A/C Pro

#PopTheHood: A Dipstick’s Guide to Dipsticks

Even if you’re not a mechanic (which is pretty much everybody, except for—well, mechanics), there are some things every driver should know how to do under the hood.

Checking the fluids is definitely on that list, and is a very simple thing that can potentially help you avoid expensive repairs. That’s because the oils and other fluids help protect your vehicle from itself: they prevent wear and tear on moving parts, keep the car from overheating, and help you control it so you don’t crash into anything.

If you don’t know a dipstick from a radiator cap, this post’s for you. Below is a description of how and when to check each fluid, and what to do if it is low. Just park your vehicle on a level surface, pop the hood, and follow the (really simple) instructions.


1. Engine oil


How to find it:  The engine oil dipstick will be on the side of the engine. For a front-wheel-drive vehicle, where the engine is aligned sideways between the front two wheels, it will probably be on the side closest to the front of the car. The cap/handle for the dipstick will usually be yellow.

When to check it:  When the engine is off, and has been off for at least five minutes. The easiest way is to check it in the morning, before you drive anywhere; that way, both the engine and dipstick will be cool. How often you check the motor oil depends on how much you drive (and some other factors), but it should probably be between once a week and once a month.

How to check it:  Pull the dipstick all the way out and wipe it off with a clean rag or paper towel. Then put it back in, all the way, for a second, before pulling it out again and reading the dipstick. The end of the dipstick will be marked with the safe operating range, and an “Add” line below that.

What if it’s low?   It’s not unusual for an engine to use up some oil between oil changes. As long as it’s not leaking (leaving oil spots on the ground), or using an excessive amount (more than a quart or two between oil changes), you’ll be fine if you just make sure to add oil when it’s low. If it is leaking or using a lot of oil, you’ll want to get it checked by a mechanic.


2. Transmission oil


How to find it:  The transmission oil dipstick, if your car has one, will be towards the back of the engine towards the firewall (which is where the transmission is). It will typically have a red handle. Most manual transmissions, and some newer automatics, don’t have a transmission dipstick at all.

When to check it:  When the engine is warm and running. It doesn’t need to be checked nearly as often as the engine oil, though; once a month, perhaps, or once per engine oil change.

How to check it:  The same basic procedure as checking the motor oil. But, since the engine is running, you’ll need to be more careful about not touching any parts that are moving or hot.

What if it’s low?   It means you have a leak, which you’ll probably need to get fixed.


3.  Brake fluid


Where to find it:  The brake fluid reservoir will be a small, typically rectangular container located just in front of where the driver sits. It sits on top of a metal shaft, which is attached to a metal drum on the firewall.

When to check it:  When the engine is off, and about as often as you check the transmission oil.

How to check it:  Brake fluid reservoirs are sometimes plastic containers with “full” and “low” markings on the outside of the reservoir, allowing you to check just by looking at it. If you can’t see the level that way, you’ll need to remove the reservoir lid and check the level inside.

What if it’s low?   There are two possibilities. It could mean that your brake system is leaking and needs to be fixed (brakes are important, y’all!). Or, it could just indicate that the brake pads are worn and need replacing. As the brake pads get thinner, more fluid gets stored in the wheel cylinders instead of the reservoir; putting in new, thicker pads will cause the level in the reservoir to rise.


4. Power steering fluid


Where to find it:  The power steering pump is one of the belt-driven accessories at the front of the engine. It will have a cap labeled as “Power Steering Fluid,” or perhaps a picture of a steering wheel.

When to check it:  When the engine is off. Check it every month or so, or if you notice the steering wheel getting harder to turn.

How to check it:  Remove the cap and check the dipstick. It works the same as the engine or transmission oil dipsticks, except that it is much shorter.

What if it’s low?   It means you’re leaking power steering fluid. You can add fluid to keep driving, but you’ll need to get the leak repaired to fix the problem.


5. Coolant


Where to find it:  There should be a plastic coolant reservoir in a corner of the engine compartment, linked to the radiator by a hose. The cap should be labeled as “Coolant.”

When to check it:  Any time you are under the hood, since you just have to look at the reservoir to see the level, and it’s marked with both the “hot” and “cold” levels depending on whether the engine is running. WARNING! NEVER REMOVE THE RADIATOR CAP FROM THE RADIATOR WHEN THE VEHICLE IS HOT!!

How to check it:  Just look and make sure it is at or above the correct “hot” or “cold” marking.

What if it’s low?   You have a leak somewhere. But, you can add coolant to drive your care somewhere without it overheating. Coolant is typically a 50/50 mix of antifreeze and water. Adding only water is a bad idea unless you have a fast leak or are going to be replacing the coolant shortly.


6. Windshield washer fluid


Where to find it:  It’s another plastic container in a corner of the engine compartment, usually much smaller than the coolant reservoir. It will have a cap labeled “Washer Fluid” or with a picture of a windshield getting sprayed with fluid.

When to check it:  About once per oil change.

How to check it:  Visually. There is no dipstick, because there is no “correct” level of washer fluid; either you have some, or you don’t.

What if it’s low?   If it looks low, you can add more to keep from running out.


There is one other “fluid” of a sort under the hood. The refrigerant in your A/C system is in liquid form part of the time, though it turns into a gas as it cools the air. (See “How a Car A/C Works” for a full explanation.) Instead of using a dipstick or checking visually, the amount of refrigerant in the system is measured by checking the pressure. If your car air conditioner is not as cold as you’d like, you can check the pressure with a gauge. If it is low, you can add refrigerant and seal the leak that caused the problem with a can of A/C Pro.

Questions? Feel free to contact us and ask the pro.