Too scared to do the thermostat upgrade??? Poll...

[hanleyclifford]

I like the Indigo FWC thermostat I recently installed, which mounts separately from the engine. It diverts the flow back to the pump until the coolant temperature reaches 180*, then it diverts it into the HX. There is no restriction in the flow, and flow is not diverted from going into the block. I do not have a bypass from the side plate. The thermostat housing on the front of the head has been empty since the last engine rebuild in the late 90's. For years I used the Honeywell mixing valve that Indigo used to sell, but when it melted internally during an overheating episode caused by FW pump water seal failure (which never happened with the old grease-cup style water pump), I decided to get a thermostat that wouldn't melt. Usually these t-stats are mounted at the exit of the manifold, but I have mounted the Indigo unit directly on the HX upper end, and it keeps the operating temperature just under 180*, if I can believe my gauge.
My only problem is that when I shut down the engine when it is near 180* and turn it back on before it cools down, the temperature alarm, whose sensor is on a tee fitting at the exit of the manifold, sounds when the gauge temperature is 180*. The alarm is supposed to go off at 200*. The gauge sensor is on the front of the head. Apparently hot coolant left stationary in the hot engine builds up enough heat to trigger the alarm sensor, but not enough to make the temperature gauge read too hot. I also had this problem when both sensors shared a tee fitting on the front of the block.
I'm glad I haven't had to worry about removing thermostat housing studs from the head. After I removed the ruined mixing valve, and before I installed this new thermostat, I had a manual valve and bypass that diverted coolant away from the upper end of the HX, into a tee at the lower end, and back to the pump, partially bypassing the HX. With this I was able to reach a temperature of 130 to 150*, but thought this was not hot enough. Now I don't have to mess with a bypass valve, which seems to me to restrict flow as much as a thermostat.

Thanks for that Cap'n. When penning my remark about thermostats I had the thought in the back of my head that someone was going to bring up the Indigo option - and sure enough...I do like the system you have described and can readily understand why you are happy with it. I should have added that the thermostat issue is of greatest importance in the case of RWC where flow restrictions lead to trouble quickly. FWC is much more forgiving in this respect and in fact the late head thermostat arrangement with FWC can be very satisfactory, but unless it has been upgraded with the Moyer Marine bronze replacement housing I wouldn't trust it for a New York minute.