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Oil in upper intake---why??
I?m getting ready to buy a 1987 Thunderbird Turbo Coupe, but before I can do that I need to sell my 1990 Thunderbird LX, which has a 3.8L v6. I?m doing some repair work before I sell it and one of the issues I have is for some reason I have a lot of oil inside my upper intake manifold; enough so that it is bypassing the throttle body butterfly (I assume when the engine is not running) and running into the air intake tube. Does anyone know why I?m getting oil in the upper intake? Where?s it coming from? Only thing I can think of is it?s getting blown up past the valves from the cylinders and into the upper intake. Does this sound logical? If so, what?s causing it to do this? Or could this be a bad or malfunctioning PCV Valve causing this? Any ideas? Thanks for the help.
 

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Does it have a lot of miles on it?

Check PCV first as Catskinner mentioned.

If PCV is good, it could be worn rings. To check that you'll need to do a compression test and white down the readings. Pressure readings doesn't really matter just as long as they are within 10% of each other. Then add a few squirts of oil in each cylinder (one at a time) and test again. If the readings improve significantly then you your rings are worn.
 

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Does it have a lot of miles on it?

Check PCV first as Catskinner mentioned.

If PCV is good, it could be worn rings. To check that you'll need to do a compression test and white down the readings. Pressure readings doesn't really matter just as long as they are within 10% of each other. Then add a few squirts of oil in each cylinder (one at a time) and test again. If the readings improve significantly then you your rings are worn.
I will probably just replace the PCV valve just to rule it out and for peace of mind. They're only a few dollars. I can definitely do a compression test. To answer your question, the motor was rebuilt about 50,000 miles ago.

Question.... if the rings are worn then there's oil bypassing the rings from the oil pan?? and being forced up past an open valve and into the upper intake and then through the throttle body? This confuses me because the flow of the fuel and air is flowing down into the heads & cylinder, not in a backwards direction up out of the head and back into the intake against the air/fuel flow. At least that's what my logic tells me. I'm not wrapping my head around this scenario. Can someone clarify this? How does worn rings force oil up through the heads and into the upper intake and through the throttle body? Maybe I'm just having a brain fart, but this isn't making logical sense to me.
 

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In the case of worn rings, fuel, air and moisture will go past the pistons into the crankcase and will cause dilution and contamination of the oil. This leakage past the rings is called blow by. Blow by is controlled by the PCV system and is re burned by sucking it back into the fuel system via the intake.

Here's a trick you can do. When you replace the PCV valve, make sure the engine is at normal operation temperature, and with the engine running pull out the PCV valve. If you see a decent amount of smoke puffing out the hole, you have blow by.

Here's a really good article on Blow By. Keep in mind there talking about older cars/engines (kotex (breather element), oil in air cleaner ect) but its the same principal.

Well, here's the story. The crankcase, that which contains the crankshaft and connecting rods, is the bottom side of the engine - you can see the bottom of the pistons from under there. Compressed fuel and air mixture burns in the cylinder on the top of the pistons. When the rings become tired and worn they allow some of this compressed and burning mixture to leak past and escape into the crankcase. That is called "blow by". This is as easy to fix as maintaining a small web site or using the best small business web hosting.

In old engines that blowby simply vented into the atmosphere via a tube called a crankcase vent tube. The EPA found bad stuff in that blowby gas and mandated that the engines must suck up that stuff and burn it to render it harmful in some other way. In came the PCV which stands for Positive Crankcase Ventilation, named after the then head of the EPA Pierre Positive.

This system makes the engine suck the junk out of the crankcase via the PCV Valve into the intake manifold and back thorough the system. Welll, if that system is sucking the junk out, there must be a source of air to go into the crankcase else you would just implode the engine and the oil pan would collapse. Soooo, they ran a tube from the top of the valve covers to a source of clean air so that dirt would not get sucked into the crankcase. (note: the valve cover covers the valve train but that is also part of the crankcase - air and blow-by move readily between those zones in the engine.) The source of clean air which was chosen is the air cleaner - makes sense, except for the fact that the air doesn't go thorough the air cleaner filter, so they put a little kotex-like pad in there to clean the bugs and stones out of the air.

Remember now, the air is supposed to flow from the air cleaner's Kotex pad thorough that hose and into the valve cover, circulate around the crankcase and get sucked out via the PCV Valve. When the blow-by becomes so excessive that the PCV Valve system can't remove it, it has to go somewhere! Else the crankcase pressure would become excessive and the engine would explode. The place that it goes is back thorough the hose to the air cleaner - THE WRONG WAY!!! Of course it carries any oil in the valve cover back with it and that's what you mop up two or three times a month or week if it's really bad. Bottom line?? It's time for a new box of kotex or an engine overhaul, whichever is cheaper. (there is one other solution - see below)

If you do find oil in your air cleaner it may well be that your PCV valve is stuck closed and is therefore not sucking the blow-by out of the crankcase but rather, it is blowing back into the air cleaner. Make sure to check the PCV Valve before overhauling your engine!!
 

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Discussion Starter #6
Thank you for that excellent information. Now its a little more clear on how the circulation of the crank case air flows.

So from what I'm gathering (correct me if I'm wrong) the problem is one of two things: bad pcv valve or worn rings. This motor only has about 50,000 miles on it so it's hard for me to believe the problem is worn rings. However, anything is possible and knowing my luck its probably worn rings.

So the first thing I will inspect and probably replace is the pcv valve and then go from there. But I will definitely warm up the engine and pull the pcv and see if there's any crank case vapors coming out of the valve cover.

Again, thanks for the help. At least I now know where to look for the problem.
 

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One more thing to check. You have a screw on oil cap, a PCV valve and you should also have a vent/tube in one or the other valve cover. Make sure that is not plugged off and is able to breathe. I've seen people plug these off especially when using chrome valve covers. The vent compensates for the suction of the PCV and without it, it will pull a vacuum in the crankcase resulting in the PCV valve sucking oil.
 

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One more thing to check. You have a screw on oil cap, a PCV valve and you should also have a vent/tube in one or the other valve cover. Make sure that is not plugged off and is able to breathe. I've seen people plug these off especially when using chrome valve covers. The vent compensates for the suction of the PCV and without it, it will pull a vacuum in the crankcase resulting in the PCV valve sucking oil.
I do have a vent tube on the neck of the oil filler tube and there is a hose connected to it. I forgot to check it to night to see if it was plugged or not until I logged onto this post again. I'll check it tomorrow. I've been doing a bunch of repair work the last few days and I'm almost done.

So I replaced the pcv valve tonight with a new one. The valve on the bottom side is kept shut by a spring. The pcv valve I removed seem to have a stiffer spring pressure (more resistance) than the new one I put on there. It wasn't stuck closed, but it has a little more resistance in the spring than the new one does. Not sure if this makes any difference at all, but just thought I'd mention it just in case it makes some sort of difference with the oil I'm finding in the upper intake & throttle body.

Had a question about O2 sensors. I replaced both my O2 sensors tonight and I noticed that the sensors I removed from the manifolds are a 4-wire sensor and the vehicle only calls for a 3-wire sensor & the plug only has 3 wires. The new O2 sensors I have are NTK 3-wire sensors. So would the 4 wire sensors function any different than the 3-wire sensors that I just installed? Would they cause any issues? Obviously one of the wires from the 4-wire sensor isn't being used because the plug only has 3 wires, but I'm not sure if that 4th wire is needed to make the sensor function properly?

I just replaced both upper and lower control arms with new ball joints and new strut rod bushings. Need to go get an alignment now. Will be replacing the distributor tomorrow because I used the old distributor (financial reasons) when I rebuilt the motor. And every now and then the motor will suddenly hiccup or cut out so I figured I'd replace the distributor since it has 194,000+ miles on it. Hoping that's the cause of the hiccup/cutting out and resolves the problem.
 
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