Two weeks ago I installed a Hypertech Fan Control Thermostatic 200 Deg On/185 Deg Off in my 91 TPI. With the headers I have it was a major pain. I had to get it out from the underside with a box wrench, turning 1/12th revolution at a time.
Anyway, after installation, it turned the fan on at around 150-160 and then never turned off. I figured at first there may still be air trapped in the engine, so I let it slide. Now after driving daily for a week and a half the switch is stuck on. Even cold in the morning, the fan is constantly on.
I bought it from summit so there was no problem returning it for another... Just the pain of removing and reinstalling.
This time I am going to figure out a way to test the new switch before installing it. I would recommend others do the same.

 

I can only reach mine from underneath also, but I don't recall it being that tight for a wrench on mine.

I've changed mine out several times over the years and quite honestly I don't think it's a Hypertech specific issue. I've had several different brands including Bosch and they all lost their temp setting over time.

I've actually had better luck with the Summit brand screw in temp probes. Who knows what brand they really are, but they seem to work best for me.

 

kurtis72, If you want the changes done to your memcal to lower the fan on and offs send me a pm

If you do go the route of another switch test it on the stove in some water. Have a thermometer in the water and heat it up, your your vom on ohms one lead on the body of the switch and one on the center terminal , you might want to use a little amount of water so the housing is not submerged.

 

I was thinking of installing one in my 91 but was wondering if there is any other changes needed i.e. thermostat, new ecm chip, etc.
I would like to get the temp down it is just too hot for my custom application

Thanks
Mike

 

before you return the switch, look to see if there is a partial part number stamped on it... them go to your local NAPA and try to find that switch- it's probably the same switch that comes in an Echlin box but with the Hypertech markup on it. i have a 220 on/215 off switch in my Camaro that i got from NAPA for $17..

 

oh really ? I too ran into this issue with my hypertech fan switch . i just never bothered to switch it out . mine went out maybe 100 miles after isntallation .

 

Cheaper alternative to Hypertech - and just about all others,.......

Four Seasons 35946

This fan switch turns on @ 212 degrees. The lowest on E-bay was about $12 shipped for the four seasons sensor. (E-bay item number = 310401126507)

Same part - different makers - MUCH higher price........
GENERAL MOTORS OE # = 305319
STANDARD MOTOR PRODUCTS Part # TS136 {#3053190}
(86-87 Buick Grand National 89 Pontiac Firebird TTA)



I REFUSE to pay 40 + $$ for a stupid temp switch..... NOT going to happen !!

 

My Hypertech switch did the same thing. It would turn on, but wouldn't turn off once the motor cooled off to the "off temp". I wound up bying a cheapy fan switch as a replacement and it works much better.