Water Marks

I have noticed on a few occasions when getting my car out of the garage that there are lots of small pools of water on the floor, the water is clear (no oil in it at all) i have checked the water level and it is spot on never used any to date. Looking under the car it looks like condensation, on the main engine block and these pools are only around this area. My garage is guiet well insulated and my other car parked next to it does not have this problem. If someone could throw some light on this i would appreciate it. Phil

It's not condensation from the a/c is it? Unusual at this time of year I guess unless you like it like a fridge inside your car ...

Tim I have the a/c on Auto so not like a fridge, and it was serviced 1000 miles ago nothing picked up. a/c works well. These spots are only 10P size but about 10/12 of the them. All coming from the engine area only. The water drops are coming off the metal part of the engine. I have also noticed that when water say gets into the door seal areas when i wash it they do not dry up quickly, so it may be where i have washed it and the water has stuck about may be this warmer weather will get rid of it?? Phil

philippe, I have noticed the same in the last few days when I haven't been driving the car every day - I put it down to condensation, but the description is identical to yours - under the engine bay, about a dozen small spots of clear liquid. I too park it in a garage, and in the garage is another car which was last put in wet - so I'm figuring the dampness in the garage gathering on the metal and then dripping off.

Greig Thanks for that, i'm not the only one then, would never have thought anything of it but noticed it a few times now, i always wash the car before i put it away and it is left for two weeks or so there must be moisture in the air this warmer weather should sort the job. Phil

It sounds like condensation forming but this would only happen if the part on the car where the condensation is forming is colder than the temperature inside the garage. If the car is put away warm it should not happen. This is because of something called the dew point. Basically inside the garage the air will have a certain temperature and relative humidity, for example 10 degrees C and relative humidity 70%. One of the behaviour characteristics of relative humidity is that everything else being equal it increases as the temperature decreases. So for example if the temperature drops to 5 degrees the relative humidity would increase to say 90%. The dew point is the temparature at which the relative humidity reaches 100%. Once the dew point is reached humidity cannot increase and the water vapour in the air turns into liquid water which we see as condensation. Therefore if a car has been standing outside and has cooled to the air temperature outside and it is then put into a garage with warmer air with a fairly high relative humidity, condensation will form on the cold bits of the car and then drip down to the ground. Ian. PS guess who's spent a lot of time researching dehumidified environments. I must get out more.

Ian Now that was an explanation i was not expecting. Thank you. Phil

Ian, in my case - one car has been sitting cold for some time, another with a warm engine but wet bodywork is put into the garage - could the warmth of the engine and the additional moisture cause the air temperature to rise above the temperature of the metal on the stationary car, and thus the condensation? Or is there another reason the metal engine would be cooler than the air temperature (other than it just takes longer to raise in temperature than the air)?

Now you need a thermal heat transfer expert which I am not (and people spend large amounts of money on computer systems trying to model thermal systems as it's very complex). My speculation would be putting the wet car into the garage causes the relative humidity to rise briefly to a point where condensation starts to form even without any temperature change as the water evapourating off the car goes into the air. If the starting point for a garage is 80 - 90% (which is fairly typical on damp / wet days in the UK in an unheated garage) putting a wet car inside may well raise it near 100% for a while. I imagine the design of the engine casing causes the condensation to flow to the 10/12 points during that period which is why drips appear. On other surfaces such as brake disks the condensation would form and then re-evapourate as the humidity normalised back to the ambient conditions without any tell tale signs other than those small rust spots you sometimes see. BTW the optimal humidity for garages should be between 60% and 40%. Below 60% rust stops forming on steel but below 40% tyres and leather start to dry out to much and crack. Ian.