Engine Coolant Temperature (ECT) Sensor readings

[Desert Patina]

Hello,

Remember, my car is LA3 powered, and the fan is switched with the LA3 hi and low outputs.

I've had the car run hot quite a bit, being in Phoenix, and the fan never switches on. I ran the KOEO test, and saw the blades spin briefly so I think my circuits and ECU are working right.

I tested the resistance at the ECT, and without running for several days I got 7 (k?) ohms almost exactly. Granted it was a 100 degrees in my garage at the time.

Then after running errands around town in stoplight traffic, it started pinging which to me is a good sign of starting to overheat. As soon as we parked it in the garage again it read 2.93 (k?) ohms.

The KOEO test didn't throw an ECT code. Looks like the sensor is out of spec, based on Rothfam's archived sensor testing ... http://www.rothfam.com/svo/reference/sensors.pdf

What do y'all think?

Thanks,

[spt87a]

While I don't have any info to help you - I wanted to thank you for posting that sensors.pdf link. Pretty good info in there.

FWIW - from what I see on a stock SVO the ECT has nothing to do with the fan. There is a separate cooling fan temp sensor switch on the back of the intake manifold. Maybe with an LA3 though the ECT is used.

[Desert Patina]

I've long since removed the problematic fan relay below the steering wheel, and deleted the coolant sensor (single probe, yellow-red wire).

I re-wired the engine harness with an 87 2.3 engine harness, and kept the HI and LO fan circuits from the LA3, and plugged them through a series of relays to turn on a two speed electric fan from a Volvo 740 (the easiest version of the Mark VII, Taurus two speed fans that Jeep guys love).

Not as hard as it sounds, the 87 2.3 harness is very close to the 85, and where it is mostly different I can simply use the 87 fuel rail / etc...

Again, that circuit looks like it is working. The LA3 will fire the HI and LO circuits during KOEO to make sure the relays are working, and I see the fan spinning.

But I've had a few coolant hoses blow recently, and engine pinging during moderate driving, which makes me think the engine is getting hotter than I want. I don't see the fan turning on during these slow stoplight driving conditions.

I think I'll just get the new pigtail style ECT from Motorcraft. I'm 95% sure the current one is out of spec. As I read the charts, the nominal resistance means my garage is at ~160F, and the coolant doesn't get above ~190F. Given it is Phoenix 100F+ weather, that is hard to believe in this kind of driving without the fan turning on.

Anyone know if the new pigtail style ECT's are more reliable? To me just the. new pigtail is worth it, given how fast plastic deteriorates out here.

[Desert Patina]

With a new ECT, one that is reading pretty good from the tests I've run, the fan still doesn't turn on.

But here's the deal, it seems the ECT naturally doesn't get fluid hotter than about 180 in any case. At least that is what the ECT, and a laser infra-red thermometer pointed at the exposed threads reads.

While I had the laser thermometer, I tested various parts of the coolant system, from the radiator hoses to the lower intake, the turbo line and the oil filter cooler line.

Some places read as high as 220, others mostly around 180-190 (but those places would heat up to about 205 before I manually turned on the fan by grounding the input lines). Then it went pretty quickly back down to around 150 and stayed there until the fan turned off and it went back to around 205.

So my question is, how well does the cooling system put hot water across the ECT normally? If it gets blocked, would that account for the readings?

I should also add that my dash gauge doesn't work, I'll need to replace that sensor as well (at least i hope it is the sensor and not the dash).