Open up the hood, and look for the engine oil dipstick, the transmission fluid dipstick, and the reservoirs for coolant overflow, power steering fluid, brake fluid, and windshield washer fluid. Also locate the engine oil filler cap. If you have a manual transmission, there won’t be a transmission fluid dipstick, but there might (or might not) be a clutch fluid reservoir and some sort of associated small dipstick. See Figure 1, but bear in mind that not every car puts these things in the same places.
Figure 1 – Orientation As To Where Things Are
Figure 1 shows under the hood of a 2005 Ford Focus. To photo left is the front of the transverse-mounted engine where the belts are, with the joint to the transmission more toward photo right. The larger plastic tank on the left is the coolant overflow bottle, and the smaller one near it the power steering fluid reservoir. Also near these is a yellow arrow point to the oil filler cap. The yellow ring-shaped thing is the handle of the oil level dipstick.
At photo rear and right is another reservoir, this one is the brake fluid reservoir. There is another yellow arrow, photo right and front, pointing to a not-so-obvious ring-shaped thing. That is the handle of the automatic transmission fluid level dipstick.
Right next to the trans fluid dipstick is a black plastic tubular object: that is part of the air intake, coming from the air filter out of the photo to the right. Near it are two black plastic rectangular box-looking objects. The nearer one is a cover over the top of the battery. The farther one is the fuse box.
The windshield washer fluid bottle on this car is located to photo left, at the rear. These vary in location from vehicle to vehicle. The majority of them are up front in the engine compartment somewhere.
You are most concerned with the fluid levels in the reservoirs and the two dipsticks. Consult your owner’s manual to make sure you understand what each of those fluids is supposed to be. Putting in the wrong one can ruin machinery, which is very expensive indeed! Use the right stuff.
You should do this underhood check on a regular basis. It could be monthly on a newer vehicle, perhaps weekly on one of medium age. Do most of this before every start on an old vehicle.
Checking the Engine Oil
Engine oil is characterized by its viscosity and its lubricity, which are NOT the same thing! Viscosity is the one or two-number index, such as SAE 30 or SAE 5W-20. The right viscosity grade to use is specified in the owner’s manual. Smaller numbers indicate “thinner” (really, less viscous) oils. For the two-number grades, the first is the viscosity rating at 0 F (for cold winter starts), and the second is the viscosity rating at 200 F (for hot engine operation).
The viscosity rating must be right for the moving parts (bearings of multiple types) to “float” on a film of oil. Too little and they rub together and wear disastrously fast. Too much and the oil cannot get to the moving parts fast enough, so they rub together and wear disastrously fast.
Lubricity is the two-letter index such as S-M, S-N, or C-C. The first letter indicates what type of engine (S is for spark ignition, C is for compression ignition, which is diesel). The second letter should be at least as late in the alphabet as is specified in your owner’s manual. The further into the alphabet, the more lubricity this oil has. It protects the moving parts intended to float on a film of oil, that are actually rubbing together dry when you first start the engine, before the oil gets there to make the film. Lubricity also protects those other parts which do not float on a film of oil while the engine is running (cylinder walls and piston rings, valve train parts, etc.).
The viscosity and lubricity are given in an API “doughnut” symbol somewhere on the oil container, for all oils that are actually tested and verified to meet those specifications. If that API symbol is not on the container, then that oil does not meet API specs, and should not even be used in a lawnmower! See Figure 2. Everything else on the container label is advertising hype.
Figure 2 – Where the Trustable Information Is, On An Oil Container
Figure 2 shows the back side of a typical oil container. Because this one has a custom blend in it, I marked out the viscosity, to remind myself about it being such a blend. However, the API “doughnut” is what you should look for, when buying oil. This one is marked by the yellow arrow. It contains the lubricity rating “API Service SN”, and the viscosity rating “SAE 5W-30”. The note just below it reminds the user that it meets or exceeds the earlier lubricity specs SM, SL, and SJ.
What you buy should always meet or exceed the lubricity spec, and should match the viscosity that the owner’s manual says to use. The only exception would be an old, worn engine, which should be filled with one grade more-viscous oil: such as 10W-40 instead of 5W-30. For a two-number viscosity grade, it is the second (hot engine) number you are more worried about, with an old, worn engine (so a 10W-40 would be “one-step more viscous” than a 10W-30).
There are basically two materials that get mixed together to make a modern engine oil. One is simple refined petroleum, which never actually wears out, but it does get contaminated and dirty. It has rather poor viscosity characteristics all by itself, and very poor lubricity characteristics all by itself. The other material is a family of liquid-plastic polymers that made from petroleum. This stuff does wear out, but confers much-improved viscosity characteristics, and (even more importantly) is where most of the lubricity protection comes from.
Conventional motor oils are about 80% refined petroleum and 20% polymer additives. “Synthetic” motor oils are mostly the polymers. “Synthetic blends” fall in between. Higher polymer content confers better protection, lasts longer between oil changes, and is far more expensive. Use something at least equal to, or better than (more polymer content), what your owner’s manual says. But don’t push your oil change interval any longer than what it says, or the warranty may be voided.
To check engine oil level, pull out the engine oil dipstick and wipe it clean with a rag or paper towel. Re-insert it all the way, hold it there for a couple of seconds, and pull it out again. Look at where the oil level is, relative to the “add oil” and “full” marks on the dipstick. Look at this reading on both sides of the dipstick, because for some engines, they are different due to the odd angle at which the dipstick enters into the engine oil sump. Do this twice, or even three times, before you decide where your oil level really falls. Never trust the reading the first time you pull out the dipstick! You want to see something repeatable enough to trust. See Figure 3.
Figure 3 – Image of a Typical Engine Oil Dipstick
This one clearly shows the add and full marks, with cross-hatching in between. Because the add and fill marks are holes, you can read either side of the dipstick, and see that the reading is repeatable. The oil level is “full” on this one.
The usual range between “add oil” and “full” is 1 quart. If you are down to the “add oil” mark or slightly below it (heaven forbid!), add one full quart (of the right kind of oil) through the engine oil filler cap. If you are between the marks, but below halfway between, add half a quart. If you are above halfway between, you need add nothing. But whatever you do, do NOT overfill the sump! That can blow-out oil seals, which are expensive to repair. You can use a cut-off piece of a quart oil container, for an improvised funnel. See Figure 4.
Figure 4 – Improvised Oil Fill Funnel
Figure 4 shows the cut-off top of a quart oil container being used as a convenient improvised funnel in the oil filler location. The oil filler cap is laying next to it.
The older the vehicle gets (burns oil), and the more leaky it has become (drips oil), the more often you will have to top-up the engine oil at every check. Once it is using a quart in 300-500 miles or less, you ought to consult a mechanic.
About Oil Changes
For home mechanics who change their own oil, and for folks who have been neglecting oil changes, there is an oil condition test I run, when I check the engine oil dipstick level. This “test” will tell you about 90% of what a proper, and expensive, scientific laboratory test would tell you. When you first pull the dipstick, wipe it clean with your thumb and forefinger instead of a rag or towel. This gets engine oil onto your thumb’s and forefinger’s fingerprints.
Now rub them together under ordinary contact pressure. (If you do that dry, you can feel your fingerprint ridges dragging upon each other.) If your oil is “good” from a lubricity standpoint, you will not be able to feel your fingerprints drag upon each other, no matter how much contact pressure.
If you can just barely detect your fingerprints dragging at each other, then your oil is just a little past its max change interval. As an example: if it has been about 5500 miles or so, since it was last changed, then try only 5000 miles to the next change. If at the next oil change it passes the finger test at 5000 miles, then you are “good to go” using a 5000 mile oil change interval. What you want is oil still providing acceptable lubricity when you change it. If this is longer than what the owner’s manual says, and your vehicle is out of warranty, then feel free to use this longer interval. But always monitor the lubricity with the finger test! If it ever fails, shorten your interval.
Color of the oil doesn’t much matter (even “good” oil looks dark with carbon soot blow-by, not long after you change it). Covering up the surface roughness of your fingerprints for a smooth-feeling “glide” is important: that measures lubricity in a useful qualitative way. I call this test “giving your oil the finger”, and I smile every time I think about that. Oil that isn’t providing adequate lubricity protection is allowing engine damage to occur, and that is very expensive!
Be sure and change the oil filter at the same time as you change your oil. A clogged-up dirty filter will bypass oil, but the lubrication ability is reduced by the drag of that bypass, and the bypassed oil isn’t cleaned of tiny grit particles, which act like sand in your moving parts. This reduces engine life. And that gets expensive! Filters are cheap, it is pointless to neglect this item.
Checking the Coolant (Nearly All Modern Cars Are Liquid Cooled)
This section won’t apply to any surviving air-cooled engines from decades ago. Those would be the old air-cooled Volkswagen beetles and buses, and the old air-cooled Chevy Corvairs, and some Porsches. Nearly all modern cars are liquid-cooled. The coolant is a mixture of water and anti-freeze concentrate. That antifreeze concentrate is primarily ethylene glycol, with some anti-corrosion package of additives.
First, locate your coolant overflow bottle. Some are low pressure (which you can open any time), others are full radiator pressure (which you cannot open unless the engine is cool). The cap will say, if it is under pressure. But these bottles all have some sort of cold fill mark and hot fill mark.
If your engine is near dead cold, make sure your bottle is up to the cold fill mark. If your engine is still hot after being run, you want to use the hot fill mark. If your engine is just warm, neither cold nor hot, you want your overflow bottle level about halfway between the marks. If it is low, open the cap (when cold if a pressure bottle!) and fill to the appropriate mark with the right kind of coolant mix (see just below). It really is that simple. See Figure 5.
Figure 5 – Typical Coolant Overflow Bottle
The overflow bottle shown here has clearly visible min and max marks. Some are hard to see. Often the level inside is hard to see. Shining a flashlight or drop light on the bottle from the side sometimes makes the level more visible. “Min” goes with cold engine and coolant conditions, “Max” goes with hot.
But, you need to know “for sure” what kind of coolant to use! You want to match what is in the car, even if that is different from the owner’s manual (because someone may have changed it). There are now 3 basic types out there: the old green coolant that uses the silicate additive package, the orange-to-reddish “Dex-Cool” common in more recent GM vehicles that uses the organic acid additive package, and the “Asian vehicle” type that ranges anywhere from blue to pinkish-purple (I do not know what its additive package is).
These three are NOT COMPATIBLE and MUST NOT BE MIXED! Mixing them leads to gunk and sludge formation that plugs up your cooling system, which is very expensive to fix properly. Left unrepaired, it will quickly lead to the destruction of your engine for lack of cooling, which is truly expensive indeed.
There are some “universal” coolants available from auto parts stores which can be used with either the older green coolant or the reddish Dex-Cool. I’m not sure yet whether these work with the Asian vehicle coolant. Any of the basic types or universal types can be had as concentrate, or as pre-mixed 50-50 mixes. The concentrate costs you less to use, but you have to make the proper mix with clean water. What is your time and labor worth?
What goes in the car is 50-50 mix. If you buy the concentrate, put some of that in, then add an equal volume of clean water. Better yet, mix equal volumes concentrate and clean water into an empty container, and then add that 50-50 pre-mix that you just made to the car.
Exceptions: you folks who live in the snow belt probably want to use a 60-40 mix concentrate-to-water, because it protects to a lower temperature. In the really extreme cold, you want exactly (and no more than) a 63-37 mix, which is good to about -30 F (-34 C). Beyond that extreme, you need a block heater or a heated garage. Or both.
Be careful with the spilled coolant, it is quite poisonous: a tablespoon ingested can be lethal. Pets and children are at considerable risk, as it tastes sugar-sweet, which suggests incorrectly to them that it is safe to ingest.
The older the vehicle, the more likely you will need to top-up the overflow bottle at every check, because things get old and leak. The leaks often occur at radiator or heater hose connections, the water pump, or in the radiator tank connections to the radiator core cooling surfaces. These will show dried signs or traces of leaked coolant fluid. If you see traces of a leak, consult a mechanic, and soon.
If you don’t, your coolant system will very likely fail suddenly, while you are driving, and this usually destroys your engine rather quickly when it does. Few folks notice the temperature gauge suddenly rising in time, and idiot lights are just too late by the time they come on.
If your coolant gets to be a dirty brownish color instead of its normal color, consult a mechanic soonest about a flush and coolant change. The green stuff is good for at most 3 years, the red “Dex-Cool” stuff at most 5 years. The new Asian vehicle stuff says 5 years, but I just don’t know for sure yet how long it really lasts. That life has little to do with the ethylene glycol base, and everything to do with the additive package (whichever it is). The additives are all used up in that lifetime, letting very severe corrosion start. That’s what the brownish gunky color is: corrosion products and the associated sludge.
Checking the Transmission Fluid (Automatics Only)
There is nothing like this to check under the hood, if the car has a manual transmission.
With all automatic transmissions, there is a procedure to do this correctly, which is given in your owner’s manual. Follow it.
It usually involves running the engine at idle with the engine and transmission already mostly hot from having been driven. The fluid level should fall between the “add” and “full” marks on the dipstick; not below “add”, and not above “full. Like with the engine oil, check both sides of the dipstick, wiping and re-inserting. Do this 2-3 times to ensure repeatability. Always fill very close to the “full” mark, never any more than that.
Be sure to use the correct automatic transmission fluid. Nearly all of these are oily liquids which are reddish in color. The Fords use a grade of “Mercon” (like Mercon-II or Mercon-III), the rest usually use a grade of “Dexron” (like Dexron-3). Both types are red-colored oily liquids. Many brands you can buy at the auto parts stores meet both specs, so you can use them in all these cars; just make sure it meets the spec numeral (meaning the -III or the -3, etc.) for your type (Mercon or Dexron).
If you need to add fluid, use a funnel and pour it down the dipstick tube, there is no other fill location! Take your time, and add your fluid only a little at a time (maybe a cup to at most a pint), so that you don’t overfill. It takes a few minutes for the dipstick tube to clear enough, to get a reliable reading on the dipstick, after each addition. See Figure 6.
Figure 6 – How to Top-Off Transmission Fluid Through the Dipstick Tube
Your transmission fluid, though used, should still be clean and red-looking. If it is dark (brown to almost black), or especially if it smells burnt or otherwise smells bad, consult a mechanic soonest! You might only need a fluid and filter change, or you might need a transmission rebuild. The longer this goes on, the more expensive it is likely to be.
Here’s a shortcut I use to circumvent running the full hot-idle test spec for dipstick level. Once you know the transmission is at the full mark under spec conditions, park the car and let it cool overnight. Then check the level on the dipstick the next morning on the cold engine, without running it. This level will fall a bit below the “full” mark. Note where that level is, and write it down, or better yet, draw a sketch of it! Keep that info in the car where you can find it quickly, and use it easily. Then you can check and top-off cold, to that mark, in the future. This saves you some time and trouble doing the fluid level check in the future. It’s not as accurate as the spec way, but it is accurate enough.
You will usually find you don’t need to add transmission fluid. Very old vehicles may have developed leaks that require more frequent top-off, which you can spot by the dripped fluid stain (reddish oily spots) where you parked.
Power Steering Fluid Check
Check your owner’s manual carefully, to determine what this fluid really is! Most cars use ordinary “power steering fluid”, an oily but straw-colored clear liquid. There are a few that use automatic transmission fluid (a red oily liquid) for this. None would ever use brake fluid (a mostly clear liquid with a strong odor). Use ONLY the right fluid.
Open the cap and check the level. Usually, there is a sort of tiny dipstick built into the cap, with an “add” mark and a “full” mark on it. Anywhere between the marks is good. Add a splash of the right fluid if you are low. See Figure 7.
Figure 7 – What Most Power Steering Reservoir Caps Look Like
The power steering reservoir on the Focus had min and max marks on the side of the reservoir. The one shown in Figure 7 is on a 1995 Ford F-150 pickup. That cap has its own tiny dipstick built in. Some cars have fill marks, other cars have the cap dipstick.
You usually will not have to add power steering fluid, except on older vehicles that have begun to leak, usually somewhere on the power steering pump. If this top-up gets to be frequent, that tells you something is either worn badly, or really leaking badly. Consult a mechanic at that point.
Clutch Fluid Check (Manual Transmissions Only)
Consult your owner’s manual as to whether you have one of these, and where it is located if you do. Automatic transmissions will not have this, and some manual transmissions will not have it. This fluid checks and refills the same way that power steering fluid checks and refills, except that the fluid type may well be different.
Your owner’s manual tells you what to use for clutch fluid. Do NOT use the wrong fluid type! Some use power steering fluid, some others may use an automatic transmission fluid, and others still may actually use a brake fluid! Be sure you know which, and do NOT use the wrong fluid! That can cause very expensive damage!
You typically won’t have to add any clutch fluid, until the vehicle gets old and something starts leaking. Once you notice you have to top-up this clutch fluid up frequently, something is definitely worn out and too leaky. Consult a mechanic at that point.
Brake Fluid Check
This will usually be a plastic reservoir attached to a more-or-less cylindrical metal casting mounted on a big metal can that is your power brake assist (a big metal can with a vacuum diaphragm inside, and a vacuum hose attached on the outside). That is because nearly all modern cars have power brakes. Some antiques do not. Most of these reservoirs have two chambers under a common cap. There is usually only a full-level mark. You just fill it to the mark if it is low. But you MUST use the right fluid! See Figure 8.
Figure 8 – What Some Brake Fluid Reservoirs Look Like
The brake fluid reservoir shown in the figure is on the Focus. It has an easily-visible fill mark. Many others don’t really have translucent reservoirs. You just open the cap and look inside. All of them fill to near the top of the reservoir.
Most brake fluids are made of a chemical with a strong odor, called glycol, which is also a solvent for most car paints. Don’t spill this stuff without wiping it up! There are 3 common grades, your owner’s manual will tell you which you must use. Do NOT mix them! They are DOT-3 (the most common), DOT-4 (for brakes that get a bit hotter on bigger vehicles), and DOT-5A (for brakes that get much hotter on really big vehicles).
There is also a rarely-seen silicone oil-based brake fluid named DOT-5, which is good for both very hot brakes and for Antarctic weather temperatures. Do NOT confuse this material with the glycol type DOT-5A! They DO NOT MIX! Your brakes will fail, and must be completely flushed out and all the seals replaced, and maybe even replace your very-expensive anti-lock brake system, if you do mix them! Very expensive indeed!
Most of the time, you will not need to top-up the brake fluid at most underhood checks. The level will drop a little (very, very slowly) as your brake pads or shoes wear; but it comes back up when you replace these items. If there is a leak, the level will drop, requiring top-up; but, your brakes won’t be working right, either. It is very definitely time to consult a mechanic if that happens!
Glycol brake fluid (DOT-3, DOT-4, and DOT-5A) has a definite life, mostly because it absorbs water from the humid air, which then corrodes the insides of brake cylinders and fittings. It also gets darker as it gets older, because it oxidizes from the oxygen in the air, making it acidic and corrosive. You really should have the glycol-type brake fluid replaced about every 3 to (at most) 5 years.
The much more expensive silicone oil-based DOT-5 is very rarely used, but it does not have a limited life! It does not absorb moisture from the air, or darken due to oxidation. It essentially lasts “forever”. A few people (including me) have converted glycol systems to DOT-5 silicone systems, to get the long life. The seals originally intended for glycol are not harmed by the silicone, although the reverse may not be true!
This conversion requires a very, very thorough flushing-out, because the two types of fluid are utterly incompatible with each other, and that is what does the damage to the seals and many other components. I used a strong soapy water flush, followed by a couple of clean water flushes, followed by multiple 90% strength rubbing alcohol flushes, followed by low-pressure compressed air for a day or two. This is NOT fast, easy work!
A note to home mechanics: when working on your brakes, do NOT spray the seals with WD-40 or any other petroleum-based lubricant or cleaner! Clean them only with rubbing alcohol! The petroleum exposure makes that kind of rubber swell, permanently. This renders them ineffective as seals, which means your brakes will fail to work, requiring at least seal replacement (there is no “repair” for this).
Windshield Washer Fluid Check
This is a bottle you likely will need to refill frequently. It contains a mix of water and methanol, usually dyed blue. The methanol is an antifreeze for the water, and it is also a solvent for the scum and dirt on your windshield. Methanol is deadly poisonous, so do not ingest washer fluid, and don’t soak your hands in it! Just fill the bottle back up to the mark if you find it low. If you have been using your wipers a lot, you will find it low, a lot more frequently.
Look at the Belts and Hoses
A hose that is either swollen or softened near its connection is a hose about to blow out. Consult a mechanic soonest, if you find such! It needs replacing soonest! There are two big radiator hoses, and two or three small-diameter heater hoses. The radiator hoses will suffer old age troubles more often than the heater hoses.
A belt that has cracks in the ribs or in its surface along the inside, or is rubbed shiny along its lateral sides, is a belt that is worn and needs replacing. It may also squeal or squeak as it wears, which means it is slipping (and whatever it drives is not working right). Consult a mechanic if you find or hear any of this. Belt replacement is not usually that big (or expensive) a job.
Air Filter Check
The air cleaner assembly usually has a top that opens up, revealing a paper filter element inside. There are a few cars that do not have this, instead having a “permanent” air filter that lasts the life of the car (and is very expensive). Paper filters are cheap, and should be either cleaned or replaced every so often. Your owner’s manual says how often, but do this sooner, if you live or work in a dusty region.
Hold the filter up between your eyes and the sun. You should be able to see some brightness getting through the paper if the filter is OK. If not, try blowing the dirt clear with an air gun, fed by shop air (80-100 psig). That should let the brightness through; if not, just replace the filter. They’re cheap.
If you don’t have access to compressed air, then just replace the filter if you find it dirty. As I said, they’re cheap. It’s not worth agonizing over.
Something Else You Should Check That Is Not Under the Hood
That would be your tire pressures. You need a good-quality tire air pressure gauge, a fill chuck, and a source of shop air at about 80 to 100 psig. Do this before you have driven the car, preferably in the cool of the morning. Read your tire pressure gauge at least twice to make sure your reading is repeatable.
The spec for what the tire pressures should be is usually on a sticker inside the driver’s door frame somewhere. It’s in the owner’s manual, too. Often, the pressure is a bit higher on the front tires than the rear, because of the heavy engine up front.
Do not forget to check the spare in the trunk, even if it one of the little “doughnut” spares. The spare does you no good when you are changing a flat, if it is not inflated sufficiently.
The usual pencil-type tire gauge is the cheapest, but also the least accurate. They get too inaccurate to rely upon, after only a very few years after you buy one. Round dial gauge-type tire pressure gauges stay accurate for long useful lives, but are the most expensive. The choice is yours. Just be aware of the accuracy problem.
Another Thing To Check Every Now and Then
That would be how worn your tires are. Stick a penny into one of the tread grooves such that the top of Abe Lincoln’s head is toward the center of the wheel. If there is clearance between the tread surface and the top of Lincoln’s head, your tires are too worn to be legal at inspection time. They will also skid very, very easily on the ice, or in heavy rain. Worn tires are dangerous. Just go get new tires.
The other thing to worry about is how evenly your tires are wearing. Worn-out suspension components or an out-of-alignment suspension will cause weird-looking asymmetries to how your tires wear. If you ever see anything like this, consult your mechanic soonest! This kind of thing wears tires into scrap very quickly, and tires are NOT cheap!
The last thing to worry about is when you see even wear across the tread, and on both wheels left to right, but a bit more wear on the heavier front than on the back wheels. That just means you haven’t been rotating your tires. So go get them rotated, front-for-back, keeping lefts on the left, and rights on the right. Be sure to adjust tire pressures appropriately.