94 SL, radiator fan kicks in at 220degrees
 

We've been trying to figure out a slow radiator-fluid leak for a couple months. Shop pressure test indicated radiator (original unit) was leaking and it was replaced. But the slow leak persisted.

Today we noticed that around the cap to the fluid reservoir there were signs of leakage. Got a replacement, and idled the car a while. A temperature reading was taken from under the dash that indicated the system was getting to 220 degrees F before the fan would turn on. At that point, the fan would work great and everything would cool down. But just prior, the bubbling of the radiator fluid (of a green pursuasion, in case anyone asks) was indeed leaking out the reservoir cap a bit. The shop mechanic said most other cars he has worked on have the fan kick in a good 10 or 20 degrees lower than this figure.

I was told by the dealer, when I bought the car used maybe five years ago, that the radiator was designed to allow the engine to get a little hotter than some other models before coming on. How hot is normal for this model?

Any particular mechanisms to test for proper operation of the thermostat? (I'm not even clear where it is.) One earlier post was talking about a fuse, another about checking the power to the fan, but the fan works fine, once it turns on. Is there a way the operation of the thermostat could degrade or change to a higher setting? It makes sense that if the cooling fan started at a less high temperature there would be less pressure and less inclination for the fluid to leak at the reservoir cap (or anywhere else).

Thank you! Oh, car is at 150,000 miles and just had a tuneup.

The ECTS tells the PCM when to turn on the fan. This (ECTS) is a known weak link on this car. Has yours ever been replaced? The new ones are made of brass and are more durable than the old resin type. Also check the connection for corrosion as it is a resistance type of signal. How do you know what the temperature is? The fan normally comes on at 3/4 scale.

Hoseppi is correct in suggesting the ECTS needs to be replaced. Also, get a new connector for the wires leading to it, and replace it also because corrosion builds up over time, and makes for a poor connection. Get OEM parts (should be about $40usd), and please, work on a COLD engine - no need for burned fingers.

"ECTS needs to be replaced. Also, get a new connector"

Get it from the dealer not from CheckerNapaZone

The 94 engine used two sensors adjacent to each other at the drivers side end of the engine. One is for the computor to tell what engine temperature is, the other controls the fan. They were incorrect from the factory and it is all together possible that they have been that way ever since. If a dealer is still available the parts counter man should know about the service bulletin on these parts and will have correct parts possibly. Otherwise you are going to have to take your chances with after market parts. This was supposedly corrected some 10 years ago or so.
Also, a potential problem with the water resovoir exists. It is plastic and pressurised. They can and do fail as a function of time causing leakage at the cap. I have not had that problem but have seen failed water tanks in wrecking yards.

Actually the two wire temp device is the ECTS and its resistance tells the PCM what the temp of the coolant is...The fan is controlled based on the resistance of this sensor. Once a sufficiently high temp is reached, the PCM requests closure of the AUX fan relay which then provides current to drive the aux cooling fan

The single wire temp device drives the dash temp gauge