Reddish Residue Inside Oil Cap

dukbludvl · February 7, 2005

Hey Everyone,

I just changed my oil over the weekend and I noticed for the first time (at 76,300 miles) that my 2000 Yukon has a thin layer of reddish residue caked on the inside of the oil filler cap. It also appeared to be around the inside of the filler tube near the top, too.

Does anyone know what this is or what causes this?

I've never noticed my truck leak a drop of oil, and I've never really noticed anything wrong with the oil.

Anyone else experience this?

Thanks!

Shawn T · February 7, 2005

Dex Cool? It's red, but I can't imagine it caking up. Maybe leaking intake manifold gasket. The Dex Cool is seeping down over oil filler neck and just collecting and drying around the cap. I have seen the OBS 350's do that alot.

dukbludvl · February 7, 2005

if it is dex cool, what do i need to do to fix it or at least diagnose the problem?

i can't say that i've seen the coolant level drop at all since buying the truck. i do need to flush the cooling system, though...still have the original stuff in there.

71GMC_3/4T · February 7, 2005

Change your oil, save a sample, and send it in for analysis. I'm not sure where to send it, but some people on here would know for sure.

elgineddie · February 7, 2005

John,

After 96,000 on my 2001 K2500 Burban I noticed this for the first time at my last oil change. I just noticed a few beads of condensation on the inside of the cap but don't recall if it was red or not. I would agree that you need to send in a sample to a lab for analysis. I use Blackstone labs in Indiana. They will send you a free sample kit and I think it's something like $15 to run the test. I've been sending them oil samples every oil change since I bought the truck new. VERY interesting to see how the engine wears. I will let you know what they say when I get the results. Should be soon since I sent it in last week and they email me the results in PDF format.

I wouldn't worry too much. As long as your oil wasn't milky or visually contaminated. Let the test tell you if there is antifreeze present or not. Condensation in an oil cap isn't all that uncommon. I used to have a Jeep that blew an intake mani gasket and after I fixed it I would check the oil cap like a freak everyday! And there would be condensation in it half of the time.

intruder217 · February 8, 2005

Check your PCV valve and breather tube. Sounds like moisture is building up in your crankcase.

dukbludvl · February 8, 2005

intruder -- thanks for the tip on the PCV valve. actually, i checked this weekend when i did the oil change, and even though it still seemed to be functioning properly, i replaced it. this was the first time i've replaced it.

also, just prior to my last oil change on nov. 7 (before this one when i noticed the reddish stuff), I did a top end cleaner treatment (the GM stuff, not seafoam)... i didn't notice hardly any smoke come out of it at all... could the reddish stuff be related to the top end cleaner treatment somehow?

i'm going to send in a sample for analysis after my next oil change.

sjspor · February 9, 2005

Yes, the red scale is rust, it will be on the inside of the fill tube too. If the PCV is good, or if you hav'nt changed it yet, do it. But if that is good, are you doing short drives where your not warming all the way up, or is maybe your T-Stat hanging open and your running a lower engine temp than your should? You have to run hot for a while to "boil" off the water that condesnsed as the engine cooled the night before.

Here in the North east, this is sludge season. Damp and cold...

dukbludvl · February 9, 2005

sjspor, that's it. you nailed it. last august, i moved from living about 10 miles away from work to living 1 mile away from work. LOTS of short trips where the engine does not warm up. OK. That puts my mind more at ease now. I'm still going to have the oil tested for the hell of it... it's only $20.

My fat @ss needs to start walking to work more anyway, so i'll try to cut down on the short trips when the weather warms up.

i also just replaced the PCV anyway.

thanks for helping me put my mind at ease! i was worried there for a second.

elgineddie · February 16, 2005

Jon,

I posted about a week back that I found condensation in my cap as well. I just got my oil analysis back from Blackstone and this is what they said (WHEW!!)

Nothing too unusual showed up in this sample. The condensation you found doesn't

appear to be a problem, because we found neither moisture nor anti-freeze here. We did find a jump

in iron and we aren't sure what caused that. It has read high in the past from your engine, so we think

it is probably related to something operational. All other wear still looks good and lead dropped back

to a below average level, so we doubt the iron is a problem, but we will keep an eye on it next sample.

No fuel dilution was found and the viscosity was normal for a 5W/30.

Getting your oil checked is the best thing you can do!

Later man,