# Unleaded in Diesel tank



## carsey (Aug 19, 2006)

Today, filling up we accidently put £6 of unleaded in our car. Thats about 1.5 gallons. The tank was already 1/4 full with diesel before this happened. We rang the tow truck and the guy just said fill it full for a few weeks and the petrol will mix with the diesel.

Any possible damage here??

The car still seems to go as good as it did before, plenty of power. Only thing, it had a tiny bit of trouble starting after it was parked for a hour, took 3 starts but after a hard rev, it was fine.


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## EnglishPaul (Sep 10, 2007)

I always understood diesel to be slightly less refined than petrol, and a less volitile liquid. i.e. squeeze it hard and it will go bang, rather than just introduce a small spark. If petrol is compressed as hard as diesel I believe it also to go bang, although perhaps slightly early. And since the 2 mix, I can't imagine there will be a particularly marked effect. Trust the towtruck, thats my motto.
It might not be a bad idea to get an diesel injector cleaning additive to use after a week or so just incase any residues have built up. My suspicion is that such additives are largly petrol based anyway.
Also the more you fill up at the petrol station, the quicker it will be diluted.

I hope all the Americans out there spotted the £6 for 1.5Gal. You'd think we'd all walk instead, but Britian's not that small!:wink:


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## qldit (Mar 26, 2007)

Good Evening Gentlemen, yes when these kinds of things happen there is no real problem, remember they are mineral and compatible, but with petrol the oil content is virtually nil, if you were worried you could add some standard engine oil to the tank to make up for that discrepancy, but I have operated diesel vehicles on straight kerosene with a slight amount of added oil with no apparent difference for years.

During a fuel shortage years ago one of my friends ran his diesel on straight vegetable oil without any problem, the aroma was out of this world! 
If you have ever been near a soap factory you would appreciate this.

Filling the tank with proper diesel would overcome the problem by the laws of dilution but a little added oil would remove this neccessity.

For 1.5 gallons of petrol I would suggest something in the order of a litre of standard engine oil in this instance.

Cheers, qldit.


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## devil lady (Sep 27, 2005)

If you really want to play it safe, drain the tank. Diesel and unleaded are completely different. Diesel is a light refined crude. Unleaded is processed in a cracking tower, totally different and has all heavy elements removed. They will mix while on the move but after parking for a period of time they will separate again. The same applies to adding extra oil to the tank, they will settle out. Yes you can run a diesel on vege oil etc because they are an oil, even kero has oil in it. Unleaded does not.
You will have small amounts of unleaded passing throughthe injectors which are not designed to cope with a highly volatile fuel, the injector pump seals will suffer and it's possible to crack a piston or blow a head gasket. 
For the sake of a tank of diesel, I know which I'd prefer.


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## Tumbleweed36 (May 14, 2005)

Although I think it will run just fine, just be sure you have a very heavy concentration of Diesel to the gasoline. The main difference (for this purpose) is that diesel depends upon the oil content in the diesel for "lubricity" and gasoline has none of that. If the concentration of gasoline was too heavy, then damage to the engine could occur. With the small amount you put in there, then either some additinal oil or just a very heavy concentration of diesel should take care of it.


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## qldit (Mar 26, 2007)

devil lady said:


> If you really want to play it safe, drain the tank. Diesel and unleaded are completely different. Diesel is a light refined crude. Unleaded is processed in a cracking tower, totally different and has all heavy elements removed. They will mix while on the move but after parking for a period of time they will separate again. The same applies to adding extra oil to the tank, they will settle out. Yes you can run a diesel on vege oil etc because they are an oil, even kero has oil in it. Unleaded does not.
> You will have small amounts of unleaded passing throughthe injectors which are not designed to cope with a highly volatile fuel, the injector pump seals will suffer and it's possible to crack a piston or blow a head gasket.
> For the sake of a tank of diesel, I know which I'd prefer.


Good Evening devil lady, that is interesting, I have never observed any separation or settling in the field at all with mixed fuels, are you inferring that this is a specific gravity differential?

I would expect over time that stratification may happen but not in short order surely.

My experience stripping injector pumps was that they used standard mineral oil type seals and "O" rings as for other fuel supply systems. 

You would be shocked at some of the cocktails I have mixed in the absence of ordinary diesel fuel when the need arose. But the engines involved were generally the Detroit 71 series, which ran perfectly well on ordinary Kerosene alone.

Interesting stuff.

Cheers, qldit.


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## devil lady (Sep 27, 2005)

Basically unleaded or gasoline specific gravity is between 068-.74 while diesel is between .84-1.08. Not a huge difference but enough to settle. 
You are correct that the same type of o-rings are used however the diesel injection system is up to 10 times the pressure of a petrol/gasoline engine system. Thats where the potential for destruction lays in the pressure subjected to unleaded fuel in a diesel system.
Keep in mind Detroit specialise in 2-stroke diesels as opposed to modern 4-stroke engines. The venerable detroit will run on anything that burns including sump oil. :grin:
The problem with the new engines is the compression ratio is higher and the safety factors are lower. I've personally known of Mercedes Benz diesels that have literally blown the heads off when petrol was introduced to the system.


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## qldit (Mar 26, 2007)

Good Evening devil lady, that is most interesting, yes I was aware of the compression differences and have done quite a lot of work with both diesel engine types and injector systems.

I was also of the opinion that diesel and kerosene was a product of a cracking tower but at a lower level.

On one occasion I determined a batch of fuel was contaminated and it was re-refined.

As a point of interest we had a 71 GM series-6 engine on a power generator under constant load run non-stop for over two years, it really was an amazing machine, oil changes and servicing was carried out while the engine was running, you can guess where the old oil ended up! 

And yes I also saw a Mercedes with a split block but it was caused by the low air scoops at the vehicle front entering a two foot deep stretch of water at high speed! LOL!! 
I haven't seen any damaged engines from fuel to this point. (touch wood!)

I would have expected the calorific value of petrol to be less than diesel.

And yes Kerosene comes in the middle at approx roughly .7 to .8 dependent on temperature.
But some of the heavier types are virtually in the dieseline bracket.

Very interesting thankyou for that.

By the way it was 31degs C here today, not bad for winter! 

Cheers, qldit.


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## carsey (Aug 19, 2006)

We are choosing the option just to keep it full until the petrol gradually goes through the system with high amounts of diesel. I will keep you informed as to how its going. All's ok up to now, no power losses and starts fine. Sometimes starts 2nd time over but thats nout to worry about.


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## qldit (Mar 26, 2007)

Good Evening carsey, good plan, hopefully the laws of dilution will prevail, it goes something like 3 half fills is 99% contaminent free.

Cheers, qldit.


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## devil lady (Sep 27, 2005)

Do hope it goes fine Carsey.



> By the way it was 31degs C here today, not bad for winter!
> 
> Cheers, qldit.


lol rub it in, it was 16c here yesterday but about 19 today.
Side note to the discussion, diesels old name was distillate, from the distilling process. Though I'm not 100% sure if they process it more these days. :smile:


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