When and Why to Change Your Engine’s Fluids

Everyone knows that the key to responsible car ownership is maintenance. The plan is to follow the maintenance schedule as it is outlined in your owner’s manual.

After all, no one knows your vehicle better than the manufacturer, therefore the maintenance intervals set by the manufacturer must be best for you vehicle. Unfortunately this isn’t always the case.


Maintenance schedules that suggest a long interval between services have become a selling point in today’s competitive market. Each car builder claims that their vehicle needs less maintenance than the other guys, so they really are pushing service intervals a bit too far.

They claim that due to advancements in engine oil, anti-freeze and transmission fluid, it’s not necessary to change them as often as it was in the old days, and this is true. Engines and transmissions are also made better and are more tolerant of longer maintenance intervals.

Engine Oil

Today most manufacturers are recommending that you change your oil every 7,500 to 10,000 miles under normal driving conditions. This is simply too long, especially for your first oil change. Break-in is a very critical time for your car engine. During this time a car engine produces more metal debris than usual.

These small metal fragments are carried to the oil filter via the engine oil, and hopefully stay trapped in the filter until it’s replaced.

Lubrication is only a small part of what engine oil does. Engine oil holds the metal debris, which are a normal product of engine operation, in suspension and away from moving parts.

The most important thing that engine oil does is carry heat away from friction producing components.

Oil changes are cheap. Change your oil every 3 months or 3,000 miles. Your oil is dealing with extreme temperature changes. It’s being contaminated by unburned fuel, condensation, and small hunks of metal.

Give it a break. Change your oil and oil filters every 3months or 3,000 miles. If you choose to go to a quick lube style store, bring your own oil filter. There have been many engine problems caused by aftermarket oil filters.

Purchase an original equipment filter from your dealer and have them install it. They won’t give you a break on the price, but it’s cheaper than a new engine.  

Automatic Transmission Fluid

Automatic transmissions are just as vulnerable to break-in issues as engines. Automatic transmissions produce a lot of friction, which translates to a lot of heat.

Besides the metal fragments that are produced during normal operation, automatic transmission fluid also needs to deal with asbestos clutch material. An automatic transmission works with a series of clutches and bands that slip and slide, creating a lot of heat and a lot of trash floating around in the fluid.

Most manufacturers recommend that you change your transmission fluid every 100,000 to 150,000 miles. This is insane, especially for the first service.

Here’s why the first service is so important for an automatic transmission:

An automatic transmission is hydraulically controlled by valves located in a valve body. These valves slide inside of bores, and it’s a real tight fit.

All it takes is for one small metal fragment to hinder the movement of a valve, and you’re next stop will be the dealer or the transmission shop. It’s important to get that break-in metal out of your transmission.

You should have your first transmission service done at 30,000 miles. If your transmission has a replaceable filter, have it replaced. You should change the fluid every 60,000 miles thereafter, replacing the filter every other time.


Anti-freeze is a tricky one. Automotive technology has come a long way since the old green anti-freeze. Most manufacturers recommend changing your anti-freeze every 100,000 miles.

Under normal conditions this isn’t unreasonable. Today’s quality anti-freeze, in a sealed cooling system, as part of a healthy engine, should easily be able to survive 100,000 miles.

Engine issues such as a blown head gasket can introduce combustion gases or engine oil into the cooling system, contaminating the anti-freeze. I suggest that you keep an eye on the appearance of your anti-freeze. Remove the cap only when the engine is cold.

High pressure 180 degree anti-freeze really hurts badly, so wait till the engine cools down. Check the color of the anti-freeze. If you see it turning a rust color, replace it.

This should only happen if tap water was introduced to the cooling system. They recommend a 50 50 mixture of anti-freeze and distilled water. It’s important to use distilled water because tap water contains minerals that promote rust.

If the coolant looks good, no leaks, no engine issues, 100,000 miles is a reasonable interval between anti-freeze changes.

When determining service intervals, be sure to consider extreme driving conditions. Conditions that classify as extreme are extended idling, towing, extreme hot or cold climates, short trips that don’t allow the engine to warm up, aggressive driving, and frequent steep hills. If any of these apply, you might want to consider shorter service intervals.

The service that I’m asked about the most is the fuel injection service, or fuel induction service. During this service the technician turns off your fuel pump and runs your engine on a fuel injector cleaner. The cleaner flushes gummy buildup from your fuel injectors, and it some cases your intake valves depending on the configuration of your fuel system.

So how important is it to have your fuel injectors cleaned? If you use a good name brand gasoline, you keep your oil changed, and your engine doesn’t idle for excessive amounts of time, you can skip this service.

If you drive a really high mileage vehicle you might want to give it a shot, it might improve your fuel economy. Do not perform a fuel injector service on turbocharged engines, it could damage the turbo.

So if your repair shop recommends that you purchase a service before your service manual says it’s due, ask him why. You might just find that he’s not trying to squeeze you for another buck; he’s actually trying to save you lots of bucks down the road.  


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