911tracker85

I have an 84 928S US.

I have determined the sensor in the radiator is not working. if I jumper across the contacts the fan runs. I let the car sit and idle until the temp guage almost reached the red and fan never ran. AC currently not working, so that is another 'adventure' and I am reading a lot of postings and troubleshooting guides for that.

rather than replace this sensor in the radiator and have to deal with replacing coolant, wanting to just put a manual switch insde the car.

I was trying to decipher the wiring diagram but .... and I tried a search but so far did not come up with a thread that enlights me on this idea.

anyone know how much current runs through that sensor? or do those wires go to some relay that runs the fan? and if I do install a manual switch, will that have some unexpected effect on the AC?

thanks in advance for any advice.

911tracker85

after digging more in the WSM and wiring diagrams, appears the temp sensor does carry the entire voltage to the fan.

so off the find a 20amp relay, and assoc wire/manual switch.

but I will still appreciate any thoughts about what I am about to do. in particluar any effect this would have on AC. when I was testing, I see there are two leads connecting to the temp sensor, but so far not sure what the other lead does.

WallyP

It is possible to change the temp switch without losing more than a few ounces of coolant. The temp switch doesn't forget to turn the fan off or on...

The early cars have a refrigerant temp switch that is supposed to turn the fan on, but it doesn't work very well. Adding a relay that runs the fan in parallel with the compressor clutch works better.

michael j wright

I installed a Hayden fan controller, works great! also runs after shut down until temp drops.

911tracker85

Michael.

thanks for this info. I knew there had to be a better way than trying to replace that OEM sensor.

looking at the hayden contollers now.

if not for this forum and all the knowledge/experiences shared, I would never have gotten my 928. could not afford to have one without doing a lot of work myself. I am OK on my 911 but I knew 928s were a lot more complex. even the early cars as I decided to buy.

Mrmerlin

I would replace the sensor in the bottom of the radiator first and try it, adding on extra circuits isnt the best thing.
Why the big worry about coolant loss??
Remove the coolant bottle cap and let out any pressure, replace the cap then ,
Get a pan and the proper sized socket unscrew the sensor and refit the new one?
Refill the bottle this will take all of 10 mins MAX
B4 you replace the switch test it, remove the wires and see if the switch closes when the rad is at operating temp, if not then follow above method

DR

^^ What Stan said ^^^.

On the pre-S4 928s I use a socket with a long extension thru the grille and can change that sensor quickly without a lot of coolant loss.

911tracker85

mrmerlin.

I have already determined the sensor in the radiator is not working as described in my first post.

maybe I will try to replace the OEM sensor. did not know how much coolant I would loose trying to replace. one thing I like about reading the hayden controllers is they are adjustable, so can lower the setting for the fan to kick on. since my elec fan has not been working, don't know what to expect of 'normal operation' from it with OEM sensor. but with the local temps here in the Cinci area running around 90, want to try to optimize my cooling.

I still have the OEM viscous fan that seems to work OK, but when sitting and idling for a bit in 90 temps, the car starts getting hot. does take a while to really get up near the red. and once I get the AC working it will just add to the cooling load.

I know I have good cooling as when driving it does not overheat.

Ironically I had an issue this past winter where the temp would go up a little when I turned on my heater. stumbled across a thread someone else experienced this. apparently due to a air pocket in the system. I need to go back and read that thread and try the proceedure when I do this item.

thanks again for all the input/suggestions.

Lizard928

Another vote for replacing the sensor in situ.

It is very quick and easy with very little loss when done properly.

DR

FYI, this is not a definitive test of that sensor, if your thermostat is stuck or the waterpump impellor has failed or is failing you would still run hot without making the lower corner of the radiator hot enough to activate the fan switch.

Mrmerlin

OK so fix the sensor, also remove the thermostat and see if the rubber seal behind it is in good condition.
You can remove the sensor and let it drain into a pan then remove the thermostat and replace the rear seal and then add a new O ring to seal the thermostat ( you should replace the thermostat as well)
My 84 Euro had a front fan that wasnt working, i replaced all of the parts previously mentioned and when the car got to about 3/4 on the gauge the front fan would come on and keep things cool. The system works good if all of the parts are in good working condition.
Adding band aids to your car to cure broken parts is kind of like hacking, please take the time to fix things properly and you will be rewarded with a well engineered car, that works without you having to worry about systems operation

dimmer

I would suggest checking the fan controller which is located to the right of the passenger seat under the carpeted cover. I had similar problems and it turned out to be corrosion on some of the pins to the controller (the wires to the sensor go to here). After cleaning the connector, my fans worked perfect.

James Bailey

Early cars pre S-4 do not have a fan control unit....

911tracker85

I do appreciate all the advice. but some is a little confusing.

I do not have an over heating problem in motion. just when prolonged idling how that it is hot.

during cold/cool weather it does not get very hot even when idling a bit. so from all the other threads I have read about the cooling sysytem on rennlist, my only conclusion is the fan not coming on. I don't have a good pyrometer but when I let it sit and idle to get very hot, the area of the radiator where the sensor is felt very hot also, did not even have to touch to feel the heat.

I do not believe I have a thermotat or WP issue, in fact all were replace by the PO about a year ago along with the timing belt.

based on the prevailing wisdom, and wanting to keep my car mainly stock, I'll order a sensor and replace. I'll post a final note when done about the results.

thanks again.