Apparent Water Condensation In Diesel Fuel System - 2008 D4D

May 13, 2014

hi,

Short version: I seem to get water condensing in my fuel tank or thereabouts when it is rainy and cold, and my 2008 Verso D4D is due for 80K service shortly so interested in things I might have checked at that time.

Details:

I would say that this has happened since I bought the car around 2.5 years ago, but has definitely gotten worse over time. Normally I would tend to run the tank down to 1/8th or so before filling up, but over this past winter I had to change to trying to keep it above 3/4 to alleviate the problem - and this works. I also note that I tend to fill the tank to the top, including letting the foam die down and adding more.

It seems very much like water is condensing inside the tank and when I fill it this washes the water off and into the fuel. I have had two occasions of limping down the shoulder of the M25 unable to get over 40 mph immediately after filling the tank. On these events I put in fuel dryer and it solved the problem, when it is not that bad I find that it 'burns through' after a few days (time to use perhaps the top 1/8th of tank or so) and performance returns to normal. The problem only develops after filling the tank, and doesn't happen when the weather is warm and dry. Things were going well during the spring, but just filled up during the recent rainy spell and it is 'lumpy' again.

As noted the 80K service is coming up, the dealer ever so kindly did the engine swap for me at 60K. At the 70K service I asked them about these problems and was told there is some system to collect out water in the fuel and that if this over-fills I will get a warning light on the dash (never seen such a warning). Had them connect up and scan the diagnostic system and it showed no issues in the log.

I can't say I have been able to check every time but on the last few tank fills I have listened when opening the cap and hear the 'swish' of air influx when the seal is opened. I now make an extra point to close the fuel cap to where it clicks a few times, and I make sure the 'cap retainer' plastic lead fits nicely around the cap and does not get in the way of the outer flap (this doesn't seem to make any difference).

It seems clear that the rest of the diesel using world does not have this problem, with the possible exception of boat owners where I found the hint about keeping the tank full all the time. I have a decent auto mechanics background if anyone has some technical diagrams to point me at for parts that might be going wrong, but don't have any knowledge of specific diesel fuel tank components that might address this.

I am interested in any thoughts, comments or suggestions you may have.

rob.

May 13, 2014

One area to look at is the fuel you are using. Supermarket fuel contains a higher proportion of Bio diesel that produces a higher level of water that the fuel of pre bio days. Try filling with a premium fuel and see whether the problem persists or is reduced.

Incidentally, in winter with very low temperatures, made worse by snow lying on the roads so chilling the fuel tank more, Supermarket Bio fuel that may contain hygroscopic contaminants, makes it more prone to waxing and so choking the fuel filter.

I understood that T was introducing a new design filter to combat this problem. Has it arrived yet?

May 13, 2014

Biodiesel isn't that much worse than normal diesel for water so I doubt that would cause this.

Are you sure it's water that is the problem?

Diesel fuel tanks can suffer from water contamination, but even if it gets mixed in with the fuel it should mostly get trapped by the fuel filter (Good point, get that checked and drained/replaced if need be! In fact, if it's never been changed, would be a good time to change it!).

The biggest problem with diesel tanks and water is usually not the water itself, but the microbes that can grow in a layer between the diesel and the water. Petrol is pretty toxic to such microbes but diesel is more tasty so it can grow if a tank is rarely brimmed and enough condensation forms to create this diesel/water layer.

Normally the crud floats on the top, but it can get sucked into the fuel system if the tank is run low and it also gets churned up when fuel is pumped into it and I have a feeling this is why you're getting this problem when you refuel.

You can get additives which breakdown all the microbes but it may take a few tanks worth to completely flush it all out if it's pretty bad, and you'll probably need a new fuel filter (Don't worry, even the proper Toyota ones are dead cheap for diesel cars).

I don't know if there is such thing as a fuel tank drain/flush to try and get it out faster tho'...

The tip for always brimming a diesel tank when you refuel is a good one tho' as it minimizes the amount of air and water vapour that can hang around in the tank (Also makes calculating mpg's easier :D). Also is a good idea if the car is going to be left standing for extended periods.

May 14, 2014

I do generally buy fuel at Sainsbury's or Tesco's, but last time was at Texaco -- and seems like the public would get pretty excited if the other customers had occasional 40 mph on the motorway experiences like mine.

No I'm not sure it is water contamination, but it is definitely tied to filling the tank when the weather has been cold/wet/humid -- times when I might see condensation on windows around the house.

I was going to say that of course Toyota changes the fuel filter regularly but just checked the receipts and can't actually see a charge. Also says to replace every 40K miles or 6 years (got the car at 36k) so will definitely highlight that for the upcoming 80K service.

I had not heard about microbes being an issue, looking for additives I see that the "Wynn's Fuel Dry" that I've been using from Halford's claims to 'prevent the growth of bacteria' -- perhaps I shall put that spare bottle I have in when it gets to the last 1/2 tank before the service.

Still, seems like this (fuel filter) should be a problem year-round instead of just when it is cold and wet? Maybe under the cold/wet conditions I am overloading a reduced capacity of the filter to keep the water out?

Also, seems like if it is related to churn that it would get better by leaving the car to sit over night? That doesn't seem to be the case, seems like regardless of timing I have to burn through a few days of commuting to get it back to normal.

One other thing that does seem to help is turning the car off for a minute or so, after that it seems like I can get up to a higher speed initially before it starts going bad again. As if there is some circuit that water (?) collects in that gets blown out empty when starting....

thanks for the comments so far, happy to hear any more thoughts!