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So I did an oil change about a week ago and the next morning after driving maybe 10 miles I open up the oil filler cap to adjust my oil level to find milky white residue under the oil cap. My first thought was that there was just condensation in the block and it didnt have time to fully burn off since I hadn't driven that far. By the time I finished my drive which was about another 100miles the residue was gone. Every day for the past couple days I have had the same residue under that cap. I am really worried that I have some leak somewhere. I have pressurized the coolant system but am not really sure how to interpret the results. The radiator cap says 88kpa or about 12.7psi so I pumped it up to about 13lbs and after two hours I was down to 7psi. This could be from a leaking tool but it could also mean a number of other things. Anybody have an opinion on this or has anyone experienced the same type of thing. Truck seems to run fine and I have not noticed the coolant level go down besides normal fluctuations. It has been really cold here (frost every morning) which has not been the case until recently so that is why i suspect normal condensation in the block.
 

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If you drive your truck primarily only short trips at a time, it's probably not a big deal-especially since it disappeared after that 100 mile trip. My truck is used mostly for short trip stuff, but I always try to let it get to operating temp before shutting it back off. Let it run a little longer each day, and see if it goes away.
 

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It's condensation. As you saw, it burns off after the oil reaches operating temperature. Switching to a full synthetic motor oil can help alleviate these symptoms.
 

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Did you check radiator fluid for cross contamination or pull and inspect plugs? Is radiator fluid dropping from one morning to the next? Just a few ideas.
 

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My 01 does the same thing. Goes away once engine gets hot. Codensation, but if all plugs are good color and the oils/anfitreeze/tranny fluids are in good condition then there is nothing to worry about
 

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When pressure testing your cooling system over a long period ( like 2 hours ) you must make sure you are doing it cold. Otherwise if done hot, as the coolant cools, it contracts which will naturally lower your pressure reading.

Go by your coolant level, if it is staying at a constant level ( probably best to test it cold in the morning ) then don't worry. Antifreeze does not evaporate ( the glycol portion ) so if it was antifreeze under the oil cap it wouldn't go away. The milky color is consistant with condensation mixed with oil.
 

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Discussion Starter #12
No it is not that bad at all. Generally it isnt inside the filler tube just on the underside of the cap. Lol if it looked that bad I would be crapping my pants and on the way to a shop! Another thing I did was put the pressure gauge on there and run the car up to operating temp, which brought the pressure up to about 11psi, which is right under the radiator cap specified psi of 88kpa or 12.7psi. The gauge didnt flicker or twitch while it rose, just steadily rose and then stayed at around the 11psi. I know that alot of time if there is a crack in the block somewhere the gauge will flicker as it goes up or it will build way too much pressure. I will see if I can post up a picture today of what it looks like. I think I may just be paranoid, but rather paranoid and stress a little now that let it go and run into a bigger problem down the road. Thanks for all the responses and pictures.
 

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If it's just a small amount of residue on the underside of the cap it's to be expected. The cure is to avoid real short trips in cooler weather where the oil doesn't make it up to temperature and or allow for ample warmup. My jeep's done this for YEARS.

With older motor oils in the past it could eventually cause severe sludging problems. Especially if it's a vehicle continually used this way like a volunteer firetruck, farm equipment or the little old lady sedan driven to church on Sundays. One of the WORST things you can do to a vehicle is to start it occasionally but not drive it.
 

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Discussion Starter #14
Yeah I dont see oil in the coolant, checked all spark plugs and they are normal color light brown/tan. Im gonna do another oil change and throw synthetic in to see if it corrects the problem. Thanks for all the help everyone.
 

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No worries about it. No need to uselessly change oil - simply when u drive punch it a little bit. Run with overdrive off - will help. Engines NEED to run hard time from time to get really hot so they dont develop illnesses like old people cars do.
 

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When I used to make short trips to work, under 3 miles each way, I never had that kind of buildup on the underside of my filler cap. Then again I've used mobil 1 synthetic since the first oil change.
 

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I think this is normal for many engines. It will burn off. The try or brand of oil has little effect. If this stuff mixes with dirty oil, it turns into an acid that will cause damage over time. TundraAdrenalin's example is a little more than normal condensation.
 
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