Dirty, Cheap way to Knock a few Degrees Off

[Strife]

The following is a report of something I recently did; use this information at your own risk!

I still get very nervous about temperature on my car. It lives at 84C, but if I do high-speed travel and get stuck in traffic it can go to 95-100 (this is without the air on) and go down very, very slowly. After examining the wiring diagrams, I put small 2" jumper with 14 gauge wire stuffed in the wiring connectors of the high pressure switch. This is mounted on the receiver/drier at the front of the car (an 86 560SL, caution, earlier models are different). This enables the electric fan to be operational at all times that the ignition is on. This is the "low speed" of the fan, in which the current goes through the sandbox resistor to the left of the receiver/drier. This has not knocked down the "normal" temp of the radiator,which is to be expected, but did knock the peak down about 3 degrees C and it recovers faster. I will remove the jumper in the fall. I'm especially nervous about temperature because I know for a fact that 1 degree of water temperature = >>1 degree in the engine itself. I have the timing resistor mod and I don't want to tempt knocking.

Note that if you have functional air conditioning and use it, the fan should be engaged anyway when the air is on (if it isn't, something is wrong). The fan blows through the condenser and then through the radiator, so you wouldn't think it would make a noticeable difference, but it did.

If you are interested in doing this, note the following: it is VERY important that you do the HIGH pressure switch, NOT the low pressure switch. The low pressure switch is there to protect the compressor from operating in a no/low refrigerant condition (in which it probably has little or no oil), which will destroy it and possibly take other parts out with it also (belts, pulleys, crankshaft pulley bolts, etc). On _this_ car, the high pressure switch merely engages the low-speed mode of the fan via the relay.

Also note that theoretically this will cause the fan to wear out faster, and also the relay and the "pre-resistor"; but because it isn't cycling and if the air is on you are using the fan at low speed anyway. It also does make a little noise.

You should not even THINK about doing this until you make sure that you are not masking a problem. Nice, clean 50/50 radiator fluid? Cap good? Bottle good? Any leaks? Thermostat good? System burped? I noticed something interesting; I had a leak, and got no condensation in the overflow bottle after a heating/cooldown cycle; after identifying and fixing the leaks, I did.

I also cleaned the radiator; I blew it out as best i could with a garden hose. This may or may not have helped, but some bug parts and dirt did wind up under my car. It would have been far more effective to remove the radiator and condenser, but I didn't do it because the radiator wasn't really that bad. This made no measurable effect on temperature in my case. But on a high performance (= marginal) system like this every little thing helps.