Stihl HP Ultra 50:1 (Oil Mixing Guide)

STIHL HP Ultra is two-stroke engine oil for making a 50:1 fuel mix when your equipment manual specifies that ratio. Measure 20 mL of oil for each 1 L of gasoline, or about 2.6 US fluid ounces per US gallon. Use fresh, approved gasoline, mix safely, label the container, and never use this fuel mix in a four-stroke engine.

If you’re heading out soon, the key is to measure the oil rather than guess. Too little oil can leave a two-stroke engine without enough lubrication; too much can also affect how it runs. I check the machine’s manual first, then measure the fuel and oil for the exact batch I need.

What 50:1 Means for HP Ultra

A 50:1 mix means 50 parts gasoline to 1 part two-stroke oil, measured by volume. When the machine’s manual calls for 50:1, use the amounts below as a measuring guide. Check the manual before mixing, because the machine’s fuel instructions take priority over a general ratio.

Measure the gasoline first, then measure the matching oil amount. These figures refer to the volume of gasoline, not the final volume of the mixed fuel. A graduated oil measure or a marked mixing bottle is more reliable than a kitchen spoon or an estimate by eye.

The ratio is not a measure of oil quality or fuel strength. HP Ultra is a two-stroke engine oil, and the 50:1 figure tells you how much to add when your machine specifies that mix.

Equipment Setup and Fuel-Mixing Safety

Good mixing starts with the correct machine and clean materials. HP Ultra is for two-stroke premix applications that call for compatible oil and a 50:1 ratio. It is not bar-and-chain oil, and it does not belong in a four-stroke engine or in a machine with a separate oil reservoir.

Before you open the fuel can, check the machine’s manual for the required fuel type, octane rating, and oil ratio. STIHL commonly specifies gasoline rated at least 89 AKI for its equipment, but requirements can vary by machine and market. Follow the manual for your specific model.

Use gasoline with no more than 10% ethanol (E10), unless your machine’s manual explicitly allows otherwise. Do not use E15 or E85. Keep gasoline clean and fresh. Dirt or water in the fuel can cause running problems and may damage the engine.

Set up outdoors or in a well-ventilated area, away from flames, sparks, smoking, and hot equipment. Wear eye protection and fuel-resistant gloves. Use a clean, approved fuel container that is made for gasoline and can be sealed securely.

Quick check before mixing:

• Confirm that the engine uses two-stroke premix.
• Confirm that its manual specifies 50:1 and the gasoline grade.
• Use clean, fresh gasoline that meets the manual’s requirements.
• Keep the fuel container and measuring tool clean and dry.
• Keep ignition sources away from the mixing and refueling area.

If you cannot confirm the ratio, pause and find the manual or manufacturer’s instructions. Do not assume that every two-stroke machine uses the same mix.

How to Mix HP Ultra at 50:1

Mixing in two stages helps the oil spread through the gasoline. Measure each amount carefully, keep the container closed between steps, and label the finished batch. A clear label also helps prevent a mix-up with straight gasoline or fuel intended for another machine.

1. Start with a clean, approved fuel container.
2. Add about half of the measured gasoline.
3. Measure the HP Ultra with a suitable graduated tool. Use the table above for the batch size.
4. Add the measured oil to the container.
5. Add the rest of the gasoline, close the cap, and shake the container thoroughly.
6. Label it with the mix ratio and date.

For example, for 5 L of gasoline, measure 100 mL of HP Ultra. Add about half the gasoline to the can, add the oil, then add the remaining gasoline and shake. Do not pour oil into the machine’s tank first and try to estimate the gasoline amount afterward.

In the shop, I have seen a common source of confusion: a person remembers that their machine needs “two-stroke mix” but not the ratio. That is not enough information to mix safely. If you do not know what is already in a container, do not try to fix it by adding oil. Prepare a fresh, correctly measured batch instead.

Field Operation and Safe Refueling

Safe refueling means the engine is stopped and cool, the area around the fuel cap is clean, and the correct fuel is ready. A correct mix does not remove the need to follow the machine’s starting and operating instructions. Keep bystanders clear and use the protective equipment listed in the manual.

Before opening the fuel tank, wipe away dirt around the cap so debris does not fall inside. Refuel without overfilling, close the cap securely, and wipe up spills. If fuel spills on the machine or ground, follow the manual’s cleanup and restart instructions; do not start a machine with fuel on it.

A common shed-side example: you have a partly filled can and cannot remember when it was mixed. Check the label if there is one. If the date or contents are unknown, avoid using it. Fresh fuel with a known ratio is a better choice than guessing, especially when you are about to work with a chainsaw.

Never run straight gasoline in a two-stroke engine that requires premix, even briefly. Gasoline without the required oil can remove lubrication and cause rapid piston and cylinder damage. If you suspect the machine has been filled with straight gas, stop using it and consult the machine manual or an authorized service provider.

Maintenance, Inspection, and Engine Care

The fuel mix is one part of engine care, not a cure for every running problem. If the engine stalls, runs poorly, or seems to lack power, first stop safely and check the basics in the manual. Do not keep operating it while trying to diagnose a possible fuel or lubrication fault.

If you suspect the mixture has too little oil, contains the wrong fuel, or has become contaminated, stop using it. Drain and dispose of suspect fuel according to local rules, then prepare a fresh batch at the required ratio. Do not add oil to an unknown mixture: you cannot reliably know how much oil is already in it.

After use, stop the engine and let it cool before cleaning or handling fuel. Check for leaks or damage, and follow the machine’s maintenance schedule. If you notice a fuel leak, stop using the equipment until it has been checked and repaired.

Storage and Seasonal Fuel-System Care

Fuel condition changes over time, so make only as much mix as you expect to use promptly. As a conservative limit, use conventional premixed fuel within 30 days, or sooner if the manual says to. Keep it sealed, labeled with the ratio and date, and stored away from heat and ignition sources.

Do not rely on smell or appearance alone to decide whether old fuel is usable. If a container’s age or contents are uncertain, or the fuel may be contaminated, do not put it in the machine. Dispose of it according to local rules and make a fresh batch.

For storage between uses or at season’s end, follow the equipment manual’s fuel-system instructions. Procedures can differ by model, so do not assume that one storage method suits every machine. Keep fuel out of reach of children and never store it in an unapproved container.

Conclusion: Check, Measure, Label

For a machine that calls for a 50:1 mix, the working measurement is 20 mL of HP Ultra per 1 L of gasoline, or about 2.6 US fl oz per US gallon. Confirm the manual’s fuel requirements, mix in a clean approved container, and label the batch. If the fuel or ratio is uncertain, make a fresh mix.

Frequently Asked Questions

How much HP Ultra goes into 1 L of gasoline?
Use 20 mL of HP Ultra for 1 L of gasoline when the machine specifies a 50:1 ratio.

How much HP Ultra goes into 1 US gallon of gasoline?
Use about 2.6 US fluid ounces per US gallon of gasoline for a 50:1 mix.

Is STIHL HP Ultra always mixed at 50:1?
Use 50:1 only when the equipment manual calls for it. The manual’s instructions for your machine take priority.

Can I use this mix in a four-stroke engine?
No. Do not use two-stroke premix in a four-stroke engine unless its manual specifically requires that fuel type.

Can I use HP Ultra as bar-and-chain oil?
No. HP Ultra is two-stroke engine oil. Use the bar-and-chain lubricant specified for the machine’s oil reservoir.

What gasoline should I use?
Use clean, fresh gasoline that meets your machine manual’s octane requirement. STIHL commonly specifies at least 89 AKI, but check the manual for your model.

Can I use E15 or E85 gasoline?
Do not use E15 or E85. Keep ethanol at 10% or less unless the machine manual explicitly allows otherwise.

How long can I store a conventional 50:1 mix?
As a conservative limit, use it within 30 days, or sooner if the manual specifies. Label the container with the date and ratio.

What should I do if I do not know the ratio in my fuel can?
Do not guess or add oil to try to correct it. Set the unknown fuel aside for proper disposal, then mix a fresh batch accurately.

What if I accidentally used straight gasoline?
Stop the engine and do not continue operating it. Follow the manual or contact an authorized service provider for next steps.

(This article was written by one of our staff writers, David Hensley. Visit our Meet the Team page.)