Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Engin rust?

I have rust on my 2004 VW Passat dipstick. How does this happen, what does this mean for my engine, and what should I do? The car is still under warranty. I change the oil every 3,000 with synthetic oil.

Thanks John.

If there is rust on your dipstick, that indicates the continued presence of a large quantity of moisture in your crankcase. And, while a 3k oil change does sound like you are being diligent about maintenance, I have to ask:

How many months elapse between those oil changes?

While 3k oil changes are normally sufficient for someone who uses a vehicle exclusively for short trips, if that person only accumulates those 3,000 miles over a period of…let’s say…six months, then the motor oil is being chronically diluted with the water that is a byproduct of combustion and is not burned off by short trips–and even the more expensive synthetic motor oil will not compensate for that type of abuse. That is why manufacturers have a “severe service” maintenance schedule listed in their maintenance books. A car that is subjected to only, or mainly, short trips is a car that is experiencing severe service.

So–please tell us how many months elapse between your oil changes.

If you are actually changing your oil on a timely basis for a car that only does short trip driving, or if you are not subjecting your car to only short trip driving, the only other explanations that I can think of are either dilution of your motor oil by a leaking head gasket, or possibly a clogged PCV valve. Is the motor oil “milky” looking? Is the engine running roughly? Is your Check Engine light illuminated?

You really need to provide us with more information, but in the meantime, I have to tell you that the presence of rust on your dipstick is not a good thing, and is a likely indicator of premature engine failure.

More details, please!

I have never seen rust on an engine dipstick. I would have guessed it would be impossible for a dipstick to develop rust. The steel is constantly coated with oil, which is a surefire way to prevent the formation of rust. I often give some of my little-used tools, such as handsaws, a light coating of oil to prevent rust.

I am not sure just what you are seeing. It may not even be real rust. In any case, your car is still under warranty. Check with the dealership’s service manager. Get his opinion. Maybe he’ll give you a replacement dipstick.

While it is rare, I have seen rust on a dipstick. Back in the late '60s, I can recall seeing a fairly heavy coating of rust on the dipstick of a Pontiac (Catalina? Bonneville?) that was only 2 or 3 years old. Just as with the OP, it could only occur if there is a consistent excess amount of moisture in the crankcase–and that is definitely not a good thing.

Getting a new dipstick is probably a good idea, but that will not eliminate the root problem. Hopefully it is an issue that the warranty will cover. But, if as I surmise, this is a vehicle that has been subjected to Severe Service without being maintained in accordance with those conditions, that would not be covered by warranty.

I work at Valvoline Instant Oil Change (yes I know it’s not the most reputable place, but the one I work for is really well run) and every day I always see at least a few vehicles with rust on the dipstick. I haven’t brought it up yet because i’m not sure what to make of it but it is definitely something that happens.

I’ve seen a number of dipsticks with rust on them and am also curious about the type of driving you do. If it involves a lot of short hop 2-5 mile type trips then it could be that moisture that accumulates in the crankcase is not being burnt off.

We do an oil change about every 4 1/2 months. You’re correct, it’s primarly driven on short trips however we drive it seven day’s a week.
The motor oil is not “milky”, and the car seems to be running fine.
The “rust” is about half way up the dip stick if that means anything?
Thanks for your help.John

I have only seen two and they were almost ‘eaten’ through.

I had no idea what caused that then ('70s?) nor do I have a solution now BUT, where the OP seen the rust on his is where I also seen the rust.

Half way up would be approximately where the dipstick would pass through the outside tube and into the engine crankcase, no?

I’m thinking of the temperature difference between the (outside) top half and the bottom half of the engine. I have to agree with the moisture theory.

Too far fetched?

I had this problem with a 95 Dodge Dakota pickup, in fact the dipstick was replaced under warranty. I changed the oil every 3 or 4 k, but had a fairly short commute to work. Have you checked your oil filler cap for any “milky” residue? This also indicates excessive moisture in the crankcase. At the time I had a 20 minute drive to work, so it wasn’t long enough to burn off the accumulated condensation in the crankcase. I replaced a bad PCV valve and did at least one longer drive (+30 min) during the week, this was enough to eliminate excess condensation.

I would replace the PCV valve on the VW to start and try and get some longer trips during the week.

Check your coolant level also, a steady drop in level could indicate an intake gasket leak which would put coolant into the crankcase. This is what happened with my 2000 Blazer. Hopefully this is not your problem.

Ed B.

You state the rust is about halfway up the dip stick, and the oil is clean looking with no milky color.
This would indicate that the dipstick tube has a fair amount of condensation accumulating. This is at a high point, above the oil level on the dip stick.
Short trips can contribute as the condensation gets no chance to evaporate. This condition is basicly harmless, but I’m not comfortable with any debris on the dipstick that could fall into the oil. I would clean the dipsticks with light sandpaper.


Great, thanks for your help. I have to bring the car in for another safty recall this week (the third one) and I’ll ask them to change the PCV valve and go from there.

Maybe one longer trip a week, where the engine gets fully warmed up and stays there for a while, would be a good idea.

Like the others have said, you need to drive this car for an extended period at least once a week to burn off that excess moisture. You said you drive it every day, but on reach 3000 miles every 4-1/2 months. This amounts to 22 miles a day. Very little. You should try to take it for a drive that will stretch 25 continuous miles at least once a week, or a typical 30 min drive. And, maybe take it for a ‘one-tank’ trip once a month. A one-tank trip is to visit something that is at least 100 miles away, and can get you there and back in one tank of gas.

I’m glad to see that my suspicions have been confirmed. The situation is not a good one, but at least this is a problem with a fairly easy solution.

As others have suggested, you need to drive this vehicle for a longer period of time at least once a week. Most likely, driving for about 45 minutes or so would allow you to “cook” off the moisture that you accumulate with all of those short trips each day.

Another alternative would be to change your oil every three months, rather than every 4 1/2 months. However, since you use synthetic oil (as required by VW, I assume), this will tend to be a bit pricey. Then again, the cost of gas for your once a week longer drive will add up. Either way, at least you have two options for eliminating the excess moisture that is building up in your crankcase. But, I want to point out that your exhaust system is likely going to have an early demise for the same reason–the buildup of excess moisture from short trip driving. More frequent oil changes will not help the exhaust system, so perhaps the once a week longer drive is your best option.

And, as both I and edb advised, it is probably a good idea to replace the PCV valve as a very cheap bit of insurance.

Thanks for your time, and help.