Best to just close the hood sometimes
Automatic transmission fluid and coolant levels are often misunderstood
A certain segment of vehicle owners was extremely perturbed when carmakers (almost in unison) deleted the automatic transmission dipstick.
These types are easily recognized in their natural habitat; in a driveway or parking lot just about anywhere with their heads under the hood, checking who-knows-what because no-one-knows-why.
Other than cost savings (possibly only a few dollars per), the other main reason auto execs made this deletion (some prefer the term de-contenting) was that too many vehicle owners were mistakenly adding too much or not enough fluid.
AUTOMATIC TRANSMISSION FLUID
ATF (in most modern vehicles) has to be measured when the engine, and therefore the transmission, are fully warmed up and, depending on the model, with the engine running.
Some makers require the shifter to be moved to each position before putting it back in park for the final measurement. And just like measuring engine oil via a dipstick, the vehicle has to be on a level grade. Adding too much automatic transmission fluid can cause it to froth or foam which can cause internal clutches to slip.
Correctly measuring and adjusting this fluid’s level isn’t rocket science, but apparently it was too much for most carmakers’ customers, hence the disappearance of the dipstick and fill tube. In some cases, a dipstick is available to repair shops as a special tool, and some models require a computer scanner to verify the amount in the gearbox. Some require the use of both.
If you’re curious about your vehicle’s transmission fluid level and it does still have a dipstick, remember that it’s a closed system before adding or removing some. If your gearbox isn’t exhibiting any unusual symptoms and there’s no sign of any external leak, then close the hood.
COOLANT
Engine coolant level is another particularly confusing issue found in the engine bay. Most vehicles use a coolant overflow reservoir that is semi-opaque and has hash marks on it representing low and high levels.
These systems are there because engine coolant expands and contracts with temperature, physically taking up more space when it’s hot.
Most under-hood examiners assume an empty or extremely low bottle level means it’s time to add coolant, and off they go to their favourite auto-parts store. Then, they fill the bottle to the warm level and later call their shop for a service appointment when coolant starts leaking out of the bottle.
Unless the bottle is completely dry, don’t add fluid. As
with transmission fluid problems, check for symptoms of low coolant before topping off. Is there a visible leak? Is the engine overheating? Does the HVAC system fail to deliver warm air on command?
A big word of caution; not all coolant reservoirs are the same. Some are pressurized and some are not. A non-pressurized reservoir is safe to open regardless of engine temperature and comes equipped with a plastic fliplid.
Pressurized ones should only be opened with the engine completely cooled down and can be identified by a metal pressure cap (similar to a radiator cap). Mistaking one for the other can lead to some pretty severe steam or splash burns.
If you can’t tell the difference and the engine is hot, close the hood.