2003 Honda Civic - accidental diesel in tank

I accidentally put $20 diesel in my 2003 Honda Civic today. I’m very worried about it not running tomorrow or it just stopping and it being pricey to fix. First time thus has happened. Should it be ok or do I bring it to a mechanic?

The engine may be difficult or impossible to start tomorrow. An engine can run on a mixture of diesel fuel and gasoline when hot but it is difficult to start the engine when cold, diesel fuel does not vaporize like gasoline does.

The fuel tank should be drained and filled with gasoline. Normally this is not costly, perhaps $300 but there are some that want to replace everything in the fuel system which is unnecessary.

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Thanks so much for replying!

Do you think I should get my car towed to a mechanic, if it does start that is. Is it okay to drive? It would be about a 10 minute drive. What if I put more gas in it?

Sorry for all the questions, I haven’t done anything this stupid to my car before.

That would be the best thing to do . How did you do this ? If you are in the US the diesel nozzle should not go in a gas vehicle fill pipe.

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I would have it towed. The less diesel you pull into the rest of the fuel system, the better.


You could do this yourself and save a trip to a shop and a bunch of Doomsday Hoopla. Depends on your mechanical aptitude however, it isn’t difficult to recover from this situation.

Pull your fuel pump relay from the fuse box… Unhook your feed line to the fuel rail/injectors… Grab a suitable funnel and length of rubber hose and a 5 gal fuel container.

Turn your ignition key on and jump terminals 87 and 30 at the empty fuel pump relay socket and let your fuel pump simply pump the diesel out and into the container. When it cannot pump any more fuel, pull out the jumper, shut the key off, re-connect your fuel line, reinsert your fuel pump relay and fill your tank with gasoline.

That’s it…you’re back on the road again. No need for self flagellation, no need to drop the tank, no need to call NASA, or panic. Oh yeah…no huge bill either.


Of course, then you have to get rid of 5 gallons of diesel/gasoline fuel mixture…

As I’ve gotten older, I’ve started shying away from any DIY work involving car fluids…

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That’s the kind of DIY attitude and advice that keeps this site interesting - and helpful!

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yrs ago i had a fuel pressure tester hose kit and i ran out of gas for my mower so i pumped a 1/2 gal or so into the gas can using the valve port on the fuel rail. i think AZ will let you borrow a fuel pressure tester.

How do you get rid of $20 in diesel mixed with some gasoline?

How would I do it? I would gradually consume it by using small amounts in each tankful for my smaller engines like mowers, blowers, chipper etc. Probably even hasten it by adding small amounts to my older cars as well. Come to think of it, I have a neighbor with an older diesel truck. He’d probably eagerly accept it. Mixed in with nearly full tank of diesel, unlikely to be a problem…

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We have a bimonthly hazardous waste disposal, it would be accepted there and disposed of properly for no charge.

I don’t like the do-it-yourself suggestion. To many ways to end up spilling, and at worst, starting a large fire. Have it towed, have the shop drain the tank, fill it up, and if it’ll start drive it for 20 miles. If it won’t start, then they’ll have to clean out the rest of the fuel system.


Blackbird , you could but the average person has no business trying this in their own garage or driveway. Plus where I live disposing of the drained fuel is impossible .

Wow lol I’m new to cartalk and I didn’t expect so many great and interesting replies! I got it towed and they drained the tank and put in $20 gas for me. The total charge was $195 dollars. I’m thankful it wasn’t more and happy it’s done. First time I put
diesel…and last. Too much on my mind and wasn’t thinking. Lesson learned. Thanks everyone! Ps…to the diy suggestion on car repairs isn’t for me.

Diesel fuel is a lot less volatile than gasoline, due to the fact that it’s hard to ignite without compressing. It’s flammable, but harder to light than gasoline.


Frances , because I am nosy please tell us how you did that . Also that really sounds like a very reasonable charge by the shop.

How I put diesel? I had received a text earlier in the day from a friend who found out she has cancer. I was not thinking clearly. I made a mistake. First time for everything…but never again.


It’s part diesel, part gas, so still flammable.


Here’s the good news:
Diesel is a fuel OIL.
As such it is a lubricant.
This accident probably extended the life of your fuel pump by several years. It may have even helped with your upper cylinder lubrication, extending the life of your piston rings and cylinder walls

Here’s the bad news:
Diesel burns with a carbon soot.
Expect to replace your spark plugs soon.
When you take it in for a “tune-up” make sure the mechanic knows about the diesel incident or he will think your car is burning oil.

How do I know that the diesel will fowl your plugs but preserve your motor? Experience.
I use a lead substitute in my mower gas. When I can’t find (or afford) a lead substitute, I use a 200-250:1 two-cycle mix for all my mowers. If I only have enough to cycle mix for my trimmers, I use 40-50:1 diesel mix. In my diesel trucks I run 150-200:1 two-cycle in the summer and 125-150:1 cetane booster in the winter.

Results: a decade ago, I was replacing spark plugs every 250-500 hours (2x oil change) and mower engines every 1500-3000 hours. Now I replace spark plugs every 150-200 hours and I have one Kawasaki engine with 5800 hours (in car years that’s 350,000 miles), the rest of my equipment has similar results.

Results 2:
My personal diesel truck on USLD #2 summer blend, 1150 lb/ft torque, 375 BHP.
My personal diesel on USLD #2+#1 winter blend, 1175 lb/ft, 398 BHP
On summer blend with 150:1 — 1195, 402
On winter blend with cetane — 1205, 426
These flywheel numbers are reverse estimated from wheel numbers.

Side note, on JP8 with 2-cycle, 125:1, and a full shot of methanol, 29 pounds of boost, 1420 rwt @ 2100, 480 BHP @ 3150. And then I exploded my rear differential before I could make a full pull