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'91 164L 3.0 V6 12V 5-speed
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Discussion Starter #1 (Edited)
I had to pull the engine out again because I'm getting too low idling oil pressure when the engine is hot/warm. I'm seeing a pressure between 5-8psi (idle probably 900rpm), and I'm worried that when the weather gets warmer the oil pressure light will stay on and I have a serious problem. Otherwise I think oil pressure is pretty good: cold idle & revving over 80psi and revving hot engine at 3500-4000rpm 60psi.

Oil pressure has been measured with a mechanical gauge. I was using 10W-60 oils.

PO had probably changed main and big end bearings as they were good and the crank had worn quite seriously. I had the crank ground (only main journals were worn so only those) and nitrated and got a new set of bearings. With the refurbished crank and new bearings, main clearances were still too big: about 0,05mm. Could that cause the low oil pressure?

I believed that the oil pump had to be worn with all that material from crank and bearings circulating with the oil. Today, I measured the pump and it seems to be within tolerances found in the workshop manual (I have the Kartalamakis book and he's a bit more strict about the pump tolerances, those figures were not met with my pump.)

With the engine on a stand, where should I look to find that lost oil pressure?

Also, I noted when I was stripping the engine down that the oil filter was empty. If it has a habit of draining itself it could explain why it took 2-3sec to raise the oil pressure on start-ups after awhile. Is this by design or what could cause this?
 

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On the 12v V6 164 engines the red light sender is in rear of front head and oil gauge sender is located in rear of the block valley between the heads. So both far away from oil pump. On the 24v 164 engines the red light sender is located on the rear engine mount with the oil filter and the oil pressure gauge sender on rear of front head.
 

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Ol filters should all have non return flaps or valves in the outside ring of holes. Usually a rubber disc covers the holes inside the filter mounting plate.
 

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"revving hot engine at 3500-4000rpm 60psi".

That's a good number, where it counts, since cruise rpm is around 3-4k rpm. I wouldn't worry too much about the hot idle number. Not much happens there, and loads are very low.

"I'm seeing a (hot idle) pressure between 5-8psi (idle probably 900rpm) "

I found this:

The official Alfa Romeo specifications for 164 engine oil pressure are:
Engine at running temperature (194F) (see Alfa Factory Mechanical Manual, page 1-95)
800-900 rpm . . . . 11.6 psi
5000 rpm . . . . . . 65.2 psi
Minimum/Maximum Oil Pressures (warm engine) (see Owner's Manual page 86)
Idle (800-1000 rpm) . . . . . . . . . . . . . . . . . 7 psi minimum
High Engine RPM (5500 rpm) . . . . . 57-85 psi maximum

I've read that 4-7 lbs at hot idle can be considered normal for the V-6 by many. Some like higher of course. I think that if you are close, no harm is being done.

You didn't say if the red low pressure light is ever on otherwise except at start up. You also didn't say what pressure sender you are using. The OEM senders fail after a while and start reading very low, if not zero. But you have checked the pressure with a mechanical gauge.

I'd probably just use the 15W-50 Mobil 1 and their small 24V engine oil filter and just drive it. This works in my cars.

I am surprised that the crank was damaged, as the nitriding really does protect the crank throws. I ran a race car for a short while with excess oil pressure which had such a nitrided crank, and the shell bearings would fluid erode down to the copper backing after a couple races with zero damage to the crank throws. I could just throw in standard shell bearings again and off we go with proper clearances.

The dreaded PO must have run this 164 engine just plain dry.
 

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The Busso engine does run at very low oil pressures at idle. My GTV6 engine would idle so low and the oil pressure get so low the low oil pressure light would flicker as I opened the throttle from idle.

Oil pressure doesn't have much to do with bearing protection per se. That is effected by the wedging of the oil film due to rotation within the clearances. This is one reason why oil qualities are far more relevant to non rotation lubrication requirements such as cam lobe to lifter interfaces and piston rings, neither of which depend on oil pressure but film strength.

Oil pressure is all about oil cooling. The required pressure is to ensure oil passes through the clearances quickly enough that it never overheats within the clearance. Obviously, at idle the required flow rate is much lower than at higher power outputs.

If the oil filter was empty then that would be devastating to bearings. The oil pressure is developed inside the filter first. The oil pump must fill the filter to 100%, no air at all, before oil pressure can rise to the required level in the galleries. That is why all oil filters, or the system between the oil pump and the filter, must have anti drain back valves to prevent the oil filter from emptying while the engine is shut off (and why I go to the trouble of filling the new filter with clean oil as much as I can before screwing it in place). That is why oil filters also all have an overpressure activated bypass valve. If the filter clogs the oil galleries still get oil at full pressure. Dirty oil is better than no oil. Much better.
 

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'91 164L 3.0 V6 12V 5-speed
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Discussion Starter #6 (Edited)
I have no idea what has happened with the engine when the crank got worn, can't even imagine. And even more strange that all the big end journals are in a good shape, I would have thought those were the first to take a hit.

Oil pressure light could light up if the idle rpm dropped a bit (the car ran very rich which caused unstable idle). But only when the oil was hot.

One of the main problems with this low idling pressure is that when the pressure is low, hydraulic belt de-tensioner isn't working as intended and tensions the belt way too much. Timing belt was making noises because of this and that's the main reason I want to solve this asap. Otherwise the pressure is pretty much within the range I've read about this engine.

I thought that the piston oil cooling squirters (in con rods) were a possible reason for the low oil pressure but that doesn't seem to be the case. First there isn't any valves that could be jammed open and secondly those aren't continuously fed with oil.

The oil filter seems to be defective. I tried to blow in the opposite flow direction and there really wasn't much of a resistance so the rubber flap doesn't prevent it from draining. Will use a better filter next time (defective came with the car).

Although I like the thickness of 10W-60 (others are like water to me) oil, I really wouldn't like to think that it the only oil I can use in the engine.

With the engine out I can also solve the very weird grounding problem of the temperature sensor body. The overtemp light would stay on because the middle section of the thermostat body wasn't grounded properly: paper gasket up and down, rubber hoses to the head and probably junk between the 7mm bolts and the middle section => no ground = light on.
 

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"One of the main problems with this low idling pressure is that when the pressure is low, hydraulic belt de-tensioner isn't working as intended and tensions the belt way too much. Timing belt was making noises because of this and that's the main reason I want to solve this asap. Otherwise the pressure is pretty much within the range I've read about this engine".

If the oil pressure is within the expected range for these engines, then I guess I would consider the timing belt to still be in it's expected tension range, ie, as designed. Esp considering that there are those who eliminate that feature of the de-tensioner when they use a modified, ie, fixed tensioner with long term success.

In almost all cases, it is the serp belt making noise because it is set too loose, not the timing belt if it is too tight since it is a toothed belt, unlike the serp belt. Plus, the timing belts are really strong in tension the way they are designed with high tensile strength longitudinal fibers (maybe Kevlar) easily taking that load. I've heard of cases where a stray rock has actually poked a hole in an Alfa timing belt, and the belt has continued to function as it should without failing, there being enough fibers left to still provide an adequate margin of safety.

Check the tension of the serp belt before doing anything else. I usually set it by ear since the manual stated tension is considered pretty darn high, potentially reducing the water pump and idler pulley bearing life. I usually set the one in the 91S so it may make a slight chirp/squeal for a sec or two when I start the car from cold when the a/c is turned on. I almost never use the a/c, and the squeal goes away in a couple of seconds, if even that long. Somewhere around 70 lbs tension or so. I really don't measure when I set it.

I'm not convinced yet that you have anything to worry about.
 

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10W 60 is very heavy oil for this engine. North American spec cars ran 10W 40 semi synthetic from the factory fill. I used 5W 40 and even 0W 40 for many winters. It is a surprisingly stubborn myth that high viscosity oil delivers better protection. That is incorrect if the engine is designed for lower viscosity oil. The heaviest oil I would use would be 15W 50 full synthetic which I use only for topping up in summer. I have used 5W 50 full synthetic in the past but, really, if Alfa is fine with 40 weight and semi synthetic at that then 0W 40 or 5W 40 will work fine.

As I say, oil pressure is not a significant factor in bearing separation. Film strength is very important and synthetic oils deliver higher film strength than conventional oils.
 

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The accessory belt on my 164 is also tensioned "just so". It squeals for a very short time after a cold start. At least it did shortly after a new belt was installed. Now it no longer squeals even a little bit. Better that tension is initially set a tiny bit too low than too high for accessory belts.
 

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measured the oil pressure in its 3.0qv, on a warmed-up arrow it drops almost to 0, when re-gasing it immediately rises to 5 bar, I'm afraid my 3.0 busso is already over (
 

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In reply to Del's comment about belt strength, he's right. Gates have informed me their re-inforcement is glass-fibre not kevlar but still massively strong. I once had a stray bolt (assume it was a bolt dropped into the V a day before it happened) punch a hole through the cambelt. It jumped a couple of teeth on the cam wheel involved but didn't snap. Was able to change the belt, reset the timing and all has been fine ever since.

Also agree that squealing/belt noise is the serpentine belt/aux belt not cambelt. The only thing that could make the cambelt squeal would be failing idler/tensioner bearings - which have no place being on the engine a second longer. Serpentine belt squeal is a bane on the 24v engines if tension/bearings not all happy bunnies.
 

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This has been said many times but I will say it again. It is very common on the 164 for the oil pressure sender to fail in such a way as to show zero or very near 0 oil pressure at hot idle. If your red oil pressure light is NOT coming on, you likely are fine. The fix is either a new sender or to check the hot idle oil pressure with an external gauge. IF the red light IS coming on THEN you likely actually have a low oil pressure problem for real. I wouldn't want anybody to give up on a 164 simply because a $50-$60 part has failed to show a correct reading. There are other alternatives to the standard Alfa (Veglia) and aftermarket (Facet, etc.) senders. A search on the forum will get you discussions regarding options for that sender (now a Bosch branded part, IIRC?). Of course there is also the drill or poke a hole in the top of your old sender trick, to try to get it to start working (also discussed many times on the forum).
Charles
 

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The initial post refers to checking the pressure "with a mechanical gauge" from which we infer an externally connected tool. The dashboard gauge is "electrical" in that it converts a mechanically developed pressure from diaphragm movement into a gauge display. That system is pathetically unreliable. An external mechanical gauge with a direct readout should be capable of showing actual oil pressure.

However, low oil pressure at idle speed is not a problem. If oil pressure rises with rpm in accordance with Alfa specs then all is well. Oil pressure results from the flow restriction presented by the bearing clearances. Lower than spec oil pressure indicates excess clearance. It does not by itself indicate imminent engine failure. Putting higher viscosity oil in the engine to boost oil pressure caused by excessive bearing clearances is just a fool's errand. High viscosity is basically irrelevant to bearing protection. Film strength and correct flow rate are critical. If your engine was designed for 0W 20 oil then that is what you must use or you risk bearing failure because the bearing clearances are too tight for higher viscosity oil. Flow rate declines, oil temperature inside the clearance skyrockets, film breaks down and the bearing fails. The later versions of the Busso engine were engineered for 40 weight oil in most climates. The W number is largely irrelevant because that viscosity is only an indication of cold temperature flow rate, a number only relevant to cold start protection. Generally speaking, the lower the W you can use the better, the only drawback to low W number oil is the issue of wide range multi grade effectiveness, long since dealt with by oil formulation engineering.

Maximum loading on the oil film occurs during high rpm lift off. Maximum inertia forces on an unloaded engine exceed the maximum loading imposed by only bmep at any rpm. If you are hearing the dreaded con rod bearing double click or low knock, or worse the low rumble of main bearings on the way out, then you remain blissfully unaware of the extensive damage being wrought at high rpm and low piston loads because you can't hear the horrible noises being made at high rpm. By the time you can hear these problems it is far too late. Your engine needs a rebuild.

An idling engine places very little pressure on the crank journals. Extended idling is very bad for splash lubricated or non pressure lubricated areas like piston rings and cam faces and lifters and for that reason should be avoided. An engine should be switched off rather than left to idle for several minutes.
 

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I assumed the original poster had used an external gauge as well, the second poster (vaaster) with oil pressure concerns I am not as sure about. Sounds to me that the original poster has put the work and research in that probably indicates the need for a new oil pump due to wear/damage.
Charles
 

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Some glass fibre has higher tensile strength than Kevlar. Once embedded in the "rubber" matrix in addition to tensile strength the total belt strength would also depend on the adhesion between the fibre and the "rubber". Also, glass fibre cannot stretch. Kevlar is not completely inelastic. One source says Kevlar fibre stretches 2%, another says 3-5%. Not a lot but too much for a cogged timing belt.
 

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Yup, worked at the Big (not so big now, lol) B with that stuff, running structural engineering tests on coupons, and built up structure, of various layups using Kevlar, S glass, carbon, etc in preparation for use on NASA contracts, the stealth bomber (I can admit that now, working in the the Black Hole in those days), and the 777 and 787. Each type of fiber and the various ply layups with the resin matrix's provided different strength characteristics, to be used in different sections of the aircraft.

One very nice thing about at least the carbon fiber layups is that they basically have no fatigue problems, even when heavily damaged, as fatigue tests we ran clearly showed. The material did not crack and the damaged areas didn't grow in size over several fatigue lifetime tests of the structure. Also is great that it does not corrode. Kevlar was good, but the fiber could shrink slightly in the cured matrix, allowing moisture to get in, reducing the strength a little. Kevlar was commonly used in high performance sails, sans matrix, just as cloth. S type glass, et al, was not used in the work we did.

Meanwhile, back to the assumed oil pressure problem...

Using mech gauge, I'd like to see a curve of pressure vs rpm , idle to 5k, hot oil.
 
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