I have a 1990 Rs Camaro with a 5.0, and at idle the vehicle is overheating, Ive boiled it down to the cooling fan switch on the bottom of passenger side of the block. Ive already replaced it once, but it still not coming on even when encountering activation temperature, which is 205F I believe. It does turn on when the A/c comes on so as far as I know its not electrical, Ive also replaced the temp sensor and thermostat, I need some help!

 

The sensor at the bottom of the block is the knock sensor. The cooling fan switch is in the cylinder head between 6 & 8.

Common for the exhaust heat to damage the connector for the switch. IIRC, the turn on temperature is about 226° F. For a lower turn on temperature get a switch for a '86 - '87 3.8l turbo Buick.

RBob.

 

Sw555 Wells
koeo ground the switch wire to verify the circuit works

 

The connector is a little melted but still works with a power probe, also I've tried lower fan cooling switches.

 

First thing you need to clarify is what "sensor" you're working on.

The knock sensor goes in the block, about an inch above the oil pan rail. Its history is evidence of some of the finest industrial subterfuge ever perpetrated: back in 1955 when the small block Chevy was being designed, the engineers at GM didn't want their counterparts at Frod and Xler to know that they were already working on EFI. So they disguised the designed-in knock sensor port as a coolant drain hole. [/humor] However all that may be, that hole is ¼" NPT; the knock sensor is a large-ish thing; the wire that plugs into it is blck if memory serves.

The fan switch goes in the pass side head between the #6 & #8 spark plugs. It's the same casting hole that, on the driver's side between the #1 & #3 plugs, has the temp gauge sending unit. It's 3/8" pipe in heads from the mid-70s and newer, originally ½" pipe. AFAIK all fan switches are 3.8" but it's easy to get a bushing at the hardware store to put one in older heads. Its wire is dark green with a white stripe.

They use the same style of connector; a single-pin round Weatherpak. Both go into coolant: the one of course drains that whole side of the block, the other only down to the head.

Not sure what "power probe" is or what is meant by "works with". But I do know, if you ground the green/wht wire, it should operate the fan relay. That's all the fan sw does... when its temp is reached, it shorts the connector to ground (its case). A potential cause of malfunction is that the switch is not well grounded to the head casting.

Make sure you're working on the right sensor and have the right color wire hooked up to it.

 

If this is a single fan installation, the temperature sensor in the head is not a switch, but a RTD. That sensor would have black and yellow wires connected to it. That sensor reports to the ECM, and the ECM programming decides if and when to operate the fan. In such an installation, the sensor is usually in the front of the intake.

In a dual fan installation, the secondary fan is controlled by a switch which is usually mounted in the RH head. It will sometimnes have a gray wire. That switch operates the secondary fan relay, which also should be checked for proper operaton. This secondary fan switch parallels the A/C pressure switch which should also operate the fan. The stock temperature setting of the secondary fan switch is closure at 238°F.