How much time driving at operating temperature is adequate to boil off condensation in the engine, exhaust, and gasoline?

Question

Let's say I drive for a total of 20 mins, round trip, each day for 4 days a week (a normal commute to the train station each day for work).

The problem is that it's likely not enough time to hit operating temperature and remain at operating temperature long enough to boil off the condensation that forms inside of the engine, exhaust, and gas, all of which accumulate over time and cause rust and corrosion.

This means that I likely need to go for a long distance drive on the weekend so that I can bring the temperature of the engine, exhaust, (maybe gas?), high enough and long enough in order to boil off the condensation to prevent rust and corrosion, but how long would I need to drive at operating temperature to boil it all off adequately?

Answer 1

As jwh20 states, there's a lot of factors here. However, 20 minutes of continuous driving should be enough to get rid of any condensation in the oil in most vehicles. While the coolant may take five minutes to get to temperature, it takes the oil longer. I say "most vehicles" because there are always those outliers which will take more driving.

The exhaust will take a little bit longer. This also depends on how it is driven and at what atmospheric temperature. If it is -20°F (-29°C) out, it could take a skosh longer than 20 minutes (in my approximation) to completely ensure the exhaust tract is completely heated to ensure it is good. If you're talking about 90°F (32°C), it might only take five minutes.

As far as gas goes, no amount of running the engine in any kind of weather will remove the water from the gas, other than it passing into the engine and getting vaporized through the normal combustion processes. It's just not going to happen. Until the fuel is ejected through the fuel injector, the two are completely separate. There are a few ways to get rid of the water, however running to create heat is not one of them.

All that said, if you are only running your vehicle 10 minutes each way, you probably aren't getting the job done. You should consider driving it a bit more on the weekends. Get out. Enjoy the open road. Your vehicle will thank you for it.

Answer 2

I can't say that I have ever seen a hard-and-fast answer to this because there are many variables. Things like the engine's normal operating temperature, how much moisture we're talking about, etc.

I've heard and read that about an hour of driving AFTER you get the engine to operating temperature will be sufficient to drive out excess moisture.

From personal experience with a motorcycle that has a glass sight window to show the oil level that often shows "milky" when there is water will clear up nicely after an hour or so of riding.

Answer 3

It all pivots around water's boiling point of 212F (100C) at standard temperature and pressure (close enough to standard outdoor conditions).

Your thermostat has a setting of 160, 180, 190 or as high as 210. Note that this is near the boiling point of water at STP, but, the cooling system is pressurized. You can see the coolant temperature on the engine's "Temp" gauge. Note that it has a happy place it normally lives. Once it's there, the engine is at operating temperature. If your engine doesn't behave that way, it may have a stuck thermostat. Stuck wide open, obviously, since if it was stuck closed, you'd be forced to fix it.

Water inside the air passages of your engine (pistons, intake manifold etc.) is negligible; no problem there.

Engine oil gets pretty hot - hotter than coolant. In fact, performance cars have "engine oil to coolant heat exchangers", where the coolant cools off the oil. So it's a safe bet that when the car reaches operating temperature, the oil has already spent some time above 212F, and any water therein has boiled off and been pulled into the PCV system (positive crankcase ventilation) which is designed to prevent build-up of explosive gases.

Manual Transmission oil - if you have a stick shift, there is little you can do, but stick shift transmissions have very little ventilation, and they don't run hot, so they have very little condensation.

Automatic transmission oil - Automatics make heat from operating in torque-converting mode (non-lockup). This applies to around-town driving with low speeds and lots of start-stops. However, the car does not leave transmission warm-up to chance. The transmission has an oil cooler - but it's not oil-to-air like you'd think; it's oil-to-coolant. It releases heat into the engine coolant, with the amusing side effect that if the transmission oil was cold, it's warmed by the engine coolant to at least its setoff temperature. Fully warming the engine then doing around-town driving should quickly drive off any water in the ATF.

Power steering is a closed system; little opportunity for condensation.

A/C freon is a closed system. The water in your A/C evaporator is supposed to happen.

Driving the water out of your coolant is not something you would want to do.

Ditto windshield washer fluid.

Getting water out of your exhaust system is very hard, because the combustion products are H2O and CO2, so there's a lot more water in there than in ambient air. Some cars have an electric smog pump that pumps ambient air into the catalytic converters (so the engine can run slightly rich to make the reducing cats happy, and then slightly lean to make the oxidizing cats happy). I suppose you could rig it to run the smog pump for 15 minutes after the engine is shut down. I just replace my exhaust system every 12 years or so when it rusts.