Whether or not you can or should use starting fluid to aid starting a diesel engine is a hugely debated topic. As a professional diesel engine parts supplier, I set out to do some extensive research and find a definitive answer.
Some swear by giving their diesel a quick squirt of starting fluid when struggling to turn over on cold days. Yet others warn this can cause catastrophic damage. So who’s right?
Should You Use Starting Fluid on Diesel Engines?
After digging into manufacturer documentation, diesel forums, and expert insight, the short answer is no — you should avoid using starting fluids on most diesel engines. Modern diesel engines are finely tuned and designed to start in cold weather when properly maintained. Relying on starting fluid masks underlying issues and risks serious damage from pre-ignition and detonation.
However, some older diesel engines may explicitly allow careful use of starting fluids as a cold start aid. So let’s explore the reasoning in more detail.
How Do Diesel Engines Work?
First, a quick diesel engine primer. Unlike gasoline engines, diesels rely on compression ignition. Intake air is compressed until hot enough to spontaneously combust injected fuel.
There’s no spark plug — combustion timing is entirely controlled by precisely timed fuel injection. That leads into why starting fluids can be so problematic…
Risk of Pre-Ignition & Detonation
With no spark plug, there’s no way to control when a starting fluid/air mix ignites. Compression raises in-cylinder temperatures high enough that starting fluid can pre-ignite before the piston reaches top dead center.
This premature combustion can lead to detonation — an uncontrolled pressure spike that can break pistons, rods, and even crack engine blocks. It’s no wonder manufacturers warn to never use starting fluid in most diesel applications!
What About Diesels With Glow Plugs?
Glow plugs pose another risk, providing a red hot ignition source that makes pre-ignition even more likely. Never use starting fluids in diesel engines equipped with glow plugs or other intake heating elements.
Are There Any Exceptions?
Some older diesel engines with relatively low compression ratios and without glow plugs may recommend careful use of starting fluid.
Consult your owner’s manual — if starting fluid is explicitly approved, use sparingly (short 2-second bursts into the air intake after disabling glow plugs). Still, address the underlying reasons why the engine struggles to start when cold.
Maintenance & Proper Starting Procedure
Rather than reaching for the starting fluid, ensure:
- Fresh fuel that hasn’t degraded from sitting
- High-capacity batteries fully charged
- Block heater used in extreme cold
- Glow plugs functioning properly
- Fuel filters changed as specified
- Air filters checked and within service limits
- Low pressure fuel system inspected
- Proper weight oil for expected temperatures
Consult your owner’s manual for the prescribed cold starting procedure. With everything functioning properly, even diesels without glow plugs should start with minimal cranking in cold weather.
If not, you likely have an underlying fault to address instead of masking it with starting fluids. Now let’s explore solutions to common reasons for hard starting.
What to Do if Your Diesel Won’t Start
Let’s talk through some of the most frequent culprits behind cold starting difficulties:
1. Weak or Dying Battery
Cold weather already puts more strain on batteries. Combine sitting unused for extended periods with older batteries at the end of their service life, and you may not have enough amps to swiftly crank and start the engine.
Testing Battery & Alternator Health
Most auto parts stores offer free battery testing services that measure cranking power and health. This straightforward battery load test can confirm if yours are up to the task.
While you’re at it, also have them test alternator output. A faulty alternator slowly drains batteries even when the vehicle is parked.
When to Replace Batteries
If your batteries fail testing, or are over 5 years old, replacement is the fix. Topping off with distilled water can buy time, but worn out batteries with degraded plates need retirement.
Install fresh batteries sized appropriately for the application. Diesel engines in large trucks, heavy equipment, boats, etc. require deep cycle batteries to handle sustained cranking demands.
2. Sticking Injectors or Glow Plugs
As diesel engines accumulate run time, carbon deposits and gunk buildup can stick vital components like injectors and glow plugs. This hinders cold starting.
Fortunately specialized diesel fuel additives help clean deposits. Products containing ingredients like Power Service Diesel Kleen can dissolve residue when added to fuel periodically.
For stuck injectors that disabling glow plugs and carefully spraying starting fluid won’t free up, professional cleaning or replacement may be required.
3. Low Cranking RPM & Oil Viscosity
Two other culprits that prevent establishing enough heat to fire off the engine in winter is slow cranking speed and thick cold oil.
Preliminary engine rotation must be fast enough for compression to sufficiently heat in-cylinder air. And while thinner oils strain the lubrication system less when cold, they reduce protection in high-heat running conditions.
Using slightly heavier oil offsets diminished winter flow rates. A high quality 5W-40 or 15W-40 diesel oil improves both ends of temperature extremes. Match viscosity to OEM specifications.
Verify batteries provide robust cold cranking amps (CCA) for proper RPM. Clean corrosion on connections, charge fully, and replace aging batteries.
4. Air Intake Obstructions
It goes without saying restricted air filters hinder cold intake airflow. But iced-over inlet piping is just as problematic. Thoroughly check the air path leading to the intake manifold.
Clear intake piping ice blockages with gentle heat. Remove and properly clean or replace clogged air filters per maintenance intervals.
With the fuel, electrical, and air delivery systems squared away it’s unusual for any properly maintained, modern diesel engine to not start swiftly in cold climates. Practice diligent preventative maintenance steps to avoid crutching on starting fluids.
Are Diesel Additives & Lubricants Safe Alternatives?
Some promote using substances like WD-40 or even gasoline sprayed into the cylinders or intake as either cold start aids or diesel fuel substitutes/extenders. Let’s explore some severe downsides to these methods:
Gasoline in Diesel Engines
Pouring a bit of gasoline into an older tractor or heavy equipment running tank empty is a traditional field fix. But this cure might prove worse than the symptom when done repeatedly or in excess.
Gasoline lacks the lubricating properties of diesel fuel. Injecting straight gasoline into cylinders accelerates wear. And even small amounts blended with diesel throw off cetane ratings.
Using unleaded gasoline can damage fuel delivery components not designed for compatibility. While convenient in a pinch, rely on proper diesel fuel instead whenever possible.
WD-40 Risks
Some mechanics recommend spraying WD-40 into air intakes as an alternative for sticky old diesels. However WD-40 is a water displacing solvent, not a fuel or lubricant.
While WD-40 may free up stuck rings to promote temporary starting, it does not properly ignite. Runoff collects in the sump eventually tainting engine oil, reducing its effectiveness. Treat WD-40 only as a short-term diagnostic — not an ongoing remedy.
The best approach? Adapt a diligent maintenance schedule. Change filters and fluids on time, fuel with high quality diesel (including anti-gel additives in winter), and proactively replace aging parts before they leave you stranded. A little prevention goes a long way!
Even with a sound maintenance regimen extreme cold inevitably raises the degree of difficulty to start diesel engines. Let’s explore some other procedures to assist firing off diesels minus the risks of starting fluids…
Alternative Safe Cold Start Aids
Rather than resorting to pouring gasoline or spraying engines with starter fluid or other flammable chemicals, try these tactics first when battling cold:
1. Pre-Heat Engine Block
Rather than combat cold diesel startup woes, avoid them entirely with block heaters. Heating elements warmed by extension cords plugged in ahead of time keeps oil viscosity and coolant flowing for rapid warm ups.
Block heaters conveniently hook up out of sight beneath the hood. Just run a cord out the grill. Set a timer to flip it on 2-3 hours before needing to start.
Make sure your block heater still works if your vehicle came equipped. Check for leaks at the heater or cord and replace dysfunctioning units as required.
2. Battery Blankets & Warmers
Bolstering starter battery output for improved cold cranking helps establish quick engine momentum. Insulating battery cases protects them from direct exposure and keeps juice flowing strong.
Secure battery blankets around your batteries or try self-adhesive heating pads stuck directly on the cases. This fights the brunt of winter’s draining effect. Warming cold oil also yields quicker oil pressure buildup.
3. Windblockers & Shelters
One of the best remedies for truly bitter cold diesel startup woes is simply keeping engines out of the elements. Placing windbreaks around equipment forces frigid breeze away.
Fully sheltering machinery in garages or under tarps is ideal when forecasts dive far below freezing. The less brutal the ambient air temperature, the easier achieving ignition becomes.
While wind and cold absolutes strain diesel startups, properly formulated fuel still ignites with adequately conditioned engines. Let’s cover best practices for keeping diesel fuel in top form…
Winter & Cold Weather Diesel Fuel Prep Tips
Petroleum diesel fuel is manufactured and distributed according to various climate specifications per region. In other words, winter diesel stands up to frigid temperatures far better than summer blends.
Diesel properties like cloud point and cold filter plug point determine operability margins given ambient conditions. Winter blends remain fluid and pass through fuel filters at lower temps than summertime diesel versions.
So if you experience difficulty starting in extreme cold with summer fuel still in tanks, try adding diesel anti-gel formulas. These lowers diesel’s freeze point to prevent thicker, unpassable consistency.
Biogenic diesel additives containing alcohols like Power Service Bio-Kleen work well for this scenario. Maintaining fluidity down to -50° Fahrenheit keeps fuel injecting properly into cold cylinders. Treat diesel per instructions.
The benefits of diesel fuel additives go beyond cold flow readiness though…
Additional Perks of Diesel Fuel Additives
Topping off tanks with specialized fuel supplements confer other unseen advantages as well:
- Injector & fuel pump lubricity enhancers reduce wear
- Detergents maintain injector cleanliness
- Corrosion inhibitors protect tanks
- Cetane boosters promote easier ignition
- Improved combustion lessens smoke & emissions
So while biogenic diesel anti-gels ready fuel for the unique demands of cold operation, other additives present welcome peripheral support too.
Always stick to manufacturer approved diesel additives. Prescribed dosages deliver optimized performance — more is NOT necessarily better!
The Bottom Line on Pouring Additives into Diesel Engines
While some promoters claim directly pouring motor oils, transmission fluids, or other additives into air intakes or fuel tanks benefit diesel engines, more harm than good arises from this practice.
Any deviation from factory fill specifications risks reducing oil system effectiveness. And accidental overdosing diesel with concentrated additives throws off vital fuel properties.
Instead stick to reputable diesel additive formulas used as directed. Addressing mechanical issues, upgrading failing parts, and safeguarding operating conditions makes far more impact.
Modern diesel engines are remarkably resilient when properly maintained. But neglect invites a mountain of expensive headaches best avoided!
So let’s recap using starting fluids or alternative quick fixes in diesel engines:
Conclusion – Should You Use Starting Fluid in Diesel Engines?
Starting fluids pose an unacceptable risk of pre-ignition and catastrophic damage in most diesel applications. But a properly maintained, modern diesel engine should NOT require any sort of starting aid.
Rather than reaching for starting fluids or even pour-in diesel additives, always thoroughly vet the:
- Battery & electrical charging systems
- Air intake tracts for obstructions
- Fuel quality & characteristics
- Operating conditions & environment
Upgrade worn parts and fluids to factory specifications. And most importantly — follow prescribed maintenance intervals!
While field fixes like battery blankets, engine block heaters and windbreaks help significantly, nothing substitutes practicing due diligence in preventative maintenance.
Hopefully this extensive guide better explains both the risks of improperly using starting fluids and why modern diesels are designed not to need such extreme measures! Let me know in the comments your experiences dealing with cold diesel starts!