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Does diesel fuel sit on top of oil?

Mar. 07, 2024

Diesel getting into your oil supply is the last thing you want. However, few drivers know what causes oil to mix with diesel or why it's harmful.

How Oil Can Mix With Diesel

So here, our vehicle experts at All Bay Diesel explain how oil and diesel merge and why you should avoid this at all costs.

Broken injector nozzle

In most cases, a broken injector nozzle causes oil to mix with diesel. Unfortunately, injector nozzles don't need exterior damage to break; their seals will wear down over time, allowing diesel fuel to sneak into the oil.

In other common cases, the injector nozzle's sealing ring will fall off, or the spray nozzle will fail. With the latter, the injector nozzle won't spray the diesel as it's supposed to and will instead dump it into the engine. That prevents the fuel from burning and allows it to seep into the oil.

Worn down fuel pump sealing

If broken injector nozzles aren't the cause of oil mixing with diesel, it's likely worn-down fuel pump sealants. All fuel pumps have a seal that blocks diesel from mixing with the oil, with many pumps having multiple seals for added protection. However, those seals wear out over time; if they break completely, the diesel and oil will merge.

Malfunctioning exhaust gas regeneration system

Your diesel vehicle's exhaust gas regeneration system recirculates gas from the exhaust into the intake manifold. If it breaks, the fuel will get into the oil supply. 

A failing exhaust gas regeneration system can be what causes oil and diesel to mix, resulting in two issues. The first and most common is a clogged Diesel Particulate Filter (DPF). Clogged filters can prevent the exhaust gas regeneration system from recirculating gasses to the proper spots, which lets them leak into the crankcase and merge with the oil.

DPFs can also fall out of diesel vehicles if you don't correctly install them, creating similar issues to a severe filter clog. 

Broken High-Pressure Pump Components

The hardened gaskets in your diesel vehicle's high-pressure pump will give out with enough wear and tear. When they do, this can force diesel fuel into the oil storage. Similarly, the pump's plungers can produce insufficient pressure, leading to fuel and oil mixing.

These problems often happen in older vehicles that haven't received engine maintenance in years, but new, heavily-used trucks can go through the same issues. Unfortunately, it isn't easy to diagnose which part isn't working, and it's even more challenging to fix those components. Fortunately, All Bay Diesel can remedy these concerns quickly.

When you schedule our mobile diesel repair service, we'll inspect your vehicle from top to bottom to find every reason why your oil and diesel fuel have merged and quickly repair the problems. 

Engine Cracks

A cracked engine cylinder head isn't what causes oil to mix with diesel the most, but it is the most severe related issue.

Cylinder cracks happen near the combustion chamber when you install fuel nozzles too tight. The cracks might not even be visible, but it only takes a microscopic opening for oil to escape. Unfortunately, once the cracks form, they'll grow and allow more oil to leak until you've repaired them. 

Engine cracks can also form on the cylinder walls, often resulting from collisions. Unfortunately, these cracks can spread to your engine's rail and fuel lines, causing the oil and diesel to mix and generating other leaks that will worsen until you repair them.

Dangers Of Diesel Fuel Dilution

You now know what causes oil to mix with diesel, but you might still wonder why this problem matters. Oil and diesel mixing might not sound bad, but it can destroy your vehicle's longevity and efficiency in three ways:

Inadequate oil viscosity 

Oil lubricates your diesel engine's moving parts so they don't grind together, overheat, and wear down. The oil needs to be at a specific viscosity to grease the components. When diesel fuel dilutes the oil, it becomes too runny for adequate lubrication.

Driving with ineffective oil is nearly as bad as driving with no oil. Both situations strain engines long-term, forcing you to pay for expensive repairs and replacements. Poor oil viscosity can also cause short-term issues like engine failure or overheating. 

Lower additive content

Diesel fuel doesn't just lower oil viscosity; it also drags down the lubricant's essential additive properties. These additives prevent engine wear and tear by layering around the components and taking the brunt of the damage. So instead of metal scraping against metal, your engine's operation is a protective layer bumping into itself.

However, when diesel fuel dilutes the additive content, the oil won't have enough strength to form that layer around your engine's moving parts. That absence of protection adds to the short and long-term damage your engine faces when oil and diesel mix.

Oil contamination

Oil and diesel fuel are not compatible substances; when they mix, it drags down the oil's effectiveness through oxidation. 

Oxidation brings down the lifespan of oil and happens naturally, but a splash of diesel speeds up the process. You can identify oxidized oil by its darkened color, increased viscosity, and sludge deposits. It's crucial to replace your oil as soon as you spot these signs.

Oil oxidization shortens the lubricant's lifespan and turns the oil against the engine, causing rust and corrosion that can destroy an engine. To prevent these issues, you need help from a mechanic that knows what causes oil to mix with diesel and how to fix the problems. All Bay Diesel is the best team for the job.

Call All Bay Diesel To Fix Your Diesel Vehicle's Oil Leaks

No matter what causes oil to mix with diesel in your vehicle, blending the two elements will render your oil ineffective. Luckily, All Bay Diesel will quickly get to the root of the issue so you can return to the open road in a flash. 

Call All Bay Diesel today at (925) 522-1780 to learn more about what causes oil to mix with diesel or diesel runaway causes and solutions.

View Full Version : LItte bit of gas in the diesel container?


Tom Fischer

I had gasoline in the diesel container not long ago.
Thought it was empty.
But saw there was a very tiny amount left, just as the guy was putting diesel in again.
Maybe a 1/2 ounce of gasoline 87 octane, mixed in with 5 gals of diesel.
Does that make any difference?

Didn't put it into the machine yet.

Thanks!

Mark Bolton

Nope, not an issue. I drove tractor trailer for a very short time and an old trucker who taught me a lot use to talk about drivers spiking their tanks with a couple gallons of gas for extra power. I can only imagine it wouldnt work very well with modern engines today.

I have it happen all the time where I have to use my diesel cans for gas and vice versa. Youll be fine.

ray hampton

I will guess that diesel fuel weigh more than gasoline so the gasoline will be on top of the diesel

Mark Bolton

I will guess that diesel fuel weigh more than gasoline so the gasoline will be on top of the diesel

They are the same product at different stages of refinement. They will mix instantly. Some older diesel engines even stated that up to a 30% mix is was acceptable. Kerosene, is commonly mixed with diesel to reduce gel'ing in the cold. None of them will float ontop of one or the other.

Steve Rozmiarek

I work with a guy who put a 1/4 tank of gas in his diesel pickup. It worked fine, but we still give him grief about it.

Mike Henderson

That small amount of gas will not cause any problems. The difference between diesel and gas is that gas doesn't have any lubrication properties so if you put all gas in a diesel engine the injector pump will probably die because it's lubricated by the diesel.

But a small amount of gas in diesel will not cause any problems.

Mike

ray hampton

They are the same product at different stages of refinement. They will mix instantly. Some older diesel engines even stated that up to a 30% mix is was acceptable. Kerosene, is commonly mixed with diesel to reduce gelling in the cold. None of them will float on top of one or the other.

Since diesel weigh more than gasoline , why won't it float on top of diesel , water weigh more than the fuel, If you add water to your gasoline or diesel tank , will it mix or go to the bottom of the tank ?

Mark Bolton

Water and petroleum are not soluable by each other. You know the old phrase "oil and water don't mix". However oil and oil do.

Bill Cunningham

We used to use a spray bottle of gas sprayed into the turbine to flash up the diesels when ether wasn't available..Yes gas will mix with diesel, and No, water won't mix with diesel because it's an entirely different composition.

Tom Fischer

Thanks for all the replies. Don't know much about the water/fuel thing, but I was told to always put diesel Stabil in the tank over the winter, which has a desiccant in it.

Charles Wiggins

You may want to read through this to help you decide what to do. http://www.turbodieselregister.com/mixing_gasoline_and_diesel.htm

ray hampton

We used to use a spray bottle of gas sprayed into the turbine to flash up the diesels when ether wasn't available..Yes gas will mix with diesel, and No, water won't mix with diesel because it's an entirely different composition.

I never own a diesel engine BUT IF the FUEL station add water to the fuel tank the way that water are pump into your gas tank,, I bought gas at a certain station that got caught adding water to your gasoline and after I hung the nozzle back up, the water kept on running out of the hose connection , must been a double hose setup

Mark Bolton

You may want to read through this to help you decide what to do. http://www.turbodieselregister.com/mixing_gasoline_and_diesel.htm

Very interesting read. Probably should have asked Tom what he was using the diesel for. I assumed a small piece of equipment given the 5 gallon can. I highly doubt anyone is considering adding gas to the tank of their 60K cummins pickup :) A couple ounces in the bottom of a 5 gallon can is a different story.

The above read of course is pertaining to large percentages of gasoline and its additives going into the motor, likely turbo, of a vehicle similar to the upper left corner.

As an aside, with the money they lay out for a diesel and its overwhelming operating costs over its lifetime, I know several locals who wont even put blended bio in the tank for fear of problems. Sure glad I dont own one.

Tom Fischer

Yes,. it's a Kubota turbo diesel, Lastec 3696 ZTR.
Pretty loud, but pretty fast.
Got it used a few years ago, 500 hours on the clock.
I told my wife I was having a mid-life crisis.
She said, go ahead, get it. :cool:

260464

Mark Bolton

Wow, I'll bet you can knock it down with that. See guys around with similar mowers and looks like they can mow at about 30mph

Tom Fischer

Well, it doesn't go 30, but the book says it can mow at 9 MPH, which is a pretty fast run.
I can't go that fast, because 9 MPH is for a lawn that is like a billiard top, and I haven't gotten mine rolled anywhere near that.
But it is an 8' cut, with hinged decks, no scalping.
And I said loud too.
Sticker on the back says 105 db.

When this machine was new (2005) it was the largest Zero Turn made in America.
(... some pithy saying about the age of the boys and size of the toys)

Steve Losing

Had a construction crew at my place last summer and they ran there diesel skidsteer out of fuel. They asked if I had any starting fluid and I did not have any. They then asked if I had any unleaded gas. They put fuel in the tank but could not get the fuel pump to prime so the unit could be started. He then took and opened the air cleaner took a piece of an old rag towel soaked it with gas laid it on the air cleaner, the minute they started to crank the engine if fired and away it went. So I learned a new and very useful trick if I ever run my truck or tractor out of diesel.

Craig Matheny

Yes,. it's a Kubota turbo diesel, Lastec 3696 ZTR.
Pretty loud, but pretty fast.
Got it used a few years ago, 500 hours on the clock.
I told my wife I was having a mid-life crisis.
She said, go ahead, get it. :cool:



260464

Tom I have about 1000 sq feet of grass at my house would yo have that done in 1 or 2 passes?

Does diesel fuel sit on top of oil?

LItte bit of gas in the diesel container? [Archive]

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