Hello Friends, sorry for the bad English.
I know this is the subject of several posts, but I couldn't find an answer for my problem. Since last December I'm the proud owner of a Punto Cabrio 1.2 16v 86 hp. Very fun to drive, here in my country, where is warm most of the year. I'm not a mechanic, but I can do simple tasks. Actually, I was hopping to improve my mechanical skills by working on this car.
So here is the thing: since i bought the car, it is loosing coolant at a rate of almost 1 litre each two days. The problem is that the motor runs smoothly, no vapour coming out of exhaust pipe, the fluid on the expansion tank is clear, and the oil in the motor too. Also there's no coolant plash underneath the car. So where is the coolant going? The only thing I noticed is a smell of rust coming from the heater matrix. Is it possible to loose one litre of coolant each two days trough the matrix without leaving any traces? Today I went for the first MOT test since I owned the car and it failed. The report states CO to high and lambda to high to (1,041). The technician mentioned some blue smoke and told me that probably the motor is burning oil. Is this related to my original problem?
Thanks.

The technician mentioned some blue smoke

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It does sounds as though you may have an engine problem.

If the heater matrix was leaking you probably would smell it - and possibly find some damp on the carpet.

However, that smell may actually be coming from the engine. Coolant can leak to atmosphere from the head gasket. It well may be this is the case and the reason you're not seeing coolant anywhere is because it has evaporated because of engine heat.

A high CO level and blue smoke points towards something amiss in the engine., either in the cylinder head/valves - or with the pistons/rings. A compression test will tell you for sure.

I would suspect that your coolant loss is either due to it leaking to atmosphere via the head gasket and then evaporating due to engine heat - or it is being thrown out of the exhaust because of a failing/burnt head gasket.

You can buy 'cylinder head sealant' which you add to the radiator - the radiator, not the coolant bottle:
https://www.ebay.co.uk/sch/i.html?_odkw=polytunnel+cover&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR1.TRC0.A0.H0.Xcylinder+head+repair.TRS0&_nkw=cylinder+head+repair&_sacat=0

You can also buy 'engine restore' which is added to the oil:
https://www.ebay.co.uk/sch/i.html?_odkw=engine+reconditioner&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR4.TRC2.A0.H0.Xengine+restore.TRS0&_nkw=engine+restore&_sacat=0

I think if I was in your situation I would first get a compression test done.
https://www.ebay.co.uk/sch/i.html?_odkw=engine+restore&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR12.TRC2.A0.H0.Xcompression+tester.TRS0&_nkw=compression+tester&_sacat=0

A litre every two days is a lot of coolant to be loosing tbf - usually if its going into the cylinders due to head gasket you get white smoke (water vapour) out the pipe even when the cars warmed up - at this kinda rate of loss I'd expect that'd be noticeable. I doubt the loss of water would adversely affect the emissions. Its possible a pipe union or around the waterpump or somewhere is leaking but only when under pressure i.e. when cars hot and as it cools its stops leaking but when it is leaking its hot enough for it to evaporate off. That would leave some residue so go round the car and search for and weird looking residue where pipes join etc. You can get caps that go on the expansion tank that allow you to add pressure to the system without running the engine then you can go round searching for the leak while there is pressure but everything is not hot, makes it much easier

Your tester is correct that blue smoke means oil is being burnt but it would be good to know under what circumstances.
Does it puff some blue smoke on startup and then clear?
Does it only make blue smoke under load?
Does it only smoke blue smoke on over run (when coasting, like down a long hill with no accelerator)?
Does it smoke a bit all the time?
All these tend to point to different problems so if we know when and how much it smokes we may be able to give you a better guess as to what the problem is.
I would say here that burning oil doesn't result in high CO levels, it results in high HC (hydrocarbons) but completely unburnt fuel also results in high HC.

For both the water and blue smoke issue a dry and wet compression test is a good thing to do. This being that you do a normal compression test and record all the figures and then do it again but drop a teaspoon of engine oil down the spark plug hole into each cylinder just before doing the test. It should come up with the same result (tiny bit higher usually) but you are wanting it to not make a significant difference - the oil on the wet test will help seal piston rings and valve seals if they are failing and you get higher compression. And all cylinders should be about the same compression - if one or more are lower than the others that points towards either head gasket failure or posting rings or valve seals - if the wet test comes out the same as dry but with a low cylinder or two it usually means head gasket failure.

Coming back to the emissions, if it had high CO and nothing else that points to the car running rich - to much CO is when you get incomplete combustion. This can be cause by quite a lot of things but a few things to try would be:
1. make sure the car is fully at operating temp when the test is done
2. check the spark plugs and ht leads, a problem here can cause a weak spark resulting in incomplete combustion
3. very dirty air filter - these engines do not have a MAF (mass airflow sensor), the engine uses the MAP (manifold absolute pressure) and engine speed to calculate how much air is there and therefore how much fuel it needs to inject - thus is the air filter is really dirty it may not let enough air past to achieve full combustion. It would have to be very very dirty for this but they are cheap so if it doesn't look new then just change it anyway.
4. O2 sensor defective, reading lean all the time. Bear in mind here the Lambda value on the emission test is an actually reading of the gases and not what the lambda sensor is telling the ecu.
5. MAP sensor vacuum hose being clogged or broken (reading a heavy load all the time).
6. Coolant temperature sensor having high resistance or open circuit (reading "cold engine" all the time).
7. Throttle position sensor stuck or open ground, (reading wide open throttle).
8. Leaking or bad injectors.
9. Ruptured fuel regulator (fuel leaking directly into intake)
10. Contaminated, restricted or bad catalytic converter.


Think I'd start with a compression test and go from there. If that looks ok then I'd give it a light service, oil, filters, plugs and leads, then give it a good 'italian tune-up' on the way to the test. Ask the tester to hold the revs really high for a minute before the yest as well to make sure the CAT is properly hot as they need to be to work properly - this is why most modern cars have the CAT as part of the exhaust manifold, they get hot really quickly there but on these older puntos its a fair way down the pipe from the engine so just sitting idling for a long time tends to not result in very high CAT temperatures.

Thats all i can think of right now. Let us know how you get on

Thank you very much for such a complete explanation. This is like lesson in auto mechanics! It's going to take me some time to process all the information, but the suggestion of doing the compression test looks interesting. I'll try to do that in the next couple of days and post the results. And I will also try to document in which circumstances the blue smoke appears.
Regarding the coolant loss, yesterday I look under the car (there is another problem, this time with the starter !) and there are some residues of the green fluorescent coolant that I recently start to use. Now I'm convinced that there is a leak. I'll try to find a pressure cap to test the cooling circuit under pressure.
Thanks

Whereabouts is the residue you found?