My cooling fan switches on normally about 50 % of the time, the other 50% of the time the car heats till 240 degrees + , then the fan switches on, this is not good. I've changed the fan sending switch a couple times but that didn't help at all. I know my fan motor is good so its not that. What could it be and how can i fix it? Thanx.

PS..I have a GM Crate engine and there is no computer.

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1986 IROC-Z
GM Vortec 350 Engine
Holley 600 CFM Carb
Hedman Headers
700r4 w/shift improver
4 wheel disc
Richmond 3.73's/Auburn Posi
Best ET/MPH: 14.10/102

"So what DOES the back of a mustang look like anyway?"

 

Skate,

The factory setting for the primary cooling fan is supposed to be 223°F cut-in. Given the allowable variation in CTS sensors and dash instrument inaccuracies, the temperature might be completely "normal" by factory standards.

Of course, that temperature is uncomfortably high for many of us, and is one of the major reasons to install a different thermostat and aftermarket fan control. Too cold is just as bad, but reaching 230°F + in traffic is no fun either.

Perform an archive search on fan controls or thermostats, adn you'll find varying opinions and suggestions. I've had good success with a 180°F thermostat and an auxilliary fan switch set to close at 200° and open at 187°F.

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Later,
Vader
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"Fear is how I fall, Confusing what is real..."
Adobe Acrobat Reader

 

This may be a cheesey way to do it, but I use a dual throw switch to activate both fan relays. The switch I put under my dash, and everytime I disagree with my firebird's stock fan temp switch, I just flip the switch and she cools back down. Can be done for less than $5.

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Mint black/black 1987 T/A GTA 305 5-speed, 55K,
3.45 factory POSI,SLP cam, SLP runners, Taylor wires, hurst comp plus shifter, K&N conical rig, AFPR, coated shorty headers, no cat, no smog, 3in. mandrel-bent single exhaust, flowmaster, TB air foil, 160 stat, SFC's, lower control arm adapters, Aluminum Driveshaft, ported upper and lower, Mobile ES and 10 disc, kickers all around and q-logic kick panels...Perf 350, rear batt, lowering springs,cowl hood, & NOS coming soon!

 

I had a similar problem. I have two fans (91 Z28 305 tpi). The drivers' side would always come on as its supposed to (via the computer at ~230°F), but the passengers side (controlled by the coolant sensor switch on at 200°F and off at 185°F that I got from Summit) would sometimes work and sometimes not. I know when they come on because I have a L.E.D. on my dash for each fan indicating when they are operating.

Grounding the sensor wire would turn the fan "on" as its supposed to, so I though that the sensor switch (albeit new) was bad until I check the relay pin contacts. The problem turned out to be the relay coil pin(s) making bad (and thus intermittant - the worse kind of problem to troubleshoot!) contact with its associated socket on the relay socket. Removing the wire/socket from the relay socket and moving the contact so it would make better, or more firm, contact with the pin solved the problem.

FYI I found the same problem (intermittant) with the hatch pull-down latch assembly. Sometimes it'd work, sometimes not. One of the pins on the motor was not making good contact with its associated socket.