I thought on NCs you had to slightly over fill them. The dealer always overfilled mine when serviced, it didn’t use any between services anyway.
Hi,
I sure that Martin does not mean the oil pressure warning light, but the oil level light. I too drive a diesel car and have the same problem, black oil and a black dip stick. When the oil level warning light comes on there is still plenty of oil in the engine and the level on the duo stick is not below the lower marker.
1 Like
Thanks for the PM, but we have put that one to bed now. 
yeah, you don’t get an oil pressure light in many regular cars do you. So its not just me then, good, and as you say experience tells you that even when the light comes on, the dip stick, if you can mange to read it, will still tell you its got sufficient oil. Its clearly a phenomenon well know to those of us who drive dirty old diesels, (or not so old) and the one after the one I never dipped, as Nick noted, didn’t have a dip stick at all.
So I was all up for saying my “oil marys”, but not sure I will now… 
Allegedly, a good few had their dipsticks moved onto the driver’s seat. 
6 Likes
I find it interesting to read how your dealer overfilled your NC, which I would have thought went against what was recommended?
I have spent years on the racing scene, listening to and taking advice from engineers far more qualified than I was. And all the one’s I spoke to were adamant that overfilling an engine was likely to lead to damage to the crankshaft.
I remember on one occasion some years back accidentally overfilling an engine, which resulted in me removing the drain plug, to release some of the new oil back to a more ‘acceptable’ level.
Right or wrong, for me it was better to be safe than sorry.
1 Like
Good Post.
As I said previously “Over Filling” can also damage your engine.
A little amount should not cause problems.
How much you over fill will be engine dependant.
The sump is designed to hold an additional amount to safe guard problems.
As stated, the oil will expand to some degree, that is why you will find the dip stick is easier to remove when hot (expansion).
Dry Sump systems are another matter, (Chieftain and Challenger tanks have them for very good reasons!).
To “briefly” explain why.
If you over fill, the crankshaft when spinning fast will make contact with the oil, froth it up and “STARVE” the pick up point to the oil pump.
Instead of getting the pure liquid form you are getting the froth like on the head of a beer.
Now we all like to drink the beer and not the froth! 
Therefore, the lubrication will not operate correctly and can cause damage. (As the previous post for race cars).
The frothing will cause less positive lubrication, therefore more friction, then more heat and damage the shell bearings (another story).
Some of you will say is the crankshaft that close to the sump oil level? Again, engine dependant.
But the manufacturer will not design it too high as that will be detrimental to the height profile of the engine.
Also, it can over pressure the sump area causing oil to be burnt and also damage oil seals and therefore leaks.
Is it likely to happen to your car? Best advice do not over fill.
2 Likes
It would be interesting to know how many nc engines died from surplus oil as opposed to oil starvation. This engine was probably not intentionally designed by Mazda to prematurely fail but they may not have adequately assessed the combination of low oil level, engine oil use and cornering effects on what is a fairly highly stressed unit. This along with the engine chosen being more rarely used in it’s longtitudinal orientation. Added to the “mickey mouse” oil pressure gauge it’s a source of worry for most informed nc owners. I am a member of the 4mm high club.
1 Like
A very good question indeed, to which I think would be near on impossible to answer, (in the main).
The thing is, Mazda never built the car to race.
That is just how things have developed.
The engines if looked after are quite bullet proof really on the whole.
TBH I am sure that 99% of users will have no problems.
I remember in my Teaching/Instructing days when students would ask questions of the “What ifs”.
Some found out the expensive hard way mind!
Sometimes there is just no easy or definitive answer.
Enjoy your day. 
2 Likes
They didn’t overfill it to the point of oil bubbling out of the oil filler! Just to the point of slightly over the top mark on the dip-stick. They also, at the time of pick-up, told me it was best to not let the level too far below full. It’s 8 years old now, only done 38k has never needed me to top it up and the oil pressure is still as good as the day I bought it.
Am I not right in saying that the “oil pressure gauge” doesn’t actually measure true oil pressure, but is a computed value, based on certain engine parameters including rpm?
Oil pressure is measured from the pump out put (pipe) which is designed by the engine manufacturer.
Likewise, it will be higher when the engine is cold due to the oil being cold, (slightly thicker).
The higher the RPM the higher the oil pressure needed to protect the shell bearings and other components.Basically the shell bearings actually float on the crankshaft and are protected/cooled by the oil.
Yes it will be “electronically” measured is a simple answer.
Yes, apart from early NAs that is the case. The NC is even more guilty of that than earlier cars.
I think you will also find FoMoCo in a great number of places on the engine.
Both daughters had to know what the dipstick is for their UK driving test. However their instructress told them to ask Dad to show how to use the one on his car as the Bini doesn’t have such a thing! Hopefully the examiner either wouldn’t ask to be shown on a test in a not-really-a-mini-at-all, or would be pleased the student knew there wasn’t one fitted?