The Mystery of the Ford Focus
Losing Coolant

This is one of the most deceptive faults you'll come across on a Ford Focus petrol. The car loses coolant steadily, there are no visible leaks anywhere, and the only other clue is a very brief misfire on cold start that disappears almost immediately. Many owners - and some garages - miss this entirely.

The culprit is usually a failed head gasket or, more commonly on Fords, a cracked water jacket in the engine block - allowing coolant to seep into the cylinders. Here's how to diagnose it properly.

Tools You'll Need

Step-by-Step Diagnosis

01

Check & Rule Out the Obvious

Before going deep, do a full visual inspection of all coolant hoses, the radiator, water pump, and heater matrix connections. Check underneath the car after it's been parked overnight for any drips. If everything looks dry - that's actually your first big clue.

02

Note the Cold Start Misfire

Start the car from cold and listen carefully. A brief stumble or misfire that disappears within 5–10 seconds is a tell-tale sign that coolant has pooled in one or more cylinders overnight. Once the engine fires it off, the misfire clears - which is why so many people dismiss it.

Pro Tip: If you have a diagnostic tool, check live data or stored misfires. You may see a misfire count on cylinder 3 or 4, which are most commonly affected on the Focus.

03

Pressurise the Cooling System

With the engine cold, remove the coolant cap and attach a coolant pressure tester. Pump it up to around 1.0–1.2 bar (the standard pressure for most Ford Focus systems). Leave it pressurised and watch the gauge - if it drops, you have a leak somewhere even if you can't see it.

Pro Tip: Keep the system pressurised for the next step - this is what forces the coolant out and makes it visible.

04

Remove the Spark Plugs & Use a Borescope

With the system still under pressure, remove all four spark plugs. Insert a borescope (endoscope camera) down each cylinder and inspect the walls carefully. With the coolant system pressurised, you should be able to see coolant actively seeping or weeping into the cylinder - most often it will appear on the cylinder walls as a wet patch or small droplets forming.

Pro Tip: Do this in a darkened area if possible - the borescope light makes wet patches much more visible.

05

Identify the Source - Head Gasket or Cracked Block?

If water is seeping in, you now need to determine where it's coming from. On Ford Focus petrol engines, a cracked water jacket in the block is surprisingly common and can look almost identical to a head gasket failure. A cracked block is more serious - a head gasket can be replaced relatively straightforwardly, but a cracked block typically means the engine needs replacing.

Pro Tip: A combustion leak tester (block tester / sniff test) on the coolant reservoir can help confirm combustion gases in the coolant, which points more towards a head gasket. However, a cracked water jacket can also cause this.

06

Confirm & Advise the Customer

Once you've confirmed coolant ingress into the cylinders, the vehicle should not be driven until repaired. Present the customer with the findings and explain the two possible causes. In many cases on older Ford Focus models, given the cost of a replacement engine vs the car's value, this can be a write-off decision - be honest with the customer upfront.