Mustang72fan

I was recently checking/adding oil to my 2007 (non-classic)Silverado with a 5.3L (197XXX miles) and I noticed when I removed the oil cap that there was moisture hanging on the underside of the cap. Along with that there was a light layer of yellowish film covering the cap. I have always made a habit of checking this since I owned a Ford truck for a couple weeks (then returned it) if you catch my drift.

Anyway I since dried the cap off, got my oil changed (valvoline synth blend), and checked it again after about 2 weeks to find the same amount of moisture residing under the cap. There is no creamy white or yellow buildup. The moisture is Clear - no discoloration.

I live in Minnesota and its COLD. I havent noticed this before winter hit, but Im really questioning if that has anything to do with this situation.

I take very good care of the truck and change oil no more than 4k miles. I dont hammer on it and it doesnt see the offroads.

Also, Every morning before I drive to work I hit the auto start and let it warm up for 5 mins (or however long the factory auto runs it) and then drive about 15 miles to work. Same when I leave work - but only do that when temps go below 40 or so. Summertime I'll start up and drive away.

Lastly, about 10 months ago I got the coolant system flushed and they switched it from Dexcool to the Green stuff. It was done by a reputable shop and I have consulted them at least twice regarding the safety of that switch to Green Coolant. They assured me that it wouldnt be a problem because they changed ALL of the fluid. So I took the truck in for the oil change when I saw the moisture on the cap and informed them about my concern. They did the oil change and said the coolant reservoir was about half a quart low on coolant - This is the only outstanding evidence that really ties into the moisture cap issue aside from the moisture on the cap alone.

So what do I expect to encounter here? Should I take further steps? Monitor the coolant usage? Is there even a problem at all?

I have heard waaaay too many opinions from people on why this is occurring so I ask if you dont have a professional advice to please refrain from commenting.

Thanks!!

kevinkpk

You stated the coolent is low, is there any external leaks? Is the level on the dipstick normal? The dexcool was an "issue" with the plastic turkey trays, I had my 2000 suburban flushed, and refilled with dexcool a couple years ago with no issues. The lumina I drive states to use dexcool, I use glycol alcohol (green) in it. I did have to replace the lower intake gasket a few years ago do to leaks. Top off the resevoir anti-freeze, and monitor it, and dipstick, if you have no external leaks. Depending on how much water you have could be normal. Older cars such as that Olds in my avatar use a hot air to intake air mix for the crankcase supply.