I am about to delve into why my fans are not stepping up to high speed.

I have the factory mod to turn on fans low when key is turned on, and the fans do work on low.

And, when the engine is hot, the fans stay on (low) when the engine is turned off. The fans turn off after a minute or two.

So I noticed the high speed never gets engaged - even while sitting in stand-still traffic at 100 degrees F.

I check with my Innova Equus 3130 scan tool and the live data shows ECT is 210 F (yikes). It's a 192 F thermostat and when enough air goes across the radiator, it cools down to 192 - 194. Replaced the thermostat this past winter.

Is it that sensor on the bottom of the radiator that tells the fans to go to high? Also - would that be the same signal that tells the fans to continue running after the engine is off?

I can short the wires near the trinary switch to make the fans go to high speed.

It appears the relay (DBC 11617 right? ) looks unique and probably cant be switched out with another, right?

So in that case, what's a good method to test? I have the wiring diagram pdf, but haven't looked for the pin assignments on that relay.

Also - I have a copy of the various ohm resistance readings for the sensors on the thermostat housing - someone on the XJS forum made that (possibly has nothing to do with fan operation?) .

But I don't know what the readings should be from the sensor on the radiator.

Anyway - I have seen lots of scenarios on the forum, but I haven't seen this - where the fans work fine, just don't go on high.

 

What are you asking? You say you have the pdf but have not looked for pins on the relay. Do you need explanation, or are you looking for someone far away to diagnose your problem? If you need step by step, then by all means ask and you will get help. The questions you should be asking YOURSELF are:
1) Is the power supply to the high speed circuit OK? (fuses)
2) Does the high speed relay have voltage to the coil (sensors )
3) Does it pull in (relay coil/ connector)
4) If it pulls in, dothe contacts supply power? (bad contacts).

On an X-300, the fans are pretty easy to troubleshoot, assuming you have the schematic, a 12 volt test light (easier to use than a meter), and the know how. As I said, if you need help for a step by step, just ask.

 

Is the temp gauge on normal ?

 

Sorry - could not get to it this weekend -
Instrument gauge reads normal.

My question is really: Is it that sensor on the bottom of the radiator that controls / triggers the high speed operation.

If so, at what temperature will the high speed kick on?

My observations on those hot days only showed it going up to 210 and maybe the high speed only kicks on at 212 ?

I was getting worried about reaching the 212 point, but now I realize 212 is not so bad with the coolant - it does not "boil" at 212 like straight water.

 

Hi speed is engaged by high head pressure acting on the trinary switch on the a/c hi pressure line, OR by the temp switch on the lower left side of the radiator. I forget the exact on/off T's & P's but they can be found in the books -Electrical guide, I think, but it may be the service manual.

 

Yes - I see on the electrical diagram now: 100 degrees C, 212 F.

It is drawn right next to the refrigerant switches so I didn't connect it mentally to the lower left radiator location.

Radiator Thermostatic Switch: Not the sensor itself, but a switch that gets its input from the sensor, right?

 

A service bulletin ordered a modification to eliminate the refrigerant switch and allow the fans to run at low speed all of the time. You can tell if your car has this be looking near the firewall for a connector with a jumper plug installed near the high pressure AC line.

The mod was to be sure the fans were never commanded to start at high speed which could blow the fuse.