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After reading about various EGR-related issues with some of the Honda V-6s as they age, I took the top cover off the manifold of our 2005 MDX (128k miles). It was quite dirty inside, with lots of small carbon deposits. These appear to be the same as what's coming up out of the EGR pipe. The EGR pipe itself is free and clear, though it is lined with carbon -- like the chimney of an oft-used fireplace. The bits of carbon laying in the intake manifold are odd to me, though.

The flap running lengthwise across the middle of the intake manifold opens at about 3,600 rpm, and equalizes both halves of the manifold. It doesn't seem to me that it would be all that effective at creating more power, but it must work. It's hard to hear this transition in the MDX because of its quiet intake ducting, but you can certainly hear it in the Ridgeline -- the intake noise turns deeper and louder.

It appears to be very varnished, and I imagine that's coming from the PCV line. This engine has ALWAYS discolored fresh oil very quickly -- the oil is significantly darkened after only 1,000 miles or so. The PCV gasses enter the intake manifold via the silicone hose in the lower left of the photo and travel around the perimeter of the upper intake manifold through a channel that is sealed by the top cover with a thin paper gasket. There is a small hole in the top of each intake runner through which the PCV gasses are delivered.





Our MDX's intake manifold is either dirtier than it should be, or our '09 Ridgeline's intake manifold is cleaner than it should be. It has 99k miles. The MDX's intake manifold is a monobloc cast aluminum job, and I understand the 2006-2008 Ridgeline uses the same type of intake manifold. The 2009 and later Ridgeline uses a newer design split-case magnesium casting. It uses the same PCV design, with gasses traveling around the perimeter of the upper intake manifold; this manifold cover uses a nicer pliable thick rubber seal instead of the other one's flat gasket. But it's so clean in this one -- and indeed, the 8k mile oil that I drained out of it when I bought it looked as discolored (or even less so) as the 3k mile oil that's in our MDX right now. The current oil in the Ridgeline has about 2k miles on it, and it's still a golden tan color.





What do you think would cause these engines to run so differently, in terms of what's being deposited into the intake manifold? I have no issues with how the MDX's engine is running -- tailpipe emissions seem to be clean with no particulates, it returns fuel economy commensurate with the EPA estimates, etc. But I'd still like to clean it up some if I can. Since it was new, it's seen regular oil changes at <= 5,000 mile intervals, and always with a name brand conventional or synthetic oil. The Ridgeline, on the other hand, has survived on Jiffy Lube Pennzoil conventional oil changes for its first 95k miles, at maintenance minder intervals (~8k miles), and it's clean as a whistle.

I'm wondering if 2006-2008 Ridgeline owners have observed the same type of intake manifold varnishing that I'm experiencing in my MDX. Any ideas?
 

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I sorta doubt many have taken a look there on their J35 motors. I know I haven't.

Also, your pics are not showing on my end? Can you see them?
 

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I wasn't aware that the Ridgeline had an "active" (you call it a "flap" opening at around 3600rpm) intake manifold. You refer to both your MDX and the Ridgeline as having one . . .

I will be adjusting my valves next month before it gets too cold and will post what I find in my 06's
 

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@speedlever: Sorry...yeah, I can see the pictures, but it seems like Google wasn't allowing public access to them. Here's a link to the pics:

https://goo.gl/photos/grxiEsXjFoY6wQxb8

This cover has to come off to remove the intake manifold, so I was hoping that someone who's done the valve adjustment themselves might remember (or have pics).

@eurban: yes, there is a butterfly flapper valve that runs down the center of the intake manifold on all most Honda J35 engines. On your Ridgeline, look at the left side of the intake manifold -- at the end. There's a small black plastic stepper motor with a Denso sticker on it. That's the motor that controls the butterfly valve.

After looking at everything some more, I think one of the major factors may be the PCV system itself. On the MDX (again, similar to a 2006-2008 Ridgeline's J35A9), the PCV valve is on the left side of the engine (as it sits in the vehicle), directly next to the silicone PCV hose that connects to the manifold. There may not be a lot of opportunity for moisture or oil droplets to fall out of suspension there. On a 2009+ J35Z5 engine (plus other J35s with the magnesium intake manifold, I presume), the PCV valve is on the opposite side of the cylinder head cover, and PCV gasses must, presumably, travel the entire length of the cylinder head cover before entering the hose to the manifold. The PCV "channel" in the upper intake manifold is significantly cleaner in the magnesium manifold vs. the aluminum manifold. Maybe the Ridgeline's J35Z5 engine has a more robust oil separator in the cylinder head cover.

The EGR area is also significantly cleaner in the Ridgeline's manifold vs. the MDX's manifold. The only significant design difference is the MDX's engine pulls EGR directly from the #6 exhaust port area on the right side of the front cylinder bank, whereas the Ridgeline's engine has an EGR tube that leads down to the front exhaust pipe after the catalytic converter. So the Ridgeline's engine is receiving presumably "cleaner" EGR gasses vs. what the MDX's engine gets.

I don't think anything upstream of what we see here would introduce oily gasses into the intake manifold. There are no fuel injectors at the throttle body. There's a crankcase breather in the intake tube downstream of the air filter, but that should be pulling air OUT rather than dumping air IN to the stream.

Earlier engines with the cast aluminum intake manifold, the same-side PCV system, and the pre-cat EGR tend to look like our MDX's...after looking at a bunch of pictures of earlier Pilot and Odyssey engines this morning on the web. Some of those owners build PCV catch can systems to try to prevent that oily residue in the manifold. I'm thinking that maybe Honda has come up with a bit of a "built in" oil separator system in the later engine design, with the PCV valve across the cylinder head cover from the hose connection.
 

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My 06 ridge looked like your MDX at about 130k ish miles. When I did the valves I replaced the PCV as well and cleaned the inside up a bit. I am at 170 now. Maybe Ill pop that cover off and see if its dirty again or not.

That butterfly flapper thing is the Variable intake system. Its used to get the best torque/MPG etc throughout the whole RPM range. It changes the length of the runners.
 

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Wish I'd thought to have some pics made of my Pilot's J35 when it was open for the TB/WP and valve adjustment. The mech says the cam lobes were perfect and no sign of any sludge at 121k miles. (Mob1 5w-20 all its life).
 

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Cause of difference. One car does mostly short trips the other long runs which helps burn up deposits
That would explain a lot more than the choice of octane. Top tier gas though, not any 'last stop' stations.
 

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That would explain a lot more than the choice of octane. Top tier gas though, not any 'last stop' stations.


Why do you think that?


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Running quality gas that is of the octane that is right for your vehicle is the best you can do. It will have sufficient cleaning agents to keep your engine clean depending on the age and condition of the engine, of course.

The idea that higher octane gas is 'better' is hogwash.
 

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I meant that higher octane fuel contains more additives and could have contributed to the increased discoloration in the MDX.


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That's kind of a twist... for a long time gas companies pushed higher octane gas because it had more additives to keep the engine cleaner, which I never bought into anyway.
 

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My 06 ridge looked like your MDX at about 130k ish miles. When I did the valves I replaced the PCV as well and cleaned the inside up a bit. I am at 170 now. Maybe Ill pop that cover off and see if its dirty again or not.

That butterfly flapper thing is the Variable intake system. Its used to get the best torque/MPG etc throughout the whole RPM range. It changes the length of the runners.
I know this was a couple years ago, but did changing the pcv valve help?
 

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Curious to know. I just did my valve adjustment and the front head was dirty with a slight bit of sludge, whereas the back head was immaculately clean. I'm not sure how that happens.
 

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Curious to know. I just did my valve adjustment and the front head was dirty with a slight bit of sludge, whereas the back head was immaculately clean. I'm not sure how that happens.
Just my opinion, (heat) relationship to the radiator and air flow.
 
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