Aux Fan Switch Question 380SL

[300sdToronto]

Hi

I just bought a 1982 380SL. 118K miles. Yesterday in a traffic line up of about 20mins in +70 deg F driving home, I noticed that the coolant temp nudged up till it was sitting somewhere around the 105 to 110 C mark.

This seems a tad high as I understand the aux fan switch should cut in at 105C and I assume is designed to keep the temp at or below that level.

So two questions:-

1. Where is the switch? Somewhere in the block, I know, but there is a lot of plumbing on that engine compared to my 300sd!!
2. Does the switch energize the fan by completing a circuit to ground or by opening a circuit to ground? I don't have a wiring diagram yet and with this info I should be able to jumper the wire attached to the switch, and test the fan and wiring properly. If I can get the fan to cut in properly, then I assume we are dealing with a new switch.

I have seen the postings recommending the use of the 100C switch in preference to the 105C original.

Comments gratefully accepted.

[donbryce]

Others will correct me if I'm wrong, but I believe the engine coolant and ambient air temperature is responsible for triggering the mechanical fan clutch via the flow of air through the radiator. The auxilliary fan, electrical and mounted in front of the radiator on the condenser, is for additional airflow to assist the A/C refrigerant cooling in the condenser. The auxilliary fan is switched by a temperature switch on the receiver dryer, and influenced by the circuitry in the automatic climate control system, if your model is equipped.
I'd be looking at the coolant thermostat, fan clutch, coolant level, blockage in the cooling system, etc., rather than the auxilliary fan.

[ScottinSoCal]

Originally Posted by donbryce

Others will correct me if I'm wrong, but I believe the engine coolant and ambient air temperature is responsible for triggering the mechanical fan clutch via the flow of air through the radiator. The auxilliary fan, electrical and mounted in front of the radiator on the condenser, is for additional airflow to assist the A/C refrigerant cooling in the condenser. The auxilliary fan is switched by a temperature switch on the receiver dryer, and influenced by the circuitry in the automatic climate control system, if your model is equipped.
I'd be looking at the coolant thermostat, fan clutch, coolant level, blockage in the cooling system, etc., rather than the auxilliary fan.

You're not wrong - it does all those things, but it also should kick on without the AC operating if the engine temperature climbs above 105C. The sensor for this is located on the front of the engine block and it usually has a red cap on a brass module. There's just a single wire connecting to it. You can quickly test function of the fan by grounding out the wire. The aux fan should kick on and stay on as long as it's grounded.

300sd: The temperature displayed on your temp gauge may or may not be the temp that sensor is showing. The sensor for the temp gauge is located at the back of the engine block on the passenger side. The sensor for the aux fan is located at the front of the engine block. There can be a significant difference (up to 20F) between the two locations.

[300sdToronto]

Thanks for the posts - relatively similar arrangement to my 300sd from the sound of it. I'll go poking around and test the fan this weekend.

The car just passed its Ontario safety with no problems. Yaay.....

Now I can get plates