Mechanical temp gauge problem

[ragtag]

So I did something I have never done before. I bought a set of cheap mechanical gauges for my 327. The temperature gauge works just fine when cruising around town but when I hit the highway the gauge jumps to 225 and then down to 210 (when the thermostat opens) even though the engine is actually about 185 when checked with a heat gun. I don't think their is any fix short of replacing it with quality gauge but I wonder if anyone else has experienced this?

[wayne petty]

is there any thermostat bypass hose or circuit other than the 5/16 hole in the mounting leg of the water pump???


normally .. there is a bypass circuit..  that allows the coolant from the behind the thermostat to be circulated back into the water pump.  then into the block.. up thru the back of the heads.. forward thru the heads and into the intake crossover where its blocked by the closed thermostat..  the pressure of the water pump pushing forces it thru the bypass or heater core circuit again..


because the bypass or heater core circuit is smaller than what the water pump can flow..  there is mechanical pressure built up inside the block and heads that does not show up at the radiator cap...

this in block/head pressure increase raises the boiling point of the coolant.. so it does not boil at the hot spots around the exhaust valve seats, exhaust guides.. combustion chambers and exhaust ports..

this is an important feature that is lost on some classes of racing that use restrictors instead of thermostats..  they went to 30 pound radiator caps.. that had in previous radiator designs.. expanded the oval tubes at high pressures and flows until the tubes had removed any air space between them. this causes the radiator to be worthless after one race..

so .. coolant is going round and round pump block heads bypass pump block heads bypass... until it picks up enough heat to open the thermostat..

at that point.. some cooler coolant is introduced  and the thermostat closes.

this allows the coolant to circulate and pick up heat.. while the coolant in the radiator is stopped so the fan can take the heat out of it..

during cruise.. the thermostat opens just slightly.. because of the heat you are building up.

so... do you have a bypass hose between the coolant behind the thermostat and the return fitting in the water pump.. or to the radiator lower tank.. so the bypass flow goes in there .. and drops straight down to the lower hose and is pulled up by the water pump...


there are threaded blocks available that fit under the thermostat housing.. so you can run bypass hoses..