Engines

Engine variations

The following table provides a quick overlook of the main engine types used in BXs:

All gasoline engines are four-cylinder, aluminum alloy, in-line, overhead camshaft, water cooled engines mounted transversely. The engine type can be found on the engine number and manufacturer's plates.

1124 ccm gasoline engines

A few models exported to Italy and Greece were fitted with engines normally used only in the AX.

1360 ccm gasoline engines

The 150A/150C engines share a common oil system with the gearbox.

1580 ccm gasoline engines

1905 ccm gasoline engines

*

All diesel engines are four-cylinder, aluminum alloy, in-line, overhead camshaft, water cooled engines mounted transversely. The engine type can be found on the engine number and manufacturer's plates.

1769 ccm diesel engines

1905 ccm diesel engines

Engine oils

The primary job of the oil you put into your engine is to stop the various metal surfaces from grinding together, causing rapid wear of the parts. At the same time it has to dissipate the heat generated from friction, to transfer part of the heat of combustion away, to hold the byproducts of the combustion in suspension, not allowing them to stick to the engine parts. The oil has to comply with all these requirements under significant pressure and a wide range of temperatures ranging from the chilled engine in a winter morning to the high temperatures in an operating engine. In addition, it has to retain its performance under these varying circumstances and to remain reasonably stable until the end of the recommended oil change period.

The most significant physical property of an engine oil, viscosity, describes the resistance of the oil to flow. Viscosity decreases as temperature rise. In the engine, the heat produced by the combustion and internal friction results in a thinner (less viscous) fluid. When the film between the mating surfaces is thin, the lubrication is not satisfactory. As the viscosity of the oil decreases because of the rising temperature, the lubricant will be less able to withstand the load, this generates more heat which, in turn, reduce the viscosity even further. Thick films, in contrast, give a stable lubrication: as the temperature rises, the viscosity drops together with the coefficient of friction between the sufaces. This reduces the heat which, in turn, rise the viscosity slightly. Like a feedback, this process stabilizes the thick film between the mating surfaces.

All oils respond with decreasing viscosity to increasing temperature, however, the amount of viscosity change due to a given temperature change depends heavily on the chemical composition of the liquid. The property of resisting changes in viscosity as the temperature changes is called viscosity index (VI); the higher this index, the better the oil resists viscosity changes. A lubricating oil with a low viscosity index would be detrimental in an engine: at low temperatures (cold cranking) the oil would be too viscous for proper circulation while at high temperatures (normal operation) it would thin out to the extent of letting the oil film between the mating metal surfaces break, resulting in severe wear.

Conventional (mineral) oils are mixed from different compounds (fractions) separated from crude oil by progressive boiling and distillation. Low viscosity fractions generally have lower boiling points. When mixed and used in the engine, they retain their boiling point meaning that at higher temperatures in the engine the low viscosity fractions will vaporize, leaving behind the high viscosity components. This prevents the oil from thinning too much as it warms up.

The engine oils contain many other additives such as anti-wear agents, extreme pressure agents (helping the oil hold up between surfaces with high contact stress), anti-rust agents, corrosion inhibitors, detergents and dispersants (to remove dirt and sludge as well as to hold them in suspension), friction modifiers, pour point depressants (to inhibit wax crystal growth at low temperatures; this is important for good cold cranking performance), viscosity index improvers (to rise the VI; these improvers wear out causing both the viscosity index to drop and the improver itself to remain in the oil, to be held in suspension), seal swell agents, anti-foam agents, antioxidants and metal deactivators.

Synthetic oils are manufactured by reacting various organic chemicals together. The basic components are thermally more stable. To achieve the same viscosity index, synthetics require considerably less improver. The base stocks used in synthetic oils have lower pour points, so there's little or no need for pour point depressants.

Contrary to popular belief, synthetic oils are not better than mineral ones as far as their specification is concerned. The advantage of synthetics is that they retain nearly the same quality while they are in your engine, up to the minute of the next oil change. They also can deliver the same performance in a much wider temperature range and they have a much lower tendency to form deposits. The minerals, on the other hand, start to wear out quickly as the improvers wear out and the lower viscosity fractions with lower boiling point start to boil off or oxidize. As a consequence, you should stick to synthetic oil not because of higher but more consistent performance.

As far as the oil manufacturer is concerned, stick to quality brand names. Citroën prefers Total but Castrol, BP, Shell, Aral, Valvoline, Agip or Amsoil are also excellent brands. Synthetics are more expensive than minerals. Their higher production costs make them impractical competitors in the lower product range, hence, synthetics are generally produced to meet the elevated requirements of higher quality engine oils, giving a higher price to start with. The more stable composition of synthetic oils makes it possible to change them less frequently than it is recommended with mineral oils, compensating for the price difference—although this is not necessarily wise, the oil itself might stay stable but the contamination resulting from use will still be present and might warrant the oil change at the recommended intervals.

If you (or a previous user) have been using mineral oil in the engine for years, you can still switch to synthetic without too much trouble, although some people mention that the new oil might dislodge old deposits of the mineral oil, causing minor leaks. Using engine flushing oils can aggravate this problem so it is best avoiding them; just change the oil and the filter.

Oil additives

The advice is plain and simple: never use them! There are many oil additives and so called engine treatments (often sarcastically referred to as snake oils) available on the market but they all share one thing in common: none of them was ever proven to be advantageous, actual tests found quite the contrary more than once. Manufacturers routinely claim that independent laboratories tested their products scientifically but they don't rush to disclose the names of those laboratories or the circumstances under which the tests were conducted.

The most popular oil additive is PTFE: this is the same old Teflon you know from your kitchen. As Teflon is a registered trademark of DuPont Chemical Corporation, oil additive manufacturers have to use a substitute name, the acronym for its real chemical description, polytetrafluoraethylene. DuPont issued an official statement ten years ago stating that "Teflon is not useful as an ingredient in oil additives or oils used for internal combustion engines".

The manufacturers claim that PTFE, present as a suspended solid in the oil additive, coats the moving parts of the engine. However, the reason for having an oil filter in the lubrication system is actually to filter out and retain the suspended solids present in the first place. PTFE particles can therefore clog the filter, reduce the oil pressure in the engine and lead to oil starvation and major engine damage. Some manufacturers claim that their PTFE particles are much smaller than the particle size the oil filter is designed to filter out, but they forget to add that PTFE expands radically when exposed to heat. In consequence, even if the particles were small enough originally, they may not be when the engine reaches its operating temperature. Be sure to avoid any product that says "Shake well before use" on the label: if the solids in the product will settle to the bottom of the container while sitting on the shelf, just imagine what will happen inside your engine...

Another material used in those engine treatments is zinc dialkyldithiophosphate (ZDDP). Unlike PTFE, this additive can be found in virtually every engine oil sold today. It is used as an extreme pressure anti-wear agent which does not come into play unless very extreme conditions like revving over the redline zone are present. Research shows that more zinc does not give more protection but can damage the catalytic converter. The amount of zinc to be found in major brand engine oils is a good compromise between engine and converter protection.

The engine oils on the market contain a wide selection of additives already in the mixture. Many of those additives are carefully selected to achieve an effect in groups of two or more that none of them could attain individually. Adding more additives to this formula, even if nothing more than something that was already included in the package will eventually upset the balance and negate the original effect of the mixture.

When quoting favorable opinions about their products, manufacturers often use testimonials of professional racers or teams. Beware of those testimonials: high performance racing presents substantially different requirements on engines. Some of these oil additives are in fact capable of producing less engine friction, improving gas mileage and engine power. Alas, all these come at a price: reduced engine life. While this is not an important issue in high performance racing where the engines are designed to live a very short life (a few races or even only a single one), you would probably not accept those benefits if you had to pay for them with a complete engine rebuild.

And don't believe in infomercials. It's not too complicated to find people who stare with their mouth wide open and praise any product if you happen to pay them generously. Even seemingly convincing tests like draining the oil from the engine and spraying the crankcase with water are bogus. Water is a good cooling agent and lubricant for the engine so it's no wonder and certainly not attributable to their 'revolutionary breakthrough product' that the engine runs smoothly for some time without trouble. Naturally, you wouldn't want to see what remains of that engine after the shooting... And as independent tests show, a usual engine in normal condition can easily run up to 50–100 kilometers with the oil removed (but, of course, will be completely destroyed in the end), without the need for any wonder oil treatment.

The major oil companies are rich, powerful and aggressive corporations, with significantly more muscle power than independent additive companies. With all their capabilities and resources in research and product development, you can rest assured that if any additional material was really efficient without being harmful, it would have already found its way into the products of those major oil manufacturers a long time ago. In contrast to the unknown laboratories the additive manufacturers claim to endorse their products, well-known independent research laboratories, state universities, major engine manufacturers and the NASA did collect a considerable amount of evidence against the effectiveness of those additives.

Recently, Quaker State, Inc.—the company behind the most widespread engine treatment, Slick 50—had to agree to a settlement with the US Federal Trade Comission which bans them from making certain advertising claims for which they have no factual or scientific background. Manufacturers of other products (eg. Motor Up, Dura Lube, STP and Prolong) also had to pay fines or face legal actions. For more information visit the US Federal Trade Commission and use their search engine to look for "oil additives".

Air and oil filters

Citroën specifies Purflux oil filters but there are other manufacturers producing similar units as well. For the air cleaner element, Citroën specifies Miofiltre, Lautrette and Quillery but only using its part number instead of some manufacturer code.

Some manufacturers produce replacement air filters. Probably the most widely known of them is K&N. These filters let more air flow through them, thereby increasing the performance of the engine. However, they fall behind in collecting dirt and dust particles: this means more damage to the engine in the long run, especially if you use your car in a dusty environment. You have to decide for yourself whether the higher performance is worth the higher risk.

Martin GUTKOWSKI

The best oil filter to use is Purflux. It has a patented internal structure different--and better--than the others. Both Champion and Bosch suffer from the fact that they are manufactured at many plants all around the world. Although the technology is supposed to be the same everywhere, there are significant differences between the quality of those filters. If you can be absolutely sure that your Bosch filter came from Germany or the Champion one from France or Belgium, it's all right. Otherwise, with Purflux (don't mix that with Purolator) you won't take any chances.

Avoid lesser quality filters. I have already lost a camshaft due to a Fiam filter. I bought the filter in good faith at a Citroën dealership and, in spite of a premium quality synthetic Castrol engine oil and more frequent oil changes than recommended, the eighth lobe of the camshaft (the one farthest from the source of lubrication) was gradually eaten away. The lubrication system was checked to see the cause and the filter was the only part found to be guilty.

Washing the engine

Steam and water cleaning older engines with fuel injection is always a little bit risky. Humidity getting into some parts can make re-starting a challenge. Note that we don't speak of permanent damage, only that you'll have to wait or dry those parts with compressed air. If you do this yourself, there's no problem, but at a garage, when other cars queue up behind you, it can be bothersome.

To be on the safe side, wrap the distributor, coil, airflow sensor, throttle position switch and other related parts into plastic bags and don't direct high pressure water flow directly onto them. I use regular cleaning, grease cutting products on the dirtier spots, loads of kitchen paper towels and a common garden hose with a nice, pistol-shaped nozzle. It's easy to aim with, and it can be operated briefly by pushing its valve button for a second or so. I clean my engine once, maybe twice a year, on a warm, sunny spring or fall day, and never ever had any starting problems. To tell you the truth, I also spare the plastic wrapping and take care of where I aim with the water instead (although a little bit of water won't harm the wiring and the connectors, why should we spray them intentionally?). Granted, it's more tedious than going to a non-specialist garage and letting them attack the engine--but a lot safer.

Note that a thin layer of oil, although it might spoil the shiny look of the metallic parts of the engine, does an excellent job of protecting from corrosion. If you wash it off, your engine bay might start to rust. There are special products like Valvoline Engine Guard which form a transparent, invisible protecting film on the surface. You should consider using them after you have cleaned the engine.