How long drive /minutes to burn off moisture in exhaust system?

I have 1992… I’ve heard it takes about 5 miles continuous driving to burn out the moisture in the exhaust system… can I just let the engine idle for 15 min… ( I remember in the early 90’s for some reason , it was stated that idling was bad for an engine). Once every 2 weeks? I drive 1 mile to work.

I’d be more worried about the damage you’re doing to the engine than the exhaust if that’s all your driving.

I hope you’re changing your oil every 3 months to get the moisture out of it.


It is better to drive it around than just idle. For a few reasons… heats up quicker under some load, pushes a bit more air and fuel through the engine to warm and dry. Plus, helps clean off the rust buildup on your brake drums and rotors, warms up and distributes grease in all the driveling bearings, axles, ect.

Better to do that once every 2 weeks than idle for 15 minutes just sitting in the driveway.

Unless you haul rocks for a living, it’s time to consider a bicycle, motorcycle, scooter if you drive 1 mile to work.


I wonder if these short drives contributed to the ticking in your other question about your car.

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I wouldn’t idle it. I’d take it out once a week for a 30 minute drive, part on a freeway if available.

This appears to be the perfect situation for LSV ( low Speed Vehicle ) if a highway is not involved .

I agree, but would feel OK letting it sit much longer than a week. I parked my old Toyota truck for the winter at a remote location. It need a tablespoon of gas down the carb to start. The harder problem was mice in the HVAC.

If it wasn’t being driven at all I’d agree, but 1 mile per day puts some water/gas into the oil.

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Good point. I agree. It’d be interesting to know how long the OP has had that car and that usage pattern. My hunch is it won’t do as much harm as some worry about, and the muffler degrades more than anything else.

I take my car out every Friday night for carry out. I usually drive for 20 minutes, even though the restaurant is five minutes away. Sometimes it’s a straight shot, but I never miss the long drive the next week if I’m in a hurry to get food one week.

Q My daughter has a 1999 Volkswagen Jetta with a 2.0-liter engine and 108,000 miles. When I remove the oil filler cap, I notice moisture buildup inside the engine – a white sludge around the fill cap area. I can usually wipe out most of the moisture with a clean rag. I have been changing the oil on a more regular basis every 2,000 to 3,000 miles in an attempt to reduce the moisture. In the summer, the buildup is less noticeable than in winter. The coolant maintains the proper level, and oil consumption is about two-thirds of a quart per 2,500 miles. Any thoughts on what might be causing the moisture buildup?

A The low mileage would seem to indicate infrequent use or short trips – both of which can promote condensation inside an engine. Other potential causes are low engine operating temperature, a blocked PCV (positive crankcase ventilation) system or a failed temperature regulator thermal vacuum valve, which is designed to preheat incoming induction air.

As the engine warms up, moisture in the air inside the crankcase condenses into liquid form on the cold internal engine parts and is carried throughout the engine by the motor oil. If the engine does not or is not allowed to reach and maintain full operating temperature for a reasonable period of time, it never evaporates, and it turns into a whitish goop on the oil fill cap, dipstick and inside of the valve cover.

Changing oil more frequently helps remove this buildup, but the best answer is to make sure the thermostat is bringing the coolant up to full operating temperature and driving it at that temperature for at least 30 minutes every few days.


I owned that 92 car since new. Within the last 15 years, I just don’t drive much anymore except to work or within a 3 mile radius. Once a month, I may drive 20-30 min drive (both ways).

prolonging the life of your exhaust a waste of time. If you are successful in idling the engine and keeping the muffler toasted dry you can look forward to one or more failures of some much more expensive components.

If I move my car to be washed for example, after I finish I drive the car about 3 blocks, how far should it take to raise the temperature of the exhaust from 100 degrees to 200 degrees?

I lived one mile from work for 3 years when I had a 61 Dodge Dart Phoenix. My oil got so much water and unburned gasoline in it that it would raise my oil level. I changed it when it got a quart over. Never hurt the engine though, the car went to the junkyard with a good engine because of body

If you have an automatic transmission with a dipstick ir takes about 8 miles just to get the fluid to operating temp to check the level. Idling or driving less than that just makes things worse.