Fluctuating Oil Level

[Zebedee]

This is an odd one.

Went for a blast yesterday and after about 40 miles the oil level light came on. Odd as I'd checked it before I set off and it was at the max dot. Pulled over and checked the oil level and sure enough it was only just above the bottom dot, but was above it, just, so I carefully rode home stopping every 5 - 10 miles to check the level again. Each time I checked it was at the same level, just above the bottom dot but didn't seem to be getting any worse. Each time I set off again (yes, checked after waiting a few minutes with engine off) the light would come on after less than half mile. But then weirdly, after about 25 miles it just went out and didn't come on again. When I got home I checked the level and it was back to the max dot line.

TL;DR
Is there any way that something could stop all the oil from getting back into the sump and / or explain why the level would show as being so low, randomly?

Thanks guys.

[willandrip]

That level sensor is known for your symptoms.
It is fitted to numerous models and is often quoted as doing what you state.

Often a replacement of the sensor only cures it for a short period.
An oil change helps prevention.

The oil bubbles/froths and prevents the sensor operating as designed.
I think in your case, the oil amount was exactly the same prior,during and after the ride out.
It just had not settled in the sight glass.

Most run the oil higher by a fraction than the upper sightglass mark.
As long as the level can be seen in the glass and not totally above it they operate fine.

[Zebedee]

An oil change helps prevention.

The oil bubbles/froths and prevents the sensor operating as designed.
I think in your case, the oil amount was exactly the same prior,during and after the ride out.
It just had not settled in the sight glass.

Most run the oil higher by a fraction than the upper sightglass mark.
As long as the level can be seen in the glass and not totally above it they operate fine.

I think you're right. I'm used to the sensor's ways and the oil burning habits of these bikes (nice to know it exists right through the EXUP years 89 - 95...) but this was a new one on me. As you say, I think it is related to oil type, the previous owner was using some off brand (to me) fully synthetic oil that I suspect was the wrong grade too. I'll be changing it for Castrol Semi Synthetic asap (it's stupidly difficult to find big brand (global) semi-synthetic motorbike oil around here (the US) so have had to order it from eBay) along with a new OEM oil filter.
Hopefully that will stop this odd behaviour. It's never fun when you're giving it rice and mid-corner that bright red light comes on.

[TomcatMJ]

I had this behaviour with my 3BF (the US-FZR 400) after remounting the lower Fairingparts. Accidentaly i didn't realize that during the remounting the Oillevelsensors Connector was pulled off and so some Minutes after start the Oil-Lamp flushed on, too, but the Oillevel was proper and the Oil i had in the Motor was 20W40 Mineraloil as recommended by the Servicemanual (like for every FZR). Reconnecting solved the Problem definitely but it took some time and researches to find the spot
If you now want to change the synthetic oil to semi-synthetic oder mineral Oil keep in Mind that it might be a good Idea to bath the clutch's frictionplates around 24 hours in the Oil you want to use so that it will replace the already soaked synthetic one in the plates,because otherwise it might happen that the clutch gets slippery due to the already soaked Oil in combination with the new one.

cya,
Tom

Edit: Don't forget your bike has an Oilpump and so its adviced to check the Oillevel when its warm but already standing for around 5 minutes so that the Oil had a chance to get back in the Oilpan (and also the Showglas Level would then be showing correct / real Level of Oil, not immideately after running the Motor)