How to read a dipstick!



I know next to nothing about cars, but I do know how to read a dipstick, at least that’s what I thought until my most recent adventure at my local oil change place. After the most recent oil change, my 2002 Subaru Forester (not turbo; 128,00 miles) began to miss horribly upon hard acceleration. I checked the oil. According to my owner’s manual, it was way overfilled (way above both the F hole (indicating full when cold) and the notch (indicating full with thermal expansion). I took it back to the oil change place. They said it was not overfilled and that even if it were, that would not cause misfire. They checked vacuum lines and sent me on my way. The check engine light (which came on when the missing started) went off temporarily, but came back on; the misfiring continued. I checked the oil again. They overfilled with oil, again! I contacted an online subaru expert. He said have them change the spark plugs. He said that the problem could have been caused by overfilling with oil (which he said is common due to slow drainage in the crankcase). I took it to a new mechanic (the one I use for big jobs). Indeed, a spark plug was not firing. He also noticed oil in the spark plug wells and suggested that I had worn out head gaskets and that overfilling with oil would not cause this problem. Who’s right? By the way, the second mechanic said I was low a quart of oil and added a quart. I later checked it, and it was about a quart higher than when I last checked it, which in turn was about a quart higher than the notch, cold! I guess I don’t know how to read a dipstick. Any comments?


To read the dipstick correctly, pull it out, clean it off and then fully insert it, pull it out and read it.

The markings are exactly as intended; F is full, but only after the car has sat for 1/2 hour or so after being shut off. The oil in the top of the engine has to drain down.

Your “worn out head gaskets” are likely VALVE COVER GASKETS which are attached to the heads. If you really had worn head gaskets the engine would likely not run at all.

Some Jiffy Lube places may fill the engine too fast and as a result overfill. Others will go the the nearest quart, and put in 5 quarts when you only need 4 1/4 quarts. A little bit of over filling will do no harm. But a lot will.


Quickie oil change places almost always overfill the engine, and should be avoided like the H1N1 virus. I wouldn’t go to one of those places even to ask directions. You have no idea how many Subarus have been destroyed by chain oil change shops.

Sometimes they drain the front differential instead of the engine, then pour four or five quarts of oil in the engine and send the customer on his way. Which means the engine has eight or nine quarts in it and the front differential has none.

The engine and differential are usually both damaged before the customer realizes what has happened.

Overfilling the engine can cause significant problems, and you should read the dipstick according to the owner’s manual.

Having said that, the dipstick on my Subaru Legacy is the most difficult to get a reading on of any car I’ve every owned, and I’m always questioning myself about how much oil is actually in the engine.

Here’s what I do: I change the oil myself, replacing the filter and adding the correct amount of oil as specified in the manual. Then I start the engine and let it run a minute to circulate the oil, then shut it off and let it sit for several hours to assure the oil has drained into the crankcase.

Then I check the oil (cold) and see what the dipstick looks like when I KNOW the crankcase is full.

You don’t know how much oil the quickie-change place put in the engine, and they will never admit to under- or over-filling. If the second mechanic added another quart you could be WAY overfull.

Is the mechanic you’re using familiar with Subarus? I don’t see how a head gasket problem would allow oil to get into the spark plug wells. Oil in the wells comes from leaking valve cover gaskets (o-rings), which are entirely separate from the head gaskets, and cost significantly less to replace.

Leaking head gaskets cause other problems, like overheating and loss of coolant. You don’t want leaking head gaskets.

Either change the oil yourself or let a competent mechanic do it. Stay away from oil change shops.


Docnick and mcparadise:

Thanks for your comments and suggestions. You’re both right. I misspoke. The second mechanic mentioned valve cover gaskets, not head gaskets (I was thinking of the latter because I had that problem with an old truck).

To the second mechanic’s credit (I’ve talked with him since the original post), he admitted that he had overfilled with oil, recognized that he had not waited long enough for drainage, and agreed to drain the oil and fill it properly. He is a foreign car specialist, but not a subaru specialist, per se.

I will of course check to make sure it is done right this time. Next time, I’ll change the oil myself.

It is comforting to know that I can read a dipstick properly.