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Discussion Starter #1 (Edited)
Short version: oil pressure light from time to time stays on for a couple of seconds, only! after starting the engine warm/hot (30min-1.5h, after the last run). What could be the cause?

Here's what is going on. After I got the car I changed all belts, tensioners, water pump, oil, all fiters, gasket between oil filter housing and engine, rod bearings!... and much more. Work was done by official Alfa workshop.

Everything worked fine for a couple of days, but then one day, when turning the warm/hot engine on (around 30min-1,5h after last run) the engine oil pressure light stayed on for a few seconds (around 3-4). Pressing the throttle pedal does not affect the light whatsoever - if I turn the engine off and start again the light goes off immediately. It was happening rarely, but never! when the engine was cold. In any other occasion the light went immediately off and it never ever turned itself on during driving - be it heavy or normal.

So first we changed oil pressure sensor, and it was the same. Then I decided to change oil filter once again, and while at it the valves that are attached to the oil filter housing were changed as well (just in case they were the reason). After that the whole year oil pressure light went off immediatly every time after starting the engine and I thought the problem is solved for good. So I thought the first oil filter had some sort of fault and was not functioning properly.

One year round, new oil change and oil filter. And after a couple of days, the problem returned. So I decided to change just the oil filter once again, and for 2 months everything was fine, but now it startted to happen again. It happens once a week, more or less.


I have no explanation of this, and am left without ideas what could be the reason.
Oil filter was genuine Alfa Romeo every time, and I am using Motul Sport 5W-50 ester synthetic engine oil. I know people using 5W-50 on 2.5, 3.0 and 3.2 engines and they do not have this problem, so I do not think it is the oil (I know the official spec for 3.2 is 10W-60 grade oil). Could ester oil, having better cleaning capabilities, clean some old sludge that gets stuck somewhere in the oil filter and then causing problems?

Anyway, any explanation would be much appreciated.

The engine works fine and smooth, there are also no strange sounds coming from it, and no sound change when the light stays on and then turns itslef off (or at least I did not notice it). I covered 12.500 miles without other engine issues so far.
 

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Noone with any sort of explanation or idea? There seems to be so many people here knowledgeable of 3.2 engine, I was hoping for better response...
 

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Try checking the oil pressure using a mechanical gauge. At least that way you'll know if it's a mechanical or an electrical problem.
 

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What Chris said.

Did you cut open any of your old oil filters?
 

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I had the same issue recently with my facelift 156 JTD.
Long story short, when turning the car on the oil pressure low warning would flash up. After much fault finding and changing the oil pressure switch twice, I started noting noting the circumstances in which the warning would flash up. The car had been fitted with an after market stereo, and I noticed the warning only flashed up if the stereo facia was clipped on. Weird right!! The loom was intact, no cutting or modifications had been made.
Any way I changed the stereo and it's never done it since.
Does your car have an aftermarket stereo? Possibility same problem.
 

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Discussion Starter #7
to all: Thanks for replies! I do not think that the problem is of electrical nature, as the light staying on, seems to appear under certain circumstances - that is, ONLY when car was driven, and properly warmed up, and then staying turned of for some time and then restarting. But it doeas not happen every time under these cirumstances, and I did not find a method how to replicate the issue every time, yet.

In all other circumstances like cold startup, or sturtup shortly after the engine was running, the light goes off immediatley.

@chris155: I was planning to measure pressure with the gauge, but when the filter replacement solved the issue last year I did not. So perhaps I will try it this time. Can you maybe tell me where would be the best location to fit it on a 3.2? It would help of course to have a gauge in the cabin to be able to read it when the light stays on... any recommendations?

@pud237: I did not, it is a good idea though... will probably do it the next time when I change the filter (which might be soon). Could it be that my oil somehow "damages" the filter (or at least some of them)?


What about this pressure bypass? What is its functrion, when does is have to open? And if this is the issue why would it malfunction only in circumstances described above?
What does not make sense to me is why for one year everything was okey, and now after oil and filter change the issue returned... argh...

Part 8, 9, 13 and 17 were already changed just in case they were causing the issue. I honestly do not know function of 9 and 13 - so if someone can explain I would be thankful.
 

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the bypass isa pressure limiter, as the oil pump would keep on building pressure until something bursts, usually a cooler hose or the oil filter.

part 13 looks like the oil cooler thermostat, and 17 looks like a pressure relief of some sort, or a 1 way valve maybe
 

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There's a blanking plug in the front face of the front bank iirc. Just above the exhaust manifold. I think it goes into the high pressure feed to the tappets. I'd use this to measure the oil pressure as its relatively accessible.
 

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Discussion Starter #10
An update. I did an oil and filter change. I used Mann oil filter (W 714/3) and Motul 8100 X-Power 10W-60 oil.

Oil pressure light behavior is so far normal. The light goes out even before the battery and engine lights turn off - just as I was used to with my previous 3.0 busso.

I did not yet install oil pressure and oil temp sensor+gauge, maybe sometime in the future.


Anyway, from now on I will not use genuine Alfa Romeo oil filters anymore, just Mann probably. I do not have any explanataion why this was happening. It could be oil or filter or the combination of both.

Thanks again for help.
 

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I do not have any explanataion why this was happening. It could be oil or filter or the combination of both.

Thanks again for help.
In the filter, there's the anti-drain valve that is supposed to keep oil in the engine. When this valve doesn't do its job perfectly then during each engine start the oil pump has to fill all oil galleries. When you change oil and the filter, you will notice that during the first start, the oil pressure light needs more time to go off.
 

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Discussion Starter #12
In the filter, there's the anti-drain valve that is supposed to keep oil in the engine. When this valve doesn't do its job perfectly then during each engine start the oil pump has to fill all oil galleries. When you change oil and the filter, you will notice that during the first start, the oil pressure light needs more time to go off.

I know (thanks for the input though), and that valve is the only thing that comes to my mind as a reason for all my troubles. Maybe in the genuine AR oil filter from certain production line/time just doesn't function well with ester based Motul Sport 5W-50, who would know...
 

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I know (thanks for the input though), and that valve is the only thing that comes to my mind as a reason for all my troubles. Maybe in the genuine AR oil filter from certain production line/time just doesn't function well with ester based Motul Sport 5W-50, who would know...
However, there is no such thing as a "genuine AR oil filter" .... AR gets it's filters from other well-known manufacturers, just like all other major car supliers, and sticks an AR stamp on them.....
 

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to all: Thanks for replies! I do not think that the problem is of electrical nature, as the light staying on, seems to appear under certain circumstances - that is, ONLY when car was driven, and properly warmed up, and then staying turned of for some time and then restarting. But it doeas not happen every time under these cirumstances, and I did not find a method how to replicate the issue every time, yet.

In all other circumstances like cold startup, or sturtup shortly after the engine was running, the light goes off immediatley.

@chris155: I was planning to measure pressure with the gauge, but when the filter replacement solved the issue last year I did not. So perhaps I will try it this time. Can you maybe tell me where would be the best location to fit it on a 3.2? It would help of course to have a gauge in the cabin to be able to read it when the light stays on... any recommendations?

@pud237: I did not, it is a good idea though... will probably do it the next time when I change the filter (which might be soon). Could it be that my oil somehow "damages" the filter (or at least some of them)?


What about this pressure bypass? What is its functrion, when does is have to open? And if this is the issue why would it malfunction only in circumstances described above?
What does not make sense to me is why for one year everything was okey, and now after oil and filter change the issue returned... argh...


Part 8, 9, 13 and 17 were already changed just in case they were causing the issue. I honestly do not know function of 9 and 13 - so if someone can explain I would be thankful.
Not too sure my two penny worth will help but here goes . Oil pressure low - engine not running OPS contacts are closed. Oil pressure normal, contacts open. Oil ingress in your wiring loom may be causing an intermittent short. Have you done an Insulation Resistance and loop resistance check on your loom? In the case of Oil Ingress, just as with water, the low impedance either cause may not be permanent. Disconnect your leads from your OPS and leave them open. Then check with a DVM from the other end to ensure there is high (megohms) resistance to the bodywork. At the same time check the loop resistance - should be low (ohms). I don't know if the system is single wire to ground or duel wire. If it is dual wire, both legs should have the same impedance to ground. Oil, grit or dirt could be causing and intermittent loop across the switch body. Either way you need to check the integrity of the wiring first before speculating where else the problem may lie.
 

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Not too sure my two penny worth will help but here goes . Oil pressure low - engine not running OPS contacts are closed. Oil pressure normal, contacts open. Oil ingress in your wiring loom may be causing an intermittent short. Have you done an Insulation Resistance and loop resistance check on your loom? In the case of Oil Ingress, just as with water, the low impedance either cause may not be permanent. Disconnect your leads from your OPS and leave them open. Then check with a DVM from the other end to ensure there is high (megohms) resistance to the bodywork. At the same time check the loop resistance - should be low (ohms). I don't know if the system is single wire to ground or duel wire. If it is dual wire, both legs should have the same impedance to ground. Oil, grit or dirt could be causing and intermittent loop across the switch body. Either way you need to check the integrity of the wiring first before speculating where else the problem may lie.
Its a single wire on the oil pressure switch. I have seen an oil pressure switch which leaked oil into its plug but not on an Alfa V6, and they have already changed the switch, I doubt a new switch would have the same fault and any oil in the plug would have been rectified at the time (you'd hope!).
 

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Discussion Starter #16
However, there is no such thing as a "genuine AR oil filter" .... AR gets it's filters from other well-known manufacturers, just like all other major car supliers, and sticks an AR stamp on them.....
Of course. ;) It is just that there is no brand name stamped on the genuine filter (just Made in China if I remember correctly), so I don't know how else to call it :)
For sure it is not the same as Mann, as Mann's filter is shorter and internals have a little different design.


@sizewell: I really doubt that problem was electrical in nature, as it started to appear right after oil+filter change, and now it is fixed with another oil+filter change.
 

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Its a single wire on the oil pressure switch. I have seen an oil pressure switch which leaked oil into its plug but not on an Alfa V6, and they have already changed the switch, I doubt a new switch would have the same fault and any oil in the plug would have been rectified at the time (you'd hope!).
Fair point. Is it possible the insulation has been "nipped" somewhere causing intermittent short (small puncture in the insulation) to chassis - Chassis being the effective "Return". or maybe it is trapped somewhere and moisture/oil fouling causes partial/full short to ground (chassis)? An I/R measurement between single wire and ground (chassis) should still show low impedance on loop (ohms) and Infinity - megohms when open circuit.
 
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