Will a 998 thermostat work on a 907ie?

Thanks in advance

If you could get it to fit yes, but the orientation of the 90º outlet is wrong and won't line up with the 907 pipe. A thermostat from an 851 will fit - if you can find one.
It may be worth exploring thermostats from the Aprilia range. Many of these use similar thermostats, one of which might have the same configuration.

If you would try to install the 998 thermostat the side exit would show forward instead of towards the rear of the bike.

What`s the diameter of the hose connections of the original thermostat and what`s the opening temperature (which is stamped on the housing)?

You can put car thermostats in ketchup for 15min after scraping the hard stuff off. Descaler or molasses might work as well. The question is how long it will continue to work.

I found an 851 thermostat and it's working fine. Thanks a million