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Discussion Starter #1
My Chevy 350 jet boat fouls plugs #3 and #6. I noticed that the Holley carb vacuum port for the PCV feeds into the dual plane rpm manifold adjacent to the fouling cylinders. The plugs are darker and black up the threads but not shiney or gooey. The engine runs at 4,400 rpm's for sometimes an hour at a time. It has consumed some oil, maybe 1 quart per 10 running hours. I have Profitm valve covers with factory style baffles, a generic GM PCV and a push-in breather on the other cover. Is this set up likely causing the fouling on the third plug back on each side? The other plugs are perfect, new rebuild.
 

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Don't think so sound like you have clearance issues in those cylinders. Build up of oil residude from bad rings, bad oil seals or bad valve guides. I am assumeing it must smoke like hell when yo try to start it fresh or after it set assuming thso valves are open.














if you use standard seals they are
 

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E-7 Sheepdog (ret)
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That would be one hell of a lot of oil thru the PCV, I agree with the above, you've got oil controll problems related to rings or valves (seals and/or guides).
 

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Discussion Starter #4 (Edited)
The engine is a Vortec 5.7 from a '99 crash and burn truck with less than 20,000 miles on it, cross hatching on cylinder walls, looks new. The heads were gone through by a reputable machine shop, new seals put in. Good compression 195-205 PSI on all cylinders. Running one heat range hotter than stock plugs AC R44LTS, Edelbrock RPM Air Gap Manifold, Holley 600 vacuum seconday, 66 primary jets, 0.070" secondary plate, 4.5 power valve, Crane Gold 1.5 roller rockers, 10 degrees initial timing, 32 degrees total timing, 160 degree thermostat.
 

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dont know if this is your issue or not but i had a similar problem with 3 and 6. Turned out my distributor cap as not seeated properly and just so happned to end up on those cylinders. 3 and 6 fire back to back so that was my problem. Mybe those cylinders arent firing properly.


If you run WOT for a hour strait are you losing a bunch of oil thru the push in breather? If hes not burning up the oil maybe hes just spittin it out. I know my SBC gets all kinds of nasty up there just after an afternoon of mixed driving.
 

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I doubt it's the PCV. It would be easy to test the theory, just cap it off and run with a breather in each cover, (you would probably also find the inside of the pcv hose to be an oily mess). If it continues I'd pull the intake and look for signs of leakage.
 

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you might check your firing order. said #3 and #6 and then also 3rd one back on each side? looking at the front of the motor chevy runs 2-4-6-8 on the left and 1-3-5-7 on the right, sometimes you cant feel the mis at higher rpms.
you could also check for a misfire by letting somone else run your boat and you could clip your timing light on the cylinders that a fouling. check at different rpms if it is in the ignition you will see the light flashing unevenly.
what distributor and cam are you running? gm has distributor gear problems on those motors and the timing cant be set with a light on the '99 distributors
 

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You more than likely have a leaking intake manifold from the underside, extremely common on a 350 Vortec.

The first thing I would do is remove the intake and see what the gaskets look like, I have seen over a dozen leaky intakes on the Vortec configuration.

Make sure the torque sequence is followed to a tee.

People very seldome torque these correctly...

Good luck!

GT:)hand
 

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I would agree that the proper torque is the only way they will hold.
Just seems a little odd that the problem is on the 3rd cylinder back on both sides.
We do 2-3 intake sets on those trucks a month but most of them for coolant leaks (dexcool plays hell with air in the system).
 

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Discussion Starter #10 (Edited)
Oops, cylinders 5 and 6 are the ones. I had tried going up one heat range to AC R44LTS. The plugs are cleaner than with the AC MR43LTS plugs but may be too hot. I looked under the microscope at them after a day of running and the porcelain has small white beads, only viewable with the microscope. I guess it is starting to melt and bead-up. Nobody has posted this online - little beads. I looked...a lot! Anyway, the manifold gaskets are these special Felpro marine gaskets. They are made out thick black rubber with some aluminum sheet embeded in them. Maybe I did not torque them enough. The Vortec truck stock gaskets are the rigid plastic ones requiring inch pounds. I torqued these marine ones to about 10 ft. pounds. I could not find a proper torque value for non-plastic Vortec intake gaskets. Any of you know the gaskets I'm referring to? The engine does not run like it has an intake leak. It idles very smooth @ 600 RPM's with the idle screws 1.25 turns out. Yesterday it used 3/4 of a quart of oil on a 115 mile trip using about 55 gallons of 93 octane.
 

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Unfortunately the only way you are going to find out if it's an intake leak is to pull the manifol. It won't necessarily make it run bad if it is leaking, but if the gasket didn't seal properly it will let a lot of oil thru.
 

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The Man
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Go to the Home Depot/Lowes and over to the air tool section and pick up a cheap air line air/oil separator and a couple of barbed hose end fittings and place it in the pcv line to see if there's any oil getting past the pcv valve. If there is it'll catch it. We've had to do that to several LS1 engines to fix oil consumption issues. The small ones like this are ideal.
 

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Go to the Home Depot/Lowes and over to the air tool section and pick up a cheap air line air/oil separator and a couple of barbed hose end fittings and place it in the pcv line to see if there's any oil getting past the pcv valve. If there is it'll catch it. We've had to do that to several LS1 engines to fix oil consumption issues.
That right there is a helluva idea...Gotta purge something from the memory to remeber that one...

GT :)hand
 

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Discussion Starter #14
I bought a Husky Water separator last week at Home Depot but the drain valve didn't close on any of them, maybe they need to be under pressure. I returned it and have been looking for a better one, maybe even a real catch can from Summit, Jegs, etc. Anyone have one that stays shut until you drain it? What should I torque the manifold to? It's an Edelbrock Air-gap RPM with the marine thick black rubber gaskets.
 

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Discussion Starter #15
I have been using Pennzoil 10w-30. I see others online are using 15W-40 or straight 40w. Is there a noticeable decline in oil burning by increasing the viscosity? Currently it spikes at 80+ PSI on start-up, then drops to 40-50 while warmed-up cruising. I do go out in extreme winter conditions up here in Massachusetts in ice-filled rivers, but I want recommendations for summer oil. Any of you run straight 40 or 15-40 or 15-50?
 

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AKA OhOneWS6
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Go to the Home Depot/Lowes and over to the air tool section and pick up a cheap air line air/oil separator and a couple of barbed hose end fittings and place it in the pcv line to see if there's any oil getting past the pcv valve. If there is it'll catch it. We've had to do that to several LS1 engines to fix oil consumption issues. The small ones like this are ideal.
All my time on the LSX boards and I have never seen that fix. I've owned two LS1 cars and 2 LSX based trucks. All have had minor oil consumption issues. This looks like a good fix. Wish I had known about this 8 years ago when I started my LSX journey.
 

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The Man
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All my time on the LSX boards and I have never seen that fix. I've owned two LS1 cars and 2 LSX based trucks. All have had minor oil consumption issues. This looks like a good fix. Wish I had known about this 8 years ago when I started my LSX journey.
Yea, I stumbled across it when my '01 WS6 started using a bit..pulled the lid and looked inside the intake through the TB and it was covered in oil mist. For some the truck style pcv valve has worked..it's hollow with a small hole at the end, but it didn't work on mine. I started my lsx journey back in '98 with my first T/A..I seem to end up with a LSx about every other vehicle lol. That mod is called the "Home Depot catchcan" mod :D
 

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Discussion Starter #19
I bought a better one from Sears. It has a functioning release valve. It also came with a mounting bracket, but I Zip-tied it to the aluminum box frame of my engine compartment because the plastic nut would break in the wave poundings I get into. I also got a new PCV with a stronger spring.
 
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