I just went through this! My 235 ran hotter when worked and cooled very very slowly if at all when idled. I had installed a new recored radiator, all new hoses and tstat and a new water pump. Previous owner let it sit with water in it! Although you have the opposite happening, I would recommend one thing to verify things!
First of all, do not trust a gauge! Try using a quality laser temp gun. You will be able to look at temps from front to rear of the head and out to the thermostat and radiator and also the return to the engine. This will give you an exact picture of just where the issue is.
My issue was plugged coolant ports at the head gasket and more rust build up in the head. As others have recommended, a good flush may do the trick too. There is a industrial coolant system flush called Thoro Flush by Irontite. It's a powder and can only be run in the engine for no longer then 12 minutes according to their directions. It's not cheap either, $15-$18. I tried it first and although it helped slightly I still ended up pulling the head and having the machine shop hot tank it and go through it. Just my two cents worth, some of these guys on here have incredible knowledge, don't be afraid to use it, good luck and let us know how it goes!
Troy
Last edited by Wrencher88; 05/11/2017 4:52 AM.
