How to keep your V6 oil cap from leaking

[TopNotch]

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.

[GTRS Fiero]

Great write-up!  Only 1 thing missing: the size or part number for the o-ring.   

[MikeMac]

Great writezup.  Only 1 thing missing: the size or part number for the o-ring.

I guess you could take the cap off the car and let it cool some before taking it into NAPA or another parts store and look through the o-ring assortment. Remember the let it cool some part!

[GTRS Fiero]

I guess you could take the cap off the car and let it cool some before taking it into NAPA or another parts store and look through the o-ring assortment. Remember the let it cool some part!

Sure, assuming they have the correct size.  Of course, I could also re-invent the wheel.  There are plenty of suitable boards at the store. 

I am curious about the cooling part.  The cap only leaks when it's hot, not while the engine is off.  Whatever temperature changes the cap undergoes, the seal will also have to undergo.  Why let the cap cool off?  If I can take it off with my bare hand, how hot can it be?

[TopNotch]

I have an O-ring kit I bought years ago with sizes ranging from tiny to about 2 inches. I just picked one out that fit.

[GTRS Fiero]

I currently have Rodney's cap saver, which works, but could be better.

I guess the dial calipers will have to do.  Still, good idea.

[TopNotch]

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.

[scottb]

The oil cap leaks while the car is running due to the pressure being built up and the thermal expansion of aluminum; i.e. the hole in the valve cover gets bigger. You want the cap cold so that it is at its smallest dimension so the oring fits tighter.

[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.

[GTRS Fiero]

The oil cap leaks while the car is running due to the pressure being built up and the thermal expansion of aluminum; i.e. the hole in the valve cover gets bigger. You want the cap cold so that it is at its smallest dimension so the oring fits tighter.

Good explanation, thanks.  I'm going to test with a spare cap and valve cover.

[scottb]

How are you going to simulate the pressure thst builds up under the valve cover?

[GTRS Fiero]

How much pressure do I need to simulate?  I can seal the valve cover to a piece of steel, then add pressure through the other hole.  It isn't a lot of pressure, or there wouldn't be a breather tube to release crankcase pressure.

[TopNotch]

If your positive crankcase ventilation (PCV) system is working, there won't be much pressure at all. The leaking from the oil cap probably isn't from pressure, but from splashing. When the engine is running at high RPM, there's oil splashing all over the place under the valve cover.
(And I wonder why people have to make some things so complicated?)

[GTRS Fiero]

(And I wonder why people have to make some things so complicated?)

I guess that would be me.  My intent was understanding for both myself and future readers.

And I'm not the only one.  When I say things in technical terms for my area of expertise, people often ask for clarity.  This is not my area of expertise.

For example, stating that the local and remote network IDs must differ for successful communication over a VPN.  That is generally a true statement, although there are ways around it.

I did not know about the O-ring kit.  Additionally, if the hole gets bigger, it would have seemed that I would want the cap to be tight when the hole was at its largest.  Usually metals expand when heated, which should make the hole smaller, in my mind.  But not my area of expertise.  Either way, the seal would be small, because it was cool.  Usually, plastic would deform to the aluminum hole when heated, making the plastic cap smaller.  I would think that, if this makes a big difference, the cap should be frozen, and a slightly smaller (heated) seal used.  I suspect that the seal just needs to be the same temp as the cap.

[scottb]

(And I wonder why people have to make some things so complicated?)

Usually metals expand when heated, which should make the hole smaller, in my mind. 

Curious as to why you think the hole would get smaller as the metal expands?