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Do you know the good oil?

I have been going through between one to two litres of Mobil 10-40 per month on my NA8 with 160k up on the odometer. Before I started using Mobil 1 0-40 I was going through around 1 litre of Mobil 1 5-50-oil a month.

The recommended oil is 10-30 but I figure that using the best quality should give the best results. When I last took the valve cover off everything was bright and shiny. I have spoken with mechanics who rightly believe that a heavier oil will not burn off as quick but the engine runs much harder with the synthetic 0-40 oil than ever before. If you believed the claims of the manufacturers you would be tempered to give up drinking alcohol substituting your favourite drink for a chance to reap the cross benefits of their good oils and live happily ever after without a squeak, stiff joint or care in the world.

The NA has a full MX5 Mania cold air intake, the head have been done and the CPU on the car has been overridden by an Adaptronic ECU. The engine is tuned to run on the rich side pulling 103 kw on the MX5 Dyno. When cold starting you can smell fuel and a light plume of smoke or unburned fuel billows out the exhaust. If parked in the open for any length of time on super hot days the idle goes to pieces and the car often stalls. A black/dark grey film is removed from around the inside of the exhaust pipe when the car is washed each week. Accelerating from scratch in the evening shows up light smoke or more likely excess petrol vapour in the lights of following cars on take off but none otherwise from what I can observe driving through the day. .

I accept that a modified car after 160k will burn more oil than a 60k or 6k car. Is one to two litres a month normal for a 150k+ MX5. What is considered normal oil consumption for aging MX5 engines. What has been your experience with oils for a NA8 or even a NB which are have similar characteristics.

The best practical advice comes from people who know and drive MX5s, so if anyone has the answers or suggestions as to what brand or grade is the good oil then let me know?

No, that's not normal. I've got an NA6 with an NA8 engine; modified intake, exhaust and ecu. I go though well <1L in 5000kms.

you provide a lot of detail which might not be relavant but I believe you should be checking the condition of the engine starting with a compression test with someone trained to interpret. If the engine is starting to show its age then the root cause is not the oil but the condition. Ultimately burning a bit of oil is cheaper than a rebuild but that might not be a criteria. A surprisingly good indication is getting a mate to drive behind you over say an hour with twists and turns and acceleration and decelleration- engines that are not good start to show it.

Mileage is also only a pointer- how it has been dríven eg on the extreme- thrashed takes it toll.

Let us know how you get on

That amount of oil loss is more than considerable.
Going by your descriptives of smokey plumes, I would hazard an educated guess that at least one cylinder's, perhaps more, piston rings have deteriorated somewhat.
At 160,000km, a well-maintained engine should have no oil-burning issues.

Perhaps the headwork you got done has something to do with it?

Mine is creeping close to 150,000km and I check my level a few times a month, I only travel around 2,000-3,000km every 6 months and then change the oil, I don't notice any loss.

When you check the oil on your dipstick, does it appear less viscous that usual? ie. fuel has gotten into the oil and thinned it?

The viscosity of the oil you have been using is fine, and the shorter the change intervals the less important the brand/quality of oil, but Mobil is fine either way so you are not going wrong there.

Any signs of oil in your radiator fluid?