Also I'm not sure it's running that different with the sensor plugged in, is that a confirmation that it's bad?
Also I'm not sure it's running that different with the sensor plugged in, is that a confirmation that it's bad?
Posts: 445
If you are not getting any fans, even with the AC turned on, then possible suspects are (1)cooling fan relay, (2)the fan fail relay (usually has two fused jumpers), or (3)the cooling fan thermal trip.
1. The cooling fan relay might be the most likely problem. You may have Dave's electronic version or just a regular mechanical relay. If you make a jumper with some wire and a a couple of male spade connectors you can remove the relay and install the jumper. This will bypass the cooling fan relay to see if it is the issue. If the jumper gets your fans working then it may be (A) bad relay, or (B) the circuit that pulls in the relay. A) It's fairly easy to bench test the relay. B) most likely suspect is a diode between the otterstat and the fan cooling relay that may have gone bad and is not letting the otterstat pull in the cooling relay.
2. A fused jumper can also be placed across the thermal trip (or just take a DC volt meter reading. ~12 volt reading would mean it is open and not resetting.
3. Inspect the fan fail relay socket. This should be jumpered with two inline fuses (or you may have Dave's electronic fan fail relay). Check the connection and the fuses. The single connector with two wires stuffed in it is prone to heat and may have failed. If you have Dave's relay, they're pretty robust and not known for failures, but you could remove it and put in a temporary fused jumper (with one fuse jumper you would check one fan at a time).
If you are getting cooling fans with the AC on then disregard all this and take another look at the otterstat to make sure it was installed correctly and the diode mentioned above. With the car hot, you could check continuity of the otterstat and verify it's contacts are closing.
Ron
Last edited by DMC-Ron; 09-08-2018 at 03:08 AM.
The fans do come on if I turn the a/c on or jump the otterstat wires. Or at least they did prior to changing the otterstat out last week. I called Mike @ MW about it and he said sometimes the fans take longer to come on in a stationary idle from a cold start - sometimes til it's between the 220 line and the red line. Has this been anyone else's experience? I'm not sure I've ever actually idle-checked mine like this before, usually they come on just below the 220 line but that's when I'm stopped after driving.
If the FV buzzes even when warm does that mean it's working correctly?
A lot of cars the fans turn on around the 1/4 mark and some cars don't turn on till the 220 mark. Don't know why that difference. But the fans should turn on after the thermostat opens and the engine heats up some more. What you can do is feel the coolant hose on the drivers side of the engine and note what your temp gauge reads. Then note where the gauge reads when the fans turn on. I would not think the gauge should go much more than 1/8 movement higher. Some vendors sell an otterstat that turns the fans on at a lower temp than the stock otterstat did.
The FV should always buzz but you still need to check the mixture with a dwell meter.
Dave M vin 03572
http://dm-eng.weebly.com/
Location: Northern NJ
Posts: 8,570
My VIN: 10757 1st place Concourse 1998
The point at which the fans come on varies because of the setting of the O switch and the accuracy of the temp gauge. Get an infra red thermometer and check the temp if you have concerns. Typically HC is high if the engine is not at operating temp (below 180). I don't think your high HC is due to the fans but getting the fans running right is so important to preventing overheating that you MUST get that fixed ASAP. Then you can concentrate on getting your HC lower.
David Teitelbaum
Location: San Francisco Bay Area, Calif.
Posts: 2,072
My VIN: 0934
Club(s): (NCDMC) (DCUK)
+1 also.
And along the lines of getting the cooling system sorted:
1. Are you positive the system is fully bled, including the radiator? I haven't checked the previous posts to see about this.
I recently assisted on a D suffering from a high-gauge-temp-before-fans-switch-on-during-long-idle problem. Like you, the owner knew to keep an eye on the gauge and was concerned about the fans not coming on soon enough during long idles.
A verified rad bleed - with no other intervention - solved that problem on that car.
March '81, 5-speed, black interior
I called the shop this morning to remind him to keep an eye on it if he idled it and he said he'd already retested it on Fri and it passed. He sent me the printout and it was back to where it should have been. He never did change the O2 sensor so idek what that was all about? Unless he happened to take it in fairly soon after I idle-checked it and it was warmer than it had been previously.
I'm going to pick it up tomorrow and I'll see how the temp behaves on the way home.