Uh…Houston? We’ve got a problem…

Okay, so I’ve reported previously that I’d seen oil dripping from the engine from both the front and rear of the oil pan.  Today, I stopped by the auto-parts store and got 3 bottles of gunk and 3 spray cans of brake cleaner (the non-chlorinated stuff).  I spent the morning spraying, scrubbing, rinsing, and repeating until it was as clean as I could get it without pulling the whole thing out.  As you can see from the pix below, its pretty decent.

Once I got it clean it was time to hunt for the leak.  I put the whole car on stands to keep it level, and started the engine.  I put the hood down, and let the engine run until the radiator fan had cycled on and off several times.  I put the hood down to help build some heat and boil away any standing water.  Once I got the engine hot, and the water all evaporated, I began the hunt.  I found what looked like streaks under the front main seal, and on the bottom of the bell housing.  Since there had been so much water, I couldn’t be sure these streaks weren’t just from oily water vibrating and dribbling down.  So, I wiped these streaks away.

Next I held the engine at 4,000 rpm for 15 minutes.  This seemed to be the maximum oil pressure point.  I didn’t see the needle move any as I rev’d above 4k.  I figured 15 minutes would be a good amount of time for any oil to begin to find its way out any leakage spots….either leaks due to crankcase pressure or oil pressure.  I found a few leaks:

  • Front main seal & joint to RTV gasket
  • Cylinder head gasket, passenger side, rear engine.
  • Spark-plug well cylinder #4.

Here are the pictures of each area.

First the front main seal.  You can see a small dark line directly in the center of the front main seal lip.  I had wiped this area clean before running the engine.  I took pictures from all different angles.  I couldn’t see any oil coming down from the crank, or any area around the timing belt cover/water pump/etc.

front-seal (2)front-seal (3)front-seal (4)front-seal (5)

front-seal (9)front-seal (10)front-seal-1

The only other oily area near the front main seal was on both sides of it, in the joint where it transitions to RTV.  You could see wetness on the top and bottom.

front-seal (1)[4]front-seal (7)front-seal (8)front-seal (6)[4]

Next is the passenger side rear, cylinder head/engine block mating surfaces.  This is in the area just below the CAS.  It looks like there is a little seepage coming from between the head and block.  It was hard to tell if it was getting bigger. I guess I will watch it over the next few days.  Obvously I have pix of a starting point for comparison.

passenger-side-head-to-block-rear-corner (1)passenger-side-head-to-block-rear-corner (2)passenger-side-head-to-block-rear-corner (3)

Finally, the plugs.  I’d actually “thought” I was done hunting for the oil leaks.  I bought a new set of NGK’s when I got the degreaser, and just figured I’d install the plugs before calling it a day.  <Sigh>…

Here are the plugs in order:

Cylinder #1:

Not great, the plug is kinda dirty, and the electrode is pretty white.


Cylinder #2:

Similar electrode color, but there are more carbon deposits on this one.


Cylinder #3:

Pretty similar to #1, really.


Cylinder #4:

Oh dear!  The plug was completely dripping in oil.  By the time I took the picture some of the oil had dripped off.


Finally all plugs together, side by side.


This is the exhaust side of the head-gasket.  I can’t see anything leaking.

drivers-front-head-to-block (1)drivers-front-head-to-block (2)[4]

So, I’m not really sure what all this means, to be honest.  I looked down the plug well and the tops of all the pistons were caked in a rough, bumpy coating of carbon.  I do not see ANY white smoke coming out of the tail pipe either under acceleration or deceleration.  Given the oil seepage at the back corner of the head/block interface…perhaps its just a poorly installed head gasket, or warped head/block.  Certainly the head needs to come off for inspection, at least.

I looked very carefully at the CAS.  I couldn’t see any oil coming from around its interface to the head.  I’ll watch it over the next few days…and if I take the head off, I’ll certainly replace the o-ring…for good measure.

Maybe I should get another head?  Maybe I should do a leak-down test to see where the leak is….that’s probably a good idea, before I get too much more involved.  Hmmm….need a testing, I guess.

6 comments to Uh…Houston? We’ve got a problem…

  • Going by the look of the plug and the fact that it has oil on the thread and the hex back towards the porcelain, I would tend to think that the oil is not originating from the cylinder.

    I am not familiar with the Miata engine so I am not sure of the location of the plug in the head in relation to the valve cover, intake/exhaust manifolds etc. rather possible from the valve cover area and happens to be pooling in the spark plug recess/cavity.

    • Yeah..that’s what one of the guys on specmiata.com thinks, too…Valve cover gasket. It’s certainly easier than a head! I’ll order one along with a CAS o-ring, timing belt, and main seals. Might as well have the bits for whenever the time comes.

  • AMG

    I’m going through similar troubleshooting with my low mileage donor. I have the same front oil seal leak. Seems like my cam seals are leaking as well. Time for a timing belt and water pump replacement while I replace all of those seals…

    • Yeah..I can’t tell exactly where the rear leak is coming from. It looks like a head gasket, but I guess it could be cas and I just can’t see the oil draining down. Similarly with the front…it could be coming from under the timing cover. Dunno. It is very slow. I still don’t have a whole drop in the bottom of the engine.

  • AMG

    I just replaced the timing belt, tensioners and all seals at the front of the motor. No more leaks. 🙂

  • Good to know. That is already on my list of repairs, too.

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