Technical Oil pressure readings

[RDS]

Hello all

If anyone is able, please could they post oil pressure readings from the dash gauge at different rpms and state if engine hot or cold etc and engine condition or mileage. I appreciate that this won't be exact but a guide only.

I'm getting 2 bar at 2000rpm and 4 bar around 3000 warm engine but less than 1 bar at idle. 25000 miles on clock.

Thank you
Rds

 

[MD14UCM]

When I owned one of these in the 1980s I got 4Bar from about 40mph to motorway speed. At idle I think it was around 1.5Bar. If very hot then just under 4Bar at motorway speed but I thought that the temp and pressure needles both were horizontal and the rpm and speedo needles vertical on the motorway!

 

[NEG]

I wouldn’t put much faith in the accuracy of the oil gauge TBH, my 1500 seems to read approx. 3.5Bar on the motorway but typically is around the 2Bar mark in normal driving.

 

[Iggy64]

I agree with comment about accuracy of gauge reading. Mine varies quite a bit between hot and cold but probably averages 3.5 to 4 at 3000 rpm plus and 1.5 to 2.5 below this.

 

[F123C]

I worked as a Fiat Mechanic back in the day. We were frequently pestered by owners asking about their oil pressure gauge readings and worrying unnecessarily.

As others have said, these gauges are not particularly accurate - think of them as a styling feature, to make the car look 'sporty'

As long as the oil pressure warning light doesn't come on at tickover or at any other time, your oil pressure is probably fine. If you're still worried or want to verify your gauge readings, you can always connect up a proper test gauge (an accurate one ) at the oil pressure switch or gauge sender unit tapping point on the engine.

Most Fiat oil pumps of that era, were gear type pumps driven from the camshaft or auxiliary driveshaft i.e. at 1/2 crankshaft speed, so will never be likely to generate impressive oil pressure at idle or low speed and at higher engine speed, the pressure relief valve may open to control pressure.

Afaik, a petrol engine needs 10 p.s.i. of pressure per 1000 rpm, so about 7psi at idle (just about the trigger point of the oil pressure warning light sensor), 30 psi at 3000rpm (cruising?) and 60psi at 6000rpm. It wasn't unusual on some Fiats for the oil pressure warning light to flicker on and off at idle after a fast drive (oil hot). Was never a problem, providing the light went out as soon as the engine speed was raised.

There's little point in trying to generate higher oil pressures, puts more stress on oil pump drive components, absorbs more power, can aerate the oil - frothy oil doesn't lube bearings very well. Some Fiats used to shear the serrations in the oil pump drive gear.....others could burst oil filter canisters if the pressure relief valve stuck...


Conversion factor:- 1 Bar = 14.5 psi

AL.

 

[RDS]

Many thanks to all those responding. I agree with all the comments in fact,I've been used to fairly accurate mechanical gauges in other cars and have been bemused by the stylistic and practical 'offerings' by fiat. I appreciate all the info and responses.

Cheers
RDS

 

[pbruecken]

Many thanks to all those responding. I agree with all the comments in fact,I've been used to fairly accurate mechanical gauges in other cars and have been bemused by the stylistic and practical 'offerings' by fiat. I appreciate all the info and responses.

Cheers
RDS

I have struggled with the low pressure readings on these guages for a while so this winter I took some measurements. The aftermarket sender ranges resistor readings from about 350 ohms at 0 psi to 0 ohms at 110 psi in a somewhat linear fashion. The guage doesn't read 55 psi till the sender hits about 60 ohms so at 55 psi the guage only reads about 25 psi.

 

[RDS]

I have struggled with the low pressure readings on these guages for a while so this winter I took some measurements. The aftermarket sender ranges resistor readings from about 350 ohms at 0 psi to 0 ohms at 110 psi in a somewhat linear fashion. The guage doesn't read 55 psi till the sender hits about 60 ohms so at 55 psi the guage only reads about 25 psi.

hello there

Many thanks for the info however i am a little confused by your post: are you saying that the sender is linear in its readings but the gauge is almost "stepped" in its display? The result being that the gauge under-displays at low resistances and then suddenly jumps?

Out of interest please can you let me know how did you connect the Ohmmeter to read when the engine was running and generating pressure?

Thanks in advance.

RDS

 

[pbruecken]

hello there

Many thanks for the info however i am a little confused by your post: are you saying that the sender is linear in its readings but the gauge is almost "stepped" in its display? The result being that the gauge under-displays at low resistances and then suddenly jumps?

Out of interest please can you let me know how did you connect the Ohmmeter to read when the engine was running and generating pressure?

Thanks in advance.

RDS

I set up a gauge and sender on my bench this winter. I found the sender had about 350 Ohms resistance at 0 psi and had about 175 Ohms at 55 psi. The gauge read about 25 psi at 175 Ohms on the sender using a circuit that mimicked the car connections using 14 volts. I built a small dc current amplifier to install between the sender and gauge to correct the readings. I will install it this spring and see if it works.

 

[RDS]

thank you for the info!

RDS

 

[pbruecken]

As per a request for my amplifier on the oil pressure gauge:

The sender I purchased from Midwest Bayless in Ohio seems to vary its resistance from about 350 Ohms to zero when the pressure goes from 0 to 110 psi. So at 55 psi the sender reads about 175 ohms and so on.

The gauge reads about 30 psi when the sender is at 175 ohms and reads 55 psi when the sender is at about 100 ohms. This makes the gauge read low. As I understand the gauge, it has 2 coils that generate magnetic fields that oppose each other to move the needle. I removed the gauge and measured the resistance from the +12 V to the middle conatct and got 115 ohms. I also measured the resistance from the middle contact to ground and found it to be 165 ohms.

I built a small current amplifier and ran the sender to drive a PN2907 transistor to drive the gauge. It made the gauge run within 10 psi of the actual pressure, which was better. I may put another stage in this circuit but for now, it is better.:idea:

 

[RDS]

many thanks for your dedication to the cause and to sharing the info
RDS