First - Hallo to everyone. We are delighted to have joined the MX5 owners club and look forward to meeting up in the New Year. Before we can do that, a problem needs to be sorted so I seek your help and advice.
We have a very early 1.6 (import) automatic which has been in the family for about 10 years and has been solely ours since 1st May 2008. Very low mileage (or kilometreage?) - just over107000kms. and until a few months ago, not a single problem. Suddenly, HUGE clouds of white smoke from the exhaust. This really is not just ‘a bit more smoke than usual’ . Someone from the met. office would be forgiven if they interpreted it as a serious weather condition.
The local Mazda dealers did a lot of tests - for which they did not charge me - and finally concluded that it was the valve stem oil seals. To cut a long story short - the rather expensive answer was - - they weren’t the problem. A good friend of mine who is an excellent engineer and a vintage car owner and former racer (and also the only person to doubt that it could be the valve seals) ran a number of tests. The most worrying thing he discovered is that after running the engine through all the gears the oil level in the gearbox went from 4cms above full to well below the minimum level. Rod’s E.W. Manual doesn’t say much about automatic gearboxes. Have I blown a seal between the engine and gearbox? The fact that the smoke is very white but not acrid suggests a link. Any suggestions good people?
Hi. I don’t know what your problem will turn out to be, but I think there’s no way any fluid could get from the gearbox into the exhaust (the smoke is definitely coming out of the exhaust pipe, right?. White smoke generally implies water getting into the cylinders, rather than oil. Is the coolant level in your expansion tank OK?
Hello Geoff. Thank you for your reply. We thought the problem might be water but the compression is good although there does seem to be an unusual amount of condensation/water spitting from the rear exhaust during the first five minutes or so. Alan
As has been said above white smoke is water . If you have no water losses from the coolant system then I woudn’t worry as this means it is just condensation burning of as the exhaust heats up . Since the very cold weather has come mine does this too, but as usual I expect it to go when the car warms up, and in the new year when the weather warms up it will stop completely.
Hello Richardn Thank you for your reply. The odd thing about this is that it started in July when I was using the car everyday. It started quite suddenly in that there was no earlier stage with a small amount of smoke - it went from everything (seemingly) being fine to simply vast amounts of smoke. Alan
Just thinking about the auto box - I’m not at all familiar with them, but I recall there’s a capped-off vacuum hose barb on the back of number 4 runner of my car’s inlet manifold, which I read was only used on automatics. However that hooks up to the auto box I don’t know, but I wonder if it’s possible for a fault to allow oil to get drawn through there… That would certainly make for a smoky exhaust.
Ok, digging into the personal archives [I can find nothing in the servicing manuals or on miata.net] 1970 Lotus Elan+2, the brake servo started to leak and I ended up with brake fluid in the body of the servo, this got sucked into the inlet manifold and I’m sure it produced white smoke…???-----
Found this in the Automatics section of Miata net (lots more autos over there): http://forum.miata.net/vb/showthread.php?t=213272 “Thick grey exhaust smoke”
“Another item you might check is presence of automatic transmission fluid in the vacuum line going to the back of your intake manifold. You
can’t really see it but if you reach back you will find a hose
connected to a spigot at the rear end of the intake manifold. You can
just pull it off and bend it up so you can see it. Then take a q-tip
swab and insert it in the hose. If it comes out with any pink stains
you’ve got a leaking
modulator valve. It’s an inexpensive piece available at any NAPA store
but you have to crawl under the car and unscrew the old one. I did mine
not too long ago but my symptoms were a little different. If I idled a
long time at a stoplight it blew a lot of transmission smoke for a short time”
That sounds like it might be exactly what you’ve got too.
Hello again Thank you very much for all the info. I have a feeling that you are getting near the mark. My friend Peter (the engineer I mentioned in my original note) pointed out that modern automatic gearboxes are electronic but the one on my -almost- twenty year old MX5 will work off engine pressure therefore there must be a physical link. One of the tests we did was to introduce a small amount of automatic gearbox oil into the air intake after the engine had been running for about 20 minutes and the smoke had cleared. It produced exactly the same type of white smoke. The trick is finding the link and to this end Peter has booked my car into a garage he uses, on Monday and apparently we are all going to get into the pit and see if we can spot pipes that we didn’t expect to see or going in an unexpected direction. After all the helpful comments I’ve been getting from people I’m beginning to feel very confident that I’ll back on the road very soon. I will let you know what happens Thanks again Alan
Hello again Geoff. An MX5 enthusiast and a guitar enthusiast!! I used to have a Senator and one of my brothers still has an original Club 40. Back to white smoke - we checked the brake vacuum servo pipe but there was no trace of oil. Martin Young a club member has come up with something and my engineer friend Peter ( I mentioned in my original note) has got the same suggestion from an automatic gearbox specialist. Apparently there is a fine pipe behind a diagphram within the gearbox. If that is compromised in some way it will cause the problem that I have got.We are going to check it out on Monday and I’ll let you know.Thanks again for all the information Alan
Yeah, it sounds like this is your problem, right enough. Did you see this thread too: http://forum.miata.net/vb/showthread.php?t=229074
There’s info there on Mazda part numbers for the replacement part:
"Okay so for anyone who wants to know I found the part numbers. BU55-19-823, Vacuum Diaphragm ( Vacuum Modulator valve )
BU55-19-825, Rod Diaphragm
0338-19-822, ‘o’ ring seal
I am not sure if you need the rod diaphragm but it seems that they belong together in the engine parts list.
"
And also some fitting instructions:
" Pull off the vacuum hose first. There’s an o-ring that seals between the modulator
and the transmission case, so it should only be hand tight. You may
need a pair of pliers, small strap wrench, or whatever to get the old
one loose.
The level of fluid should be above the opening, so be prepared for some
spillage, or drop the pan first. The diaphragm pushes against a small
rod which should stay in the transmission when you remove the modulator, but it does come out easily. Make sure you don’t drop it and that it’s in place before you screw the new one in.
"
Hello Martin Thanks to all your efforts we decided not to bother going to the garage and spend time poking about in the inspection pit - we now know what we are looking for and that link to the Miata web site was just perfect. I think I owe you a bottle of something not just a drink!! Have a great Christmas and I look forward to meeting with you at some Club event next year Thanks again Alan
I haven’t got it fixed yet but I’m confident that we are getting there. My engineer friend Peter has run several tests including checking the vacuum line that goes to the back of the intake manifold as suggested by Martin Young. Apparently any pink stains - presumably from the automatic gearbox oil, in the vacuum line means a leaking modulator valve. But… nothing! However, after a conversation with an automatic gearbox specialist over near Tonbrige, we found out that you don’t always get these useful tell-tale signs and the modulator valve definitely sounds like the problem. He sounds like a very knowledgable and consequently busy man and the best I could do was to get ‘pencilled in’ for next Thursday. I’m very optimistic that that will be it. I will let you know as soon as I know.
