Fuel filter light; what to do?

If you are driving a vehicle along, and you notice a light comes up on the dash that you aren’t familiar with, you should pull over when safe and investigate. Your owners manual is generally the first place to start, and one of the more common items that can pop up is your fuel filter light.

Believe it or not, but many 4WD log book services do not cover the fuel filter. Isuzu do not change their factory fuel filters until the light comes on, and that’s pretty poor in my opinion.

Regardless, you should be running clean, quality diesel fuel through your engine and that means ensuring your fuel filtration system is in good condition.

Reliable 4WD
If you get a fuel filter light illuminate, what should you do?

What fuel filter lights are there?

In general, you’ll have two fuel filter lights that come on. One is in relation to water in the diesel, which is very, very bad, and can destroy your motor if you don’t get onto it quickly. I’d pull over immediately if you see this, and turn the engine off. Check for water, and treat it as a pretty serious mechanical issue.

Water going into your motor can cause immensely expensive problems (like a full motor replacement), and that’s without the tow to get you to a mechanic!

The other one is related to flow, and comes on when the engine cannot get the flow of fuel that it wants. This is generally from a blocked filter, and if you have an older diesel instead of a light on the dash, you’ll just get no power at all.

We had a 2 micron filter (no idea why, that’s what the previous owner put in) on our 1HDT 80 Series, and the filter blocked up on the way to Jurien Bay (presumably algae) and it would just die at the worst possible times, limiting your speed to what ever fuel you could get through.

A quick carpark stop and a mate who’s a guru with engines and we had a new filter (always carry a spare) installed and it was good as gold.

30 micron pre filter
We always carry a spare primary, and secondary fuel filter now

The fuel filter light comes and goes

If your fuel filter light comes and goes, its due to a lack of flow, and it will almost always come on when you have your foot down a lot. As soon as you back off the throttle the fuel filter light will go away. You are generally OK to keep driving like this and just get the filter replaced as soon as possible, but keep an eye on how often it comes on.

Draining water from your diesel fuel filter

Most diesel fuel filters have a tap at the bottom which you can undo and drain water from, or they might have a bowl that you can remove. Either way, letting water go through your fuel filter and into the engine is not something you want to mess with!

Draining water from fuel
Our Isuzu manual shows how to drain water out of the OEM fuel filter

Do you know what to do if a fuel filter light comes on? If it goes away, I’d probably keep driving, but if it stays on you should pull up ASAP and make sure there’s no water in the filter!

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