I noticed a little oil on the garage floor the other day, where the diff sits over. I had a look and there is oil present on the diff. I cleaned it up, checked a couple of days later, and I’m 90% sure that it is coming from the diff cover gasket. Certainly not from driveshaft oil seals. Is the diff cover gasket just regular builders silicone? Or is there anything better I could use, please?
I’ve already got crush washers for the filler plugs. Thanks for any advice.
I’m not familiar with MX5 diffs but most diffs have a breather on top of the casing that can get blocked and leak.
They just need unscrewing and washing/blowing out.
Just a thought before you start stripping things down.
Maybe someone knows if they have.
Cheers mate, sounds like good advice. I’ll have to have a good look, just a pig to get at.
i would strongly recommend checking the breather also, mine was difficult to blow air through, spring loaded valve inside so ordered a new one from Mazda dealer which doesn’t have the valve and easier for it to breath.
On mine the crush washer on the filler was leaking after the service where the diff-oil had been changed. Took it back to the dealer and they re-filled it and put new crush washers on both drain and filler, under service warranty. No leaks now.
I noticed the leak because like you I saw the odd drip on the floor, but I also could smell it on the exhaust after a run!
Did unblocking the breather stop the leak? Or did you have to replace the gasket / crush washers, due to the blocked breather forcing the oil out?
I bought my car from a Mazda dealer and it has warranty remaining. I’m not sure if this would be covered, as I expect warranties not to be worth the paper they are written on.
On mine there was no wetness near the breather (right at the top of the rear cover on the diff), but loads from the filler plug and below it., even after I washed it with brake cleaner it returned in just a couple of hundred miles. All three shaft seals were also clean and dry. It was a lot quieter too after the refill, so I assume a lot of the oil had escaped in just the three thousand miles.
It is definitely well worth a claim on the dealer, the oil is expected to last in there for several years with no leaks, so if it is leaking that is because something has been done incorrectly. My dealer didn’t argue at all.
Cheers Richard. The car is booked in for Tuesday next week, no point me lying about on the drive if the car has a warranty
I took the car to my local Mazda dealer. I should of really read the warranty small print, as I find most warranties a waste of time on the whole. The Mazda warranty does not cover any oil leaks, unless they require the engine or gearbox removed. They are awaiting a reply from Mazda UK. I’ve resigned myself to doing this myself, as I have never had any interest in the prices that main dealers command. I’ve only ever had one oil leak in nearly 30 years of driving, so I find Mazda’s exclusion pretty mean, but I’m not particularly surprised.
The technician stated that it was leaking from the diff cover, just as I thought. I asked if the breather was ok, and he didn’t seem to know what I was talking about (another reason why I dislike main dealers, you expect the best for the prices they command, but in my experience it is anything but…). He also stated that they would have to order some special sealant to do the job. Obviously it’s highly unlikely they are going to be touching the car, barring a miracle. So I just wondered does anybody know what the sealant is? Or is it just regular builders silicone?
I’ll also take a look at the breather, as they obviously didn’t.
Hmm, I took mine back to the place that had done the work. That is the key point.
If you bought the car from a dealer it should be fit for purpose, and an oil leak is not fit.
However with a not-new car, in most cases your claim is against the specific dealer that sold it to you (since that is the most recent car inspection), or if reasonably later (several months, lots of miles) against whoever did work for you on the diff (if there was someone), otherwise it is down to you and how much you want to pay…
It might not actually be a problem. The first thing to do before any more speculation is to check the oil level.
If it is OK it might simply have been overfilled (forward tilted car), and is merely adjusting itself via the breather.
If it is not OK then the leak source needs to be pin pointed. On mine it looked like the seal between rear cover and diff was leaking, but after I washed the whole diff clean that joint never got wet again, it was just the excessive dribble from the filler down the middle of the cover which was then fixed with a new washer.
I guess the sealant is the usual RTV silicone (oil-resistant) that gives you about ten minutes to clamp the pieces together. The pdf drawings on the Mellens site indicate that the cover does not seem to be a stressed member, but it does need sealant on the mating surfaces during re-assembly.
Don’t use bath sealer or builders silicone, there are so many variations in quality and setting times that some are not even good enough for sealing baths, let alone solvent laden hot car bits.
The main problem with removing the cover would appear to be trying to get access to the bolts at the top of the diff cover, first to undo them and then to torque them up correctly, and I’ve not found a figure for that torque. The next prolbem is to keep it all spotless and not let anything drop in from the underneath of the car, a steam clean might be a good idea.
Good luck
Cheers Richard, very informative, excellent post.
Where I bought the car from is 90 miles away, on crap roads, so I’m not going to bother with that. I agree I do need to check the oil asap. Had word back today that the warranty claim was declined, as expected. Information seems really thin on the ground about the breather location. I’ve looked on google images, on other MX5’s it appears to be more or less directly above the fill plug. I need to get under mine again. I have a feeling that I’m going to take the car to a good independent garage that I know. I have some decent jack"able" ramps that get the car up very high, but I guess these are not that good for the car being level, as some oil will be left with the car inclined forward. I have a couple of syringes though with extension tubes, then again the diff looks pretty small so not really sure if there is much room for that. This is if I remove the cover that is.
Thanks again
Just a bit of an update with this, just in case anybody else has the same issue. I decided to check the oil level in the diff, so removed the fill plug, filled it up. It hadn’t lost that much oil. I fitted a new crush washer. I also removed the breather from the diff, I had to cut a 14mm combination spanner in length to get access to this. A 14mm stubby ratchet spanner would be ideal. The breather wasn’t blocked as I could blow through it, using a bit of pressure. I cleaned it, and blew compressed air through it.
I’ve used the car for quite a bit now and the leak has gone. So I reckon it was leaking from the fill plug, a new crush washer sorted this. Really disappointing service from the Mazda dealer, obviously they’d of fixed it, as they would of had to drain and re-fill the diff to replace the diff seal. This would’ve cost me a fortune as the access is poor. Really disappointed with the service, why I avoid main dealers if I can, in my experience they don’t seem to really investigate the fault, and are too eager to do extra unnecessary work, at inflated prices.
I’m happy though, cost me 50p. Really deceiving diff leaks, an old mechanic I know, always told me to try the easy cheap fixes first. So true.
Glad you got it sorted cheaply and easily