Science behind my heating oil 'waxing'?

[kentvegplot]

Central heating has been playing silly beggars since last week - it turns itself off after about an hour, because no oil is getting through. Spoken to my heating engineer, who explained that the oil is going waxy and clogging the filter because of the cold weather. (He's been out to look at it, and confirmed this is the problem)

When I politely pointed out that we had it much colder earlier this year, he said the problem is the difference between the tank temperature (which apparently is still relatively warm) and the temp outside. As the oil goes out through the narrow pipe, it will start to freeze at only -2, whereas if the tank was already properly cold, it wouldn't freeze until -8.

What this means is that, in the midst of all this freezing weather, we have heating for about an hour, then have to wait about an hour (after pouring hot water over the pipe where the filter is) before we get about another hour. Needless to say, it's hard to keep warm like that (that goodness we still have a woodburner in one room).

But I'm struggling to understand this explanation of the problem - can someone please explain the science behind this ??

Thanks

[scarey55]

Very interesting!
I have a friend who tells me that she always wakes up to a cold house because the heating has gone off sometime in the night. They have tried everything that they can think of but I don't think they have heard of this.
Sorry I can't help you with your question but I'll pass this on to my friend - perhaps it will help her, thank you.

[Glutton4...]

I can't help with the science, but if you lag your tank, and the exposed parts of the pipe it may help. In cold countries, Lorry and Bus operators get round this by having a heater in the system, I think. You can also buy an anti-waxing agent for adding to the vehicles' tanks. I guess it could be worth a morning on Google, to see what you can find. Good luck!

[SarzWix]

Perhaps it's something like condensation? Which only happens when warm meets cold. If it was cold meeting cold it wouldn't do the condensation thing?

[bishop]

think he must mean the sudden drop in temperature from a warm tank to -2 is enough to start the waxing process, though oil and diesel uassually remains ok till -9.5 that is the temperature that it starts to go cloudy and leaves a waxy deposit that as you say gradually blocks the filter . putting an additive in will stop this, they use additives in allaska that keeps oil systems and diesel ok to -52.
oil and diesel will not freeze to a solid nature can not get cold enough to do this,

[PAULW]

I had this problem driving a lorry back in 1980, the diesel was waxing up as I drove along causing the lorry to stop running I had to get out, tip the cab forward and then pump fuel towards the engine, there is a winter diesel that has an aditive to prevent this happening the other thing someone came out with was to put a gallon of petrol in the tank of diesel the reason is petrol is a spirit and has a much lower freezing point and this will help prevent it from jelling.

[pigletwillie]

We get it at work when hot oil burners filters clog up, we just take the filters out until it hets warmer other wise they go off. The filters look like they are full of diesel jelly.

It goes when it warms up but if you take out your filter it will cure your problem. Put it back in when it warms up a bit.

[Snadger]

At one time lorry/tractor drivers used to put a paraffin heater under the diesel tank on cold nights!

[Aberdeenplotter]

the science is simple. The liquid becomes viscous(thick) and won't flow. If it gets really really cold, it will solidify. Farm diesel now normally comes with an anti freeze agent added to prevent problems

[Hilary B]

No I don't get the 'science' on this. As far as I have ever known, freezing point is freezing point, but hydro-carbons (the main constituent of all things which start from crude oil) are a bit of a law unto themselves in such things.I would think it is the FILTER which is too cold. If you can find a way of warming that, or do without a filter for a while, it may solve things.

[Aberdeenplotter]

If you can't understand the science, melt a candle totally and see how the wax is quite mobile. then see how the was doesn't run about so well as it cools. Same principle with your heating oil. Also think of the lava spewing from a volcano and how it runs quite well when hot and see what happens when it gets cold. Bit more dramatic but same effect

[Two_Sheds]

my heating engineer... explained that the oil is going waxy and clogging the filter because of the cold weather.

Perhaps you should only run your central heating in warm weather then

[kentvegplot]

TS - that's what I thought too

It's not that I don't understand the principle of the oil thickening as it gets colder (I do have a pretty good science background) but it was the explanation I had that the warm oil is effectively starting to crystallise that puzzled me.

In desperation, I asked a teenager (my stepson). He explained that sudden cooling (such as warm oil suddenly hitting very cold narrow pipes) means that the oil doesn't go through the usual slow process of thickening, but starts to form crystals (like the 'snow' in a snow globe, I gather). This then blocks the filter.

I do like the idea of maybe removing the filter in extreme weather (or perhaps one of them - we've two between our tank and the boiler itself). In the meantime of course, we've had a thaw and the CH is behaving itself.....

[Hilary B]

If you can't understand the science, melt a candle totally and see how the wax is quite mobile. then see how the was doesn't run about so well as it cools. Same principle with your heating oil. Also think of the lava spewing from a volcano and how it runs quite well when hot and see what happens when it gets cold. Bit more dramatic but same effect

That does not explain why it goes thick at varied temperature depending on such things as difference between tank temp and pipe temp. Most things have a temperature at which they go from solid to liquid (or vice-versa). Hydrocarbons and their derivatives do tend to make the change more gradually than some other substances, but even so, the actual 'setting point' tends to be a characteristic of the substance.

[Capsid]

Isn't it simply explained by the oil cooling rapidly as it goes through the pipe? There is a bigger surface area to volume n the pipes compared to the tank.