Overheat due to airflow problem
10-30-2009, 06:57 PM
#1
6th Gear
Thread Starter
Join Date: Oct 2009
Location: Las Vegas, NV
Posts: 6
Likes: 0
Received 0 Likes
on
0 Posts
Overheat due to airflow problem
I own an 1989 928 S4 with 65k miles and after a nice drive and return home... a quick trip out at night had me running temps in the red. After getting her back to the garage and doing some preliminary checking I replaced the thermostat once it was cool. Habit at sudden overheats on any car. Though I did replace the Wahler thermo with a Stant 195 and it has a vent hole which i possitioned on top the whaler did not... supposed to keep bubbles out but with the closed and open circulation of the 928 engine not sure. Also I run a waterless coolant due to the extreme temps in Vegas... it performs much better than even the best water based... Evans NPG+ and also creates a lower pressure system with less wear and tear on the cooling overall and a boiling point of 375 so not hotspots on the engine due to steam.
Upon further inspection i discovered the true cause to the overheat and it is electrical in nature. One of the temp sensors, sender unit or control unit for the louvres and fans is out leaving the louvres shut and the fans not operating. So no airflow = no cooling. Some of the checking will require an ohm meter which i will have to get (my old dead) but this is what i eliminated so far. I do not think it is the sender unit or the fans as when i push the AC button the fans come on. The temp sensor mounted on the right of the recirculation manifold works as i tested by connecting and reconnecting dash guage worked and did't work. The temp sensor to the left as you face the engine i still have to test (ohm meter) as do i need to test the cooling water sensor, the manifold airflow sensor and finally the control unit itself inside the car to the right of where the passengers foot would rest also an ohm meter job. There is also the auto trans temp switch and the ac pressure switch in the circuit but my guess is failure on these would not lead to loss of fan and louvres control. In fact the manual says that louvre system failure is supposed to result in them locked at 100% open not 0% which is the case with me.
My question is this, based on what I have eliminated so far and with the collective knowledge of this forum, is there a "most common" cause to this fault?
Hoping it is the cooling water sensor, though most difficult to reach it is also tied into many of the functions of fan and louvre.
Thanks
Upon further inspection i discovered the true cause to the overheat and it is electrical in nature. One of the temp sensors, sender unit or control unit for the louvres and fans is out leaving the louvres shut and the fans not operating. So no airflow = no cooling. Some of the checking will require an ohm meter which i will have to get (my old dead) but this is what i eliminated so far. I do not think it is the sender unit or the fans as when i push the AC button the fans come on. The temp sensor mounted on the right of the recirculation manifold works as i tested by connecting and reconnecting dash guage worked and did't work. The temp sensor to the left as you face the engine i still have to test (ohm meter) as do i need to test the cooling water sensor, the manifold airflow sensor and finally the control unit itself inside the car to the right of where the passengers foot would rest also an ohm meter job. There is also the auto trans temp switch and the ac pressure switch in the circuit but my guess is failure on these would not lead to loss of fan and louvres control. In fact the manual says that louvre system failure is supposed to result in them locked at 100% open not 0% which is the case with me.
My question is this, based on what I have eliminated so far and with the collective knowledge of this forum, is there a "most common" cause to this fault?
Hoping it is the cooling water sensor, though most difficult to reach it is also tied into many of the functions of fan and louvre.
Thanks
10-31-2009, 05:55 PM
#3
6th Gear
Thread Starter
Join Date: Oct 2009
Location: Las Vegas, NV
Posts: 6
Likes: 0
Received 0 Likes
on
0 Posts
fuses and wires all in order. I cannot test the control unit as my linconshire cd rom manual that is to be for 1981-1994 shows only a test proceedure for a car that is not a 1989 a unit with two multi prong plugs... where the control unit is supposed to be on my car there are two boxes that both look like control units each with a 20+pin connector. The Flap positioning motor works as the flaps move just not when they are supposed to... fans on with ac and when i shut down the car the flaps then open in the front. Any other suggestions anyone?
10-31-2009, 06:03 PM
#4
Team Owner
open the front flaps and then pull the fuse for the flaps.
There is a turn wheel under the rubber boot for the flap motor
There is a turn wheel under the rubber boot for the flap motor
10-31-2009, 07:12 PM
#5
6th Gear
Thread Starter
Join Date: Oct 2009
Location: Las Vegas, NV
Posts: 6
Likes: 0
Received 0 Likes
on
0 Posts
I removed the fuse with the car thus locking the flaps open. However my fans do not kick on either so likely as long as I am running at highway speed i will be okay but not at a stop. The fans do operate with the AC on so there is some type of relay or temperature switch that is not working properly to kick the fans on. In the Manual it indicates that the
Cooling water switch affects flap position and fan voltage as does the automatic transmission temperature switch, ac pressure switch and intake temperature... all of them failing at once could not be the issue but I wonder if just one of them failing would be enough to cause the fans and flaps to stop operating properly.
Cooling water switch affects flap position and fan voltage as does the automatic transmission temperature switch, ac pressure switch and intake temperature... all of them failing at once could not be the issue but I wonder if just one of them failing would be enough to cause the fans and flaps to stop operating properly.