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What happens if you pit diesel in an unleaded car, will it...

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Question by kerby
Submitted on 11/22/2003
Related FAQ: Gasoline FAQ - Part 4 of 4
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What happens if you pit diesel in an unleaded car, will it damage the engine?

Answer by Richards.good.stuff
Submitted on 11/24/2003
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I have tried this at various times, so i believe i have a practical answer.  Will it damage the engine? That depends on the amount added and the engine.  There are two immediate impacts of diesel fuel mixed with gasoline: the octane is lowered and the fuel vaporization is reduced.  The lowered octane may cause the engine to knock.  Some engines have knock sensors and the electronic controls will adjust the timing and other engine conditions to try to control the knock.  If the knock remains significant it can damage the engine by causing metal fatigue eventually leading to failure of critical parts like pistons, connecting rods, heads.  Some very old engines (e.g. 1950's tractors) can accomodate lower octane, but the ones found in recent autos are normally running close to the knock threashold. The reduced volotitility caused by the added diesel will cause hard starting and will probably result in some unburnt hydrocarbons remaining in the exhaust gas from the engine; these may be reacted in the catalytic convertor causing it to overheat.  A modern electronic controlled emission system controls the oxygen level in the exhaust gas going to the convertor so the significant increase in hydrocarbons with controlled oxygen may save the convertor, but will likely result in unburnt hydrocarbons exiting the exhaust.  This will result in a smell and air pollution.

So if enough diesel is added to produce any of these problems it is a not a good situation.  I would consider draining and replacing the fuel or if practical diluting it with fresh gasoline to eleminate the symptons.


Answer by @richards
Submitted on 2/10/2004
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how much diesel would cause engine damage?

what would happen if i put 1/6 of diesel and 5/6 of unleaded?


Answer by alibaba
Submitted on 6/20/2004
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what about the opposite? What happens if you put unleaded in a diesel engine? whoops.


Answer by Hidden
Submitted on 7/11/2004
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I dont think you can put unleaded fuel into a diesel engine.  The nossle is different from what I've seen, and it will not fit into the car (at least newer ones).  But that's just from personal experience.


Answer by lrip
Submitted on 8/26/2004
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I recently had diesel fuel found in my gas tank.  It had a hard start until it just didn't start anymore.  Supposively it doesn't ruin the engine (at least in the amounts that I had).  The tank needs to be flushed, the fuel lines cleaned, fuel filters replaced and the spark plugs cleaned/replaced, cylinders reoiled and worked a few times in order to get it up and running.


Answer by Trooper
Submitted on 10/17/2004
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What happens when you put super (not unleaded) fuel on a diesel car ?


Answer by Grumby
Submitted on 2/2/2005
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Just to clarify Richards.good.stuff response. Diesel fuel has no OCTANE at all. Gasoline is made up of 7 and 8 chain hydrocarbons. The 8 chain is the octane. Diesel is compromised of 19 and 20 chain hydrocarbons and thus is much more stable and controllable. How does this translate into the real world? Well this would place the "virtual octane" level somewhere around %200+ and I would imagine that it would be the reverse of knocking due to early burn. It would probably misfire and not burn all the fuel in the chamber. That funky smell Richard refers to is probably the smell of unspent fuel vapor.


Answer by jon
Submitted on 7/25/2005
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well, it certainly appears clear that Hidden is misinformed. I just accidently put 2 gal of diesel in my ford escort the other day. I was told to fill it the rest of the way with unleaded and run it out. I have gathered a few other opinions as well. One response was to run it out as soon as possible. Another is to pay aroun $300 to drain and clean the tank. Yet another option and the one I opted for was to use up 1/4 tank replace it use 1/4 tank replace it and so on -  so as to dilute the diesel. This seems to make sense to me. Yet, I'm not at all sure what effects it may have on my engine. Any advice would be much appreciatted.


Answer by Cody
Submitted on 9/18/2005
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I accidently put 5 gallons of diesel in my jeep today, and I'll probably siphon as much out as I can but I talked to a mecanic and he said you can have it almost half and half and it won't hurt it, the only thing you have to worry about is your oxygen censor frying cuz of the exaust


Answer by newbie
Submitted on 10/13/2005
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You CAN put unleaded in a diesel engine. My husband just did :(
My advice would be DON'T!
Petrol kills diesel engines. Dead. If you do do it, DON'T even unlock the doors of your car as this actually primes the fuel pump on modern diesel cars.
If you do unlock the doors or worse still get in and drive then you cause hideous damage to your engine that can cost between 7000 - 12000 to put right. And it may not be covered on your insurance.
For heavens sake put a sticker on your petrol cap before it happens to you :(


Answer by Unknown
Submitted on 3/6/2006
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what happens if you accidentaly put water into your petrol tank?


Answer by marco
Submitted on 4/27/2006
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Actually, you can put unleaded in a diesel, my stupid bro-in-law has done it not once, not twice but three times!!!! He bought his car new and has had it 3 years!! DOH!!


Answer by Brent
Submitted on 8/10/2006
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I just did this in my dirt bike...  Lots of knocks so I ended up draining the diesel.


Answer by Hidden
Submitted on 9/12/2006
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Hey moron - you can put unleaded in a diesel it is the opposite that the nozzels play a role.  The diesel opening is large and will accomidate both the large nozzel of the diesel pump and the smaller unleaded nozzel.  Get a clue before posting things on the web and contributing to the 90% of misinformation that is out here!


Answer by charlie.neck
Submitted on 12/27/2006
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I accidentaly put 2 gallons of diesel in a 2005 toyota, I already had less than a quarter of a tank... I spent one hour trying to figured out what to do, suddenly I decided to dilute the diesel by filling the whole tank. Fortunately, nothing happened but I continued to dilute by filling up the tank in every gas station that I found.


Answer by Marbles
Submitted on 2/25/2007
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My Uncle's new idiot wife put unleaded in her brand new mercades benz that he just bought her. The car won't even turn over now. He is not to happy.


Answer by Michael
Submitted on 5/11/2007
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Hidden is right (I think). The other day I was going to pump gas and I wasn't thinking all the way and I picked up the diesel pump. My car is unleaded, bad combo. Fortunately, the diesel nozzle was too big and I was like, "What's going on?" I noticed I had the green pump in my hand and hooked it back up and pumped regular gas. As far as the consequences of having the wrong gas in your engine, I can't say. I'm not that savvy. Yet, watching the Amazing Race 3, several teams put unleaded in diesel trucks and they ended up breaking down, so obviously it isn't good. :)


Answer by Dr.nick
Submitted on 5/18/2007
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It will go BOOM !!!!!!!!


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