Running with no thermostat is a very bad idea. It holds the coolant in the engine until it has reached proper temperature of 190 to 200 degrees. First of all, pistons are "cam ground", meaning they are slightly oval-shaped and they do not fit well. They expand unevenly when hot, and that is when they become perfectly round. That is when they fit the best making them stop slapping, and quieter. Ninety nine percent of engine wear takes place in the first few minutes of driving when it is still cold. That is why the engines in vehicles driven mainly on the highway last so long. I had 420,000 miles on my 1988 Grand Caravan before it rusted apart, but the engine was still running fine and never needed any repairs. You are driving your car with the engine constantly cold, so that excessive wear it taking place all the time.
The next issue has to do with the engine oil. One of the many additives in oil is the "dispersants". That is what makes the oil pick up and hold carbon, blow-by gases, and debris so it can be carried to the filter. Cold oil remains thicker, then that gunk settles to the bottom of the pan or it clings to moving parts and cylinder walls. Hot oil flows easier so it is faster at keeping lifters pumped up, and it does a good job of spraying from the ports in the connecting rods, onto the cylinder walls. Cold oil will just dribble out of those ports. That lack of oil on the cylinder walls leads to piston scuffing.
The lobes on the camshaft are lubricated, in part, by a mist of vaporized oil. Cold oil does not vaporize.
The biggest problem do-it-yourselfers run into is not knowing the cooling system has to be burped to get the air out when the coolant was low or the system was empty. The 2.2 and 2.5L engines have multiple ways of doing that. The first is to look for a threaded hex plug on the top of the cylinder head, right behind the thermostat. Remove that plug while filling the system, and replace it when the coolant reaches that level and starts to run out. If that plug is tight or the hex is rounded out, there will be a temperature-controlled vacuum switch and/or a coolant temperature sensor there that can be removed. If the two-wire coolant temperature sensor has to be unplugged to be removed, do that when the ignition switch is off to avoid setting a diagnostic fault code that could confuse someone in the near future. At worst, if the sensor is unplugged with the ignition switch on, the check engine light will turn off the next time the engine is started after the sensor was reconnected. The fault code will self-erase after fifty engine starts.
There should also be a single-wire coolant temperature sensor, with, as I recall, a purple wire. That one is for the dash gauge and it's okay to unplug that with the ignition switch on.
The blow-by of burned and unburned gas that sneaks past the piston rings collects in the oil where it forms sludge. Sludge does not flow easily, but it softens and dissolves into the oil when it is hot. Once removed by the detergents and carried away by the dispersants, it collects in the filter.
Failure to burp the cooling system will lead to overheating. Thermostats have to be hit with hot liquid to open. Hot air will not do it. That is also why an elusive cause of overheating is a leaking cylinder head gasket. The combustion gases pool behind the thermostat, then the hot coolant can reach it to cause it to open.
The last way to burp the system is convenient if you are also replacing the hoses. With the top radiator hose removed from the thermostat housing, you can poke small screwdriver or pick in to push the spring-loaded center plate of the thermostat open. That will let air out, and the level in the radiator will drop. Keep filling the radiator until coolant comes through the thermostat.
To answer your question about the temperature gauge, yes, it will read correctly when there is no thermostat, but it is correctly reading the abnormally-low coolant temperature. The gauge may not be linear though. Some read too cold until the actual temperature is almost to 200 degrees, then they become quite accurate in the middle of the pointer's range.
As a point of interest, in my opinion the Shadow/Sundance are two of the best cars Chrysler ever built. They are as tough as little ostrich eggs, and easy to fix and diagnose.
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Friday, January 19th, 2018 AT 4:18 PM
