Automatic transmissions are impressive systems, designed for smooth gear changes and a more comfortable driving experience. But like any complex part of your car, they need regular care. One of the most crucial tasks drivers often overlook is knowing how to check your Automatic Transmission Fluid (ATF). This fluid keeps your transmission cool, lubricated, and working efficiently. In this guide, we’ll walk you through how to check automatic transmission fluid step by step, explain what to look for, and show you how to top it up — all with practical advice tailored for UK drivers.
Why Checking ATF Is Important
Your transmission fluid is the lifeblood of your automatic gearbox. It lubricates moving parts, keeps the system cool, and transmits hydraulic pressure for smooth gear changes. Over time, ATF can degrade, get contaminated, or just run low, and that can cause problems. Low ATF symptoms include:
- The car is not shifting smoothly
- Transmission slipping
- Delayed or rough gear changes
- Overheating transmission
- Unusual noises or vibrations
If you ignore these warning signs, you could be looking at expensive repairs or even a failed transmission. Regular checks are the simple way to catch issues early and keep your car running reliably.
When to Check Transmission Fluid
For most cars, you should check the ATF level at least once a year or every 30,000 miles, whichever comes first. But always refer to your car’s owner’s manual ATF section for the manufacturer’s recommendation, as some modern cars have sealed transmissions that don’t need routine checks.
Other good times to check ATF include:
- Before long journeys
- If you notice signs of low transmission fluid
- After towing or heavy use
- If the car is not shifting smoothly
Should the Engine Be Running or Off for ATF Check?
For the most accurate reading, the engine should be running and at normal operating temperature. This is because the transmission fluid circulates through the system only when the engine is o,n and the level changes as fluid moves through the torque converter and transmission pump. Always check the fluid with the car in Park (P) or Neutral (N), handbrake engaged, and on a level surface.
Cold vs Hot ATF Reading
Transmission fluid expands as it warms up. Most vehicles are designed to have the ATF checked when hot, after a short drive or about 10 minutes of idling. Some dipsticks have markings for both cold and hot readings. If you check it cold, the level will be lower, so always follow the markings and your owner’s manual for guidance.
Step-by-Step: How to Check Your Automatic Transmission Fluid
Prepare Your Vehicle
- Park on a flat surface.
- Engage the handbrake.
- Start the engine and let it idle for 10 minutes.
- Move the gear selector through each gear briefly, then back to Park or Neutral.
Find the Transmission Fluid Dipstick
- Open the bonnet and look for the transmission fluid dipstick – usually yellow, orange, or red handle, near the back of the engine bay.
- If you’re not sure, check your owner’s manual ATF section for the location.
Remove and Clean the Dipstick
- Pull out the dipstick and wipe it clean with a lint-free cloth or paper towel.
- This removes old fluid and gives an accurate reading.
Check the ATF Level
- Put the dipstick back in and pull it out again.
- Look at the fluid level indicator: there are two marks or notches for the minimum and maximum safe level.
- The fluid should be between these marks. If it’s below the lower mark, you need to add transmission fluid.
Check Fluid Colour and Smell
- Healthy ATF is bright red or pink and has a sweet smell.
- If the fluid is dark brown, black, or has a burnt transmission fluid smell, it’s overheated or contaminated and needs to be changed.
- Milky fluid means coolant contamination – a serious issue that needs attention now.
Signs of Low Transmission Fluid
Knowing the signs can help you catch it early. Low ATF symptoms include:
- Hesitation or delay when shifting gears
- Transmission slipping (engine revs, but speed doesn’t increase)
- Unusual noises – whining or grinding
- Fluid leaks under the car
- Overheating warning lights
If you notice any of these, check your ATF level ASAP.
How to Top Up ATF
If your fluid is low:
- Use a funnel to add transmission fluid through the dipstick tube.* Add a little at a time and check the level after each addition to avoid overfilling.
- Only use the type of transmission fluid specified in your owner’s manual – the wrong type can damage.
- Never overfill; too much fluid can cause foaming and poor shifting.
Types of ATF
There are many types of ATF, and using the right one is critical. Common types are Dexron, Merco, and specific fluids for certain makes (e.g, Honda, Toyota). Check your owner’s manual or consult a professional if unsure.
What If Your Transmission Is Slipping?
If your transmission is slipping, don’t ignore it. Low ATF is a common cause, but it can also be worn internal parts or other issues. If topping up the fluid doesn’t fix the problem, book an inspection with a professional mechanic as soon as possible to avoid further damage.
DIY Transmission Fluid Check vs. Professional Service
Checking your ATF at home is easy for most cars with a dipstick. But many modern cars have sealed transmissions that require special tools and procedures. If you’re unsure or your fluid looks burnt or contaminated, it’s best to have a professional mechanic do a full transmission service.
FAQs
How often should I check my automatic transmission fluid?
Check your ATF at least once a year or every 30,000 miles, or more often if you notice any low ATF symptoms or drive under severe conditions.
What colour should transmission fluid be?
Healthy ATF is bright red or pink. Dark, brown, or black fluid with a burnt smell means it’s time for a change.
Can I check ATF if my car doesn’t have a dipstick?
Some modern cars have sealed transmissions. In these cases, checking or topping up ATF usually requires a visit to a professional garage.
What should I do if I find a fluid leak?
Transmission fluid leaks can cause serious damage. If you see red or pink fluid under your car, book an inspection immediately.
Can I add transmission fluid myself?
Yes, if your car has a dipstick and you use the correct fluid. Always add slowly and don’t overfill. If in doubt, seek professional help.
Visit ABS MOTs Auto Centre for Transmission Service
Regular ATF checks are part of automatic transmission maintenance to avoid costly repairs and keep your car shifting smoothly. If you’re unsure how to check your transmission fluid, think you might have low ATF symptoms, or want a professional transmission service visit, ABS MOTs Auto Centre. Our experienced technicians use the latest diagnostic tools to keep your gearbox in top condition, so you can drive with confidence, mile after mile.
Book your ATF check or transmission service with ABS MOTs Auto Centre today!
