How to keep your V6 oil cap from leaking

[GTRS Fiero]

Interesting.  Doing the same google search, cold contracts the hole, opposite the freon theory.  I do seem to recall in grade school about the thing with the hole apparently being full of the same material.  Sounds familiar,

[MikeMac]

We used to heat the hole and freeze the bolt. Or whatever we were trying to fit. I've seen machine shops install bearing races that way on big diesel stuff. Think locomotives and big power generators.

[TopNotch]

I must say, my simple fix for the leaking oil cap has elicited quite a discussion of holes. Try this experiment. Insert the oil cap into the valve cover hole, but do not turn it tight. Try wiggling it back and forth. You'll see that the hole is quite roomy. It's not the size of the hole that affects leaking, but the seal on the cap outside the hole. After inserting the O-ring, you'll find the cap harder to close, because of the additional seal.

[MikeMac]

I must say, my simple fix for the leaking oil cap has elicited quite a discussion of holes. Try this experiment. Insert the oil cap into the valve cover hole, but do not turn it tight. Try wiggling it back and forth. You'll see that the hole is quite roomy. It's not the size of the hole that affects leaking, but the seal on the cap outside the hole. After inserting the O-ring, you'll find the cap harder to close, because of the additional seal.

Pat, I think we are all getting stir crazy. But we will all be experts on expansion and contraction of metals!

[Fierofool]

GTRS---The freon theory was used on a stud or bolt to shrink the bolt or stud.  It didn't affect the hole if you take the nozzle from the freon source and cap it over the bolt or stud.  I had suggested that to a few on PFF to extract broken manifold studs and they were successful in extracting them.  We did that on so many broken bolts on golf course apparatus that had been submerged in lakes for years. 

Give this some thought.  If you heat a sheet of metal with a hole in it and the sheet expands but the hole gets smaller, wouldn't it cause the hole to break out of the sheet of metal making a progressively larger hole as each hole shrunk away from the plate? 

[GTRS Fiero]

Give this some thought.  If you heat a sheet of metal with a hole in it and the sheet expands but the hole gets smaller, wouldn't it cause the hole to break out of the sheet of metal making a progressively larger hole as each hole shrunk away from the plate?

In my mind, no, but it does sound familiar from grade school.  I thought I dropped this.

If I heat a metal ruler, it expands in all directions: height, width, and length.  If i hold it in the middle, when heated, the ruler will expand away from the center.  If two rulers are placed near each other, and both rulers are heated equally, they will expand toward each other.  If the ends of 4 rulers are arranged such that their ends touch in a square, then heated equally, the ends will expand toward each other.  So far, so good?  Now, connect the corners of those 4 rulers, making a square hole.  Now heat the 4 rulers.  What happens?  According to google, the hole will now grow in size.  One of the problems with thermal expansion is that the objects tend to heat unequally, resulting in warping.  In my mind, when the metal expands, it should expand anywhere it can.  If you think on it, having a hole is easier than not.  To illustrate my point, have people line up, shoulder to shoulder.  Then, have them move to an arm's length from each other.  The further from the center they are, the further they will have to move.  Now, suppose that the original line of people had a gap.  Obviously, the expanded line wouldn't have to expand as much in this area.  Now, try this in 2D.  A grid of people.  For your point, the metal would warp slightly around holes when heated.

[TopNotch]

If i hold it in the middle, when heated

Yikes! I hope you're wearing an "Ove glove".

[GTRS Fiero]

If you have a stock V6 Fiero (or one with stock valve covers), you probably know about the leaking oil cap. Here is a way to stop it leaking for good.
In this picture notice that there is a gap between the outer seal on the oil cap and the center.

For this fix, you need an O-ring the same size, or slightly smaller than, that gap, as shown above.

Place the O-ring over the gap as shown in this picture.


Press the O-ring into the gap.

Now replace the oil cap. That's all there is to it. You may have to hold the O-ring in place when you replace the cap, but after it's been exposed to engine heat, it will stay put.
I did mine before last year's Run For The Hills, and it hasn't leaked a drop since.

I've been looking at my oil cap.  I wonder if there are different designs.  The gap betwen the outer rubber piece and the inner plastic piece seems to be narrower, on my cap.

[GTRS Fiero]

Go to Amazon and search for O-ring kit. Anyone who works on cars should have one. I even fixed a friend's medical oxygen concentrator with one of my O-rings.

Ordered.

It (they) arrived today.  I ordered one in SAE and one in metric.  Neither one has a size that fits, but there does not seem to be a groove there.