Intake Port Sludge

Intake Port Sludge

Joined: December 29th, 2003, 3:59 am

January 7th, 2012, 4:06 am #1


Have something strange - pulled off my intake manifold today - noticed that the bolts were just barely "tight".  Just a 1/16 of a turn and they were finger loose. So, that was strange, but even stranger when I got the intake manifold out of there, I noticed, on the floor of the intake "runner" in the head going to the valve was "sludge" on the bottom of the runner.

It was thick - I bet in some spots it was 1/8" thick when I scraped it out of there, and it was black as night and was somewhere between oil and dirt.  One part had a lip sticking up far enough that I'm pretty sure I know where the 20-30 hp that I lost this year went.

I scraped it out, then drenched it in carb cleaner and rubbed it down.  It's still somewhat "black".

Any thoughts on what might have caused it? 

Do I need to get the port "shiny" again?  (and if so, any thoughts how with the head still installed?)

Thanks guys!
Quote
Like
Share

Joined: February 28th, 2008, 4:15 pm

January 7th, 2012, 7:09 am #2

Aluminum intakes go through heat cycles that "crush" the gaskets and need the bolts checked from time to time. Sludge my be from reversion or poor low rpm fuel atomization, what does your carb have for boosters? If you are using a PCV valve then it could be oil.
Andy
Quote
Like
Share

Joined: February 3rd, 2003, 5:22 pm

January 7th, 2012, 2:58 pm #3

most likely oil as mentioned. The PCV valve and PCV system is a culprit as no valve cover breather opposite the PCV will do it and/or a stuck PCV. I'd also check the backsides of your intake valves with a shop light for heavy oil deposits. Worn valve guides, brittle valve seals can also add oil where you don't want it. Reversion can drag oil passed from the valves pretty far up the intake manifold

And yes, one must often re-tighten intake bolts a few times after some heat cycling.
Last edited by machoneman on January 7th, 2012, 3:15 pm, edited 1 time in total.
Quote
Like
Share

Joined: December 29th, 2003, 3:59 am

January 7th, 2012, 7:09 pm #4

Aluminum intakes go through heat cycles that "crush" the gaskets and need the bolts checked from time to time. Sludge my be from reversion or poor low rpm fuel atomization, what does your carb have for boosters? If you are using a PCV valve then it could be oil.
Andy
I'll have to check those bolts more often in the future than I had been checking them, that's for sure. 

I have EFI, so no "carb booster".  And am running E85.  I do have a PCV valve though!
Quote
Like
Share

Joined: December 29th, 2003, 3:59 am

January 7th, 2012, 7:11 pm #5

most likely oil as mentioned. The PCV valve and PCV system is a culprit as no valve cover breather opposite the PCV will do it and/or a stuck PCV. I'd also check the backsides of your intake valves with a shop light for heavy oil deposits. Worn valve guides, brittle valve seals can also add oil where you don't want it. Reversion can drag oil passed from the valves pretty far up the intake manifold

And yes, one must often re-tighten intake bolts a few times after some heat cycling.
Hmmmm, I have a breather on the side opposite of the PCV valve, but my PCV valve could be stuck.  I haven't replaced it in a long time.  Is it just sucking in a ton of oil?
Quote
Like
Share

Joined: February 3rd, 2003, 5:22 pm

January 7th, 2012, 8:10 pm #6

I'll have to check those bolts more often in the future than I had been checking them, that's for sure. 

I have EFI, so no "carb booster".  And am running E85.  I do have a PCV valve though!
if it's stuck open all the time.
Quote
Like
Share

Joined: February 7th, 2007, 1:05 am

January 8th, 2012, 3:18 am #7

Have something strange - pulled off my intake manifold today - noticed that the bolts were just barely "tight".  Just a 1/16 of a turn and they were finger loose. So, that was strange, but even stranger when I got the intake manifold out of there, I noticed, on the floor of the intake "runner" in the head going to the valve was "sludge" on the bottom of the runner.

It was thick - I bet in some spots it was 1/8" thick when I scraped it out of there, and it was black as night and was somewhere between oil and dirt.  One part had a lip sticking up far enough that I'm pretty sure I know where the 20-30 hp that I lost this year went.

I scraped it out, then drenched it in carb cleaner and rubbed it down.  It's still somewhat "black".

Any thoughts on what might have caused it? 

Do I need to get the port "shiny" again?  (and if so, any thoughts how with the head still installed?)

Thanks guys!
the sludge was in the head? If not, then it was a leaking gasket, and you were sucking oil from the valley. Is there a witness mark/clean area where you see the beginning of the sludge trail? Did you inspect the intake gasket for deformation or tear, or cut, etc.? If it was reversion, then it would be in more than one port, and the plugs would show evidence of oil/sludge. Joe-JDC.
Quote
Like
Share

Joined: December 29th, 2003, 3:59 am

January 8th, 2012, 3:30 am #8


The sludge was in the intake port of the head, kind of in a rectangular area about 1" past the intake side of the head, going down the port about 1.5" and was about 1" wide.  It was on the tight corner, so I assume that was the "slow air" area.

Intake gasket was discolored from new (darker), but no tearing until it was removed from the head.

The intake itself was "dark" with oil or whatever it was, but it didn't have any buildup on it.  Plugs didn't show much, but burning E85 leaves them pretty clean.

Jay
Quote
Like
Share