Since your engine has been recently rebuilt we will assume that this is likely not a source for the oil. Of course, a third potential leak path is past the piston oil control rings. There are many different styles of these separators and they most often include a removable liquid reservoir and often either a built-in separator or a stainless steel mesh that helps pull liquid oil from the vapor. Most of this information came from our friends at M/E Wagner who make a billet adjustable PCV valve.Īnother solution to minimize the oil entering the intake through the PCV is to introduce a vapor separator in between the intake manifold and the PCV valve. This increases velocity through the baffle and caries oil with the air. Another possibility is that the baffle is incorrectly positioned and is too close to the bottom of the PCV valve. If the PCV valve is located in the valve cover but is not protected by a baffle, this can pull quite a bit of oil into the intake manifold. The reader didn’t mention this, but we’ll assume because this is a street engine, that it is equipped with a PCV valve. With oil on nearly all the spark plugs threads, the intake could still be the problem or there is another possible source. This will also point you toward the solution. If oil is present on only one side (like the driver side for example) then this indicates you have a leaking intake gasket on that side of the engine. It’s not unusual for this intake gasket leak problem to only occur on one side of the intake manifold. ![]() You didn’t mention this, but look to see if the oil on the spark plugs occurs only on one side of the engine. Over time, pressure will push this oil up into the threads where it will remain as a liquid because it’s not exposed to combustion. Not all of this oil will burn and, over time, a small amount can be pushed up into the threads of the spark plug because the threads are not sealed on the chamber side. We’ve covered how to test for this in a previous tech column, so we won’t detail that here, but this could be one source of the oil entering into the combustion chamber. Despite the serious oil burning problem, it did not show up as a blue haze in the exhaust since the oil was vaporized along with the incoming air and fuel. We had a small block that burned a significant amount of oil and we eventually traced it to this poor seal at the bottom of the intake port where manifold vacuum was able to pull the oil past the intake gasket and into the port. We’ve seen this happen many times on lots of different engines. One possibility is that there is a mismatch between the top and bottom of the intake ports between the heads and the intake. We will also assume, since your engine is relatively new, that the Edelbrock cylinder heads are equipped with good Viton rubber valve guide seals so we can eliminate those seals as a source of the oil. There are several potential sources for this oil. ![]() As you mentioned, we will assume that there are no external leaks, which leaves the source of this oil as originating inside the engine. We’ve seen this spark plug thread situation many times on small and big block Chevys and also wondered about the origin of this oil. It’s no surprise to our friends that most of our experience is with Chevrolet and GM engines. Can you tell me where that oil is coming from? T.H. I might add a half-quart in between oil changes, but the engine does not smoke-so it can’t be burning oil. The engine does use a little bit of oil but I consider that to be normal. I asked around and a couple of people mentioned leaking valve covers but my engines are always really clean so that’s not it. Most, but not all of the plugs had threads coated with oil. However, I noticed wet engine oil on the threads of the spark plug. The last time I pulled the spark plugs, the porcelain area looked pretty good, with a light tan color like it should be so the air-fuel ratio is probably pretty close. I have a 355ci small block Chevy that was rebuilt about a year ago and we included a set of Edelbrock aluminum heads, a Comp flat tappet cam, and an Edelbrock dual plane intake with a 750 cfm Holley carburetor.
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