divil

Lately, my radiator fan will only run for about 5 - 7 seconds at a time, then stop for around 3 seconds, then start again. It still comes on at around the right temperature and stops completely when the temp is back down - it just won't run for long periods uninterrupted like it used to. Anyone run into this before? I haven't touched the cooling system lately.

Mike Murphy

No idea. Other than perhaps the temp sensor is failing and reading are swinging wildly up and down in large blocks.

Tedro951

Does this happen when A/C is off?

gpr8er

have you checked the fan resistors? They are behind the glove box under the dash, the wiring gets fried from the amp draw of the fans.

divil

Yes - it's always off because it's not working

Not lately. Mine are actually in a different location (in the battery tray behind the battery). The wiring has been in rough shape for a while, but I don't see how it would cause this frequent on/off behaviour. I'll take a look though.

gpr8er

Not lately. Mine are actually in a different location (in the battery tray behind the battery). The wiring has been in rough shape for a while, but I don't see how it would cause this frequent on/off behaviour. I'll take a look though.[/QUOTE]
Resistance caused by deteriorating wire will cause problems, heat and current fluctuation

GPA951s

So is the Fan Running just on high? it is one of two things.. The 3 pole switch in the Radiator, or as stated above the fans... I Cut all my Resistor wires out of the race car and deleted the Resistor blocks.. Now my car does the same thing... only runs on "High" but it only runs after if come offf track...

divil

I'm actually not sure which speed it's running at. I had assumed it was low speed but now that you mention it it was kind of loud. Maybe it is running on high. But it's definitely happening at the temperatures that would normally result in low speed. I wonder if running on high speed could explain why it only runs for a few seconds - because it's actually cooling things down that fast?

GPA951s

Yes that is exactly what is going on... The fan comes on high... Cools the RAD so fast it shuts off, When it shuts off because there is only one speed working. Under "Normal" conditions, the temperature would never get that high, The fans would come on normally on low and run there cycle and shut off.... With the low speed in-operable the fans come on high for a short time and then off... Residual heat transfers and they come on again... and so on.... Till it actually IS cool... For my track car I don,t care but I can see were this would be kinda annoying on the street..

Humboldtgrin

It’s a bit of a process but I had replaced all four wires from the resistor block to the power distribution block on my 89 NA. Ok it was a **** show, but it works great now.

MAGK944

What GPA951s says makes sense, however before you get any deeper into fixing stuff first check that your fans are actually only operating on high speed. You can do this quite easily by disconnecting one terminal from each of the low speed resistors and seeing if your fans are still coming on as before. If they are then yes it’s your resistors (or more likely the wiring to them) that’s the problem.

PaulD_944S2

Forget all this. Short fan on-time is due to a bad radiator fan resistor.

Check and replace one or both fan resistors located under the rain cover next to the battery.
They should be about 7.5 ohms if they are good, they will have open resistance if they are bad.