by David Finlay (23 Feb 06)

I like to do my bit for the environment whenever possible, and as my friends will tell you I'm always on the lookout for a bargain, so I was intrigued by an offer made last year by the Green Solutions Trading Company. Green Solutions markets the Unicat4 fuel additive, which has been on sale in Canada for the past 30 years but has only recently arrived in the UK, and according to Managing Director Paul Davey it's "a more efficient option than using branded premium fuels.

"Because an engine's combustion cycle isn't 100% fuel-efficient, a small percentage of fuel is always lost unburned at the exhaust stage. Unicat4 improves the combustion of hydrocarbon molecules, the largest of which would only be partially burned without treatment."

So that's the science. What are the effects? According to Green Solutions, a car using Unicat4 will use less fuel - one customer is quoted as having gained 105 miles per tankful from the moment he started using the additive - and perform better in exhaust emissions tests. Engine performance will also improve.

But I wasn't being asked to take anyone's word for it. Green Solutions sent me two bottles (one for petrol engines, the other for diesel) and invited me to try the product for myself. Realistically, there was only one way for doing this. I drive a different test car every week, but never for long enough to check fuel economy over several refills, and anyway they don't belong to me.

However, as you'll know if you've read my previous articles (In Praise Of Cheap Old Cars and The Cavalier Lives On), what does belong to me is a 1993 Vauxhall Cavalier 1.6 Envoy. It was immediately nominated as the test bed for the project to establish how well Unicat4 works, if it works at all.

Green Solutions urged me to put the car through an exhaust emissions test before and after using the additive, but I must admit I didn't get round to doing that. Nor did I make any effort to see if the engine was producing more power. The Cavalier is getting on a bit and I don't fancy checking the 0-62mph time, or holding it at full throttle on a dynamometer for several minutes, in case something explodes or falls off. I would have to say, though, that if its power output actually did improve during the 3362 miles of this test, it wasn't by enough for me to notice it.

Checking the fuel consumption was simple enough for me to be able to do it and easy enough for the car to survive it, so I did that instead. And quite methodically, if I may say so. I did not consciously drive the car any differently whether or not there was any Unicat4 in the tank, and I tried to make sure that every tankful included roughly the same proportions of city, rural and motorway driving. I even went to the trouble of establishing a baseline by measuring the economy for three tankfuls before trying the additive.

The first reading was 37.5mpg, the second 39.0mpg - close enough. The third was more disappointing, at 35.2mpg, and it took a while to find the reason for that. What had happened was that I had left the car sitting in cold conditions for a fortnight, and the right rear brake had locked on. It did not fully release until the time came for an MOT check a few weeks later, though the effect was so slight that it made no noticeable difference to the car's behaviour, except in terms of fuel consumption.

It was after this that, but before I knew what the problem was, that I started using Unicat4. I was slightly alarmed by the extra fuel use at the time, but it's now clear that things were not as bad as they seemed. Over the next two tankfuls the Cavalier returned 35.1mpg and 34.3mpg, a performance which isn't worth comparing with the original figures. More significantly, however, it was worse than the car had managed with the brake problem and with untreated fuel.

Before the brakes were fixed I tried one more run without the additive and found an improvement to 35.6mpg. So far it wasn't looking good. Unicat4 is quite cheap - a 946ml bottle, which contains enough juice to treat over 1500 litres of petrol, costs just £27.49 - but that's not much of a consolation if it makes the car more expensive to run.

It didn't seem fair to leave it at that, though, and as soon as the brakes were fixed and the Cavalier was issued with a new MOT certificate I was able to try out a new test. On two consecutive days I had to make 410-mile trips between Slough and Glasgow, driving on exactly the same roads - and at exactly the same time of day, so traffic conditions were comparable. I filled the Cavalier's tank at one service station before I left, filled it again halfway through the combined journey and filled it for a third time at a service station literally across the road from the first one. Outward-bound, I didn't use the additive, and on the way back I did. How much closer a comparison do you want?

If Unicat4 worked, at least in terms of fuel economy, I would have used several litres less on the second trip than on the first. In fact, I used 0.17 litres more, which can be explained by the fact that I got slightly lost on the way back and travelled an extra 1.7 miles. The fuel economy was exactly the same in each direction, at 37.8mpg.

So Unicat4 makes no difference? Well, not exactly, because the weather was quite different on the two days. While I was driving on untreated petrol, the Cavalier was being pounded by rain for hours on end, and I must have spent 150 miles steering into a crosswind. Using the additive, I drove in much better conditions. All other things being equal (which, as far as could be managed, they were), the car should have used a lot less fuel on day two even without the supposed benefits of Unicat4.

Well, that convinced me. Unicat4 had had a fair trial in several months of testing. Every time I put it in the tank, the car's fuel economy either deteriorated or stayed the same when it should have become better. Whether or not the exhaust emissions improved I don't know, though the CO2 level must have gone up since more fuel was used. I'm fairly convinced that the stuff wasn't doing any damage, since the economy improved immediately as soon as I stopped using it. But that doesn't make me any happier about the extra money I spent on petrol.

I'm left with one problem. I still have some Unicat4 left, and there's a full bottle of the diesel additive I haven't even opened yet. I'm not sure how to dispose of any of it safely, but I do know I'm not going to put another drop in my car.

Back to Technical Features index
Back to main Features index