(posted in scan and tune as well)
Crazy..My dash gauge will show the temps going all the way up to 240* or so within 2 min of me starting the car from a cold start. Then it starts fluctuating up and down and within a minute it sometimes goes back down to 150*. Meanwhile my DFI temp guage (laptop) is pretty steady between 160 and 180 (back and forth) which would make sense because that's how I have the fans set. While my dash guage is showing 240*, I open the hood and feel the radiator, It's barely even warm and no overflow in the tank. Are these two gauges running off different sensors? Where is the sensor located for the dash guage? Where does the DFI pull it's data from??? Thanks!

 

Don't know what year-on the 87 the coolant temp sensor is on passenger side just below the throttle position sensor-or below the MAF sensor-and the coolant temperature sender is back by and above the starter.I'd be checking connections here.Not sure which one gets the info. to the digital guage.

Looked at your profile-89, sucker sounds awesome-465 rwhp

 

temp for dash is located on driver side - single connection between #1 & #3. The ecm gets info from a seperate sender. The ECM sender originally is in the front of the intake, not sure where yours might have been moved to. I moved mine to where the fan sender was, between #6 & #8, since I turn the fans on manually.

Jim

I had a similar problem last year - but my dash temp would go to -0-. I think mine is do to a grounding issue with the wire going to sender. I know Cork had a similar issue and it was bad wireing from sender to wiring harness (the wire is only about 12 inches long with a connection to harness, this wire gets constant heat from exhaust/headers).

 

Keep reading. Sooner or later someone will get it right. Your digital dash gauge sensor is in the right side cylinder head, between the #6 and #8 spark plugs. Your aux fan switch is on the left side. The sensor in the front of your intake manifold is the ECT sensor for the ECM. It is what your DFI is reading from. Based on what you have written, the first thing you need to do is fill your cooling system with coolant. THEN compare the readings. They will not be the same, but the dash gauge should parallel the DFI numbers. If the problem persists, check the wiring from the gauge sensor.

RACE ON!!!

 

Thanks guys. The ECT driven temp stays fairly constant. At some points, the dash guage will mirror it exactly then all of a sudden, it'll take off and head up quickly while the DFI sensor stays constant. I could happpen anywhere include highway cruise. Looks like I need to look at that wiring for the sensor on the head.

 

I know that GM switched the locations of the senders/sensors over the years, so it's important to specify the year of the car when trying to ID the location of the sender/sensor.

I know for a fact the sender for the dash gauge on the 1986 is in the passenger side head because I removed and plugged the hole on the driver's side head (Aus fan) and my dash gauge continued to work fine, that is until I broke the digital dash. If the dash was getting it's info from the driver's side head my dash gauge would not have worked any longer.

Also, the coolant temps will vary depending on where the sender/sensor is located. As an example: would it be warmer at the South Pole? Well, not a very good example come to think of it because this involves the angle of the sun's rays not necessarily the distance from the sun, but I think you'll get the point.

After I broke the dash in the area that displays the coolant temp and voltage, I installed AutoMeter gauges in the breadbox.

I removed the Cold Start Injector sensor from the front of the intake manifold (no longer using that injector) and installed the AutoMeter sender in that hole.

Yesterday I ran Diacom and the display on the AutoMeter gauge AND the coolant temp that Diacom displayed exactly matched.

Now, before I broke the digital dash and it was working, getting it's reading from the passenger side head, the dash gauge was always substantially HIGHER than what Diacom showed.

Hope this helps.

Jake

 

After you fill it up and burp it.RACE ON!!!

 

CFI-EFI, what's the best way to burp the system?

 

Never mind, the search function is alive and well!!

 

So, is this to say the beast is staying and running again?

I haven't been up to speed since you thought about selling it?

 

It's like golf. You hit one great shot and that alone will keep you playing. It's running good (knocking on wood) and the wife's calmed down. If someone gives me what I need, I'll sell it. If not, oh well!

 

So what was resolved with the manifold? Did you get a replacement from TPIS? Or was yours remachined to spec?

 

a new fuel rail solved the problem. Somebody somewhere while this manifold was off rounded the bottom of the rail. You can see grind marks on it.

 

I burped the system before I left work. Still experienced the same problem. If the ECT is showing normal temps, is the engine ok to run? At one point on the way home, the dash showed 165* and stayed that way for 10 minutes then all of a sudden, it was at almost 250 in a few seconds!!! Does this sound like a sensor issue, thermostat issue, or air? The car was fine before the manifold was off and the radiator out 2 weeks ago! Could my t-stat have gone bad? Would the ECM still read normal with a closed t-stat?? aaaarrrrghhhh

 

Different year, but on my engine the top part of the sensor in the right head that takes the connector from the wiring pair was effed up and wouldn't stay on. From multiple times of taking it off while changing plugs and other work. I had to replace the sensor in the block. Be prepared for a big dump of coolant unsless you drain the block.

I would trust the reading from the water pump sensor that feeds the computer and think you have wiring or connection problems with the sensor in the head.