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What happens if you put regular unleaded gas in a diesel engine?

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June 12, 2014 10:55PM

If you put regular unleaded gasoline fuel in a diesel car's tank, at the very least the fuel tank and fuel delivery pumps and pipes will be contaminated and will need to be cleaned out and, if you then start the engine and let it run, it is very likely to be damaged.

Depending on the amount of damage that has been done, the work required could easily cost from one hundred to several hundreds of dollars.

This is why people stick diesel stickers on the inside of their petrol caps to remind them every time.

For more general information see the answer to the Related Question shown below.

Depends on how much gasoline is put in. When temperatures dipped below 25 degrees, truck drivers sometimes would add a small amount of gasoline to prevent the diesel from gelling. Now commercial additives are available.

Diesel fuel has a lower ignition temperature than gasoline, allowing combustion to occur simply by compressing the air/fuel mixture. Gasoline engines require a spark plug to ignite the fuel. Too much gasoline will not allow the engine to work efficiently and quite possibly not at all.

Also, diesel engines use an injector pump to pressurize the diesel so it will form a fine mist when pushed through the injectors. These pumps require the lubrication of diesel to continue to work. Excess gasoline will cause failure in the injector pump and damage the injectors.

If you put very much in then I would have the tank & lines drained to remove the gas.


I just made the mistake of filling up my truck with gas rather than diesel, only drove it for about a half a mile. Took it to the dealer today and no damadge was done. Shut it off just in time I guess. Thanks for your replys to my question.


For more information please see the answer to the Related Question shown below.

This is My Take:

I have just undergone this problem; I accidentally put Gas in my VW Jetta TDI 2011 Diesel Engine, I have had it for about a month, bought it brand new last Christmas, and this mistake happened me owning the car for less than a week, talk about Bad Luck. Had I known what I know now from my experience, I would have saved myself a lot of money. Not to mention avoid the scam of the dealership and the mental agony. I feel obligated to share my experience with you all, so you can get this problem fixed without the horrendous cost to you. This is for cars or trucks that are still under Dealer Warranty or have Full coverage Insurance.


Having put gas in my Diesel engine, I drove the car from the Gas station to my home which is about 5 miles, then I realized the mistake but it was too late. I called the dealership and told them my mishap and I was sent over a tow truck at no cost and was told "it is not a big deal" bring it over we will fix it.

Scam #1: This is NOT covered under warranty. Having Gotten to the VW dealership, I was told all we have to do is drain the Tank and replace the Filter and I will be good to Go.

Scam # 2: you have to suck out the Gas from the lines, if need be use a compressor to suck it out, Drain the Tank and change the Filter is only good if you have NOT driven the car, once driven, this is almost never help full. The dealer made my car ready and charged me $650, before I could get home the car had its Coil light on and was not catching any speed. I went back to the dealer and they said let us do it again as there may be some particles left, charged me another $650 (Total out of my pocket $1300). This did not fix it and I went back to the dealer and they said it is all messed up and gave me an estimate of $9950 which will NOT be covered by the warranty. Below is what I did, which the VW dealer said cannot be done (I claimed it on my insurance), but before you do that ready below Solution A, it is a better route than what I did.


Here are the steps you need to take:

Solution A:

1. Do NOT drive the car as soon as you realize

2. Tow the car right away to a "NON-DEALER" Independent Diesel Mechanic or shop, do NOT use Roadside assistance, or else the Dealer at some point can nail you for it as that record is shared with the Dealership, Pay Cash from your pocket and an independently owned tow company, not even AAA.

3. Tow the car to a "NON-DEALER" Independent Diesel Mechanic or shop and clean up the Tank, usually should not cost more than $300 and this should fix the problem 9/10 times if you have not driven the car and 5/10 times if you have driven the car.

4. If the car is not fixed at the mechanic's place at this point, then Tow the car back to your Home (Assuming it does not drive at all) this is imperative, however Ask the mechanic or shop to clean out all the Gas 100% regardless of if it is fixed or not.

5. If the car drives, fill up the tank with Diesel and drive at least 1 full tank, so all traces of Gas are gone.

6. Assuming the car is not fixed or barely fixed or not satisfied with the way it drives, then call the dealership while your car is at home and tell them your problem, DO NOT Mention you put "GAS" or else the warranty will NOT Cover and the dealer will love to scam you. Just mention the problem and "You don't know how it happened, it just did". This time use the Roadside assistance of the Dealership and tow the car to the dealership or drive the car to the dealership if it drives and let them do what it takes to fix it. Remember don't be a "Smarty Pants" and let the dealership fix it, less knowledge is wise at this point. No Matter how much they say that there is Gas in there, remember you know nothing about this, they will try to make this into a "NON-Warranty" and try to make you pay for it. As far as you are concerned "The car is not working or working right and it is an engine problem, So FIX IT DAMN IT" put up a fight (Verbal) if need be and ultimately by law they have to fix it as this can never be proven, it could be the gas station has contaminated diesel or whatever, not your business. Be strong and smart or dumb whatever works.

Solution B:

Assuming you were an idiot like me, and believed in "Honesty the best policy", then be ready to pay the price of honesty all the way to $10K, I am not rich and can barely make payments for the car, house, and "wife", so here is what I did, having told the dealer 100% about the exact situation and to the minute details of what had happened.

Even though my Insurance agent advised me against it and the internet did not speak about this, the dealer said: "I have seen it numerous time, it will never happen, the insurance company will never pay". The car was sitting at the dealership for over 3 weeks now, I figured what do I have to loose, (I have full coverage with Farmers) I called my insurance company. Believe me when I say, this was the easiest claim I ever filed; "a walk in the park" could not be easier. I was told I have to pay the deductible, and the adjuster went to go look at it, paid the dealership close to $10K and my car was fixed just as good as new. And Yes, I told the Insurance Company the whole scenario as to exactly how it happened taking full responsibility of the "accidental fuel contamination" (Key word for insurance claim). This can be done through your full coverage Insurance if Solution A above is not your option.

Good Luck, Its Pay Back Time Dealerships.

My wife put in 2 gal. of unleaded into a 1/2 full tank of a 2005 F-350 long bed. Then filled up the remainder with diesel then drove about 35 miles and topped it off with diesel. Drove another 35 miles and topped it off again. No problems. Actual sounded a little smother before the last top off.


If you have not put too much gas in you can also improve the ratio by adding motor oil 30 to 50 weight into the mix or even a cheap 2 stroke oil.


Remind me not to hire my car to you (the last respondent) if you come over here...

Using the wrong fuel (petrol in diesel or vice-versa) has caught many motorists but the fuel companies have helped all they can, at least in the UK, with very clearly labelled pumps & nozzles; and with differing nozzle diameters. Also UK (& I think Continental European) fuel pumps intended for general public use do not have trigger-catches, so you have to keep the trigger depressed against a strong spring throughout refuelling. Although that was introduced years ago as a safety regulation it does help you concentrate on what you are doing, giving you a brief second-chance to stop before you've added a significant amount to the tank - you can't turn it on and wander off!

Touch wood I have never mis-fuelled a vehicle, but once had to return a hire car un-refuelled because neither I nor the garage attendant could understand the strange label on the car's own filler-cap, so we had no idea what fuel it was meant to use! (On a modern car there is no definite way to tell by engine note or performance which fuel it is using.)