Ask the mechanic: Why has the colour of my coolant changed?

Thursday December 08 2016
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Why has the colour of my coolant changed?

Hi Paul, my BMW 320 E46 engine coolant fluid in the plastic bottle has developed a milky brown colour. My mechanic says it might be engine oil mixing with coolant due to serious damage. What could be the cause?

Phillip, your mechanic has a point, when your engine coolant mixes with oil, it turns to a brown milky colour.
When your engine cylinder head gasket is damaged it can allow engine oil to mix with coolant and cause the symptom you are seeing.
You can confirm this if your engine oil filler cap and engine oil dipstick have traces of engine oil and the engine overheats.
On rare occasions, the coolant - oil mix can be caused by a damaged engine oil cooler. To confirm this, disengage the coolant hose from the engine oil cooler and check for the presence of the milky brown coolant.
For BMWs with automatic transmissions a more likely cause of oil in the engine coolant reservoir is damage of the gearbox cooler which is incorporated in the radiator.
Any further delay to renew radiator coolant will cause corrosion damage of the separating plates causing intrusion of mix of gearbox oil in the engine coolant. In such a situation the engine oil will not be milky brown but the gearbox fluid will be.
Remedial action will include replacing the radiator, flushing the cooling system before replenishing coolant and a gearbox service with a filter and transmission oil change.

Hi Paul, I recently discovered that I have tiny cockroaches in my car. I have sprayed doom but that wasn’t of any help. How can I get rid of them?

Hello, cockroaches are attracted to a dirty environment or food droppings. Whilst I am unable to provide professional advice about stopping the infestation in your car, I will provide some advice. Ultimately you will need a professional fumigator to help you. Make an effort to regularly vacuum clean the interior of your car with particular attention to removing food and snack droppings in all corners and gaps. There are special cockroach bait gels on the market that are applied in very small amounts. These gels do not harm the passengers or leave the car polluted with fumigant for days. The professional fumigators can help. While it is not easy to prevent children from snacking in the car it is important to use trays paper bags to collect droppings. Do not make it a habit to store foods and snacks in the car.

Cause of noise when accelerating

I have a 2.4 litre Toyota Harrier 2002 model which makes a rattling almost grinding noise when I accelerate.
My mechanics have recently overhauled the engine but can’t explain the source of that noise. The engine seems to be under powered too. Please help.


Hello Mugabi, your Toyota Harrier 2AZ-FE petrol engine has a timing chain kit. You must confirm if the timing kit (chain, plastic guides) is not the source of the rattling noise.
If you run the engine and listen carefully you should be able to distinguish whether the noise is from the timing chain system or the valve train.
It is recommended that during an engine overhaul procedure, the technician should consider replacing the timing chain and chain guides especially if the mileage may be higher than 150,000 Kms.
The plastic chain guides will become damaged overtime depending on the quality of lubrication.
The 2AZ-FE Toyota engine in the Harrier is built with a Variable Valve timing kit. It is important to ensure that the oil pump is not damaged and has sufficient oil flow pressure.
The engine oil helps to adjust valve lift profile for better air intake and engine performance.
In the event that the oil pump fails the valve train area will be insufficiently lubricated leading to a rattling noise above the valve train.

Paul Kaganzi (0772316145)