Diesel fuel in coolant bottle

Have ever wondered how a cylinder head cracks to allow diesel fuel to get into the coolant bottle in a 6.0 Ford Powerstroke or VT365 International? Here is a picture and description of where they crack.

Refer to picture

In this cut away of the cylinder head, you can see a thin wall between the injector bore (where arrow is) and the coolant passage to the right of the wall.  Cracks are generally caused by overheating and because this area is thin, it is most susceptible to cracking.  The fuel pressure from the injector rail cast into the head (small hole to the left of the arrow) is far greater than the pressure in the cooling system.  When a crack occurs, diesel fuel easily passes into the coolant.

Kill two birds with one stone

If you have diesel fuel in the coolant, you need to buy new heads.  New cylinder heads will fix the fuel issue. Asheville Engine sells o-ringed cylinder heads which give you reliability without the worry of blown head gaskets. https://ashevilleengine.com/product/oringed-cylinder-heads-for-the-ford-powerstroke-6-0l-diesel-engine/

A Tech Tip from Asheville Engine

Many shops want to replace both cylinder heads but there is no need to fix something that isn’t broken.  You can pressurized each head individually by adapting an air fitting to the front of a cylinder head.  With a pressure gauge in the degas bottle, pressurize he fuel rail with shop air. If that head is cracked, pressure will register.  If the crack is really small, it may take a couple hours for the pressure to show on the gauge.  This is best done if the engine is at operating temp before you put air to the head.  If one head holds air, then go to the other head and do the same.  Doing this might save you a lot of work and money.

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We Keep You Strokin’

Diesel Fuel in Coolant

Diesel fuel in coolant on a 6.0 Powerstroke is the result of the head cracking just above the injector cup.

Asheville Engine, Inc.

Asheville Engine is the leading independent Powerstroke engine builder in the world, powering trucks in Guatemala, Switzerland, Australia, Iceland, Denmark and other countries around the world. We are serious about our business and keep enough inventory IN STOCK to build 50 to 100 Powerstroke engines so our lead time is generally only 1 to 3 days.


  1. Don Reeder on October 31, 2018 at 2:15 am

    What would you think is wrong when oil in the exhaust pipe

    • pwsadmin on October 31, 2018 at 2:07 pm

      There are several things that could cause that. The first thing that you should do is check to see if your engine has excessive blow-by. The easiest way to check that is to pull the rubber oil fill cap off while the engine is running, turn it upside down and try to lay it back over the fill hole. If there is a lot of blow-by, you won’t be able to set it down, it will blow off. If that happens, it’s time for a new engine.
      If you can set it over the hole, it may vibrate off but the blow-by is not excessive. If the blow-by isn’t bad, I’d recommend taking it to a qualified repair shop to have the problem diagnosed.

    • Asheville Engine, Inc. on February 24, 2022 at 3:06 pm

      I’m not sure which machine you are talking about but in a 6.0 or 6.4 Powerstroke, diesel fuel in the coolant would indicate that you have a cracked head. https://ashevilleengine.com/category/cracked-cylinder-head/

  2. Justin Neff on December 6, 2019 at 9:50 am

    How hard is it to change the injector cups on an 07 6.0 and would it be expensive??

    • Asheville Engine, Inc. on December 6, 2019 at 3:32 pm

      Justin, it’s pretty easy to do and not all that expensive. It can be done in the truck without having to remove the heads but you’ll have to locate a shop that will do it because not all will.
      That being said, it’s pretty rare for injector cups to start leaking on a 6.0 so you may want to get an opinion from a reputable diesel shop as to whether it actually needs to be done.

  3. Bobby on April 22, 2020 at 9:00 pm

    What would cause diesel fuel to get into the engine oil and over fill the crankcase?

    • Asheville Engine, Inc. on April 24, 2020 at 2:34 pm

      Bobby, Fuel getting into the crankcase can happen for several reasons and the most common is different with different engines. If you have a 6.4, the most common reason is the DPF system but it can also happen because of a leaking connection in the fuel line inside the valve cover. In all engines, it can happen because of a faulty injector or leaking injector seals or an injector cup. No matter which engine it is, DO NOT run it until you find the problem and have it fixed or you can end up with a catastrophic engine failure.

  4. John on May 19, 2020 at 5:36 am

    Is it possible to have the head gaskets go bad again after replacing one head and gaskets with arp studs. I have fuel in my degas bottle again after spending $5500. Mechanic says turbo is bad needs two injectors.

    • Asheville Engine, Inc. on May 19, 2020 at 12:47 pm

      I’d find a different mechanic if he thinks fuel in the degas bottle comes from a bad turbo or injectors and if he replaced your head gaskets previously for fuel in the degas bottle, he’s a real moron who shouldn’t be working on trucks.
      You’ve got a head that is cracked in the injector bore right where it shows in the picture in this post. Find a shop who knows how to determine which head is cracked and replace it. Most shops don’t want to diagnose which one it is and always replace both heads when they get one that has fuel in the coolant, which costs their customer twice as much.

    • Gary Moore on April 20, 2022 at 2:10 pm

      Why is oil backing up in my reservoir in my 6.0liter Ford diesel engine powerstroke

      • Asheville Engine, Inc. on April 20, 2022 at 2:40 pm

        Oil mixing in the coolant is usually an indication of a blown oil cooler. You will need to have your entire coolant system flushed (including heater core) to eliminate any oil in the cooling system and replace the oil cooler with a new one. Now would be a good time to replace the old rubber hoses in your cooling system, too.

  5. Steven Warmouth on May 30, 2020 at 11:16 pm

    Have a 02 power stroke 7.3 have got fuel in my coolant has never been hot and I bought it brand new 400 000 miles on it this is the only problem I have had with it is it the injector cups

    • Asheville Engine, Inc. on June 1, 2020 at 11:58 am

      Steven, It’s impossible for anybody to pinpoint exactly what the problem is over the phone, on a computer or any other way than doing it in person. You should probably consult a competent repair shop to diagnose the problem. Once a diagnosis is made, a machine shop can pressure test and magnaflux the heads if they need to come off. If they check out, they can do the machining to give you a set of heads that will go another 400,000.

  6. Gus on July 17, 2020 at 12:00 am

    When i pressurize coolant system coolant comes out fuel line leading up to secondary fuel filter. Thoughts?

  7. John Wicke on August 7, 2020 at 12:22 pm

    When I pressurize the coolant system i get bubbles from the #4 injector cup. is this the cup or is it likely to have a cracked head. i have removed the cup and inspected with a bore scope dont see an obvious crack just a small amount of pitting on the head/cup seal surfaces. any ideas?

    • Asheville Engine, Inc. on August 7, 2020 at 2:45 pm

      If the coolant is bubbling out around the top of the cup, it could just be a bad seal. Injector cups are cheap, I’d glue another one in place and after it’s had time to cure, re-pressurize it and see if that takes care of your problem. If the head is cracked where we indicate in the picture in this post, you should be able to see it weeping out of the crack.

  8. Asheville Engine, Inc. on August 21, 2020 at 4:46 pm

    Marlene, I’m sorry to hear that you are having an issue. Because we only re-manufacture Ford Powerstroke engines, I don’t have any personal knowledge of the engine that is in your Range Rover. That being said, it sounds like you are dealing with a dealership that does not have any good technicians to work on what they sell. If they are anything like Ford, all of the best technicians quit to start their own businesses so you may have to find an independent shop that specializes in Range Rovers to do the work.
    That being said, all engines are basically built the same. You may have an injector cup leaking or have a cracked head. Because the fuel pressure is higher than the pressure in the cooling system, fuel will always leak into the coolant if you have a crack or an injector cup leaking.
    Good Luck!

  9. tom Ramey on March 5, 2022 at 6:05 am

    who in the Asheville area do you recommend to do a instalation of one of you engines in the Asheville area?

  10. Nswana on April 17, 2022 at 8:06 am

    Hey I have a Volvo d13… When I remove the diesel filters and try to prime, It’s dripping water right from the diesel filter blaket instead of diesel fuel… What would cause this???

    • Asheville Engine, Inc. on April 18, 2022 at 12:57 pm

      I’d suggest that you call somebody that works on Volvos