What causes black crud buildup inside the oil cap?

[OilStainedNapkin]

My car (2007 4runner with 194k miles) gets a layer of black/dark brown buildup under the oil fill cap. I can usually clean it off with just a paper towel.

Anyone know what this is or what causes it? I’m assuming fumes from when oil is burned off or blow-by.

Looks similar to this pic:

 

[ZeeOSix]

Same thing can build-up on the underside of the valve cover. They don't get as hot as the rest of the engine, and can build-up condensation and deposits from short trips. Pull the filler cap off after a short trip in cold weather, and you'll probably see condensation and a milky coating (oil & water mix). What oil are you using?

Also, have you ever replaced the PCV check valve? If the PCV system isn't evacuating the guts of the engine properly, the condensation won't be evacuated very well.

 

[OilStainedNapkin]

Same thing can build-up on the underside of the valve cover. They don't get as hot as the rest of the engine, and can build-up condensation and deposits from short trips. Pull the filler cap off after a short trip in cold weather, and you'll probably see condensation and a milky coating (oil & water mix). What oil are you using?

Also, have you ever replaced the PCV check valve? If the PCV system isn't evacuating the guts of the engine properly, the condensation won't be evacuated very well.

Thanks for the response. I live in California and don’t deal with cold weather much. I don’t think this is the milky/light brown crud that typically develops from moisture and short trips which is what I think you’re referring to. This is more of a dark, tar like sludge, albeit a thin layer.

I’m currently using Mobil full synthetic (similar to Mobil super synthetic). And yes I changed the pcv at about 110k miles but the old one looked fine.

As a note, this buildup appears like 10k miles after being cleaned off.

 

[ZeeOSix]

Mobil 1 full synthetic should keep things clean. What oil change interval are you typically doing? Does it burn oil? Could be an excessive ring blow-by issue as you thought.

I'd still suspect the PCV system. Check the whole system for any issues.

Might try some Valvoline Restore and Protect if the rings are stuck, which can cause oil burning and blow-by.

 

[TomYoung]

Your car is a known slugger. You should run an engine flush like Liqui Moly and get your OCI down. The PCV valve should be replaced. If you can, remove valve covers and physically remove sludge. The hope is that there is minimal cylinder wall wear and that there are no stuck piston rings. Check out the Car Care Nut YouTube videos. You can definitely keep on driving, but a sludgy oil cap in a Toyota of any description is bad news.

 

[ka9mnx]

Time for another PCV R/R...

 

[OilStainedNapkin]

Mobil 1 full synthetic should keep things clean. What oil change interval are you typically doing? Does it burn oil? Could be an excessive ring blow-by issue as you thought.

I'd still suspect the PCV system. Check the whole system for any issues.

Might try some Valvoline Restore and Protect if the rings are stuck, which can cause oil burning and blow-by.

I stick to 5k, never over 6k.

I have some oil burning, maybe a quart over an oci but it’s done this since I’ve owned it. I think if there was major blow by, the oil would turn pretty dark. It stays a honey brown or maple color even at the end of the oci.

One thing to mention is the oil fill neck sucks very high on these 1gr-fe engines. So any oil residue or burn off will likely go to this area which is the highest point in the engine.

Will look into the

 

[OilStainedNapkin]

Your car is a known slugger. You should run an engine flush like Liqui Moly and get your OCI down. The PCV valve should be replaced. If you can, remove valve covers and physically remove sludge. The hope is that there is minimal cylinder wall wear and that there are no stuck piston rings. Check out the Car Care Nut YouTube videos. You can definitely keep on driving, but a sludgy oil cap in a Toyota of any description is bad news.

This is the first I’m hearing of the 1gr-fe being a known sludger. I suspect if there was a bunch of sludge, the oil would turn pretty dark over time. The darkest it gets is a dark maple color towards the end of an oci.

I agree that the pcv valve may need to be revisited.

 

[Sumboodie]

Blowby.

Will get white goo in places that have winter.

 

[Sam_Julier]

I get this in my Volvos in the winter. It’s the coldest part of the engine plus an area that gets condensation.

In the winter I run our cars on the highway for 30 minutes each week.

This regimen prevents this build up.

 

[TomYoung]

This is the first I’m hearing of the 1gr-fe being a known sludger. I suspect if there was a bunch of sludge, the oil would turn pretty dark over time. The darkest it gets is a dark maple color towards the end of an oci.

I agree that the pcv valve may need to be revisited.

It’s not the worst Camry, but is a sludger.

 

[Kurtatron]

Isn’t this that stuff Toyotas always have under the oil cap? Gets mistaken for sludge frequently. Both my 1MZ and 3MZ have had that.

 

[OilStainedNapkin]

Isn’t this that stuff Toyotas always have under the oil cap? Gets mistaken for sludge frequently. Both my 1MZ and 3MZ have had that.

I think I know what you’re talking about but that’s a coating in the filler neck. This buildup occurs on the inside portion of the oil cap

 

[cjcride]

Blowby.

Will get white goo in places that have winter.

Agreed, yet even brand new engines have some blowby

 

[Donald]

Why are you worrying it??

 

[OilStainedNapkin]

Why are you worrying it??

Not worried as I realize this car is almost 20 years old and nearing 200k rather it’s more curiosity.

 

[350Rocket]

Adding a catch can to my gm 4.8 seems to have kept anything from building up in the oil cap the last few years since I installed it. It's a normal thing otherwise, especially on short tripped vehicles.

 

[Donald]

My brother had a 4Runner a few years older than yours and while it looked good and ran good it had a large enough hole in the frame that his shop finally said it's not worth changing the oil and was no longer safe to drive. I told him to get the frame repair kit installed but he just bought a much newer one and traded the old one to Carvana.

 

[KrisZ]

One thing to mention is the oil fill neck sucks very high on these 1gr-fe engines. So any oil residue or burn off will likely go to this area which is the highest point in the engine.

Since the filler neck is up so high, there is likely very little to no oil splash on the cap. The dark residue is likely oil vapors. Those will leave nasty deposits, just look at the DI engine intake valves.

 

[PF52]

Since the filler neck is up so high, there is likely very little to no oil splash on the cap. The dark residue is likely oil vapors. Those will leave nasty deposits, just look at the DI engine intake valves.

+2

Some cars have a baffle there beneath the filler cap, which just creates more areas which don't get splashed by fresh oil. They often get that kind of buildup there. Also, I tend to think some cars are particularly prone to developing a "cold chimney" there by the filler cap; think of the Aztek and Buick Rendezvous and similar vehicles which had a very tall plastic filler "neck" that stuck up much higher from the valve cover.