Exhaust smoke

[Forgiven]

I have a 1990 NA. Since the last service it blues smoke on startup - quite a bit - and then continues to blow when accelerating, my wife following today said, for 10 of so kms. (Left the car for an hour or so, couldn't check on the way home.) It has a rebuild engine by an MX5 specialist only a few thousand old. I run 98 petrol (on the advice of the engine builder). Something to do with (I hope) running 98? Or the fact that it's only on the third tank since I've had it, and I let the tank get into the last 1/8th? The oil he used? Performance doesn't seem to be affected. And simple diagnostics for a simply minded non-mechanic?

[93_Clubman]

What colour smoke - NA6 tends to run a bit rich in part of the range.

[hks_kansei]

Ordinarily i'd say the piston rings are stuffed and the new oil was a little bit thinner and is able to get past them more easily now.

BUT, if you've had an engine rebuild, rings should have been replaced.


with regard to the colour of the smoke, a rough guide is:

Blueish = oil burning
Black/brown = excess fuel
White/grey = coolant/water burning



While MX5's run a bit rich, they by no means run rich enough to blow smoke other than the odd puff.

first step, check the oil, make sure it A, has enough, and B it looks normal (look for spots of water, or even worse a coffee like foam)
Also give the oil a sniff, it should smell oily, or at least a little like onions. If it smells of petrol, that's a possible sign of worn rings.
Also remove the oil cap with the engine idling, if there's a lot of air pressure pumping out of the cap hole, it's a possible sign of blowby (which is usually worn piston rings)

Otherwise, just take it back to the place that serviced it, or to the engine builder, and show them the issue.

[bruce]

Could it be overfilled with oil?

[Forgiven]

Thanks all. Will follow the suggestions and hopefully report not expensive news.

[Eunos_Frogster]

Was the head reconditioned too? My valve stem seals leaked pretty much straight after they were replaced and puffs smoke on startup


Sent from my iPhone using Tapatalk

[apsilon]

Could it be overfilled with oil?

That was my first thought given freshly rebuilt engine and problem appeared just after service.

[Forgiven]

I finally got to check the car. Because two people had, separately, suggested an overfilling of oil, that's the first thing I checked. Sure enough, it's way over the 'F'. So putting that with the colour of the smoke, blue rather than black or white, and the fact that it only started after the last service, I reckon that's the cause. I'll see what the mechanic says.

[Forgiven]

I have contacted the mechanic, and am waiting a reply. I guess it's best not to drive the car in the meantime? The oil is well over the 'F', nearly up to the top of the flat part of the gauge. (I read a furious debate about the risk from overfilling, and came away without a clear answer.)

[hks_kansei]

Overfillimg a little isn't too bad.

Overfilling a lot can cause the crank to aerate the oil, meaning it doesn't lubricate as well.

It's a an easy fix though, get a clean tray, put under the car.

Remove sump plug, collect oil into pan.

Put sump plug back.

Pour the caught oil into the engine via the filler cap (but obviously don't put it all back, just put back enough to be at the full Mark. 3.5litres off the top of my head, but check the user manual first)

And yeah, always add less than the manual says, and slowly top up as needed.

[Forgiven]

After laboriously sucking a litte oil out - a few splashes in the bottom of a baking dish - the mechanic had a look and said 'Not overfilled'. A slight strangeness, though, was that he too, got a reading of up to 'F' on one side of the stick, well above the 'F' on the other. His remedy: a bloody good run. Started it this morning. Blue smoke. Drove it, and my wife said it was stilling blowing blue/grey smoke on acceleration. Nothing to do but live with it I guess, and hope that it is a passing thing. (On the assumption that it is not big dollars, a fire extinguisher will be installed and a helmet bought for my first khanacross in a couple of weeks.)

[93_Clubman]

got a reading of up to 'F' on one side of the stick, well above the 'F' on the other.

^That's not uncommon.

It has a rebuild engine by an MX5 specialist only a few thousand old.

Started it this morning. Blue smoke. Drove it, and my wife said it was stilling blowing blue/grey smoke on acceleration. Nothing to do but live with it I guess, and hope that it is a passing thing.

Hope is not a strategy - as already mentioned by Eunos_Frogster above probably valve stems seals, but take it back to, or contact, the MX5 specialist engine builder to get their expert opinion, otherwise it could go from something you can live with, or a relatively cheap fix, to a more expensive fix.

[Forgiven]

Engine rebuilder = 'mechanic' = person who sold me the car. He say nothing wrong. Hence hope.

[StanTheMan]

Engine rebuilder = 'mechanic' = person who sold me the car. He say nothing wrong. Hence hope.

Huh....let me get this right.
Tbere is smoke everywhere? And the engine buildsr tells you therecis nothing wrong?


Sent from my SM-G935F using Tapatalk

[Forgiven]

It's only everywhere in the garage when I start up and rev the engine a bit while stationary. Then when going along, my wife's says visible, but not major, blue/black when I accelerate. I have explained this to the three-way man, and he says it probably just needs a good run. I guess I could go to somebody else and have an assessment.