Red and White diesel didn’t mix

[Oily Rag]

My diesel heater has its own 10 litre plastic tank and I check the level by shining a high power torch into the side.
I recently added about 8 litres of red diesel to about 2 litres of white to top it up.
A quick check with the torch showed the red diesel floating above the white. No real mixing. It was the same two days later when I checked.
No real issue here, but I was intrigued. Any thoughts?

 

[harvey38]

Are you sure it is white diesel and not water

 

[WoodyP]

The white is showing cultural bias and refuses to mix.

 

[NormanS]

I'm with harvey on this. My heater runs on Kero from its own tank. On our recent cruise, it was so cold that we ran short of Kero, and topped up the tank with red. Mixed fine. If the clear liquid is not mixing and determined to lie under the red, it would be sensible to take a sample of it, in case it is indeed, water.

 

[Oily Rag]

Thanks Harvey and Norman. I had already drained a small and visible layer of water from the bottom of the white diesel. The usual condensation over the winter. I took out much more than needed.
After adding the red diesel, it took several hours of running the heater to clear the white diesel and make the pre-filter show red.
There was no visible steam on the exhaust, so no appreciable water contamination of the white.
Still puzzled.

 

[Boater Sam]

I would thought that adding the red dye to diesel would increase its specific gravity, not reduce it. Do check its not clear water though!
Perhaps you have old straight diesel and HVO which do have differing SGs
If you are sure it is all fuel, try mixing it but in any case it will all burn eventually.

 

[B27]

Is it one of those tall, slim tanks?
Diffusion can be a slow process in liquids.
E.g. a layer of warm water will sit on top of cooler water for a long time.
If you're mixing 2T fuel and put the oil in last, you need to give it shake or the oil will take days to mix.

OTOH, if the OP has a heater which 'burns water' can we all have one please?

 

[VicS]

I would thought that adding the red dye to diesel would increase its specific gravity, not reduce it. Do check its not clear water though!
Perhaps you have old straight diesel and HVO which do have differing SGs
If you are sure it is all fuel, try mixing it but in any case it will all burn eventually.

I'd have thought that the quantity of red dye and chemical marker is so small as to have no significant effect on the density. Maybe they are added as a solution in a lighter hydrocarbon solvent but I'd doubt that as it might lower the flash point and probably not be in sufficient quantity to make much difference to the density.
There is some natural variation in density.and I guess winter grade diesel is less dense than summer grade

Refueler will explain all if he comes this way.

 

[Refueler]

Depends on source diesel ... not all red are same .... white or ULSD is generally similar spec as it has to meet the legal spec range.

Red can be quite wide ranging as its designed more agricultural use etc. It is also possible that it was Heating oil - BUT then it would have been on bottom not top ..

People think that fuels mix easily - no they do not - they quite often layer ....

We spend extreme effort in our work with fuels - to avoid non homogenous transfers ...