Does anybody know why there's carbon build up under the oil filler cap? 01 Sienna

[blueapple]

I noticed this really thick layer of carbon build up under the engine oil filler cap of my mom's van, long time ago. it's still there by the way, and chipping. I've never seen an engine look like that before, how about the rest of you folks out there? Do you have this?
Dealer is no help, service guy's rude and basically don't know anything about it. He said he can open the valve cover and check for sludge but that's gonna cost us 70 bucks just to open it..

By pass gas should be either vented out or mixed with engine oil, I don't know why there's build up on the filler buffle... especially that thick, in such short time.

we change oil every 4k or so. My mom used to run 87 octane, always shell or Chevron, now she switched to 92 octane, seems to run stronger on 92 and better over all on fuel consumption. Manual said 87, 92 for performance.

Otherwise the car runs great, no problem so far ( knock on wood ) with almost 40K

[ShawnM]

Thats very common. As long as you change the oil every 4K I wouldnt worry about it too much. There isnt really any oil circulation in that little filler area so the oil just kinda stays there and gets cooked. I think just about every one ive seen looked like that.

[blueapple]

Cool, thanks

[D0UG]

Hot oil fumes will form sludge when it contacts something cooler -- like a plastic oil cap.

At least that is what I have read from petroleum experts.

[kschachn]

Originally Posted by blueapple

I noticed this really thick layer of carbon build up under the engine oil filler cap of my mom's van, long time ago. it's still there by the way, and chipping. I've never seen an engine look like that before, how about the rest of you folks out there? Do you have this?

By pass gas should be either vented out or mixed with engine oil, I don't know why there's build up on the filler buffle... especially that thick, in such short time.

we change oil every 4k or so. My mom used to run 87 octane, always shell or Chevron, now she switched to 92 octane, seems to run stronger on 92 and better over all on fuel consumption. Manual said 87, 92 for performance.

There is a coating (factory applied) on the baffle. This is what you see, it is rough and looks a lot like some kind of deposit. It isn't. The underside of the filler cap should not have any sludgy material, only some varnish.

Unfortunately you cannot see into the head through the filler hole. It is true that you do have to pull the cover to see inside but $70 is a lot to do that. The new gasket is about $10 at most and it takes maybe 10 minutes to get it off and 20 to get it back on. If you are mechanically inclined you can easily do it yourself. Eventually that gasket will start to leak anyway, so you'll be doing it sometime as it is. This is a good opportunity to take a look into the upper end of the engine.

[gekishibu86]

I've acquired a 2000 Sienna about 8 months ago with 109K miles without that sludging problem. The van was used by the former owner from Half Moon Bay to San Francisco where she works. I've read all about problems about sludging on these Siennas but how come mine didn't have that problem? I realized that my Sienna was used on areas where is cool most of the time of the year and sludging problems are related to hot temps. After I took ownership, I changed my oil to synthetic (Redline 5-30W) and added Redline waterwetter in my cooling system and let my brother in law drive it to Las Vegas that summer where the temp was about 113 degress with the A/C on all the time. When he got back from the trip, I immediately checked the condition of the oil. I found nothing from the ordinary. The cap was still clean with no signs of sludging. I came to the conclusion that if you live on an area where it's hot most of the time, you have to use synthetic oil to prevent oil cook off(sludging). I think I read it somewhere that the operating temp of these engines are pretty high (265?) compared to other engines which contributes to sludging if you're using dino oil.