Auxiliary Fan

[tugboat95]

At what temperature is this thing supposed to come on?  I can make it run and I know all the wiring is good.  I do not know if the radiator temperature switch is good.  I assume it is. (Yeah, I know)  I replaced the relay so I know its good. I jumped the relay socket and its good.   It does have AC and that relay is good as well.  The AC does not work right now and I'm assuming its because there is no refrigerant in it.  I fixed a known leak in it and haven't recharged the system. I haven't diagnosed any further. This was discovered immediately after refilling the coolant with 45 dollars worth of antifreeze, so I'm not crazy about pulling the switch out to test.  I'm not sure how the AC relay plays into it especially when I can't get the compressor to come on with out the refrigerant in it.  I'm wondering if my radiator just isn't getting hot enough.  I read online that the fan comes on at 216 degrees, but I can't find this in the manual.  Anybody have in insight in this issue? I also know there is a diode in the system.  I'm wondering it its worth just wiring it up with a switch and a fuse?

[jdog]

Iirc it's like 230 or when the a/c is on

[Ωhm]

1 hour ago, tugboat95 said:

At what temperature is this thing supposed to come on?

If using the Coolant Temperature Sender (Dash Gauge) located on the back of the head, your temperature readings will be higher than specification. Radiator Temperature Switch (RTS) specification is 198°F ±9°F. This is the range for the RTS to close.

[Minuit]

41 minutes ago, Ωhm said:

198°F ±9°F. This is the range for the RTS to close.

Key point: this temperature is on the cold side of the radiator, after the coolant has already passed through the finned section. The temperature the switch is seeing is essentially the temperature of the cooled coolant entering the engine at the water pump.

 

If the coolant in the cold side of the radiator is at 198 F, I think it's probably time to stop driving. For reference, I have a CSF radiator in my 91 (4.0, automatic with A/C and an auxiliary transmission cooler), and I typically see about 130-140 F in the spot where that temperature switch is located. I run a 195* thermostat and change my coolant every year. The only time my factory temperature gauge (with a NOS Mopar sender - that part's important if you want the number on your gauge to mean anything) has ever approached 210 was climbing a very long hill at 80 MPH on a very hot day.

 

IMO: If your cooling system is healthy, this fan should never come on by itself in any sort of normal driving. If the switch and fan work and your fan is coming on, you're way too close to overheating for comfort. AMC was clearly comfortable with these engines running a lot hotter than I am. But if I'm the one you're asking, if that fan ever comes on by itself on your Renix truck (except for when the A/C is on), you've overheated and that little electric fan isn't going to overcome the problem that led to your overheating.

[omega_rugal]

AFAIK the auxiliary fan is meant to help with the extra load when the AC is on, not to handle an overheating situation...

[tugboat95]

I'm getting a temp of about 150 in that area of the radiator. Tomorrow I'll investigate it a little further and more location specific to both temperature sensors.

I've not experienced any overheating. Just wondering what made this thing turn on.

 

89 Comanche

Eliminator

2wd

4.0L

5 speed PukeGoat

Factory Original

 

 

 

 

 

[87MJTIM]

I have the REM set to display the engine temp the the ECU receives (not the gauge temp sensor or the aux. fan temp switch).  While sitting in line at a drive-thru, I watch the temp rise up to 219* before the aux fan turns on (AC not running).  The fan will run until the temp drops to ~204*.  So I know the fan and switch are working.  

[tugboat95]

What I found out today

Idled for about 30 minutes. It's only 77 degrees today, FINALLY!

Temp gauge reads right at 212. Block at the gauge sensor reads 207 to 209 This is also at the back with no air flow furthest from the radiator right next to the exhaust. It's just a hot location.

Water out of engine (hose)is 148. Water into engine(hose) is about 122.
Temps of radiator:
Into 137
Out 117
At the temperature switch its 111 to 115

Engine temps:
On the block at each injector. 156 to 170
On the block at the spark plug valley. 135 to 150. Exhaust manifold location has to allow for the injector side higher temps.
Hot side of Tstat housing is 196
Low side of Tstat housing is 160
Block at Tstat is 204

If this was one of my diesel engines I'd be very happy with the range and their relationships with each other. Should I be happy with I6 Renix???

89 Comanche
Eliminator
2wd
4.0L
5 speed PukeGoat
Factory Original

[Minuit]

1 hour ago, tugboat95 said:

What I found out today

Idled for about 30 minutes. It's only 77 degrees today, FINALLY!

Temp gauge reads right at 212. Block at the gauge sensor reads 207 to 209 This is also at the back with no air flow furthest from the radiator right next to the exhaust. It's just a hot location.

Water out of engine (hose)is 148. Water into engine(hose) is about 122.
Temps of radiator:
Into 137
Out 117
At the temperature switch its 111 to 115

Engine temps:
On the block at each injector. 156 to 170
On the block at the spark plug valley. 135 to 150. Exhaust manifold location has to allow for the injector side higher temps.
Hot side of Tstat housing is 196
Low side of Tstat housing is 160
Block at Tstat is 204

If this was one of my diesel engines I'd be very happy with the range and their relationships with each other. Should I be happy with I6 Renix???

89 Comanche
Eliminator
2wd
4.0L
5 speed PukeGoat
Factory Original

 

I'd say those are good numbers. 195 to 210 is where I like to see the operating temp at the thermostat housing but I'm picky.

 

I'd expect a higher number on the outlet hose, given that the thermostat is presumably open.

[trinity5007]

Mine always kicks on at 212. But that's slowly moving through trails or stop and go traffic. At 86 degree air temp. But that being said I have a single core rad. When I was running the thicker rad it never came on. Even with the single core. A new clutch fan helped significantly. Now the aux fan barely ever turns on. It's got to be hot hot. 

[tugboat95]

I'd say those are good numbers. 195 to 210 is where I like to see the operating temp at the thermostat housing but I'm picky.
 
I'd expect a higher number on the outlet hose, given that the thermostat is presumably open.

I kind of thought the same. But I'm new to these engines. I just don't know what normal is for THIS engine. I work on and maintain the same diesel engines day in and day out. Every engine has its quirks. I have two Cat 3516 engines. One always reads 10 to 12 degrees hotter than other. And they are were built side by side only one digit in serial number is different.

But I'm getting confident that everything on this 4.0 is working like it should, minus AC.

89 Comanche
Eliminator
2wd
4.0L
5 speed PukeGoat
Factory Original