I think it's a ten place grid penalty.
Question is: how many times? Let's say a driver has used 8 engines with 5 races to go. His ninth engine will be used for the 5th and 4th to last races. Will he get another grid penalty when he uses a tenth engine and an eleventh (likely, right)? Or will he even get penalized every time he uses an extra engine beyond the 8th, i.e., in the above example would he get a grid demotion in the 4th to last race as well?
if they use their 9th engine for the 5 remaining races, then they will only get a 10 place drop the first time they use that new engine...
if that 9th engine can last until the end of the season, then its fine..they wont get penalty again..
but if the 9th engine dies and a new 10th engine will be required for the last 3 races, then a 10 place drop will be in place due to the 10th engine.
so 10 place drop for every engine after 9th engine... (teams best hope their 9th engine can last the final 5 GPs in your example)