Chrysler Repair: overheating but no radiator fans: 94 LH body, 1994 chrysler lhs, chrysler lhs

Question
I son has a 1994 chrysler lhs and it is overheating. The thermostat and water pump both were replace about 11/2 years ago so I don't think that either of these would be the problem. When the car gets hot, the electic fans are not turning on. I check the fuse and relays under the hood as well as a fuse located in the fuse block locate on the left side of the dashboard and all
appeared to be fine. I was wondering what "triggers" the relays to activate the fans. I thought that that may be the problem. Thanks for your help. Gary

Answer
Hi Gary,
The engine coolant temp sensor is what triggers the fan relays. It is located on the top of the engine directly adjacent to the thermostat housing and has a 2-wire plug. It is basically a temperature dependent resistor which should read 10,000 to 14,000 ohms when cold, and 700-1,000 ohms when hot. So pull the plug (gently lift tab on edge) and check the resistances. Here are some more possibilities that I mentioned to another questioner with the same vehicle but whose fans were working:

"Either the energy demand of the car is excessive or the cooling capability of the system is compromised. Is there any indication that the brakes are dragging (feel wheel metal surfaces after driving it)? On the cooling side of the question:
Does the engine coolant truly get overheated as evidenced by the both fans coming on when the gauge is in the high area? If not, then maybe the gauge is inaccurate and you might want to measure the temp of the coolant. You didn't say whether you are getting any overflow from the coolant expansion bottle, but that would say it is indeed getting overheated, otherwise a temp check may be warranted.
If it is truly running above typical with the fans coming on, then the possibilities are that although you flushed the radiator some of it tubes are plugged. So check when it has gone into the high area whether both sides of the radiator structure (what are called the manifolds) are quite hot. If the manifold on one side (the side where the lower hose is connected) is quite a bit cooler than the other then I would suspect that you need to have a radiator shop rod out the tubing to restore full flow.
It is also possible that the water pump impeller has lost its ability to pump the coolant because of blade corrosion or being loose on its shaft. On the 3.3L engine the pump is external and is not as big a deal to replace as on the 3.5L engine. On the latter engine it is located internally and you have to do a lot of dismantling to get to it. You said the timimg belt has never been changed so you probably have the 3.3L engine which has a timing chain rather than belt so it won't likely wear out the way a belt does on the 3.5L engine. But if in fact you have the 3.5L it is long overdue for a belt change and that is the perfect time to replace the water pump. If you have the 3.3L with the pump driven by an external belt then you might check to be sure that the belt isn't too loose and allows the belt to slip on the pulley which will of course impair the pumping rate of the coolant.
The last possibility is that you have some air trapped in the system around the thermostat. You can check that out by draining the coolant down by a several quarts, collecting it for reuse. Then notice that there is a bleed valve on the thermostat housing to which you will attach 4' of 1/4 inch clear plastic hose from a hardware store and direct the hose out over the front of the car so as to be able to avoid coolant spilling on the drive belts and to collect the coolant for reuse. Then open the bleeder valve and start adding fluid to the coolant bottle until coolant runs freely out the bleeder valve. While keeping the coolant flowing by adding more to the bottle, gently squeeze the upper radiator hose to drive off air that might be trapped, via the bleed hose. Then close the bleed valve and continue to refill the bottle to the line on the side.
So those are the items that come to mind for what you are experiencing.
Let me know if something comes up that is unusual and I would be pleased to learn in any case what you find to be the cause and the solution."

If the sensor checks out, lets explore the circuit in greater detail. Mention which engine you have.
Roland