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Re: Radiator Fan Relay Contact Welding (w/70amp relay!)
At 08:13 PM 11/27/97 -0500, you wrote:
>Not too long ago, someone mentioned (I'm not sure the issue had its
>own thread or not) how the contacts in the 30amp radiator fan relay
>can weld together (I think the 5ktq's were the subject auto). This
>must have happened to my 5ktq sometime in the past; the relay had
>been replaced with a 70amp unit, and the original high-current supply
>wire (the large-guage red one) had gotten hot enough to melt together
>with some its neighbors in the wiring harness.
WATCH OUT!!! i own an 87 5KTQ (which I love) because the former owner
literally melted down his wiring harness because of this problem. I bought
the car from him in 1993 with only 60K miles on it for 3K USD as a result
:-) There is no fuse (actually 3 No. 8 wires feed the cooling fan and one
No. 8 wire grounds the fan...thats the "fuse") between the battery and the
cooling fan. The cooling fan had its bearings freeze and the resulting
current draw (about 120 amps) melt the No 8 grounding wire down. The former
owner took it to his european specialty shop and they replaced that melted
No. 8 wire with a good solid No. 4. Next time the cooling fan came on it
melted down the 70 amp relay (BTW that is the proper relay), the fuse box,
and all the wiring harness around it. If you have already melted wires I
would HIGHLY suggest you change them NOW!!! Or Gee um maybe you want to
sell your car extremely cheaply??
>Also, while the turbo cooling pump circuit still works, but the fan
>doesn't kick on at a low speed like it should; I haven't yet located
>the step-down resistors for the fan; they may be shot or or even
The step down resistors are located on the left side (drivers side if you
are in the US) front area in back of the front grill. They are blue and
sell for 120.00 USD. They are most likely burned and will need
replacement. Replace them do not try to reuse them. The fan has a limited
duty cycle its highest speed stage 3 cooling event (current draw of about
42 amps is normal). You will burn the motor out if all you can do is run
that fast because your resistors are gone.
>A new supply wire was put in place running to the relay.
See above but I do believe your car has had a cooling fan seize up. Get
out your Bently and rewire ANY "melt together with some its neighbors in
the wiring harness" NOW before you need to replace entire wiring harnesses.
I'VE BTDT in a big way!
>In spite of this, while leaving the drive-thru at Hardy's, the
>fan did not shut off when I expected it to. I got back to the
>office, shut off the car, and the fan was still running (again,
>I need to mention that none of the afterrun circuitry has ever
>triggered the fan as long as I've had the car). Popped the rear
>seat, disconnected the battery ground. Removed the relay, and
>while the contacts were no longer stuck together, the contact
>surfaces had the same crystalline appearance you'd see in a cold
>solder joint. I filed the relay contacts down a bit, replaced it,
>reconnected the battery, and have had no repeat since.
>The temp guage on my 5ktq rarely goes past the middle position;
>however, I've been getting overheat alarms from the computer.
>Suspecting a problem with the coolant level switch (which sets
>the same alarm), I disconnected it, and the alarms went away.
>And whenever I check the coolant level, it's OK.
Maybe not I wouldn't disconnect alarms until I knew the status of
everything in the cooling system. If coolant level switch is bad replace
it and see if the alarms continue. You may have had a major overheating
problem if the cooling fan has fried its wires.
>As usual, I'd appreciate any hints, suggestions, or BTDTs, and TIA!
>-Douglas Hurst Quebbeman (firstname.lastname@example.org)
I'm sorry about the tone of my comments but if I can save you the time and
trouble I experienced when I replaced my entire wiring harness because of
this type of problem, I will.