Powerstroke problems – Diesel fuel in coolant bottle

If you have ever wondered how a cylinder head cracks to allow diesel fuel to get into the degas bottle in a 6.0 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 over heating 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.

Here is 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 and putting shop air to it.  With a pressure gauge in the degas bottle, if that head is cracked, pressure will register.  It may take a couple hours for the pressure to show on the gauge if the crack is really small.  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, it might save you a lot of work and money.

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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.

  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.

      • Justin Neff on February 15, 2021 at 12:16 am

        I’ve not had it to a shop I do all my own mechanic work!!!! I literally just put this engine in the truck out of a truck that I wrecked!!!! I’ve changed one side with new injector cups going to do the other side in a day or 2!!! If I’m still building pressure I’m thinking I’ve got a cracked head!!! How much do you charge for a head and gaskets

        • Asheville Engine, Inc. on February 15, 2021 at 3:18 pm


          We build so many engines that it’s all we can do to keep enough heads on the shelf to build our own engines. The only heads that we sell are O-ringed and we sell those by the set. By the time that you pay shipping on a cylinder head, you’d probably be better off to go to your local Ford dealer and buy one if you have a wholesale account. We’ve got the oringed heads and head gaskets listed under “Products” on our web site. http://www.AshevilleEngine.com

  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.

  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?

    • Asheville Engine, Inc. on July 17, 2020 at 12:54 pm
      • Marlene j on August 15, 2020 at 4:42 am

        Our 2016 Range Rover has diesel fuel in the coolant .
        We had a cracked gasket and they replaced that and now the engine light keeps coming on to show overheating .
        They have flushed the coolant system out twice and test drive it and it still is over heating and they can smell the contaminant in the coolant .
        No codes will come up and they don’t know what to do . It is at the dealership and they say they have never seen this problem before .
        They tell me someone must of poured some diesel fluid in the coolant but from what I’m reading I see it can leak in on it’s own?
        They said they will flush it a third time and then want me to ok 4 hours of diagnostics to figure out what is wrong .

  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. Dylan on September 11, 2020 at 10:31 pm

    Thank you for being so diligent with responses to this post from more than 2 years ago, I’m very impressed and will be coming to ashevilleengine.com for information first from now on.

    That said, what complications arise from a bus being driven with this problem? I have an opportunity to purchase a bus that was retired with this issue, what is the ballpark price range for this repair, and what should I be aware of while inspecting it?

    • Asheville Engine, Inc. on September 14, 2020 at 3:19 pm

      Dylan, The complications from having diesel fuel getting into your coolant is that all of the plastic (degas bottle) and the rubber (hoses and seals) in the cooling system also need to be replaced when you replace the cylinder head because the diesel fuel deteriorates them. If you are doing the work yourself, all of the parts will cost $1600-$1800. If you are having a shop do it, that varies widely across the U.S. and from shop to shop. Make sure that you flush the cooling system and replace the oil cooler while you are doing it.

  10. Greg Rosser on January 14, 2021 at 10:20 pm

    I have a 2001 F250 Superduty 7.3 with powdered metal connecting rods. The truck has mild upgrades such as a wicked wheel in the turbo, Full Force Diesel stage 1.5 single shot injectors and a TS chip burned for single shot injectors. I use it as a daily driver and regularly pull a 35 foot toyhauler. Are factory forged rods reccomended over the powdered metal rods?

    • Asheville Engine, Inc. on January 15, 2021 at 1:52 pm

      Forged rods are stronger but your truck is a 2001 so it’s been on the road for 20 years without any problems. After 20 years, I wouldn’t start worrying about it now.

  11. Greg Rosser on January 19, 2021 at 7:00 pm

    Would your long block 7.3 for a 2001 model year application come with the factory forged rods or powdered metal?

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