that this was not uncommon as the Italian pumps were of better quality than the polish new ones. [emoji102]
When my engine builder assembled the engine the oil pressure was definitely low - fitted my new polish pump and guess what ??? Pressure was good

 

[AndrewHarvey]

I now shop abroad......

 

[stevehg]

Looks like a neat set-up Steve. I might relocate the switch and sender away from the heat of the exhaust and see if that makes a difference.

It was a bit of a pain getting the right fittings for sender and switch, but managed to find an ok manifold in the end. The extension hose was sourced from eBay.

cheers, Steve

 

[fiat66]

Greetings all !


Not the best time to reply as most of you are busy preparing for New years eve activities....
I´m new to this forum and never owned a Fiat 500 until this spring i imported a rebuilt " Abarth" replica.
apparently it has a 126P engine with Panda 30 head.
Oil pressure assembly is really clumsy and i recently found out its a 128 rally - Veglia sensor in combination with a oil pressure sensor that has extra long thread to fit.
Silly i thought and removed it and replaced it all with a single original oil press sensor resulting in no press indications at all !


Ok so put it all back together.
My oil press gauge is graded in ATM ( Not sure if this is original or 124, Lancia or even Alfa )
Cold engine 40 ATM, but when warm ( 110 - 115 celcius ) i get barely 10 ATM.
On idle low press light and my heart both flickers....


Any suggestions ?


Thanks !

 

[the hobbler]

According to 'the book of words', the oil pressure light can flicker (safely) when engine idling--hot, as long as the light goes out as soon as you rev the engine. If in doubt as to what the gauge is actually showing, my advice would be to get a correct, matching oil pressure gauge and sender.
Where abouts are you---it may be that there is a Forum member close to you who can help out---it is what this forum is all about!!

 

[Bleeding Knuckles]

Greetings, I also have a remote dual sensor tapping off from the standard switch location. With my set up the pressure will rise to approx 4/5 bar and the slowly reduce to some 2/3 bar when hot. I have had some extreme temperatures recently prior to getting the heads and gaskets sorted, but even when at 95 deg c and maybe more the pressure has never dropped below 2 bar at tickover and no low pressure light either.

Ian.

Thought I should show that I use a separate remote oil sender unit for a gauge with a low pressure warning light fitted. All available from ebay.

Ian.

 

[fiat66]

Hi Ian.


Interesting solution. As oil press gauge and sender unit has to be calibrated together, do i have to buy both sender and gauge on ebay ?
Can you give a link or equivalent to seller ?

I would imagine that on 126 engine an upgrade or redesign of oil system had been made as flickering oil pressure seems to be standard on 500 Classic.


For those of you with a 126 engine how is oil pressure ?


Thanks


Per

 

[fiat500]

I had a flickering oil light on my 500 when on tickover as hot as it gets. I wasn't really bothered but when I tried 10w60 oil it stopped.
But then I get niggling doubts about oil flow so may change back to 20w50 next time