Oil So Clean the Customer Said It Hadn't Been Changed: Dave, Banstead Road Garage

A customer came back to Banstead Road Garage after his service and told Dave the oil hadn't been changed. Dave got his phone out, found the CCTV footage and showed him the oil being changed. Then he walked outside and pulled the dipstick. The oil on it was so clean that the customer had simply assumed nobody had touched it.

Dave has worked at the garage for more than twenty years and has run it for about eight. We filmed with him on 6 November 2025, in the workshop on Banstead Road in Carshalton. He hardly needed our questions. Dave had the stories lined up before anyone had finished asking.

Watch the video with the full transcript

A hundred years of cars on Banstead Road

"It's been a garage here for over 100 years," is how Dave opens, before he says a word about himself. The workshop sits on Banstead Road in Carshalton Beeches, and a few streets away, on Stanley Park Road, is the second branch of The Test Station, run by Ricky, whom we filmed the same day. His story is here. It is a busy corner of south London for independent garages, and both of them put TEC 2000 into every service.

Inside it is a working MOT station: yellow two-post lifts, a Fiat 500 on the ramp, a queue of customer cars along the wall and a red tool chest with a rack of TEC 2000 cans built into the side of it. The garage does about 100 services a month. That is roughly five cars a working day, and every one of them gets the same treatment.

What goes into every service

Going by the product instructions, the engine flush goes in first, into the old oil, before anything is drained. With TEC 2000 Engine Flush the engine is warmed to operating temperature, one 375 ml can goes in for every 4 to 5 litres of oil, and the engine idles on it for about fifteen minutes. The flush comes out with the old oil and the old filter, and the fresh oil goes into a cleaner engine. The fuel treatment goes into the tank and is burned with the fuel over the next few hundred miles.

The Oil Booster is for a smaller group of cars, and Dave names them without being asked. Mini and Audi petrol engines from roughly the late 2000s have a reputation in the trade for using oil between services, and most garages have a customer or two who carries a top-up bottle in the boot. Dave's claim for Oil Booster on those cars is a modest one: it helps reduce the amount of oil they burn. He didn't say it fixes them, and anyone who has had the rings out of one of those engines knows the difference.

Two test tubes

Dave remembers how the products came into the garage. There are two Daves in this story, which is worth getting straight. The one telling it runs Banstead Road Garage. The one who walked in with the test tubes was David from TEC 2000 UK, who was standing next to the camera when we filmed.

A glass tube is not an engine. What it showed him was the two products side by side, and on the TEC 2000 tube there was no residue, sludge or dirt on the glass. For someone deciding what to put into his customers' cars, seeing that with his own eyes counted for more than assuming it would work in the engine.

"The oil was so clean he just assumed that it hadn't have been changed."

Dave, Banstead Road Garage

When a car fails its MOT on emissions

The hydrocarbon figure on an MOT emissions printout, HC in parts per million, is a measure of fuel that has gone through the engine without burning. A misfire or a rich mixture will push it up. So will an engine that is breathing its own oil. Old oil that has been diluted with fuel over thousands of short journeys gives off vapour into the crankcase, and the breather system feeds that vapour straight back into the intake, where some of it goes through the engine unburned and turns up at the tailpipe probe.

That is why testers have long known that fresh oil can bring a borderline HC reading down. What Dave describes goes a step further: flush first, so the old oil and what it has been carrying come out with it, then a new filter and new oil. He doesn't put a number on "a lot lower". He does have a car that failed on emissions and passed after exactly that job.

The V8 Jaguar that failed twice

The drive between the two tests is the standard first move with an emissions fail: get the catalytic converter properly hot and try again. It didn't work. The garage's first suggestion to the customer, Dave told us, had been a full service with new spark plugs. They tried the flush, the oil and the filter first, and the car passed.

"Customer left happy knowing that they didn't have to then spend further money on paying for a full service." It is a small story about the order of doing things. The cheap job went first, and in this case the expensive one never had to happen.

A Transit that stung your eyes

Some vans come in and you can smell them before they reach the ramp. Dave had a Ford Transit "that was smoking quite badly, as some of them do", and this time the garage used all three products together: Engine Flush in the oil, a fuel treatment in the tank and a can of Oil Booster.

There is no smoke-meter reading for that one. Anyone who has stood next to a smoking van in a closed workshop will know exactly what he means by it, though, and it was, in his words, "good news for everybody, including the customer."

The customer who didn't believe his oil had been changed

This is the story the video is named after.

A lot of drivers check their oil by colour, and not many realise how light fresh oil can look on the dipstick. When it comes out the colour of honey, they get suspicious. Dave can only think of one explanation for it:

He is not the only mechanic with this story. Sean at Turner Automotive in Twickenham, who trained at Ferrari, had a customer walk out to the forecourt, fail to see any oil on the dipstick and come back to say none had gone in. Sean settled it with a piece of tissue.

Why fresh oil can stay cleaner after a flush

No drain gets all of the old oil out. Some stays behind in the oil cooler, the galleries, the turbocharger feed, the filter housing and the low corners of the sump. There are also deposits on the walls of the engine itself: soft sludge under the rocker cover, varnish in the ring grooves. New oil is full of detergent, and the first thing that detergent does is pick up whatever it finds. In a dirty engine that happens within the first few hundred miles, and the dipstick goes dark.

A flush does two things before the drain. It thins the old oil so more of it runs out, and it takes deposits off the metal so they leave with that oil rather than waiting for the new charge. Simon at Fallsbrook Motors, whom we filmed the next day, sees the first part every time: the oil comes out a lot quicker once the flush is in.

One thing worth knowing for anyone who worries about their own dipstick: dark oil after a service is not proof of a bad job. Diesel oil in particular turns black quickly because it is holding soot in suspension, which is exactly what it is supposed to do. Clean oil after a flush is a sign that less of the old dirt was left behind to darken it. Dark oil on a diesel tells you the oil is working.

Explaining it at the counter

Every garage that puts something extra into a service gets asked what it is. Banstead Road Garage has an answer ready.

When we asked how many cans the garage gets through, his first answer was "at least 100" a month. With a hundred services and a flush in every one, that is easy to believe.

Dave's own summary, from a part of the interview that didn't make it into the film: "I'd say it's a very good product. Cost-effective in the long run for helping your engine perform better."

The products Dave uses

• TEC 2000 Engine Flush. Goes into the old oil before the drain, about fifteen minutes at idle on a warm engine, out with the old oil and filter. In every service at Banstead Road.
• TEC 2000 Fuel System Cleaner for petrol engines and TEC 2000 Diesel System Cleaner for diesels. These are the tank treatments. Dave just says "fuel treatment" and doesn't say which one the garage uses.
• TEC 2000 Oil Booster. Goes into fresh oil after the service, on engines that use oil between services.

Questions drivers ask about this

Why does my oil look so clean after a service?

Because it is new oil, and new oil is amber. If your garage used an engine flush as well, more of the old oil and the deposits that darken new oil came out before the fresh oil went in, so it can stay lighter for longer. It does not mean the oil wasn't changed, and a good garage will be happy to show you, as Dave did.

Can an engine flush help my car pass the MOT emissions test?

On a petrol car with a high hydrocarbon reading and no fault behind it, a flush with a fresh oil and filter change is a cheap first step. Dave's V8 Jaguar, which had failed its emissions test twice, passed after exactly that. It will not cure a misfire, a failed lambda sensor or a dead catalytic converter. Those need diagnosing and fixing.

Is an engine flush safe for my engine?

TEC 2000 Engine Flush is used on petrol, diesel and gas engines of any mileage and is safe for seals, turbochargers and Nikasil-coated bores. It is not for two-stroke engines. Follow the instructions: warm engine, the right dose for the oil capacity, about fifteen minutes at idle, then drain it out with the old oil and fit a new filter.

More from the same trip

This film was shot on 6 November 2025, on a two-day trip round garages in south London and Surrey. Ricky at The Test Station talks about a wet-belt Peugeot with an oil problem other garages hadn't sorted, Simon at Fallsbrook Motors about a VW Crafter whose oil filter came out blocked solid, and Joe at Joe's Repair Shop in Epsom about five years of TEC 2000 in every service.