Hey guys, quick questions. I've been slowly diagnosing my overheating problem and bought a few different things...lower temp thermostat, new lower temp hypertech fan switch and some improved gauges. The new gauge sending unit is in my manifold now vs. the head due to melting from the header heat.

All these years I was under the impression that the CTS only sends temperature info to the ECM, and thats it. After some reading, is it true the CTS sending unit also tells the ECM when to activate Fan #1?

When my fan switch started malfunctioning, the fans would not turn on whatsoever. I tapped on the switch in the head with a screwdriver and noticed my passenger side fan would slowly start to kick over and start spinning. Probably due to melting or whatever.

If the first fan to come on is controlled by the ECM, why were no fans working whatsoever until I smacked the fan switch thats on the passenger side cylinder head? Wouldn't this be the secondary fan?

Could it be the CTS is getting a much cooler reading than the cylinder head switch since its in the manifold, therefore activating AFTER rather than first?



This cooling issue is still driving me nuts.

-As of right now-
-Fan switch is in passenger side head
-CTS is in the manifold next to the thermostat
-Temperature probe for my water gauge is on the left of the manifold
-Replacement fan switch is ready to go into the second hole on the left of the manifold with a 3/8 to 1/2 NPT adapter.

Any ideas?

*Also the switch in the head right now is a low temp switch (not oem) so could that be why its activating first?

 

It depends at what temperature this was happening. Stock turn on temps are 223° driver side and 235° passenger side......Now if you replaced the fan switch with something that turns on at 200° for example, in theory your passenger (secondary) fan should turn on before your driver (primary) fan does.

But that won't happen. I have the exact scenario listed above. Stock computer chip (223° turn on) and a 200/185° fan switch. At 200° both fans will turn on. So it seems like the secondary fan will override whatever the primary fan is set for.

The CTS doesn't tell when to turn on the primary fan. But it does send the temp information to the ECM. That's why you can change the primary turn on temps with just a different chip in the car.

 

The car currently has a #4028 hypertech in the passenger side head. This is the 200 ON 185 OFF model. I have been using this in tandem with a 180 hypertech stat since 2003ish.

As of right now, I've installed a new 160 hypertech stat and have new #4026 176 ON 166 OFF switch that is waiting to go into the manifold vs the head to minimize any melting from my exhaust header.

Why would a lower temp switch alter the primary fan function?
It's coming on before the driver side fan around 140* according to my new gauge which the sending unit is mounted in the manifold.
I think why the gauge is only reading 140* is because the temp in the head is way hotter than the temp in the manifold. So maybe its 140* in the intake and 60* hotter inside the cylinder heads.

Also the driver side fan is not coming out whatsoever. I havent let the car idle for more than 15 minutes, so maybe thats why...I am unsure. But your diagnosis would mean BOTH fans would kick on when my low temp switch activates the passenger side fan...this is not happening.