Too much oil?

[MissMc]

Hi, think I've made a boob. My oil warning light came on so got out my trusty Berlingo booklet and found the max oil for my 1.9 diesel is 4.5 litres. So put 3 litres in even though the dipstick didn't show it as being low :justno: - however I put this down to the engine being warm and as I was in the middle of a journey decided to top up thinking this was the problem and didn't want to wait till I had got home and let the engine cool down.:brickwall:

The car then started blowing thick smoke whenever I accelerated and the warning light came on whenever I slowed right down. This has been going on for a week - we drove 600 miles with this problem and it is slowly, after 1 week, getting back to normal - no blowing smoke after the first day and the light only comes on occasionally (always when the car is warmed up though - short journeys don't affect it).

Stupidly didn't think it might be just a sensor problem and really should have believed my dipstick.

The question is, if the dipstick in future does show it is getting low how much oil should be put in? ie what is the low and high range in a 1.9 diesel engine? I'm thinking that if it is showing towards the low end there still might be 3 litres in it and you perhaps only need a litre top up?

[Gadgetman]

A good assumption for all cars is that the max and min marks are never more than .5L apart.
In other word, you completely flooded the poor thing...

It's also a good rule never to add more than .5L at a time.
If you need to fill more, allow some time to let the oil settle between fills.

And oil should be measured before starting, or a few minutes after stopping.

[MissMc]

Thanks Gadgetman - I had a feeling I had put too much in! Never thought the range would be as low as 0.5lt. A lesson learned

[Gadgetman]

It's because the engine is built to operate with a set amount of oil in the pan.
(You want there to be enough to keep the oil pickup submerged when the engine is running, but not so much that it slows down the crank which is situated above the sump)

Ideally, an engine doesn't 'use' oil, just circulates it, so loss should be almost non-existent. That way, a margin of .5L should be enough to cover normal losses between services.
More oil would require a lot more heat to warm up to running temperature and optimum lubrication state, so having more oil circulating would actually cause more wear.
A larger sump to hold more oil requires more space, too, and today's engine compartments tend to not have all that extra space.
There's the issue of weight, too. not only does it hurt fuel economy slightly, but in some countries, import taxes is based on the 'fully tanked up' weight of the vehicle.

I'd get hold of a pump with a thin hose and nozzle that can fit down the tube for the dip-stick and pump some of it out if you haven't already done something.