upnatm

My 4.0 began to overheat at idle this summer. The A/C began to blow warm as a result. Switch off the A/C, or begin to move and temp returns to normal
(210). My temp gauge, idiot light and audible alarm all work as designed.
I suspected the aux fan and verified that it does not run with A/C on, or at any point while temp climbs up to 260 or so. So... checked fuses, and swapped fan relay with starter relay. All was in order, so I jumped the fan directly to the battery and she whirred right up.
Since I wanted to replace the thermostat anyway (I've already installed a new water pump, radiator and hoses, along with a flush and fill kit), I also replaced the coolant temp sensing unit on the thermostat housing.
My Haynes manual says there's another sending unit on the "left rear of the block". The picture shows it to be near the grounding strap attached at the head bolt. Nada. Mine doesn't have one there. Only the injector rail.
Is there another coolant temp sending unit that I'm not seeing that tells the ECM to turn on the fan? Any ideas?
(I gave up on the local service department when they told me that jumping the fan to twelve volts didn't necessarily mean that the fan was working, even though the fan was working!

Kyle

Have you checked yet if the fan is getting power?

upnatm

I assumed it is not since it checked ok by direct connection to the battery

Kyle

Well if it is getting power then you have a bad connection, if not well then you know what the problem is.

upnatm

Kyle, you lost me. I assume that during normal operation, the fan moter is not recieving power, because If I jump the fan motor directly to the battery, the fan spins up.

Macneil

I had a problem with a faulty elec fan on my 99. I just wired it direct 12v and I have a switch in cab by my shifter now. As soon as I notice my temp climbing a bit past 100, I flick the switch on. I'll power the switch on if I'm towing my dirtbike (about 400-450lbs incl trailer/bike), or if I'm wheeling or have the A/C on. Other then that, I let the hydraulic fan take care of business.

Howler_GT

The sender that the Haynes manual talks about is for the early 90's 4.0L
They have a sender AND a sensor.
The 97's do not have this sender.

You stated that you replaced the coolant temperature sensor in the thermostat housing. Correct? Check the wires coming out of the connector.
Pull them out of the conduit and give them the once over.

I looked over at RockAuto and they list a "Temperature Switch" in thier switches/relay section. looks very similar to the Coolant temperature sensor.
IDK if there is ANOTHER component or if this "switch" goes in place of the sensor. Go over the motor again and look real close. Don't forget the radiator, carmakers are known for putting stuff there.

ONLY at a Service Department can a FAN thats running be considered NON-working. Is that what they call "Factory-logic"???

What temp thermostat did you put in?
And why were all those other components replaced?..Was there an existing cooling problem?

upnatm

Stock 210 degree. I had a core leak in the radiator and a little xtra cash so I went nuts while I had the wrenches out!!

upnatm

While I was searching for na possible elusive second temp swith/sender/sensor...whatever, I came upon ANOTHER connector in the fan wire. It's about six inches upstream from the obvious connector. Sure enough, I had volts on the relay side of that plug so's I tooks it apart...puts it back together and now my fan works as designed. THANKS FOR THE RESPONSES!!! I hope this helps someone else out...

Howler_GT

210???
What I understand stock thermostat is a 192* for a 97 (Someone please chime in here if I am completely wrong)
Do they even make a 210*?

I, personally am running a 180* in my 94 Sport but our 91 Laredo still has the stock 190* The 94 runs about 190-195 and the 91 runs straight up 210


Did you by chance notice the aux fan inoperating (for lack of a better term) BEFORE you "went nutz"?
MAY be something as simple as a pinched/broken wire.
Did you get a chance to inspect wiring?

BlueXJ

Howler you are correct 192* is the right temp by the FSM. I don't run one at all but never worry about it getting to cold here and needing the heater. Winter time it gets to low 40* to 45* and runs around 85-90* as a average fall and spring. Over 100* in the summer time.
BTW he fixed the fan now and found it to be a relay fan wire!!!

Howler_GT

I started replying then I chose to check out some of my info...posted the FIXed it before I submitted.

Oh well.
It's fixed...thats the main thing here.

Kyle

Thanks for letting us know what the fix is. Too many times people just fix it and dont let other know which doesnt really help.


Glad you got it solved

awilson42

I picked up a stock auxillary fan to install in my 93 Sport. Also grabbed what I could of the wire harness that feeds to the relay box.

Has anyone done a straight installation using the relay fuse box under the hood? I'm not sure if my powertrain module has the wire running to the relay box or not, but when the 20 amp fuse is put in (no relay yet), it blows as soon as ignition is in start position, so something odd is going on. Used an ohmmeter and cant find any obvious causes so far.

My ideal would be to use the relay box for fuse and relay, but instead of thermostat, control it from a switch in the dash.

Robert Dog

I would think that is the right way to do it...