What's this stuff in my oil filler cap?

[Steve Briscoe]

The last two times I've changed the oil in my daily driver, there has been a white grease like substance in the oil filler cap and inside the neck of the oil fill tube. I use Mobil 1 and a Mobil 1 filter and change oil every 5,000 miles even though the extended formula advertises it will go a lot further than that. When changing the oil, I did not find any water or other type of separation in the oil. My '99 Jeep Grand Cherokee has 210,000 miles on it and stills runs strong. It uses about a quart of oil every 4,000 miles. I've seen some pretty nasty things on oil caps or in oil pans but nothing like this. What is it? Thanks!

 

[Ron Earp]

I think it is moisture and oil mixture built up there in your cap/filler. Seen that sort of thing before, that is what it was for me.

 

[Alex Hirsbrunner]

Looks like water (coolant) in the oil to me. I'd throw some dye in the coolant and see if you spot dye in the oil after a few heat/cool cycles.

Regards,

Al H

 

[Pat Buckley]

I'm betting that your oil temperature never gets over 200F.

 

[JohnC]

Here's the NAPA leak test kit:

http://www.napaonline.com/MasterPages/NOLMaster.aspx?PageId=470&LineCode=BK&PartNumber=7001006&Description=Leak+Detector+Kit+%2f+Engine+Block

Very handy kit for detecting presence of combustion leaks.

 

[Pete McCluskey.]

Looks like coolant to me, I'm surpised your oil doesn't look different when you
change it.

 

[CliffBeer]

Take a look to see if you can spot oil in your coolant (coolant tank will have a similar white slime with blobs of oil floating). If you see oil in your coolant then you likely have a blown head gasket (oil and water transferring) at a minimum and perhaps a cracked head or block at worst.

Also, you can get your oil tested for the presence of a material amount of coolant - search online and you'll find several labs that will test this for you, usually for about $50.00.

Finally, it may just be a build up of condensation (immersed in oil) and everything is fine.

 

[Keith]

Do you do a lot of short runs? If so, that's condensation most likely....

Take it for a long burn......

 

[chuck smith]

definitly condensation. as the oil heats up,the moisture in the oil is vaporized off and rises to the higher places in the engine,oil filler cap,valve cover vents ect..Pat is correct in that you need to raise your oil temp and make sure the condensation is burned off. coolant in your oil would likely result in radiator boilover after brisk runs since gasses would be forced into the coolant in most cases

 

[Pat Buckley]

Do you do a lot of short runs? If so, that's condensation most likely....

Take it for a long burn......

If your oil temp doesn't get close to or above the boiling point of water then you can drive it until you're blue in the face and still end up with some cream.

That's assuming you don't have a leak of course - in which case if you drive it until you're blue in the face other things will become evident.

 

[Joe T]

Your Engine could be running to cool.
Check that the water thermostat is working ok and closing properly, or is actually the right one.
For the expense try replacing it anyway, I have seen similar problems on cars where the stat has been removed, or does not close fully.

 

[David Briggs]

I agree with trying a new thermostat, I would put in a 195 degree(95 celcius?) and also check your PVC valve, it may be plugged up with this goop.

 

[Big_Si]

Not sure how hot it gets where you are, but here in Blightly, this is a fairly common(ish) thing. It's just condensation emulsifying the oil inside the cap, nowt to worry about really. As said, running the engine (or more importanly the oil) a little hotter should help remove this, although if it's lots of effort I wouldn't bother.

 

[Steve Briscoe]

This is good information. Thank you. I hope the issue is related to the condensation theory. That will cost a lot less. On public roads, I'm an average driver in terms of speed and acceleration. The distances I drive are a mix between short jaunts and longer drives to Denver and back.

I'll get the NAPA test kit tomorrow and determine if it uses the dye technique for detecting transfer of oil and coolant between the block and cooling system. I don't see any white substance in the radiator overflow tank tonight but I'll run the Jeep at red line several times tomorrow and then check the tank again. I'll look inside the radiator cap tomorrow morning when the engine is cool before I start it to see if there is anything there. If the temperature gauge is correct on the dashboard, it indicates about 200 degrees when at operating temperature. However, the thermostat could be operating intermittently. I don't recall it being changed during the life of the vehicle and it may be time to change it as a preventative measure. I've replaced both exhaust manifolds in the past because they were cracked. I'm told it's a common problem with this engine where "minor" vibrations in the heads transfer to the manifolds. That issue could have caused a head gasket problem. I'll hope for the best. Thanks again for the tips.

 

[Lynn Larsen]

Steve,

Regardless of the precision of your temp gauge, it will still show you trends. As long as the needle is good and steady, you are probably OK. If you see brief excursions, either up or down, this might indicate an intermittent thermostat.

It will certainly do you no harm to check your oil for the presence of coolant and is probably a good idea. But, as long as the oil is good and clear on your dipstick (referring to translucence and not color) and there is no indication in the coolant itself, I wouldn't worry about it. Again, I would confirm with the test though. Obviously, if you see any indication of whiteness in the oil itself either on the dipstick or at oil change, then you want to be concerned (oil should start to loose its translucence even before you detect the whiteish color unless, for instance, one of the head gaskets goes all at once.)

Lynn

 

[Steve Briscoe]

Update -
After all the tests recommended on the forum, my preliminary conclusion is the problem is condensation. It looks like the short trips to my office of less than three miles are not offset by the longer trips to Denver. There is no transfer of dye after a few hundred miles - yet. Let's see what happens down the road. As a precautionary measure, the thermostat is scheduled for replacement. The harmonics in the heads are reported to be a minor problem and I hope there is not a small leak somewhere in the block around the heads. I'll continue to watch it. I'd like to get this daily driver beyond 300,000 miles. I view daily drivers like a 1\2 " wrench - you use it until it completely breaks and drops. Thanks again for the tips.

 

[Lynn Larsen]

Steve,

Be sure to insist on a fail-safe thermostat. These, if and when they fail, fail in the open position so that the engine will not over heat. As you probably know, standard thermostats fail by not being able to open.

Lynn

 

[Steve Briscoe]

Lynn-
Actually, I didn't remember to ask about a fail safe thermostat. I'll do that. I did ask about different temperature thermostats and I was told Chrysler\Jeep only provides one type because it would effect the performance of the ECU at anything other than OEM specs. I was given the same reason when I asked about running Bosch Platinum 4 spark plugs. I'll make sure the thermostat is the fail safe type.