I have a really strange issue occouring. My cooling fan switch (sensor) is not activating my cooling fan. Here's the strange part, the entire cooling fan circuit is GOOD, including the sensor itself. I know that the circuit is good for a few reasons. The first being that I bought a brand new sensor. The second is that if I remove the cooling fan sensor switch from the bottom of the radiator and manually heat it to its switching temperature, the fan kicks on and activates as it should. Additionally, if I remove the sensor from the harness, and jump the 2 terminals that plug into the cooling fan switch (thereby bypassing the cooling fan switch all together) the fan also runs as it should.

All this basicall tells me one thing; That when the cooling fan sensor is installed into the bottom of the radiator it's not seeing hot coolant??? I'm going to flush the radiator tonight and make sure there are no blockages, but aside from that, I don't have a clue what could be causing this. I know the coolant is getting hot, because my temp gauge gets hot enought to go out of the operating temp range, and the radiator is too hot to touch. This being the case, I can't understand how the temperature switch is not seeing this? Could this be a coolant flow problem? And if so, whats a good way to see if my water pump is generating good flow? I just rebuilt the entire motor (new water pump as well). The cooling passages in the motor and head were clear at that time, and the radiator (aftermarket aluminum) was completely emptied and refilled when I dropped the motor in. Any help or suggestions would be greatly appreciated.

Cooling fan sensor and related components:


Circuit diagram:

The old resistors are known to be finicky. Mine were bad on both my cars and the fan would not come on low speed when it should. I cut the resistor off and looped the wires, allowing the fan to come on high when it is triggered by the lower radiator switch.

Thanks Wop. Would the resistor keep the fan from coming on at any speed if it were finicky, or just low speed?

I have an update and more problems: I flushed the radiator and motor today. I ran water through the radiator forwards and backwards through both the upper and lower hose inlets until the water ran clear. The water ran good and didn't seem to be obstructed in any way. With the radiator hoses removed from the radiator, I did the same thing to the motor, running pressurized water through the thermostat housing and the backwards through the lower water pipe until the water ran clear. I then hooked up both radiator hoses and ran water into the radiator until the system was full. There's no chance there were any air bubbles left in the system.

I closed the system up and started the car. Just idling, the car's temp started to creep past the middle of the temp gauge. As the temp approached the hot mark on the temp gauge, the fan never came on. The car got hot, but fan switch on the bottom of the radiator never triggered the fan relay. I touched the radiator at the top and it was super hot. I then touched the bottom and felt a noticeable temperature difference. For some reason, hot coolant is NOT getting to the bottom of my radiator. At this point, I manually turned on both fans (cooling and A/C fan), in an attempt to get the temp back down using the fans. Even with both fans running, the temp will not come down. The only way I can get the temp back down is to stick the water hose in the top of the radiator where the cap goes and flood the system with cold water. If I have the cold water running into the radiator, the temp drops comfortably past the half way point on the temperature gauge in the car. WTF is wrong here? Is my radiator just not flowing coolant?? The thermostat is completely removed, and nothing but the radiator itself could really be impeding flow.

Additionally, I'm open to opinions on my fan setup. I have a Ford Tarus fan setup in a pusher configuration. I'd like to be able to know if it will cool well, but until I figure out why the hell my radiator won't let hot coolant get to the bottom I'll never know. And just to reiterate, the cooling fan NEVER comes on. The fan switch on the bottom of the radiator never gets hot enough to reach its switching point, and therefore will not trip the fan relay. I know the fan circuit and sensor and both good. I verified this by heating the sensor manually to it's switching point, and it kicked the fan on without issue. I also have a new sensor installed.

I can only come to the conclusion my radiator is somehow impeding flow to the point that the car is unable to cool itself down...Anyone got any other ideas WTF could be going on here?

Pics of my current fan setup:

what's your water pump like? if the pump is not circulating coolant, then the hot coolant from the top of the radiator isn't really going to be circulated down to the bottom. I would imagine some if not most of the fins of the water pump have eroded away.

*edit* it seems it would pay to read the entire first post, where I saw your water pump is new. It could be your thermostat is stuck closed therefore circulating just hot water around the block and not through the radiator. I would remove the thermostat entirely (or fit another known good thermostat) and then check again.

Hey Fuel, thanks for the response. You must be just having an off night, because you also missed the part above where I already said the thermostat was removed. I put in a brand new OEM mitsu stat, but took it out just to be sure it wasn't impeding coolant flow in any way. That being said, got any other ideas?

I know you said it is a new water pump, but have you verified it is working? If you manually forced water through the system without issue but hot coolant isn't circulating properly it suggests either the pump isn't working or it isn't producing sufficient pressure to circulate coolant effectively. Also how did you manually get the fan switch coolant sensor up to temp? Immerse in hot/boiling water? I'm just trying to see any reasons things might not be activating or at least not activating within the correct range.

Last stupid question and I am not trying to insult your intelligence here, just thinking outside the box; have you verified the fans are flowing air in the correct direction. I remember someone commenting that some fans rotate in a different direction to the Galant ones and you have to ensure you wire them in the correct way to get them flowing in the correct direction. Have you verified this on the Ford fan by checking the direction of airflow rather than how it is wired up!

Fan looks like a puller from a bmw.

Just wanted to give an update on how I have resolved this overheating issue. Well, would-be issue actually. It turns out the car was never actually overheating in the first place. For some reason, my temp sender for my dash gauge seems to be working as it should, but is displaying 30~40 degrees hotter than the car is actually running. I found this out after I hooked up my ECMlink, and saw the car operating in the 195~215 range. I am going to get a new temp gauge sender and see if this fixes my inacurate gauge reading.

From what I could find online, 200 to around 210 is about normal operating temp for a 4G63. What do you guys say good operating temp should be, and how hot do your cars typically run? Also, at what temp do you consider your car overheating?

Cruising around, I'm right around 195-203. At idle, my temps climb to almost 215 sometimes. The fans kick faithfully at 206, and they bring the temp back down to around 200. I have a Mishimoto dual 10in fan kit with the full aluminum shroud on the way to help with cooling at idle click Any imput you guys have would be greatly appreciated.

Sounds completely normal for a car with a stock 190 degree thermostat. Both my cars are exactly the same.

I just installed a 180 degree thermostat in 1051 over the weekend and am using the EGR solenoid output via ECMlink to trip the fan relay anytime the car is running and at speeds under 8mph. As soon as they add a coolant temperature parameter to that output, I'll use that instead.

OK, so last night I bought a brand new temp sender for the dash temp gauge. I have the EXACT same problem. The dash gauge rises porportinately to the car getting hotter, but the temp reads 20-30 degrees hotter than my ECMlink reads. At around 200 (according to my ECMlink) the dash gauge reads almost in the red. Any ideas?

Try another instrument cluster ? /ubbthreads/images/graemlins/dunno.gif

Actually, that's kinda what I was thinking. Would a crappy cluster yield this kind of problem even if all other factors were good???

What kind of condition is the wiring in coming off the sensor?

I know this is of no help, but I had a similar problem and it magically went away one day. All I did was change out my fluids.

Your cluster doesn't happen to have OTHER THAN STOCK gauge faces, does it? If so, the needle could be off a bit.

The wiring and connector to the sensor appear to be in good shape, although I havent Ohmed it out to really see. The gauges are stock, and don't appear to be messed with in any way. I will add though, that my speedometer does not work either. The trans cable is connected at the trans and cluster, but the needle doesn't move. Maybe my cluster is bunk? I guess I'll pull it out this weekend and check. Anyone have a spare cluster lying around that is for sale?