The guage pegs to the H after running for about ten minutes or so. I have run with and without a t-stat. System has been burped of air also. I am beginning to wonder if it might be the temp sender? It is an aftermarket sender and I have heard that they can be inconsistent with the guage. I am using the original guage on the dash. Regular V-belt pulleys and water pump is fairly new. Water is circulating.