My oil pan.

[I<3flippyheadlights]

I was under the car and looking at the oil pan in detail and noticed some small cracks. Well, maybe they aren't cracks. I don't really know. I can feel them as if they are bumps. No oil is seeping out of them (as far as I know) and I just want to know whats going on. So on a scale of 1 to 10 and 10 being skittles, what position am I in?


WP_000563 by I&lt;3flippyheadlights, on Flickr

WP_000565 by I&lt;3flippyheadlights, on Flickr

Thanks everyone

[riefdaddy]

If it ain't broke, don't fix it. They might be cracks, but apparently they don't leak, so I'd say a 2.5 on your scale. If you do anything, use a grease pencil to mark the end points of the cracks and monitor for growth. Do not use a graphite pencil (#2 lead as an example) as this will promote galvanic corrosion. I doubt you will see growth as the oil pan is not a stress panel. Do you usually have the undercarriage cover on? If not, it might have been road debris flying up and striking the pan.

[I<3flippyheadlights]

The plastic under tray doesn't cover the oil pan. Maybe I should invest in something.

[— kung fu jesus —]

Lack of road rash makes me think someone used the oil pan as a jacking point.

[riefdaddy]

That could be true. I'd guess that maybe someone tried to use the subframe and started jacking only to notice they were too far back before they caused too much damage. I've seen a few jacking incidents on aluminum pans and everyone of them ended up punching a nice hole in the pan.

Once I posted I remembered that the pan is behind the tray and hidden by the subframe.

[I<3flippyheadlights]

You would be correct in that assumption. When I replaced my motor mounts I had to jack up the engine. I put wood on the jack to distribute the weight and was careful. Was I not careful enough? Please share your wisdom KFJ, its always helpful.

[— kung fu jesus —]

I'm not a metallurgist, or engineer, I'm an industrial designer, but I've been around manufacturing long enough to be dangerous with my art-meets-science background. My reasoning is this; aluminum is a porous metal, the pans are die-cast, so looking where the cracks are near the corners and fillets it looks like deflection stress. You get that when you put localized stress on cast aluminum on a relatively flat surface. Those fins aren't structural, they are heat sinks.

I don't know if it was caused by you using the jack on it. The wood makes me think no, but I don't know the size of the block you used. The idea of the wood is to act as a bushing and as a method to distribute the weight.

I suspect more that a previous owner(?) or shop may have used it as a jacking point.

It's fine, because it isn't weeping, but if it goes, you will have to pull the engine most likely to replace it. I am wondering if it might be worth it to use some JB weld or epoxy as a sort of 'spackling' to fill the crack and bond the separation.

The idea mentioned above to use a grease marker or sharpie to track the cracks is really smart, too.

[— Agent☣Orange —]

It's fine, because it isn't weeping, but if it goes, you will have to pull the engine most likely to replace it. I am wondering if it might be worth it to use some JB weld or epoxy as a sort of 'spackling' to fill the crack and bond the separation.

The idea mentioned above to use a grease marker or sharpie to track the cracks is really smart, too.

Agree on the jacking damage idea. I'm always leery of jacking a Miata up at the oil pan but as long something like a piece of wood is used to distribute the weight, it should be okay. My jack has a wide, 6" plate to begin with and I but most common small jacks use a 2"-3" plate and that's concentrating too much force in one tiny area.

Replacing the oil pan is a hellish job so I'd avoid any more jacking on this one or else replacement will be inevitable. I like your idea of JB Weld as a sturdy Band Aid in the meantime.

[—RuckkehrMiata—]

Oil pan is a neutral-pressure zone isn't it? I have a hole in the side of mine from the previous owners brilliant (failed) oil return tap. It weeps, but I lose more oil to my aging seals than I do the hole.

[— Agent☣Orange —]

It's not high pressure but remember the crankcase does build up pressure as the pistons move and that is normally vented through the PCV valve.

[RoadsterTech]

I agree with jacking damage...
The problem with stress fractures or deflection fractures is that they can grow...
I agree with the grease pencil or acid free marker.

JB weld would stop some weeping but would not stop the growth if it occurs. You need to stop the growth line with a small drill hole and weld.
Not a good idea on a working Miata oil pan.

Flippy its sad that you didn't see this before the clutch job. For about the same amount of time you could have pulled your Engine swapped Oil pans and done the clutch out of the car on a table, then drop the Engine back in...

Monitor closely if it grows, or starts to leak, get a replacement oil pan and call for another tech session.

[RoadsterTech]

It's not high pressure but remember the crankcase does build up pressure as the pistons move and that is normally vented through the PCV valve.

Don't forget vibration as well

[—RuckkehrMiata—]

It's not high pressure but remember the crankcase does build up pressure as the pistons move and that is normally vented through the PCV valve.

Yeah I learned my PCV valve stopped working one day when my oil cap dented my hood on the way to work.
oops.

[I<3flippyheadlights]

Well I did some research on this. Seems that people who are suffering from a weeping oil pan dremal the crack and fill it with JB. Since mine isn't leaking, I'm gonna just watch it. i also read a thread on M.net that it is a normal thing with aluminum oil pans. Its just stress and no big deal. (that is my right brain interpretation of the situation)

I also have this around my oil drain plug. Strange, I know. I felt the cracks and they feel like bumps. Also very strange.

I'm just gonna keep driving this engine into the ground. Sucks that I have done all the maintaine but it still has a good amount of life in it; I can feel it. I'll just keep my eyes open for an engine if the problem gets worse.

[RoadsterTech]

fwiw my 300K mile engine did not have oil pan cracks not so sure its a common AL thing.
But if it doesn't leak don't worry about it, just monitor it every oil change.

RE new engine ... You know you want to go 1.8 anyway...