Re: re 85 hp overheating
If you verified water is getting to the head and out the snout, then it is definitely the LU. Make sure you are installing the impeller properly and using the correct one too. You can double check all the water passages in the lower unit after you removed the impeller housing and make sure there are no blockage. Re-assembly is critical so make sure the impeller housing is properly aligned with the water tube in the mid-leg.
Conduct test using muffs instead of barrel or lake just make sure you regulate the faucet pressure just enough. For now remove the t-stat and replace cover. Run motor and you should see cooling water exiting the exhaust snout, if not check the muffs make sure they are centered to the water inlet of the LU or better yet hold them in place for a few seconds and you should see water exiting the snout, if not shut down motor. There is serious blockage or the impeller is not correctly installed, incorrect type or the water tube is not aligned with the impeller housing outlet.
However, if water is exiting in the exhaust snout continue running in fast idle to see if motor overheats, 2-3 mins should be OK. If not, shut it down and re-install t-stat (on some models this can be installed backwards while on others it cannot for it will only fit one way, but if installed backwards motor will surely overheat because the sensing side of the t-stat is facing away from the cooling water). Test again, while making sure cooling water exits the snout as soon as the engine starts. If motor overheats, check the t-stat installation is correct.
