I was wondering if any one may know why my digital display (89)
is off by aprox 25 degrees compared to my scanners readings?
I checked the resistance on the guage sensor and it is on spec.
Also my main fan is comming on around 200(per the digital dash).
This is all with my new 383 wher the old L98 was right on.
Any input is appreciated.

 

My thinking is that the temps are being read from two different places.

Temps read from a sensor mounted in one of the cylinder heads will be higher that the reading given from a sensor mounted in the intake manifold near the thermostat.

Jake

 

As above - gage is from the sender in the right head (between 6 and 8) and your scan is reading the Engine Coolant Temp Sensor below the throttle body. Check the accuracy of the digital by disconnecting the harness - it should read Lo. Ground the harness and it should read 300 or max. New senders often get the two readings closer (I've got about a 3 degree variance). You can do the same basic test for the ECT (it'll probably set a code). Jumper the harness terminals together and your scan should indicate 300; disconnected, about -38; or buy another ECT (about $9) and simply plug it in with the engine cold. Your scan should show a temp that's close to ambient or about the same as the one installed on the engine. Also the ECT temp and MAT should be darn close on a cold engine.

Assuming you've left your programming alone, main fan relay is grounded at 226 unless the a/c is on. With it on, signal is from the pressure switch on the high side line. It opens at about 220 psi signalling the ECM to ground the main relay. Recloses between 170 and 190 psi and the fan should turn off. Disconnecting it should turn on the fan. Scan won't pick it up - you need a manifold gage set to check it out.

My most recent experience (a little over a year ago) with the ECT circuit was that it was indicating 230 or greater on a cold engine. The fan was running regardless of temp and there was no fast idle. ECT and wiring were fine - it was the ECM. Strangely enough, others experienced similar at the same time.

 

Excuse, me. I'm not trying to jack your thread, but I was curious as to what scanner you are using. I just purchased an Actron today, and it won't connect to my PCM.

Thanks, and again, I'm sorry for the jack.