451 CDI Oil Change

451 Diesel Oil Change (45bhp & 54bhp)

Changing the oil on a diesel smart isn’t like most other cars. You can’t just undo the sump plug and let it all drain out, the main reason is because it doesn’t have a sump plug.

You have to adopt the same service technique as used in boats, the oil is sucked out through the dip stick tube.

Important Info

If you have a 54bhp 451 CDI, you must use the correct oil, see here.

The Pump

I opted for the Pela 6000 which, for £30 + delivery, is well worth the outlay. Pela 6000: Link 1   Link 2   Link 3  Link 4
It comes with its own graduated catch tank and doesn’t require constant pumping unlike the smaller hand pumps. The box is compact on delivery.

Inside the box you get everything you need to start straight away. First it needs assembling. Screw the T handle onto the piston, push the piston onto the top of the catch tank and push the tube connection onto the remaining connection.

This is what the completed pump looks like.

The tube that sucks the oil out is a 2 stage pipe. The interference fit connection joins to a standard PVC hose which then connects to the sprung pipe.

The metal reinforcement gives the pipe enough ridgidity to be pushed down the dip stick tube and maintain straightness when it enters the engine.

Once the oil has been removed from the engine it is stored in the main tank. The tube connection can be removed and a spout connection can be added. This makes it a lot easier to put the old oil into a container. Do not (get caught) put it it down the drain as it poisons the waterways even more than the industries do already.

The neat touch on the Pela 6000 is the graduated tank. This shows how much oil you have removed from the car so it’s immediately obvious if there is any left in the engine.

Before You Start

Go for a drive to warm the car up to 3 blobs, park on a level surface and check the oil level. This will just give you a good indication of how much oil you have to remove.

Check with your owners manual for 600cc, 800cc and Roadster engines. 700cc For2 engines require about 3 litres of oil which is halfway between min and max on the dipstick. How much you put in is obviously affected by the amount you get out. You won’t get all of the old oil out so go for 3 litres and adjust from there.

Changing The Oil

The photo below shows the 54bhp diesel engine but this method is the same for the 45bhp model too.
As you stand looking at the engine, look to the right, you’ll see the oil cap and the dip stick.

Remove the dip stick…

…and remove the oil cap.

Construct the pump and push the tube into the dipstick hole (circled red). When it touches the bottom of the engine you will feel resistance. Pump the handle on the Pela 6000 twenty times and leave it. The vacuum in the catch tank automatically draws the oil from the engine, keep an eye on the graduations on the side of the tank. If it stops sucking oil, pump it another twenty times.

Eventually you will hear a slurping sound as the oil in the engine comes down to its minimum level. Check the graduations on the tank and see if you are close to the amount you should be removing. If not, jiggle the hose in the engine and try again.

It is possible to get out almost all of the oil but expect to leave about 0.1 of a litre in the engine due to the shape of the sump and the site of the pump hose. Jacking up the nearside front of the car can help the oil pool near the base of the dip stick.

The Filter

If you crouch down and look under the back of the car you will see a black dome with a hexagon head just behind the exhaust in the centre.

You will need something to catch a small amount of oil. I have used a paint tray but a take away container or your Mum’s wedding dress will be fine. Get the 27mm socket and ratchet and undo it (anticlockwise) until it comes off.

The original filter can be pulled from the dome and a new one slotted in. The dome can then be replaced and tightened until it is fully in place.
Smart recommend 25Nm (it’s imprinted on the cap) but this seems quite high to me.

Oil Capacity

Engine oil capacities are all listed here.

Oil Specification

If you are doing an oil change on a 45bhp CDI, you can choose from these oils.
If you are doing an oil change on a 54bhp CDI, you can choose from these oils.

The 54bhp CDI has a DPF (diesel particulate filter) which requires oil with low sulphated ash, phosphorous and sulphur. If you don’t use the correct oil on your 54bhp CDI, it will block the DPF and cost a lot of money to fix.