JB and all,
I'm not sure I would prefer hypothesis to actual fact. There are many valid comments being made and any number of them could prove to be correct. However, manufacturers are not going to recommend long interval oil changes if indeed it will result in engines expiring before they are out of warranty. And given that cars are doing over 100,000 before needing to have chains and tensioners replaced, it just doesn't seem to fit? I have just checked with Alfa for the cost of the oil pump and that I can only conclude is the two "Sprockets" for want of a better word, meaning the internals which sit inside the housing on the end of the crank. They quote a price of £292-48 p. Given Alfa's pricing policy, or lack of one, this seems like a service item. It is true, the pump is passing previously circulated oil, back into the galleries, via the filter and oil cooler. So in this regard, there is merit in an earlier observation it may seem like grinding paste to the oil pump. And thus require changing when indeed the chains, guides and tensioners are done.
But to define where the problem lies in the system, the oil pressure needs to be checked. The point to check this is at the entry to the block, after the oil filter and cooler, where the current oil pressure switch is;quoted as£139-80 p. Given I have not as yet had an indication that the pressure is low, I make the broad assumption, it is Ok~. But, still I'm not comfortable with this, which is why I shall be fitting a oil pressure gauge along side the pressure switch. That will establish whether or not the oil pump has deteriorated. On the assumption it is Ok~, and my engine has; it is believed, used the specified grade oil, fair wear and tear on the chains, guides and tensioners are not unreasonable at 100,000 miles.
Which leads one back to poor build quality of some engines. Although that tensioner which JB, used as an illustration of gasket failure, was not actually from an Alfa Engine, it clearly is a weak spot and should not be discounted.
These oils are used throughout the automotive industry so their should be some degree of confidence in them. But, just supposing there is an issue with them, it makes sense to eliminate all other factors first. And for me, it's the mechanical interfacing: pump, oil cooler, pressure release valve, guides and tensioners. Even to the extent checking the variable valve timing; the Voids inside the cam shaft advance/retard mechanism are large and are fed from the same galleries as the tensioners.
These Voids are capacious, and there are four of them! The more enthusiastic a motorist is;working the gearbox and throttle, could substantially lead to quite a reduction in gallery pressure, more so than with a more conservative driver. One has to bear in mind, each cam shaft Advance Void has to be filled, while the Retard Void is drained. And equally, the Retard Void has to be filled, whilst the Advance Void is drained. The timing on the cam shafts is continuous, but the "Duty Cycle" for this will be wholly dependent upon the style of driving adopted by the man in the drivers seat.
I'm more than a little suspicious, this is where the problem lies. It would be a good exercise to look at the pressure in the galleries and how they vary between the sporting driver and the "plodder" - for want of a better word. In this instance, there could be a case for permanent electric oil pressure supplementation.
But it is also true to say, if the cam shaft advance and retard were constant, then the upper timing chains would be starved. This however does not appear to be an issue, so no one, so far can be accused of being that boring a driver!
It has always been a puzzle as to why, the Alfa Romeo 3.2 Brera an 159 Engine has never met its stated consumption figures. It is only when one examines the “E-learn Disc” which was kindly given to me by a friend, it starts to appear obvious.
The 3.2 engine is a variant of the GM-Holden; modified, as is the usual practice of Alfa Romeo. In doing so, they try to maintain the myth that has sprung up around this once great company. I believe Henry Royce said, “Take the best design and make it better”. Thus initially Rolls Royce used American V8 engines. That Alfa can produce performance*engines on a shoestring*for mass production is a myth and can never be achieved by*“Tinkering around the edges”.
So why do I believe Alfa got this wrong and in what area(s)?
Variable valve Timing.
Anecdotally it is said the V.V.T. sensing is taken from all four cam shafts. Whilst I believe this is probably true of performance car manufacturers such as Ferrari, Lamborghini and Porsche, I do not think this is the case with the 3.2l Alfa engine. To do so would require a much more sophisticated E.C.U. as sampling rates would need to be four times faster and the potential for timing errors would increase dramatically. It would require a much faster E.C.U. program and to take advantage of this the sensor signals, would also need to be proportionally increased. This; the author believes, would be too expensive for what essentially is a mass production unit and disastrous with respect to vehicle warranties. So the preposition of this thesis is that timing signals are taken from a single cam shaft, notably one Inlet Cam shaft.
Given there are three detonations per revolution of the engine this would seem reasonable as it is the load on the engine, which dictates the advance or retard of the timing. This in itself being dependent upon throttle, cruise control and terrain. Plus, there is “Anti-Knock” sensing; common to the engine as a whole, which ensures camshaft advance is never so extreme as to cause continuous pre-detonation.
The load on any one cylinder is immediately reflected by a changing rate of pulses on the one cam shaft that is determining the advance/retard of the cam shafts, given they are linked by the timing chains.
“To minimize engine wear and maintain specific power output it is implicit that oil pressure is maintained universally around the engine and that the pressure is constant at all points in the engine”.
Whilst it is true various components; depending upon their load characteristics, can operate at different pressures with respect to one another, it is however of paramount importance that all similar devices share a common oil pressure.
In this regard, we can specify the oil pressure to each cam shaft advance/retard mechanism. Clearly from the diagram below, this is not the case. The degree of advance/retard is dictated by the E.C.U, but the rate of advance is specific to the rate of “Fill” of the cam shaft voids and by definition “Oil Pressure”. Whatever bank inlet cam shaft is responsible for the timing: it is thought to be the left, the “Fill” rate for the left will be different than the right. Assuming it is the left hand bank inlet cam shaft, when the E.C.U. is satisfied with the advance/retard and the V.V.T. is “Set”, the right hand bank cam shafts; in terms of advance/retard, is not going to correlate with the left.
This error will amount to a loss of specific power output and consequentially, is detrimental to fuel economy. The data provided by Alfa Romeo states the extra urban economy is 33 MPG. I personally average 25 MPG. This is a whopping loss of 24% It seems impossible to improve on this figure on long journeys, no matter how the car is driven. Both advance and retard are determined by oil pressure and thus there is an innate timing error as a consequence of the unbalanced oil pressure in the supply galleries. This alone could account for some considerable loss in economy.
Fundamentally, the oil pressure for the left bank is derived from a “Tributary Gallery”, whilst that of the right hand bank is from the “Arterial Gallery”
The arterial gallery clearly supplies the crank shaft and journal bearings as well as the right hand bank cylinder head. The demand for oil by these components is considerable and place the greatest demand upon the oil pump. Essentially the entire left hand bank has an oil supply no greater than that of one of the oil ways for right hand bank's advance/retard mechanism!!!
It Gets Worse!
Lower Timing Chain Tensioner.
From the above drawing, it it is clear a fixed guide is attached to the Oil Pressure Pump, item 3. Item 2b is the lower timing chain fixed upper guide. However, the Item denoted by 1a and 1b is the Lower Timing Chain Hydraulic Tensioner.
The oil pressure for this tensioner is derived from the Left Hand Bank's Tributary Gallery!!!!
It should not therefore come as a surprise, the consequences of these fundamental engineering failings, results in lower timing chain stretch, guide and tensioner wear, due to oil starvation. Demand for oil by the lower timing chain tensioner further exacerbates V.V.T. errors, the consequences of which are lower economy than that as stated by the manufacturer and poor acceleration.