Oil pressure light flickers at idle/normal operating temp

[turbofiat]

Fiat 131, 2 liter twin cam, automatic transmission:

After the engine has reached normal operating temperature, the oil pressure light will either flicker or kick on in D R L2 or L1 but if I put the transmission into park or nuetral it goes off. Probably because the RPMS increase. I can rev the engine a bit and the light will go off but come back on when the rpms drop. There is no tach on this car so I don't know exactly what RPMS the low oil pressure light kicks on at.

So I replaced the switch with another one. Same effect.

I am using 10W30 Castrol motor oil and a FRAM oil filter. I had a weird experience with this particular oil filter. After installing it, the engine would not build up any pressure until I removed it and filled it.

This makes me wonder if the oil pump is too weak to push oil through the filter or there is any issue with this filter. I mentioned in another post that I read FRAMs had cardboard as the filter media.

I've wondered if the oil pressure is measured before or after the filter. This might explain the low oil pressure if the filer is too restrictive.

I'm going to install a Purolator filter to see if this changes anything and top off with 20W50 to see if the thicker oil has any effect.

Is it dangerous to drive this engine with the light kicking on at idle? It would be nice to know what pressure this switch kicks on at. I could hook up a pressure guage to know for sure how low the pressure is getting at idle.

I removed the cap while the engine was idling and saw oil sloshing around in the cambox so the engine does have oil pressure.

Any other suggestions?

[Brit01]

The low oil pressure warning light on my Alfa comes on at about 7 psi!
Way too low for any normal engine running. If it's below that at idle what is it under load?

You need to get a good oil pressure gauge to see the readings above idling when hot.

Also 10w/30 for me sounds way too thin for an older car like this. Modern engines with tight clearances would be using a 30 viscosity oil.
What does you manual say?

A 20w/50 would be used in an older car I would say. I use 20w/60 in my Alfa 33 (1988, hot summers). I have about 50-55 psi at 3000 psi. This is with a 24 year old crank.

The light only comes on for a split second after an oil change and the filter is empty. I have used Fram, Coopers and now Mann. Not much difference between them. Just Mann for me is the only one here made in Germany which is better quality and had 2 non-return valves.

Also I wouldn't top up with other grade oils. Change the whole lot with a new filter.

You may also have a faulty sensor but if not you will damage your engine in no time at all with such a low pressure.

Low oil pressure usually indicates worn bearings on the big ends and/or main bearings. Worn oil pump gears and blocked oil pump pre-filters can also contribute.

[WhizzMan]

The previous poster has hit the nail on the head. I wouldn't drive the car until you've sorted this out. Only run the engine for diagnosis and no longer than required. if a 10W oil won't build up enough pressure, using 20W will most likely not help enough and won't repair what's broken inside. For instance, if you have excessive play on main or big-end bearings, running the engine longer, might damage your crank so much, you won't be able to use it anymore. The same sort of applies to a worn oil pump. This is the time to stop fiddling and do serious diagnosis and fix whatever is broken. You have already established it's not the sensor, so it must be pressure that's low itself. You need to fix that or you will most likely face a total breakdown of the engine in the near future.

[turbofiat]

I'll hook up a mechanical gage and see what readings I get. Hot and cold at idle.

I've been trying to determing what range is considered normal for a twin cam.

Before installing a set of Volvo VDO guages in my Spider, I was using a Sunpro mechanical guage that seemed to be quite accurate. The maximum oil pressure was no more than 60 PSI or 4 BAR under any condition. What I have been told the pressure relief valve pops off at. Seems like the engine ran 20 PSI or 1 BAR at idle at normal operating temperature.

The VDO gauge I have now reads much higher. Maybe because I have a 5 BAR guage and a 3 BAR sensor.

At normal operting temperature, what's the lowest the oil pressure should be?

I picked up a Purolator filter and some Shell Rotella 15W40 (what Fiat recommends) to see if this has any effect.

I have never seen an oil pump actually fail unless the pan is damaged and damages the pump. Not saying they can't fail otherwise.

One thing that makes me wonder if it's the oil filter is the oil pressure light never kicked on until I changed the oil.

But the fact that the oil filter needed to be filled up before the engine saw any oil pressure makes me wonder if there is either something wrong with this filter or the pump was too weak to push through it.

[Urbancamo]

I once faced similar problem, but not in Fiat though. Changed oil and filter and after that, started normally. Oil pressure light never came off. No matter how many times I started again and again. Normally it takes approx. 5 seconds to light come off after oil and filter change, but not in this case.
Throwed the filter as far I could, it was bone-dry inside. Got my my self another brand and after I installed that, light went off immeadiately. Both filters were meant to this specific engine.

And I know this engine was in perfect condition. I have absolute no clue what caused it. I don't prefill the filters and it's not really needed at all. This is the only time I seen something wrong in oil filter.

If your Twin Cam has a lot miles on it, you might seen pretty low pressure readings on idle when hot. But this is something you should not worry. If oil pressure light flickers on idle, then it's too low.
These Italian engines seems to have pretty low idle oil pressures. Every used Twin Cam I've seen, had oil pressure under 1 bar (14 psi) in idle.

My rebuilded Lada SOHC engine produces 0,6- 0,7 bar when hot. Oil pump is new and tight and crank clearances are in 0,05 mm (2 thou) range. Oil I use is fully synthetic Castrol 5W-40.
I think it's a feature, not a fault.
But get some and accurate oil pressure gauge and check the REAL pressure. I once fitted ordinary, industrial liquid-damped pressure gauge straight to block. Just for checking real pressure.
Gauge had 1/4 NPT thread and and oil pressure adapter had 1/4 NPTF thread, they are not perfect match but little bit of Loctite pipe sealant kept it nice and try. Cheap and accurate method. These industrial gauges don't lie and glycerine filling keeps needle nice and steady. 0-100 psi gauge works fine.

[Kovacevic]

WhizzMan is right. Time to stop fiddling and have a look what's going on inside the engine. The first port of call would be to remove the sump and have a look at the pump and pick-up. The sump can be removed without removing the engine, and the two things I would look for first would be a blocked pick-up strainer (if someone has been too liberal with the use of silicone based sealants anywhere in the engine the excess will find its way there). The other problem with 131's is that the engine sump is quite low and it doesn't take much of a knock on the underside of the sump to fracture the pump housing - it will still get oil pressure but the light will flicker. If neither of these are the issue and the pump checks out O.K., I would be looking at a bearing issue for that pressure loss, most likely mains or the auxillaury shaft bearing.

Usually the long way is actually the short way.

[WhizzMan]

There isn't much difference in minimal pressure an engine needs in between types and brands. The main and con rod bearings all work on the same principle and less than 0.5-0.7 bar or so for idle will damage the bearings eventually. On high load, depending on the amount of clearance in the bearing, the amount of pressure on the bearing and all that, you will need a higher pressure and even more important, enough flow, even during combustion cycles and direction reverses. It's hard to measure that, so "low idle pressure" is the best indication you have.

[Brit01]

These Italian engines seems to have pretty low idle oil pressures

yep.

I have just rebuilt my Alfa boxer. New bearings, all crank journals within specs. New gears on the oil pump.

Good pressure above 1100 rpm but hot idle is low, 10-12 psi.
3500 rpm almost 55-60 psi.

New gauge (mechanical).
Mann filter W19/14.

[turbofiat]

Hooked up a mechanical oil pressure guage and here are the readings I got:

Cold idle : 60 PSI
150F : 50 PSI
190F : 15 PSI in gear, 20 PSI in park or neutral.

Now I have another concern. This car has no tach being an automatic but at one point I saw the oil pressure hit 75 PSI.

Doesn't the oil pump have a pressure relief valve preventing the oil pressure from going past 60 PSI?

So now the question is , is 15 PSI at idle too low?

If not then why is the oil pressure light kicking on?

Sorry for the imperial readings. I can convert if nessessary.

[Urbancamo]

We all like imperial units for sure.

But how much there is pressure when your coolant is at operating temp and oil is real hot? Usually it takes at least two times more driving to heat oil than coolant. We don't usually drive in idle.
So we are interested what readings you are having in operating rpm range.

But depending how accurate your mechanical gauge is, I think there is nothing wrong in your engine. For pressure light flickering, somebody else can leave thoughts, now it's too late for me to think (almost midnight here)

T

[TomLouwrier]

60 psi = 4,1 bar
50 psi = 3,4 bar
15 psi = 1,0 bar
20 psi = 1,4 bar
75 psi = 5,2 bar

1,0 at idle may be a bit lowish, but I see no big problems here other than your max oil temp.

Why would 75 be too much, why should the relief valve be set at 60? The instrument in my Spider (BS1, 1608 engine) has a scale of 0 to 6 atm (more or less the same as bars). I've always had it near full scale, certainly over 5 at normal cruising speeds.

Remember that pressure in itself is not all that counts. Bearings in an engine are not hydrostatic but hydrodynamic. The real oil pressure is built up by the drag of oil film between crank and rod (or cam and head) which comes from their relative rotation. As long as the pump delivers more volume to the bearings than the bleed down rate, those surfaces are kept wet enough to maintain their lubrication. Oil pressure, especially in the main gallery, is just a convenient indicator of the system's overall performance.


Get yourself a good manual on your engine. Someone wrote down what it was built to give, takes out a lot of guessing.

regards
Tom (off to bed as well)

[turbofiat]

We all like imperial units for sure.

But how much there is pressure when your coolant is at operating temp and oil is real hot? Usually it takes at least two times more driving to heat oil than coolant. We don't usually drive in idle.
So we are interested what readings you are having in operating rpm range.

But depending how accurate your mechanical gauge is, I think there is nothing wrong in your engine. For pressure light flickering, somebody else can leave thoughts, now it's too late for me to think (almost midnight here)

T

I did several tests and wrote various readings. One was while idling at an ATM. One was after driving for several miles. The lowest I saw the pressure guage read was 15 PSI. Since the light goes off when I take it out of gear, the switch must trigger between 15 and 20 PSI.

[turbofiat]

60 psi = 4,1 bar
50 psi = 3,4 bar
15 psi = 1,0 bar
20 psi = 1,4 bar
75 psi = 5,2 bar

1,0 at idle may be a bit lowish, but I see no big problems here other than your max oil temp.

Why would 75 be too much, why should the relief valve be set at 60? The instrument in my Spider (BS1, 1608 engine) has a scale of 0 to 6 atm (more or less the same as bars). I've always had it near full scale, certainly over 5 at normal cruising speeds.

Remember that pressure in itself is not all that counts. Bearings in an engine are not hydrostatic but hydrodynamic. The real oil pressure is built up by the drag of oil film between crank and rod (or cam and head) which comes from their relative rotation. As long as the pump delivers more volume to the bearings than the bleed down rate, those surfaces are kept wet enough to maintain their lubrication. Oil pressure, especially in the main gallery, is just a convenient indicator of the system's overall performance.


Get yourself a good manual on your engine. Someone wrote down what it was built to give, takes out a lot of guessing.

regards
Tom (off to bed as well)

I just "heard" 60 PSI was the maximum oil pressure for a twin cam. That there is a blow off valve that prevents the pressure from getting any higher than that to prevent pumping more oil into the camboxes that could possibly drain out. Since this engine has some age on it, it wouldn't surprise me if the spring is worn preventing a higher than normal oil pressure.

I had this same guage on my Spider and if I recall never saw it go above 60 PSI under any condition.

I was hoping Mr. Croft would have commented on this subject by now. About proper oil pressures on twin cams and all.

I don't know much about building engines other than bolting a cylinder head and all the other bits onto a short block and droping it into a car.

The oddometer says the car has 130,000 miles on it. But the engine block is painted Ford blue so it must have been out of the car at one time or another.

Of course you can't go by oddometers on a 30 year old car anyway. The speedometers in my Spider and Yugo came from other cars.

[WhizzMan]

Springs rarely "wear" but oil pressure relief valves do get stuck. That would fit with the symptoms of an unusual high pressure with a cold engine (valve stuck half open, not enough oil can pass) and a low pressure when hot (valve not closing properly, leaking too much oil in bypass). You could investigate if that is the problem here.

Tom, you are right about the pressure inside the bearings being the main concern. Enough flow to those bearings is essential to keep that up indeed. You will need a certain pressure in the channels at certain engine speeds and load to be able to sustain that flow. However, even if there is enough flow to keep the bearing lubricated, it may not be enough to keep the oil "cool" enough while in the bearing. Overheating the oil in the bearing will make it last a lot shorter, even if no direct damage to the engine occurs. It may be beneficial to have pressure higher than absolutely required for bearing longevity so your oil won't deteriorate on you very rapidly. For production road cars and "commercial vehicles", this is most certainly an important factor.

[timinator]

Just a few points to add to this discussion. The journal does not ride on a film of oil. It is supported on a wedge of oil that is constantly moving under the point of highest loading. The bearing is not round but instead wider at the parting line of the bearing so as not to shear oil off the journal because of bearing crush. Oil in a running engine is mixed with air. The journal does not spin true to the centerline of the bearing. The pressure in the bearing area is not what you are reading on the gauge.

It is amazing to me that the oil wedge can be only .0007 of an inch. That oil can work it's magic for a huge temperature range. Finally that a Maxi-dyne diesel engine can put out 900ft-lbs of torque at 1200rpm at the factory specification of 15 psi of oil pressure and last half a million miles between rebuilds.

Tim