⚠️ WARNING: DO NOT TRY THIS AT HOME
This experiment was conducted by professionals in a controlled environment to test a dangerous internet myth. Pouring fuel into your engine oil can cause fire, explosion, and catastrophic engine failure. The Auto Pulse does not recommend this method.
Thousands of drivers online claim that pouring gasoline, diesel, or kerosene into engine oil is a "secret mechanic trick" to clean sludge, restore power, and fix noisy lifters overnight.
So, I decided to find out the truth once and for all.
I poured actual gasoline into a high-mileage engine, started it, and let it run. What happened next was terrifying, surprising, and unbelievably revealing about how dirty an engine actually is inside.
A dangerous experiment to see if fuel really cleans engine sludge.
Why Mechanics Secretly Do This
Before you judge this experiment, here is the honest truth: Old-school mechanics have used chemical flushes for decades.
Some technicians swear by a splash of diesel fuel or kerosene mixed with oil to soften baked-on deposits before an engine rebuild. Fuel is a powerful solvent. It dissolves hardened varnish, sticky sludge, and carbon buildup around hydraulic lifters.
The Danger: Gasoline thins oil to the point where the engine is barely protected. A few seconds too long, and the bearings could seize from lack of lubrication.
The Test Vehicle: A Sludged Toyota Engine
The volunteer for this experiment was a 168,000-mile Toyota 4-cylinder engine. It was tough, but it had issues:
- Noticeable ticking on cold starts.
- High oil consumption.
- Visible sludge under the oil cap.
- Low compression on cylinder #3.
The Experiment: 8% Gasoline Mix
We didn't just dump a gallon of gas in. We used a "safe" ratio recommended by engine rebuilders: 8% fuel to oil volume (about 10 oz of regular gas for a 4.5-quart system).
We ran the engine at a fast idle (1,200 RPM) for exactly 12 minutes.
What Happened? (The First 30 Seconds)
The moment the gasoline hit the crankcase, the engine instantly got quieter. The ticking sound vanished in less than 10 seconds. The solvent thinned the oil enough to flow into tiny lifter passages immediately.
But then the scary part started:
- Oil Pressure Drop: Pressure fell from a healthy 22 PSI to a dangerous 12 PSI almost instantly.
- Smell: The exhaust smelled like raw gas mixed with burnt varnish.
If I had revved the engine, the pressure would have dropped into single digits, likely spinning a bearing.
The Results: Inside the Oil Pan
After 12 minutes, I drained the oil. It poured out like black water.
Inside the drain pan, we found floating flakes of carbon, soft sludge clumps, and a metallic shimmer (early bearing wear). This confirmed two things:
- Fuel flushes dissolve sludge FAST.
- Fuel flushes break loose debris that can clog oil passages.
Did It Actually Clean the Engine?
We pulled the valve cover to see the truth. The results surprised everyone in the shop.
- Before: Thick brown varnish, baked-on deposits, and dark staining on cam lobes.
- After: The varnish layer was visibly lighter. Sludge around oil return holes was reduced. The cam lobes looked freshly washed.
The Cost: We found faint metal-on-metal scoring on the cam bearing caps. The gasoline had cleaned the engine, but it also erased the oil's ability to protect it from friction.
Compression Test Results
Did the flush free up the stuck piston rings? The numbers don't lie.
| Cylinder | Before Flush | After Flush | Result |
|---|---|---|---|
| #1 | 171 psi | 174 psi | +3 psi |
| #2 | 168 psi | 172 psi | +4 psi |
| #3 (Weak) | 158 psi | 165 psi | +7 psi |
| #4 | 169 psi | 171 psi | +2 psi |
The Verdict: Compression improved significantly on the weak cylinder. The solvent dissolved carbon around the rings, allowing them to seal better.
The Safe Alternative (Do This Instead)
While the gasoline flush worked, it caused dangerous wear. Here is how mechanics achieve the same results safely:
1. High-Detergent Synthetic Flush
Use a premium high-detergent oil (like Pennzoil Ultra Platinum or Amsoil) and run it for a short interval (500 miles). This cleans slowly and safely.
2. Professional Engine Flush Products
Use products designed for this, like Liqui Moly Engine Flush or BG EPR. These use controlled detergents that don't destroy lubrication like raw fuel does.
3. Piston Soak
If you have low compression, mechanics use Berryman B-12 or Seafoam applied directly into the cylinders (through spark plug holes), not in the oil.
Final Verdict: Should You Use Fuel?
No. The cleaning benefit is real, but the risk of bearing failure is too high. Stick to premium synthetic oil and frequent changes. That is how you keep an engine alive for 300,000 miles.
Have you ever tried an old-school engine flush? Tell us your story in the comments!
Disclaimer: This article documents a controlled experiment. The Auto Pulse is not liable for any engine damage caused by attempting this procedure.
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