Runnin Hot.

[charlie_the_tuna]

wait a minute, you mean the impeller in the lower unit, right?
where are these check balls?

[THEFERMANATOR]

Yep, the impeller is in the outdrive. The check balls are in the T-stat housing.

Does your housing look like this one? This is the common ALPHA style housing.

[spareparts]

when you check/replace the impeller, take a good hard look at the housing, look for any deformaties or scarring, also look at the lower part of the impeller housing(under the ss plate), make sure its not warped. If you have any doubt, replace the whole water pump assembly, its not that hard to do, just make sure you match up the right orings and gaskets if you get a new kit, they generally come with enough extra(wrong) parts to really confuse you. Also wrap a bit of electrical tape around the oring grove on the drive shaft when installing the lower water pump housing to prevent damage to the seals, remove the tape before putting the lower unit back together.