Help with source of oil leak

Hi All,

A few weeks ago I got the MX-5 out of the garage after its winter hibernation and checked it over before submitting it for an MOT and oil/filter change. I noticed there was some old oil around the bottom of the clutch housing, but nothing dripping so cleaned it all up and didn’t think too much of it. It passed the MOT without any issues.

I got my MX-5 out of the garage today and noticed some oil on the floor. Initially I assumed the garage had been a bit messy doing the oil change when removing the old filter. I put the car up on ramps and found where the oil was dripping from. Click the images below to enlarge them.

I cleaned up the oil, and then ran the engine for 20 minutes, when I came back I noticed there was more oil there already:

Again I cleaned it up, dried it off and ran the engine. However this time the oil hasn’t returned:

I wondered if the oil circled below could be the source. It’s not something I’ve ever noticed before, but should this hole not be covered?

Has anyone got any idea where this oil is coming from? I can’t see anything coming from the engine. In the past when the CAS gasket failed oil ended up near here, but all that area is bone dry this time. Confused on this one…



I believe that is the bell housing drain hole, which would suggest to me that your rear crank seal is leaking, or the joint around the sump if you have hit the sump on a speed hump it can do this.

could be the cas

oil from there runs down the back of the egine and ends uo in that area

I initially thought it was this too. The CAS seal started leaking not long after I brought the car, and the oil ended up about where it’s leaking now, along with making a mess of the heater hose. So it was the first thing I checked this time, and it all seems completely dry around there after extensive looking and feeling around the back of the engine.

So, regrettably I think Nick might be right. Is it a big job to change the rear crank seal?

I’d suspect the sump gasket over the rear main oil seal. There is a rubber seal that dries out that runs under the rear main oil seal housing, this is usually where the oil leaks from. You have to lift the engine slightly to give enough clearance between it and the front subframe to remove the sump, not a nice job TBH.

Took the car out today for a good run. When it came out of the garage no oil on the floor, and I couldn’t see any oil gathering on the bottom of the car. After a decent 100+ mile run today the oil is back.


Is sorting this a job best to left someone who’s familiar with the MX-5 handle?