[DeTomaso] Radiator Fans Running Constantly

[Larry - Ohio Time]

Hi Mike,

The Temp sensors can fail open (contacts always open) or closed (contacts
always closed).

I would first disconnect the 2 sensor wires and turn the key to see if the
fans run. 

If they do your problem is most likely in the relay.

If they do not run the temp sensor is most likely bad.


The temp sensor is nothing more then a temp controlled switch. It can be
tested with a simple test light. Apply + voltage to one tab and place the
test light on the other tab (make sure the test light has a good ground by
touching it to the first tab to see it light up). If it is cold the light
should not be on. As the water heats up to the temp of the switch, it will
close and the light will come on.

By connecting the two temp sensor wires together it should close the relay
and start the fan. 

Most of this can be tested with the key just on. Remember some ignition
systems do not like to be turned on for long periods of time without the
motor running. You may want to unplug it.


Larry - Cleveland




-----Original Message-----
From: DeTomaso [mailto:detomaso-bounces at poca.com] On Behalf Of Mike Reilly
Sent: Wednesday, April 09, 2014 3:36 PM
To: detomaso at poca.com
Subject: [DeTomaso] Radiator Fans Running Constantly

Hi all.  I know trouble shooting through mail is difficult but I thought I'd
ask.  I also haven't figured out how to get to the mail archives to search
previous posts so hope folks don't mind.  Situation:  I had my radiator
re-cored due to age and some leaks. My car is a late 74 (#7366).  When it
was in the car before the repair my Meriah front pusher fans worked fine.
They each came on as needed and didn't run most of the time.  With the new
radiator installed they both now run constantly even though the car is
running very cool.   They will run when I turn the ignition key before the
engine even cranks.   I have the stock wiring and only disconnected the
brown and black wires from each of the temp sensors in the radiator during
the removal and installation (took photos to reinstall correctly).  I assume
the temp senders are fine as I believe if they failed the fan(s) would stop
working.  I plan to trouble shoot it all this weekend and any leads are
appreciated.  Also I saw some great ran and headlight control kits from
'Pantera Electronics."  Anyone have experience with these?   They look to be
a similar solution to the headlight/fan control fix Mike Drew published
previously.   Thanks, Mike