Radiator Fans not coming on at all / overrheated / low coolant light

X300
1

1996 VDP, 8 zillion miles (VIN:779967)

My story:
Driving home in 85 deg. weather and the radiator light came on.
I pulled over and at idle, no fans.
Turned off the engine, oepned the water reservoir cap slowly and carefully, and it was boiling mad.
Waited for the fountain to stop and topped it up w/water I had on hand.
Limped home slowly w/heat on high and windows open.
Radiator light went off during he drive home.

So far I have:
YES - fuses are OK on continuity check w/VOM.

YES fans run when checked w/direct-supplied 12VDC from aonther battery.

NO 12VDC at the fans electrical connector that’s right under the radiator (with ingition in ‘lights on all over the dash’ position, but engine not started)
So, I assume that it’s either the relay or the temp sensor or cabling fault (not likely) - am I correct?

YES my air dam thingy got torn off ages ago - so the relay is muddy.

Pulled the relay and it looks like a somewhat muddy relay! Huh! I have no idea how to check it out.
Well, that’s not true, I have a VOM and extra battery, so I can go play and make it click and check continutiy here and there on the pins, but I’d need to sit down and understand the full wiring diagram, which I have in PDF form.

Questions:
Where is the temp sendor for the fans?
Is it the one on top of the thermostat housing?

Should I just swap out the relay with a used one off Ebay ($50)?

Should I just swap out the temp sensor (wherever it is)?
They seem cheap, might be quick-n-easy.

Should I push the whole thing off a handy cliff because I hate working on electrical?
Nah - I’ve driven it for 10 years w/no major issues and, hey! it’s a Jag, so: come on!

Thanks!

2

TSB we got when I worked at the dealer years ago.

14-04 Cooling System – Fan Fuse Failure.pdf (39.4 KB)

3

My VIN is after the TSB was issued so the fix was stock (just added that to orig. post)
And, fuses have continutiyt w/VOM. (just added that to orig. post)

Oh, and I just noticed I mis-typed, I put 1995 - it’s 1996, so I just fixed the post.
See?
I can fix SOMETHING!
: - )

4

U P D A T E - S O L V E D ! !
Diagnosed that the fan relay is bad.

Diagnostic process:
Stared at wiring diagramm for 52.25 minutes while muttering outloud the whole time.
Finally understood the all-but-inscrutable lines and numbers.

Using 12VDC source (my lawnmower’s battery) and a Multimeter (cheap HF model):

The coil that is energized by the low-temp side of the coolant temp sensor (pins 6 & 8 on the relay) is not closing. That’s the one that makes the fans ‘Always ON’ with ingnition on.
That is, I heard no ‘click’ of the coil closing.

The coil that is energized by the high temp side of the coolant temp sensor (pins 6 & 5 on the relay) clicks happily when energized = OK

Note: The multimeter didn’t actually get used, because I realized that the ‘click’ is the same as a multimeter showing continuity. Duh!

Coil ordered.

5

Charles … you said …

Note: The multimeter didn’t actually get used, because I realized that the ‘click’ is the same as a multimeter showing continuity. Duh!

Not so fast my friend. Recently I was tracking down a problem on my XJ40 which turned out to be a bad relay. Although I heard and felt a reassuring “click” from the solenoid when I applied 12v, an internal cracked solder joint kept the load side from having continuity.

6

I should have also reiterate din my update that I had NO 12VDC at the cable-connector-to-fan downstream from the relay with the ignition ON.
That meant that ithad to be the relay or temp sensor or pressure sensor.
With the relay not clicking on the ‘Always ON’ terminals, that made it seem like a no-brainer that the problem was right there.
I get my used relay tomorrow and will install it Sunday and update again.
Cheers!

7

S O L V E D
Got my used relay from Ebay - plugged it in, fans came on.
Everybody is now happy.

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