I noticed that my radiator fan does not always turn on when it should. My assumption is that the fan switch should activate the radiator fan at around 205F. However, it looks like this isn't always the case. Sometimes the radiator fan runs, but sometimes it does not. When I pulled the power plug to the radiator fan at high temperatures it reads ~14.3v on the multimeter, so it looks like the fan switch attached to the radiator is operating correctly. However, the fan does not always turn on when I plug it back in.

Is it possible for a radiator fan motor to show early signs of failure and operate intermittently? If the radiator fan motor is stuck, would it not blow a fuse somewhere?

 

How do you know the ECT is 205F when your fan doesn't turn on?

 

I am taking the temperature reading from the OBDII port to confirm the coolant temperature. Hopefully I am correct in assuming the temp reading I am getting there is the same(or similar) as that of the reading at the fan switch.

 

That is your problem. The ECT switch is in the back of the engine, where the fan switch is on the radiator. There can be a fairly significant difference between the two, always resulting in the ECT being higher.

For reference I have the modifry upgrade on my AP1 along with a 175 deg fan switch and sometimes my fan kicks on when I am still @ 3 bars (less than 190), but most of the time it is when it flips to 4 bars (over 190). This is especially the case when the car is moving and cool air is hitting the radiator

 

Ah, that totally makes sense, bgoetz. What range of temperature readings should I see at the ECT switch?

 

I think it could vary greatly. before I installed the 175 fan switch, it would typically come on @ 205, but sometimes not for a bit after (bar 5 on the modifry goes from 205-220, I never had a 6th bar illuminate). I think the OEM is 190, so there was always at least a 15 degree difference. I never noticed my fan kicking on while moving with the OEM switch.

 

Cool, thanks for the insight!

 

I just wanted to add a quick followup to this thread. I finally determined that the radiator fan motor is on its last leg. It only works sometimes, and it was just unfortunate (for me) that every time I tested the cooling system while parked, it would turn on. I finally pulled the fan from the car and tested directly with a 12 source. The fan only spun up on its own about 60% of the time. A gentle whack to the motor housing with a rubber mallet got it going the other 40% of the time. Ten years is not a bad run for the old motor, especially in Houston traffic and heat. A new radiator fan motor has been ordered!

On a broader note, cooling gremlins are certainly not fun to chase down, but It's not terribly surprising considering the age of my S2000. In the last 12 months, I have replaced parts to address the following:

• cracked coolant reservoir cap which prevented the reservoir from holding pressure - replaced cap with OEM part
• broken OEM radiator cap (inner parts and spring broke off and fell into radiator upper tank) - replaced cap with OEM cap
• leaky replacement OEM radiator cap (bad luck?) which allowed air to enter the cooling system - replaced cap with Autozone part
• pinhole leak at radiator fill neck which allowed coolant to dribble out at high pressures, and air to enter the system - replaced radiator with Mishimoto unit, and also replaced thermostat while system was drained
• failing radiator fan which allowed temperatures to climb significantly over time, when idling in traffic - OEM radiator fan motor ordered

 

glad you got all these sorted david are you ready for the next 100k?

 

Thanks!--I hope I am ready now! I've been slowly going through all the different maintenance activities in preparation for the big 100k mark