Citroëns and Unleaded Fuel

© Copyright: J.Cats.

Since the early 1930s, most fuels have had lead in them. At first the lead was used as an octane booster and exhaust valve (seat) protector. But after a while the lead was only needed for protecting the exhaust valve and exhaust valve seat. These get very hot and there is a risc of them burning or "sticking" together. The lead in the fuel is used to form a thin layer on these components which protects them from burning and/or sticking.

The octane level is usually denoted by a number in the fuel type (usually in the 85-105 range). The octane reduces the risc of "knocking" and/or "pinking" in the combustion chamber. Pinking sounds as if a small stone is rambling around in an empty sump. The higher the octane level, the better the resistance to knocking. Apart from the octane level, the compression ratio is also highly related to knocking/pinking. As the compression ratio increases, so does the risk of knocking/pinking. Most Citroën engines need 98 or 97 octane. To be certain about your engine, check the owners manual of your car. All flat twin and flat four engines are listed here, all engines suited for 95 octane are specially marked, all others need 98 octane.

In the most of europe, leaded fuel was available with around 98 octane, unleaded with around 98 (super) or 95 (normal) octane. On some engines a decrease in octane level needs a modified ignition timing to keep the engine from pinking. However as long as you stay with the proper octane fuel, (nomatter if it's leaded, lead replacement or unleaded), NO modifications to ignition are needed. Ignition modifications could even harm your engine.

Lead or more specifically the form in which it exists in fuel is very toxic so leaded fuel is being banned. So what happends? All sort of manufactures of strange goodies have jumped on the wagon and started making lead additives or devices which should protect your engine. Everybody seems to have the best product for the protection of your engine, and everybody has a freidn who has tried some sort of device which helps a lot.

Citroën acted as well. In 1983 and 1985 they send out messages stating that all engines produced after 1981, 1983 or 1985 (depending on the message) were safe with unleaded fuel. We mostly deal with Traction Avant and Citroën A-types so in 1998 I went to my local Citroën dealer to ask which 2cv engines were safe and which weren't, and more importantly, how these engines could be indentified. The Citroën guys didn't have a clue. But helpfull as they always are they let me dig through press releases and look at all parts manuals. I found several press releases stating that engines from date such and such onwards were safe for use with unleaded fuel. However, in NO parts manual were differences in valves or cylinder heads found around these dates. Citroën never changed a thing on these engines!


Citroën tested all current engines in the 1980s to see if they were suited for running on unleaded. And most of them were/are. Or, we should say that the additional wear of valves and/or seats wasn't/isn't alarming. And by 1990 the production of the last A-type was stopped so Citroën had nothing to worry about. A few more broken engines would only increase the sale of parts and/or new cars! But they could hardly say that all cars were safe because there was bound to be someone running an original 1961 2cv of which the engine might not be suited for unleaded. So they announced a so called cut-off date, all cars being produced afterwards were safe, all built before that were uncertain. And this is the 1981, 1983 or 1985 date you see in the articles. Some research amongst engine rebuilters and tuners has confirmed these findings.

Running on unleaded fuel
So what can you do to run on unleaded fuel? There are 3 basic options.

  1. Keep going.
    Most cars built after the 1970s seem to have very few problems with unleaded fuel. As long at the proper octane leve for your engine is used, the ignition won't need any modifications. A testimony to this is that most Citroëns (we've tried DS, GS, GSA and CX) run on LPG without any problems. LPG (Liquid Propane Gas) contains no lead or lead replacement. These cars usually do a high anual milages (otherwise the LPG system isn't cost effective).

    Please note that I don't take any responsibility if something goes wrong when you apply this information on your or other cars! As you will probably understand by now, there is always some risc involved.

  2. Use additives.
    There are some good additives available. Red-line and Wynns produce good proven additives. Some additives also provide an octane boost. This means that: 95 octane unleaded + additive = 98 (or more) octane leaded. However, always read the instructions on the bottle carefully before using this stuff! Most additives need to be mixed into the fuel properly and will sink tot he bottom if the car is left standing for a longer period of time. Therefore it is better to store the car with a full tank of unleaded petrol if it will not run for more then a month.

  3. Convert the engine to unleaded.
    This involves replacing the exhaust valves and seats by hardened ones as used in modern engines. Most engine rebuilters only have/use hardened components anyway. For an A-type engine this costs 100-200 euro per cylinderhead, depending on the wear of the head.

We use original unconverted 602cc and 652cc engines with unleaded 98 octane fuel. All of these cars cover more then 20.000km anually. Sofar we've had no problems at all, valve wear is checked regularly and seems neglectable on average. But I've also had some cylinderheads modified with hardened seats and valves. This is very inexpensive (less then a good second hand engine) and you get the opertunity to give your heads a new leash of life.

Common misconceptions and FAQs about unleaded fuel:

Most articles (even in good magazines) seem to be full of errors, usually because people seem to have difficulties seperating OCTANE level and LEAD contents when talking about fuels. So here are some FAQs.

  • When changing from leaded to unleaded fuel, do I have to change the ignition timing?
    No, not as long as the octane levels of both the leaded and the unleaded fuels are the same.
  • With unleaded fuel the engine will start pinking?
    No, not as long as the octane levels of both the leaded and the unleaded fuels are the same.
  • To compensate for pinking, the valve clearances have to be changed?
    No, the only way to compenstate pinking is alter the ignition(timing). But since your using the right octane fuel for your car, it won't pink!
  • What do I have to change the valve clearances for then?
    Changing the valve clearances (making the clearance bigger, especially on the exhaust valve) is SOMETIMES used to prevent the exhaust valve from burning. On some engines (I haven't come across any though) the exhaust valve sits deeper in the cylinder head because of the use of unleaded fuel. If this happends the clearance will be reduced, the exhaust valve will not close completely and this will make the exhuast valve burn. However, the best remedy for this is checking the valve clearances regularly (every 5000km if you want to be absolutly sure).

  • I want to run my car on 95 (or lower) octane fuel (either leaded or unleaded!), is this possible and what do I have to do?
    This is possible, the compression ratio has to be lowered. The compression can be lowered by adding a spacer between the crankcase and the cylinders or the cylinderhead and the cylinder.
    For 95 octane fuel, the compression ratio has to be below 8.0:1, this means a spacer of 0.67mm.
    For 90 octane fuel, the compression ratio has to be below 7.5:1, this means a spacer of 1.44mm.
    For 82 octane fuel, the compression ratio has to be below 7.0:1, this means a spacer of 2.33mm.

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