e-fan question

[F1Addict]

I'm in the process of renovating the cooling system on my '89 Renix and noticed that my e-fan is reluctant to engage. It does come on but not until my temp needle is dangerously close to the red. So, my question is... from where does my e-fan get the signal to turn on?

[XJ Wheeler]

A sensor mounted to the radiator (drivers side) sends it to the ecm. That controls the fan, and is suppose to come on at 218° or when the a/c is turned on.

Sent via messenger pigeon - i talk, he types.

[F1Addict]

Ahhh, okay, thank you. I know exactly which connector you're talking about. There must be a way to test that, I'll have to do some research.

The fan does come on when I turn on the AC.

[89Laredo]

Your gauge might be a little off too. At an indicated 210* my engine temp is actually 195 according to the cts.
Temp sender for the gauge is in the very back of the head, so it'll read a little high compared to the cts which is in the middle of the block.
You can splice into those two wires going to the temp switch in the radiator with no worries, its a low amp relay trigger circuit. Put a switch in and you can turn the fan on whenever.

[4.3LXJ]

That sender only comes on when the coolant is too hot AFTER it goes through the radiator. It does not account for an engine that is running a little to hot due to lean mixtures etc. The sensor should be on the engine, but alas it is not. Not sure how you would test that unless you put it in boiling water, which is not hot enough to activate it. I think it comes on at 220°

[F1Addict]

I was playing around with it a little today and found the following. Idling, with the AC off, the e-fan never came on which seems logical because it never went much past 210. With AC on Normal the fan would kick on and off and with the AC set to MAX it would remain on. I didn't test on Bi-Level. So the fan seems to be functioning normally with the AC leading me to believe it might be a problem with that sensor in the radiator. I'm replacing the mechanical fan clutch tonight and might hook up an over-ride switch for the e-fan while I'm in there.

Thanks for all the help.

[89Laredo]

Sounds like it was working right with the AC on.
The thing in the radiator isnt a sender, it is a thermal switch. Senders have variable resistance according to certain temperatures.
EX:
https://farm8.staticflickr.com/7300/9452902515_029b7f2c35_b.jpg
A switch simply turns on and off at a certain temperature (think of it like the furnace thermostat in your house)
Like 4.3l said it turns on ~220 which would make it hard to test.

[Carves]

The renix radiator switch/sensor/sender, uses the same, activation temp, for the fan ... as the t'stat housing sensor, in the later models ???

FWIW ... I'd get your parts store to hunt through a suppliers catalogue for a replacement ... with an earlier activation temp.

... just as an example .... http://www.tridon.com.au/Products/Product.aspx?SG=8&S=35&G=483&P=2014

[89Laredo]

I was wrong...

DESCRIPTION & OPERATION
On Cherokee, Comanche and Wagoneer models with a 4.0L engine,
A/C and/or heavy duty cooling system, an auxiliary electric fan is
used. The auxiliary fan is controlled by a relay mounted on the left
inner fender panel. A radiator temperature switch attached to the
radiator outlet tank above the lower radiator hose senses engine
coolant temperature.
When coolant temperature is more than 190(0)F (88(0)C), the
radiator coolant temperature switch closes allowing current from the
ignition switch to flow through the fan relay to ground activating the
relay. When relay is activated, battery voltage is supplied to the fan
causing it to operate. When coolant temperature is below 190(0)F
(88(0)C), the radiator coolant temperature switch opens preventing the
relay from being grounded and electric cooling fan from being
energized.
When the A/C (if equipped) is turned on, the Electronic
Control Unit (ECU) grounds the A/C relay coil allowing current to flow
through it. This activates the A/C relay which then supplies current
to the A/C clutch, fan diode assembly and cooling fan relay. The
cooling fan relay is activated and the fan operates. Whenever the A/C
is used, regardless of engine coolant temperature, the auxiliary
electric cooling fan operates.

[Carves]

Thanks ... that sounds like a "better" temp .. and gives me a base line of what I can replace the bung with, in my "all model" radiator in my '97.

Might still be worthwhile to fit a lower rated temp switch for those ... harder than DD driving tasks tho.

[F1Addict]

Yeah, there is no way this is coming on at 190º. I've seen the needle as high as 235º and the fan still wasn't on. It did eventually come on but, like I said in my original post, it was seriously flirting with the red on my temp gauge when it finally did. Rather than hunting down a new switch I'm just going to wire in an override switch, at least for now.

I did get my fan clutch replaced tonight and can now confirm that my old one wasn't working. This one makes the fan really roar when the temps start building under the hood. The fan speed never seemed to change with the old one.

Thanks again for all the advice and help.

[89Laredo]

The switch is on the cold side of the radiator. Obviously there is quite a temperature drop from the back of the head where the gauge sender is, through the radiator and then to the fan switch.
Im thinking two things are going on:
1: temperature sender or gauge is not very accurate.
2: Fan switch isnt working right.

Get an IR thermometer and verify your readings. Get it hot and measure the hot and cold sides of the radiator, if the cold side is 190*+ you need a new temperature switch.

[F1Addict]

The switch is on the cold side of the radiator. Obviously there is quite a temperature drop from the back of the head where the gauge sender is, through the radiator and then to the fan switch.
Im thinking two things are going on:
1: temperature sender or gauge is not very accurate.
2: Fan switch isnt working right.

Get an IR thermometer and verify your readings. Get it hot and measure the hot and cold sides of the radiator, if the cold side is 190*+ you need a new temperature switch.

The sender (Mopar) is about 10 months old, switched from idiot lights to gauge cluster. Gauge cluster was a JY find but was in very good shape which is no guarantee that the gauge is accurate however, when it gets close to the red, I smell coolant... so it's close. I'll get batteries for my IR thermometer and check it out.

[ParadiseXJ]

The switch is on the cold side of the radiator. Obviously there is quite a temperature drop from the back of the head where the gauge sender is, through the radiator and then to the fan switch.
Im thinking two things are going on:
1: temperature sender or gauge is not very accurate.
2: Fan switch isnt working right.

Get an IR thermometer and verify your readings. Get it hot and measure the hot and cold sides of the radiator, if the cold side is 190*+ you need a new temperature switch.

When the GAUGE reads 218 (effectively 220) the fan should come on -->via the relay --> via the switch...which is reading at the radiator at approx. 190-195 (like the t-stat actually sees).

The sensor on newer models in the t-stat housing gets a closer-to-the- stat reading, sends the info to the ECU --> to the relay --> to the fan. The two "sensors" do not operate the same way as said above. One is a switch to operate the relay, one is a sensor to TELL the ECU to activate the relay.

[F1Addict]

I put a thousand difficult miles on my XJ in the past week during another trip to the Sierras. What I discovered is that some of my low speed over-heat issues persist but my high-speed and idle issues are resolved with the new fan clutch and radiator clean/flush. While driving through the desert (ambient 97º) I was in the 220º range, going up hills the temp would rise to 235º but never go past that last white hash mark and into the red. At idle it would never go above 220º even if it idled for an hour. Going up steep trails still pushes the needle into the red and I had to stop a couple times to let it cool off. On the other hand, low speed, flat trails in the desert with the AC on never went over 220 so it has to be the slow speed climbing that's causing issues. Watch the Scenery forum for trip notes and pictures, I'll get them up sometime this weekend.