Why 12 month oil change on low use vehicle?

short journeys put a lot of moisure and soot into the oil which does not get hot enough to boil off the moisture and the soot from each cold start stays there . If you did half a dozen 500 mile trips then you could quite safely leave the oil change to a higher value.

Did you mean 500 mile trips as you said and not the 50 mile each way trips I referred to?

Yup, short trips at low revs are extreme usage, cruising down the motorway is the lightest usage. Many people get confused by this & then wonder why their cambelt's snapped.

If parked outside even if the car wasn't used at all, the oil should still be changed. Every night when temperatures drop condensation forms on the block walls. It forms dropplets that run off and drain into the oil. If not changed a steel sump will rot from the inside and fall off.

Regular oil changes are particularly important for the Corsa, which suffers from emulsion build up inside the engine.

Chris

Out of curiosity, is the engine block airtight when the engine isn't running? Just thinking about replacement of air etc, and whether new moist air can get in whilst the engine isn't running. If it can't then there's a limited about of moisture within the trapped air. Of course, if it's open to the air, then the amount of moisture isn't limited.

David Hearn gurgled happily, sounding much like they were saying:

No.

I did mean 500, but 50 mile trips without the 5 mile trips would do fine as well. Even a small car will take a good few miles especially in cold weather to get the oil up to and maintain a high enough temperature to boil off all the moisture of a cold start.

Thanks for the replies I understand now

Regards

Which, going by some engines that I know have been stored for a couple of decades, can take a very, very, very long time.

You have stored engines with unsealed breathers outside?

Storing a petrol tank in an unheated garage I've looped the pump flow back to return and plugged the vent.

It's very close to being airtight. On a modern engine, every orifice is connected to something by various hoses. Condensation traps, flame traps, fume traps, breathers connected to the rocker/cam box etc etc. I can't think of a realistic way of the engine internals being considered open to atmosphere. I know some will point to the air intake and the exhaust pipe, but really, one is so long and tortuous that it would require some humungous airflow into it, and the other has an air filter and a closed throttle in the way, so neither are going to be significant. The amount of moist air that could get in is very close to zero. The idea of droplets running down the cylinder walls and into the oil is ludicrous.

Steve

Short runs don't warm up the engine so moisture doesn't evaporate properly and will cause increased wear.

But a few questions. How old is it, how many miles on the clock, how long do you intend to keep it and do you anticipate the pattern of use remaining the same?

The thing to bear in mind is that maintenance assumes a 100K mile life (roughly). Clearly, at present usage, that is not the objective and a much high wear rate is acceptable.

When a relative died he left a 12 year old Micra with 12K which he had had serviced on the dot. The engine was perfect (but the clutch was shot). My daughter kept it for 4 years and added over 20K. It was scrapped with the engine still absolutely perfect. If the engine had missed a few oil changes... what of it?

If only it where so I wouldn't have just scrapped my 2500. It doesn't need a lot of moisture, but more relevantly there's a loy introduced every time it's started & pootles to the shops,look how much you drain out of an air compressor tank.

The air, and the moisture it contains, introduced when you start up goes into the cylinders and out of the exhaust. It doesn't go below the pistons, condense on the cylinder walls and then drip into the oil as someone suggested.

The compressor is a different animal and not a valid analogy.

Steve

Till the engines hot it does, not all of it but some of it, & the crank case pulses in pressure & does the same thing. Where do you think all that nasty mayo goo comes from?

I've yet to see an engine that doesn't have at least one 16mm breather pipe. It's all that's needed.

You have a miracle - the ZERO blow by engine? How did you make that? Even a good engine has up to 10% leakage on leak down test.

Moisture may be trapped by a mesh in the engine breathers, it then drains off the mesh onto the baffle system. The baffle system has holes that are supposed to return oil to the engine, they feed water drops in just a well.

As the moisture condenses the partial pressure in the crank case will reduce so more moist air is drawn in. Next day, it gets warm, the air in the engine expands pushing some of the dryer air out. Then at night it cools, sucks moist air in. One droplet at a time it collects a bit more water.

Only have to look at the window glass of a car parked in the open at this time of the year to see this process going on. Dry inside of all the windows with a towel and leather off and next day it's got condensation. Next day its got more, the day after yet more, next day it's starting to drip off the sunroof on to the seats. Use it and it stays a lot clearer with maybe just a misting of the glass in the morning. OK yes the cabin has got a biger hole than 16mm breather hse and heats up / cools down more than the engine under the bonnet but the process is the same. Left long enough it will collect water.

Peter Hill gurgled happily, sounding much like they were saying:

You might like to have a look for the rather immense water leak your car seems to have.

SWMBO's 205 (with ginormous external glass sliding sunroof) had been sat in the drive for a month or so, untouched, until the weekend.

Bone dry inside, a little light misting on the glass that had gone in a few minutes idling.

Or get rid of that slobbery dog :-)