Land Rovers and unleaded fuel



One of the most common questions that seems to be asked on Land Rover Forums is along the lines, "I've just bought an old Land Rover, will it run on unleaded petrol?"  Hopefully this guide will help answer that question.

A bit of background:  tetra-ethyl lead first started to be used as a petrol additive in the early 1920s.  It was used as an octane booster, allowing the use of higher compression ratios for more power and greater efficiency. However, it turned out to have a useful side-effect as it formed a microscopic protective layer of lead oxide on exhaust valve seats and guides.  Manufacturers realised that they no longer had to use hardened valve seat inserts to prevent the valves recessing into an iron head, but could simply machine the valve seats straight into the soft iron and rely on the leaded fuel to protect them.

By the late 1960s a less useful side-effect of lead in petrol was emerging.  In built up areas with high traffic density, studies indicated a build-up of lead in the atmosphere.  As a result, leaded fuel was gradually phased out in the UK from the end of the 1980s, until it was finally withdrawn from sale altogether (apart from a very small number of garages) in around 2000.  Until the mid 1980s most manufacturers, including Land Rover, continued to make iron-headed engines that relied on leaded petrol to protect the exhaust valve seats.  As it became clear that lead would be phased out, manufacturers started fitting hardened valve seats and guides which did not need the protection of lead.

For older vehicles a number of solutions to the phasing out of leaded fuel were marketed.  Many specialists started offering reconditioned cylinder heads fitted with hardened valve seats.  Fuel additives were made available which protected the valve seats in the same way as tetra-ethyl lead.  The fuel companies themselves started to sell Lead Replacement Petrol (LRP) which used these same additives (although LRP has now pretty much vanished due to falling demand).  And finally an assortment of crooks, charlatans and snake oil salesmen offered magical devices which claimed to allow any engine to run on unleaded.  Some of them were plumbed into the fuel line, others dropped into the tank. Many are still on sale today. None of them are backed by any scientific data to show that they work, so beware of anyone trying to sell you a 'fuel catalyst' or similar.  You might as well tie a lucky rabbit's foot to your carburettor - it is just as likely to protect your valve seats.


What are the main issues with running older engines on unleaded?

The main problem will be valve seat recession.  On an engine with soft valve seats running on unleaded, every time each exhaust valve closes it momentarily sticks to the valve seat ('micro-welding'). The next time it opens, a tiny fragment of valve seat is torn away.  Gradually this process allows the valves to eat into the cylinder head.  The valve clearances close up until the valves are no longer closing properly.  This reduces compression and increases the temperature of the valve head and seat which accelerates the erosion process and increases the risk of the valve head cracking.  Eventually compression in one cylinder falls to the point where  it is too low for combustion to take place.  The engine will drop onto three cylinders giving a regular misfire. A compression test will reveal problems at a fairly early stage - on a 2.25 engine all four cylinders should be around 135-145 psi, with no more than 5 psi difference between them.  If one cylinder is well down, this indicates either a valve problem or a blown head gasket - either way the head will have to come off.

The lack of lead protection may also cause increased wear to the valve guides resulting in higher oil consumption, but this will not actually stop your engine from running.

Finally, standard unleaded has an octane rating of 95, compared to the old 4-star petrol which was rated 98.  This should not be an issue with most older Land Rovers as they tend to have very low compression ratios to allow the use of poor quality fuels.  But high-compression Rover V8s may need the ignition timing retarded a couple of degrees to run on standard unleaded without 'pinking'.  On super unleaded (97-99 octane) they should be fine.


What about LPG?

LPG (or autogas) creates exactly the same problems with valve seat recession as unleaded fuel.  In fact it poses more of a problem as you cannot put additives in your LPG tank.  There is a device available called 'Flashlube' which feeds a valve lubricating fluid straight into the air intake, but I have no personal experience of how effective it is.


Model by model breakdown

Series I (1.6 and 2.0 IOE engines):  these are an unusual design in that the exhaust valves are set in the block rather than the head.  The information I have on them is limited, but suggests that although the engines are fitted with hardened exhaust valve seats, the valve guides may wear if used with unleaded fuel.  Given the difficulty of working on exhaust valves on this engine and the patchy parts availability I would recommend using a fuel additive, unless you know for certain that the engine has been modified to cope with unleaded.

Series II / IIA and III (2286cc 4-cylinder):  These have cast iron heads and will definitely suffer valve recession if driven far and hard enough.  The lead oxide coating takes some time to wear away (so-called 'lead memory' effect) but it will probably be ten or more years since any of these engines were run on unleaded, so any oxide coating will probably have worn away by now. Quite a few engines will have been fitted with unleaded-compatible replacement cylinder heads, but the majority of 'two and a quarters' will still have their original heads.

Series II / IIA and III (2625cc 6-cylinder):  The six-cylinder IOE engine is a close relative of the engines used in the Series I and the same comments apply.

90/110 (2286cc 4-cylinder): this is basically the same engine as a late Series III and the same comments apply.

90/110 (2495cc 4 cylinder):  finally in 1985 Land Rover fitted hardened valve seats to the 4-cylinder engine.  The 2.5 engine (code 17H) will run quite happily on unleaded.

V8 engines (109V8, 90/110, Range Rover, Disco 1:) these have aluminium heads with hardened seats, and the general consensus is that they will run on unleaded with no problems apart from the 'pinking' mentioned above on high-compression engines.


How can I tell whether my engine has been modified for unleaded?

It is not possible to tell whether an older 4-cylinder engine has been fitted with hardened valve seats just by looking at it from outside.  The only engine fitted with hardened valve seats from the factory was the 2.5, and this has exactly the same head casting as the post-1980 2.25, painted the same colour.  So contrary to myth, if your engine has a later, metric-threaded cylinder head this does NOT mean that it is unleaded-compatible.  So you have three possible approaches:

1. Remove the cylinder head, then remove one of the exhaust valves from the head and see if the head has been fitted with valve seat inserts.  These are usually pretty easy to spot, there will be a slight step where the insert meets the head casting.  You may consider this approach a bit drastic, but if your engine puffs out oil smoke on startup (worn valve stem oil seals), or the head gasket is suspect, that will make the decision a bit easier.  You can assess the condition of the bores and pistons at the same time.

2.  Run the engine on unleaded and monitor the valve clearances.  Valve seat recession will only be a major problem on engines that are worked fairly hard and at high speed.  If you have an old Series II that you just use to potter around on country lanes it will probably run on unleaded for years and years.  Just check the valve clearances every 2000 miles or so, and adjust any valves that are starting to close up.  Eventually you will start to have compression issues as the valve seats become pitted, at which point it will be time for a rebuilt (unleaded-compatible) cylinder head.

3.  Use a fuel additive - costs a little bit more, but if you have an engine that is in A1 condition it would be a shame to risk it for the sake of a few pence per litre.  I recommend Castrol Valvemaster - available from most car accessory shops.

It is worth looking at your old head to see if it has any of the little self-adhesive temperature strips stuck to it.  These are used by reconditioning firms for warranty purposes.  If your engine has been fitted with a reconditioned head any time in the last fifteen years, it will most likely be unleaded-compatible.  Also if you have a black-painted cylinder head on a 3-bearing (light green) block, it is not the original head - 3 bearing heads were painted the same colour as the block.


I don't think my engine is unleaded-compatible.  Should I have it converted?

If your engine is running perfectly and you are happy to tip in some fuel additive every time you fill up, then personally I would not recommend an unleaded conversion at this point.  The time that it makes sense is when the head has to come off anyway - either because the head gasket has failed, or because the engine is burning oil due to worn valve stem oil seals.  Obviously if your engine is already suffering from valve seat recession it makes good sense to have the head converted to unleaded. 

The choice is between buying an exchange reconditioned cylinder head, and having your own head reworked by a machine shop.  If you have a low compression (7:1) head you may wish to replace it with a high compression (8:1) head, which are usually pretty easy to pick up. If you have a very early engine you will be unlikely to find a reconditioned head on the shelf anywhere and will have to have yours reworked.  I have done a fair few of these conversions now, I have a very good local machine shop and will be happy to quote you for the work.  Just give me a ring or email me.