4.3 vortec W oil in upper plenum

I have search and cannot find an answer to my problem. I have a 1993 S-10 Chevy Blazer with the 4.3 Vortec W engine, 145000 miles. For the third time in the last 3-4 weeks I have had to open the upper air plenum and clean out puddles of OIL. The puddles are mostly around the head of the bolts holding the plenum to the head. The whole plenum has a fine coating of oil. It seems to be concentrated at the passenger rear of the plenum, near the small vacuum line inlet. The 3 holes in the rear of the Plenum have a coating of oil on the gasket-mating surface.

Now before you say leaking injectors / nut kit I have replaced that in both of my Chevy blazers and did replace the injectors in this one the first time the oil appeared since they were still under warranty (early August).

Plenum has no ‘washing’ or signs of gas, just the oil. There is no sign of gas in the engine oil. I have replaced the PCV since it was cheap but the old one seemed fine. I have q-tipped the vacuum lines and find nothing definitive. The oil breather where it goes into the air cleaner assembly does have a bit of oily residue. I pulled the charcoal canister and it seems fine.

Now some info that may not apply: A couple of months ago my son and I change the radiator. I connected the transmission lines and he did the oil cooler lines. Middle of July he has a puddle of oil under the truck and we found he had not tighten the nuts enough and there was oil under the hood on the front driver’s side. This week before I cleaned the plenum I was checking fluid levels and the trans was 1-1 ½ quarts low.

Where or where do I look for oil coming into the Plenum? Is it possible I am condensing oil from the breather? The beast needs work (shocks, exhaust, maybe another gas tank) so I would like to know if I am putting money into a black hole.

You probably have exessive blowby from worn rings or a bad piston. Excessive blowby will carry droplets of oil out of crankase, through PCV and into intake plenum. The breather line that goes from air filter to valve cover is for air flowing INTO the crankcase. If you have oil in it, this means that you have more blowby flow than can escape from crankcase through the PCV valve, so it is also flowing out the inlet port.

Test: Pull the PCV valve out of the valve cover, but leave it connected to the hose. Run the engine and watch how much blowby comes out the PCV hole on the valve cover. Or remove oil fill cap. If you can see/hear/smell exhaust fumes coming out the hole then it is probably time for an engine rebuild. A compression test would help determine if you have one bad cylinder or if all are worn.

for the few bucks it costs use a oil sump cleanser and then change the oil.
The best one that I've ever found but most expensive these days is do an oil change using Diesel. Then run the motor for 10 min and do a complete oil change again.
Your oil will not turn color for months.
It'll desolve any crap might be blocking any passages up.

If that doesn't cure your problem try Engine Restore, and see if it does. If it works your engine is worn, but engine restore will keep it going for a long time. http://www.atvconnection.com/atvconnection/Features/productreviews/Restore-Engine-Restorer.cfm
I hate Walmart, but I believe that you can get this product through them.

Good Luck

Thanks guys –

That’s not wanted I wanted to hear but what I was afraid of.

At engine start up I could see a bit of smoke/vapor from the oil fill tube and from the PCV. It always puffs a white cloud at start up. As the engine warmed up the smoke/vapor from the fill tube seemed to go away. There is still smoke/vapor from the PVC hole. I had to close my barn door and use a trouble light to be able to see it so it was not a great amount. I suppose I will get a compression tester, always wanted one but just didn’t need it.

I would like to try the oil cleaner. What is the diesel method? I bought 150 gallons of #2 in June for my tractor and to heat my workshop in the barn so I have it on hand. Do I just drain the oil (what about the filter) refill with #2, run for 10 minutes, drain and refill? Sounds pretty straightforward. I would like to do the compression tests before and after.

Is the Engine Restore a better way to go? Should I try it first or second?

I have heard stories of ‘pin holes’ in the piston – any truth to that?

Thanks - dkjen

another thought - can i run without the PVC hose hooked up? any risks or concerns?

Most people will tell you to use a new oil filter when doing the diesel trick, but I just drain the old filter until nothing comes out. Like I said it really cleans every thing out and you'll be impressed.
Then use a new filter with the new oil.

I would try the diesel cleanup first.
Then the engine restore.

If there are pinholes in the pistons they would have been there right from the factory, which I can't see happening.
Valves burn out way before pistons and if they were burnt you'd have a very low compression motor.

Before 1963 they never had any PVC Valves, and they just had a pipe (or hose) running down under the car.
This same trick still works with todays cars
You might want to run the hose all the way back past the cab so the smoke doesn't bother you

For what it's worth, disabling the PCV system will make you suject to Federal fines for emissions system tampering.
Cleaning the crankcase with diesel or any other substance will not have any effect on reducing blowby. Keep focused on the problem that you have.

I finally got a chance to check compression. four have 150 psi - normal. one has 140 psi and the last about 130 psi. So i don't think i have oil blowing by the rings - Right???

any suggestions where is should go next? I still intend to do the engine clean. Could i have plugged drain holes in rockers? something else? I don't seem to have oil running out of the 'bypass' hose from the PCV.

Thanks in advance for your help

130 psi to 150psi is too big of a difference.

However if you re-try the 2 low cylinders they might be right up there.
There is often a bit of carbon buildup or something that stops you from getting an acurate reading, and testing them the second try seems to show different readings

130psi to 150psi is only 13% difference from highest to lowest compression numbers. 99% of motors in the US today you can safely get away with 20% difference and have a perfect running motor. actually most manuals say max difference of 20%. under 10% is excellent, 10-15% is great/decent, 15-20% is acceptable and will usually run fine but indicates the need to rebuild in the near future; within 10,000 miles

sorry, caught myself in an edit. altered is in caps:
130psi to 150psi is only 13% difference from highest to lowest compression numbers. 99% of motors in the US today you can safely get away with UP TO 20% difference and have a DECENT running motor. actually most manuals say max difference of 20%. under 10% is excellent, 10-15% is great/decent, 15-20% is acceptable and will usually run fine but indicates the need to rebuild in the near future; within 10,000 miles

I always test any weak cylinders a second time, and they're right up there the same as the others 80+ % of the time.

I don't know if it's the connection, or like I was told carbon build up, but it works.

I know that most shops don't run the second test, and for all I know it's to try to convince people that they need a new motor soon.

compression test tests 2 things: compression ring (top ring only) and valves. compression test does not test anything related to the oil control rings (lower ring[s]). if compression test shows low numbers, its either one or more valves in that cyl that are worn, bent, or not seating properly, or the top/compression ring is worn, or the cylinder is worn and/or scratched.
when low numbers are found, to determine if its something valve related or top ring related, you pour about a capful of oil in that cylinder. if the test numbers improve, the valve[s] is/are fine and the culprit is the compression ring. when you run the test twice, without the motor running in between tests, the oil control rings may let some oil up to the compression ring, making it seal better and showing higher results.

as for carbon buildup, that actually will show higher compression results, not lower. cuz it raises the compression ratio. that is typically the case when you have one or two cylinders with higher numbers than the rest, which usually indicates those cylinders are running richer than the rest

Thanks for the discussion on compression. The instructions with the compression tester said max of 20lbs differance between cylinders.

I did not think to recheck the low cylinder and will retest when i get a chance. I was working alone, this is my son's truck and he is off at college. I will try the oil in the cyclinder if it still is low. I am driving the truck for the next few weeks and will check the plenum after a coupld tanks of gas. So far it is running good.

I did have a couple of plug wires that i replaced when doing the compression tests and the 'miss' we had at times is gone for now.

The counter guy at the local auto value store said he has heard of carbon build up on the baffle plate in the valve cover leading to excess oil thru the PCV.

I will try an engine clean with the next oil change if it keeps running good, eariler if it doesn't.

Again - thanks for all the input.

The cheapest, and best internal engin cleaner is a spray bottle with water in it.

Take off the air filter, and spray the water in (in a mist) while the engine is running. The steam desolves the carbon.

1 or 2 bottles full of water should do it.

Did you ever solve the problem with the oil in the intake plenum? I've got the same symtoms (as outlined over on www.blazerforum.com at thread: http://www.blazerforum.com/m_23885/tm.htm )

Changed several items (EGR, PCV, Last October changed spider kit & nut kit for a fuel regulator leak...) But now I've got an oily intake, and a VERY rough running engine.

Thanks,
Rex S.