'78 overheating & electric fan issues...
08-16-2009, 12:05 PM
#1
Burning Brakes
Thread Starter
'78 overheating & electric fan issues...
I've found plenty of discussions asking about the electric fan, engine temp control, etc. Much seems dependent on the year in question. Some seems contradictory. None seems to help me fully understand what I'm seeing happen.
Here are my observations-
1) One the car is warm, my temperature gauge usually reads in the 3/4 range. Often high in that range.
2) When I put a load on/off the electrical system and the volt meter drops/rises, the temp gauge rises/falls as a direct result.
3) My temp warning light works. It came on at a drive-thru Friday, I pulled into a spot, shut the car off and coolant immediately began boiling out of the reservoir.
4) Electric fan fuse is fine.
5) The fan runs fine when given power directly. Problem is not the motor.
6) When bridging the relay, the fan runs. Problem is not the wiring to/from the relay.
7) When bridging the wires at the AC freeze sensor, the fan runs. Problem is not the relay.
______________________________________
The temperature sensor near the oil fill on top of the engine does not control the fan, right? This one sets off the dash warning light, doesn't it?
What sensor controls the dash temp gauge?
PET5 shows:
"Temperature Switch" 928.605.104.00 in illustration 103-00 (Cylinder Head) at pos. 33.
"Temperature Sensor" 928.606.201.01 in illustration 105-05 (Water Cooled) at pos.33.
"Temperature Time Switch" 928.605.101.00 in illustration 105-05 (Water Cooled) at pos.22A.
What sensor controls the electric fan? PET5 refers to the part at position 22A as the "Temperature Time Switch". This thing looks to be a real pain to get to. Is it the switch that turns on the electric fan? From other threads, I believe this is the one I should be testing.
Running the engine while checking all these things, the engine became fairly warm. The upper radiator hose was hot. The lower radiator hose was just plain cold, except near the engine. Does a functional thermostat remain fully closed before the engine is up to temperature?
What the hell, replacing the thermostat can never hurt, right. How about the location of that sensor/switch for the elec. fan? Any BTDT info out there?
Once again, thanks everyone.
Here are my observations-
1) One the car is warm, my temperature gauge usually reads in the 3/4 range. Often high in that range.
2) When I put a load on/off the electrical system and the volt meter drops/rises, the temp gauge rises/falls as a direct result.
3) My temp warning light works. It came on at a drive-thru Friday, I pulled into a spot, shut the car off and coolant immediately began boiling out of the reservoir.
4) Electric fan fuse is fine.
5) The fan runs fine when given power directly. Problem is not the motor.
6) When bridging the relay, the fan runs. Problem is not the wiring to/from the relay.
7) When bridging the wires at the AC freeze sensor, the fan runs. Problem is not the relay.
______________________________________
The temperature sensor near the oil fill on top of the engine does not control the fan, right? This one sets off the dash warning light, doesn't it?
What sensor controls the dash temp gauge?
PET5 shows:
"Temperature Switch" 928.605.104.00 in illustration 103-00 (Cylinder Head) at pos. 33.
"Temperature Sensor" 928.606.201.01 in illustration 105-05 (Water Cooled) at pos.33.
"Temperature Time Switch" 928.605.101.00 in illustration 105-05 (Water Cooled) at pos.22A.
What sensor controls the electric fan? PET5 refers to the part at position 22A as the "Temperature Time Switch". This thing looks to be a real pain to get to. Is it the switch that turns on the electric fan? From other threads, I believe this is the one I should be testing.
Running the engine while checking all these things, the engine became fairly warm. The upper radiator hose was hot. The lower radiator hose was just plain cold, except near the engine. Does a functional thermostat remain fully closed before the engine is up to temperature?
What the hell, replacing the thermostat can never hurt, right. How about the location of that sensor/switch for the elec. fan? Any BTDT info out there?
Once again, thanks everyone.
08-16-2009, 01:17 PM
#2
Burning Brakes
Join Date: May 2001
Location: Santa Cruz, California
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Sounds like something is basically wrong, thermostat, engine fan thermocouple, etc. It should maintain a good temp on just the engine fan, the electric fan is a/c or super hot. Cleaning all the ground points will help your gauge surge. Replace the relays. Clean fuse contacts, sensor connectors. Maybe put a tank of fuel in and drive the **** out of it for a couple hours...
08-16-2009, 07:01 PM
#5
Drifting
You're welcome. The needle fluctuation is "normal", BTW, under two circumstances. First, clean up the instrument panel in the pod - tighten connections, etc. Second, the temp gauge doesn't read steam, so if there is some air in the system it will fall and jump back up when the steam is passed.
I had overheating problems when I first got mine too, particularly in hot weather and bumper to bumper traffic, something we don't get to often here in Santa Barbara. So my mechanic didn't believe me for a while, suggesting that the electrical connections were causing it to misread, but I finally got him to idle it for a while and measure the temp, and it proved it. Temp sensor switch on the radiator.
I had overheating problems when I first got mine too, particularly in hot weather and bumper to bumper traffic, something we don't get to often here in Santa Barbara. So my mechanic didn't believe me for a while, suggesting that the electrical connections were causing it to misread, but I finally got him to idle it for a while and measure the temp, and it proved it. Temp sensor switch on the radiator.
