The other week I noticed that Project Miata's radiator fan was cycling on and off erratically. Opened the hood. I put a finger on the fan relay. It was clicking over indecisively as if possessed -- so the fan was doing what it was being told, but it was being told wrong.
There isn't much to the cooling circuit. The ECU commands the fan relay based on advice from a coolant thermosensor.
Of those three components, the relay is the most likely to crap out. I theorized that the sporadic clicking is the relay in its death throes, and that soon it wouldn't function at all. If/when that happens then the fan won't run and engine go boom.
Short of time and feeling frisky, I ordered a new relay and popped it into the fuse box this morning. At five bucks, the stakes were low. Went for a quick spin and... no difference. Time to find my multimeter.
Jason Kavanagh, Engineering Editor @ 178,xxx miles.
adamb1 says:
01:05 PM, 08/ 2/10
In college, I had a Hyundai Excel GLS with a quirky fan. Being broke, I bought some wire and a toggle switch at Autozone, created a circuit, and converted it to a manually activated fan. Worked for the next 30k miles until I sold it.
vvk says:
01:40 PM, 08/ 2/10
I don't know about Miata but there is usually more than one radiator fan relay involved.
felonious says:
03:11 PM, 08/ 2/10
I hate it when the cheap, easy fix doesn't do it. :(
dashpot says:
04:29 AM, 08/ 3/10
I've had the same condition with the same car and it wasn't a bad relay either. Only a bad connection at the switch terminal the relay plugs into. Try slighly bending the small prongs in the relay socket, worked for me.
chochmastergen says:
07:21 AM, 08/ 3/10
The temp sensors are usually pretty fragile in old Japanese cars like that. Might have gone belly up, I'd look for the relevant sensors and check their connections.
donkeyponkey says:
03:01 PM, 10/27/10
Check fuse. Then, with key in run, engine off, air conditioner on, both fans should be running. Test for voltage-ground, at engine fans, (electrical load) working way back to relay, etc, (source.)
I would recommend that if the problem takes more than five minutes to figure out. Just grab some 12 gauge wire and a pair of wire cutters, some tape, or solder, and heat shrink. I am poor so I just grab any kind of wire handy, and strip it with my teeth. Then just make a circuit out of anything that is hot in the run position.