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Discussion Starter · #1 ·
Hi,
Am having a bit of an on-going issue with my 24v 3.0 1995 manual 164.
When first start the car, if it has been standing for a few days (the longer the worse the symptom), it takes a moment for the oil pressure to build - and then it goes over centre on the dial, to about 5 bar, until the engine warms and it drops back to between 3 and 4 bar.
Thought it was the oil filter that was supposed to stop oil draining from the passage ways back into the sump. Is there a separate valve dedicated to that instead? Never used to get such high pressure readings after start up either so makes me wonder if there is something stuck in the non-return valve (if not in filter housing) both allowing oil to flow backwards and restricting cold (thicker) oil. Or am I wrong and likely to be something else altogether?
Current filter is genuine Bosch P3351, 0451 103 351
Concerned as engine wear while pressure builds is going to be excessive and accumulative.
 

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Discussion Starter · #2 ·
Research indicates there is a non-return valve in the oil filter - which clearly is not working as it should. Have ordered some genuine Alfa filters and will post results when fitted.
 

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Discussion Starter · #3 ·
Another interesting development today. Oil pressure higher than before after oil change - normal. However, even fully up to temperature was still reading almost 6 bar at 2,000rpm - drops to 1.5 / 2 bar at idle. Really hoping not a sign of a partial blockage in the system, maybe in the oil cooler pipes? Once home, I did rev the engine to 6,000rpm and pressure stayed below 6 bar so must still be a reasonable flow. I don't know what is going on. Fingers crossed as 100 mile trip planned tomorrow.
Oil filters should have arrived today but delay in sending (phoned the dealer) and due tomorrow now - hopefully in time to fit before trip. Will update.
 

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Discussion Starter · #4 ·
Update: no blockage, the car ran fine. Oil pressure was still high (5 bar indicated) even after gauge showed was up to temperature but did drop back to normal (3 to 4 bar at 2500rpm) few minutes later, guessing after engine fully heated all through.
Today put in genuine Alfa filter, 0046805830. Oil pressure grows faster after start. Still goes to almost 6 bar when cold but drops down more smoothly/ consistently as warms and no longer goes back to almost 6 bar when driving even before water temperature up to 85-90c. Am happier with it. Will see what happens when start tomorrow initial oil pressure wise. And, more importantly, what happens when it remains parked for a few days. Will let you know.
My understanding remains that the filter has a non-return valve - hopefully better than the Bosch one.
 

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Discussion Starter · #5 ·
With OEM filter, car is driving fine. Not been left to stand longer than 24 hours yet but no indication of an issue regarding reverse oil flow while standing. Pressure still higher than would expect until fully up to temperature - could just be a gauge/sender thing. Main point is no more issue with reverse oil flow while parked, leading to engine wearing 'zero' initial oil pressure when starting.
 

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2015 Chevy (Holden) SS, 1989 Milano (Shankle Sport), 1991 164S
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It is usual for the oil pressure to read higher than normal until the oil heats up, maybe 75-80 psi? I see this all the time in my 91S on a cold start, and esp in the 94LS I owned. Once the oil warms a little, very short time, the pressure drops to it's normal ~50 psi at hot 3000 rpm cruise, ~25-30 psi at hot idle, confirmed by mechanical gauge.

Also, the same for our Milano (75).
 

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Discussion Starter · #7 ·
Thanks, Del.
Am used to difference in pressure between hot and cold, just seems to be reading a bit excessive difference at mo.
Have decided to buy a new oil-gauge sender to see what it reads. Today, 11 hours after the can ran last night, when I started it the red oil warning light went out immediately but the needle took a second or 2 before it began to climb.
Something not right - question is whether with the engine oil system or the systems monitoring it... Wouldn't bother me so much if wasn't a crucial element to engine wear.
 

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2015 Chevy (Holden) SS, 1989 Milano (Shankle Sport), 1991 164S
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If your pressure gauge reads anywhere close to what I get after warming up (translated to bar), the sender should be fine.
 

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My guess is that the sender is the problem. I would remove the old sender and install a mechanical pressure gauge and see how that reads. Cold start up, cold running, at full engine temp running, full engine temp start up, etc. If these tests show, no problem, then install the new sender. Remember that there is a soft metal washer between the sender and engine. GL!
 

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2015 Chevy (Holden) SS, 1989 Milano (Shankle Sport), 1991 164S
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I would strongly suspect \that the amount of damage you surmise happens at startup of your car is really very minimal, since the loads are very little in comparison, and there is residual oil on the bearing surfaces anyway.

After starting the engine, as the gauge starts to read pressure, I just let the engine run for maybe 20-30 secs at about 1200- 1500 rpm, enough to get the alternator light to go out and the pressure starts to read maybe 70-80 psi, and then drive off, usually not revving above about 3.5-4k in our neighborhood. The oil pressure quickly drops to it's standard ~50 psi at hot 3000 rpm.
 

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Well, I've never been quite that rigorous, but yes, I have never believed in tearing out of the driveway as soon as the engine has started. The engines need to get the juices flowing, so to speak, same as I do in the morning, lol. Don't know if it has ever been totally necessary, but it doesn't hurt., the engines in my cars always lasting many many thousands of miles and years without troubles.

Once met a young guy years ago who used to start the V8 engine in his car, and immediately rev it to at least 5000 rpm and hold it there for a minute or so to warm it up. Made my skin crawl. The engine always seemed to be ok, but still...

Some old American V8 engines were fairly indestructible it seemed.
 

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Non return valve is just a rubber flap over the outside ring of holes. The pump pushes oil against the flap, raising it off the holes. Not really possible for it to fail.

Did you change the oil with the same brand and weight?

Oil pressure has very little to do with engine protection when the oil is cold. Oil pressure is about keeping the oil cool enough after the engine gets hot.

Oil pressure is about flow whereas bearing protection is about viscosity and shear qualities,

As the journal spins in the bearing it drags the oil around creating a wedge of oil which floats the journal away from the bearing. The effective pressure inside the bearing clearance is far higher than any oil pump output pressure. The key aspect of the oil pump is volume delivery, not pressure. Oil has to be deliver quickly enough to keep the oil film inside the bearing clearance cool enough to keep working and not break down.

Viscosity and shear strength of engine oil are the critical factors for engine protection, not pump output pressure. Resist the temptation to use higher viscosity oils in the (mistaken) belief that they deliver added protection, the reverse is more likely. Use the lightest viscosity recommended by the engine maker or the oil maker.

If oil pressure alone could protect the engine then engine wear on every start would be horrendous. In fact, the engine bearings are fully protected by the wedging of the oil film for the time needed to deliver freshly cold oil to those bearings, the true function of the oil pump. For a cold engine very little oil pressure is required and the cold oil actually misleads the driver into thinking the higher pressure on a cold start is a significant factor for engine protection. The reverse is true. Cold oil can't be moved fast enough and the high pressure is a sign of deficient flow. Warm oil flows much faster and in much higher volumes at much lower pump output pressures. This is a good thing.

The high oil pressure on a cold start is an unavoidable deficiency of engine oils. A big reason full synthetic oil protects an engine better both on cold starts and very hot running is lower overall oil pressure required to deliver adequate oil flow volumes at all temperatures. Volume of flow is the critical factor, not delivery pressure.
 

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Discussion Starter · #15 ·
Thanks, Michael. Have always used Magnatec 10w/40 semi-synthetic, with a key selling point being their claim is bonds better to the metal thus reducing initial start wear.
Going to video when start it tomorrow - that will be after 48 hours sitting. Hopefully will be a normal response of immediate red light going out and then oil pressure rising. Not ordered a new gauge sensor yet - been spending too much on alternative suspension parts, with the aim of getting some better solutions to certain bushes.
 

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Discussion Starter · #16 ·
OK, this is driving me nuts. Today, after 2 days non use, started car: red light on and gauge not moving - took a full 2 to 3 seconds before red light went out and then gauge moved up. Engine sounded same throughout - unlike when first start after oil change when engine note noticeably changes (softens) when pressure rebuilds.
After parked for an hour restarted and the oil pressure gauge began climbing straght away but red light stayed on for few seconds.
Later, starting after a 2 hour park, red light went out immediately and gauge climbed after a moment's pause.
Start 4, after a 45 min park, red light out and gauge climbed immediately.
Oil pressure max reading wise, at high revs sometimes the pressure reads almost 6 bar, other times a more normal 4 bar - water temp 90 degrees C (needle vertical) in both cases.
These are not consistent readings. The oil pressure system is a basic mechanical one so even if failing would expect it to do so in quite a consistent manner. Indeed, if I never looked at the gauge/light at all, would have no other indication (audible or otherwise) anything is wrong.
Could both senders be playing up? Am wondering...
 

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I’m a Bit late to the party but There is no valve in the oiling system for that. There are a few valves, there is an over pressure valve in the pump that dumps unneeded oil back into the pan, there’s a thermal valve for the oil cooler, and there is typically a bypass valve in the filter to prevent oil starvation incase of a clogged filter.
5 bar doesn’t seem too high on cold start. My engine reads about that on cold start. Is it a stock oil pressure sending system? Also water temp doesn’t equal oil temp. Oil stays warmer longer and takes longer to come up to temp.
 

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It was interesting, with my 64 Giulia Sprint GT with it's separate water and oil temperature gauges, to see the relationship between the two during different driving situations.
 

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Discussion Starter · #19 ·
I’m a Bit late to the party but There is no valve in the oiling system for that. There are a few valves, there is an over pressure valve in the pump that dumps unneeded oil back into the pan, there’s a thermal valve for the oil cooler, and there is typically a bypass valve in the filter to prevent oil starvation incase of a clogged filter.
5 bar doesn’t seem too high on cold start. My engine reads about that on cold start. Is it a stock oil pressure sending system? Also water temp doesn’t equal oil temp. Oil stays warmer longer and takes longer to come up to temp.
Many thanks for the reply. Good to know there are no such anti-return valves in the system. I am getting pretty consistent red oil light on after start (if parked for day or more) for up to 3 seconds and then oil pressure gauge rises. Oil pressure goes up to 6 bar even with water temp up, until oil fully warm, and then it sits just under 4 bar at 3,000rpm, and all seems fine. Until park up. If left for just few hours, red light goes out instantly and gauge rises straight away. If left for day or more red light stays on for a bit and then gauge rises.
 

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Discussion Starter · #20 ·
I’m a Bit late to the party but There is no valve in the oiling system for that. There are a few valves, there is an over pressure valve in the pump that dumps unneeded oil back into the pan, there’s a thermal valve for the oil cooler, and there is typically a bypass valve in the filter to prevent oil starvation incase of a clogged filter.
5 bar doesn’t seem too high on cold start. My engine reads about that on cold start. Is it a stock oil pressure sending system? Also water temp doesn’t equal oil temp. Oil stays warmer longer and takes longer to come up to temp.
George, just had an idea from another 164 nut. If the pressure relief valve was stuck slightly open, could this allow greater reverse flow when parked and at the same time be causing the higher than normal pressure until oil fully warm? If so, would this be something that could be fixed without pulling the engine?
 
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