Question : Temperature Sensor Agreement - ECM vs. Dash?

[davida1_hiwaay_net]

Hey all, I am working on my 1988 Olds Ciera, with 2.8MPFI engine.

I've been working on a tune and noticed the ECM reads about 10°F cooler than the instrument panel gauge.

At speeds above 70 mph, the ECM reports about 215°, but the dash gauge goes into the red. I have a 180° thermostat and fan control temps of 195 on 190 off.

Under all other conditions (idle, stop & go, with or without A/C) the engine runs about 195 on the ECM but the dash gauge most always reads at 220 or higher.

The previous owner had just changed the sensor for the dash gauge, and it appears the instrument cluster its self came from a junkyard.

I remember reading a long time ago that the location of the gauge sensor (in rear head near exhaust port) is unwise because it causes a false high reading.

Should I move the temp gauge sensor to a water port in the LIM (near ECM sensor)?

Thanks in advance for any input. This is the first GenII aluminum head engine I have owned.

Sincerely,
David

[Jesuscookies]

My gauge dash will hold at between 205-210, which is 10-15 higher than it should be, unless I'm climbing the hill to my house. Then it goes up to about 235 That gauge is worthless.

[pocket-rocket]

I wouldn't say it's totally worthless, but I would say they are inaccurate. I like watching my temps rise well in advance before a dummy light would come on.

[davida1_hiwaay_net]

I wouldn't say it's totally worthless, but I would say they are inaccurate. I like watching my temps rise well in advance before a dummy light would come on.

Agreed!!!

I am accustomed to the Buick engins where the gauge and ECM sensors are next to each other and read same. I think for my own sanity, I will move the sensor to the port by the ECM sensor and see if they agree.

I think it is kind of cheezy to mount a gauge sender next to an exhaust port. Even if there is a water jacket in the head at that point, it is a guaranteed hot spot right above the exhaust port.

Thanks!
David

[pocket-rocket]

The ones in the LQ1 aren't next to each other either. The ECM one is in the coolant neck in the LIM right behind the t-stat and the gauge sender is in the end of the front head on the drivers side.

[robertisaar]

i think the better option.... would be to use the newer style sensor that has 3 wires coming out of it... that way your ECM and dash gets a reading from the exact same spot, without modifying the LIM/head.

[pocket-rocket]

i think the better option.... would be to use the newer style sensor that has 3 wires coming out of it... that way your ECM and dash gets a reading from the exact same spot, without modifying the LIM/head.

I like this idea and may adopt it when I start fixing the 92 up.

[davida1_hiwaay_net]

i think the better option.... would be to use the newer style sensor that has 3 wires coming out of it... that way your ECM and dash gets a reading from the exact same spot, without modifying the LIM/head.

You're right. I forgot about those. Have done that mod before!
David

[3100]

The temp gauge on mine confuses me. The lowest number on the gauge is 40 degrees, and it never drops below slightly higher than that even when I start it "cold" in the morning. it seems to operate normally above that, rises when sitting in traffic etc until the fans come on


any idea why it might never read below 40 or so degrees? it is actually slightly higher, maybe 45 or so, but the point is it never reads below there and the temperature here has been as low as 13 degrees at night.

[pocket-rocket]

The temp gauge on mine confuses me. The lowest number on the gauge is 40 degrees, and it never drops below slightly higher than that even when I start it "cold" in the morning. it seems to operate normally above that, rises when sitting in traffic etc until the fans come on


any idea why it might never read below 40 or so degrees? it is actually slightly higher, maybe 45 or so, but the point is it never reads below there and the temperature here has been as low as 13 degrees at night.

Your sensor may be defective or have grounding issues. If it bothers you enough, you could take it out and clean it up with a wire wheel or steel brush, apply some new thread sealer and stick it back in there and see what it does.

[armos]

I'm a little late but just another suggestion - I'd try hooking up a known resistance to the gauge to confirm whether the gauge is in good calibration. It probably is, but it's worth checking.

Many GM temperature gauges from that time period have a wiring flaw that causes the needle to slam into the peg every time you start the car. It's trying to do a "bulb test" on the gauge instead of the idiot light.
However, I think that would normally cause the needle to be pushed lower, not higher, so it might not be relevant here.

This resistance chart is from a Fiero, but I assume it would be the same. I've never confirmed if it's accurate for the CTS though, I only used it on a MAT sensor.

[pocket-rocket]

I'm a little late but just another suggestion - I'd try hooking up a known resistance to the gauge to confirm whether the gauge is in good calibration. It probably is, but it's worth checking.

Many GM temperature gauges from that time period have a wiring flaw that causes the needle to slam into the peg every time you start the car. It's trying to do a "bulb test" on the gauge instead of the idiot light.
However, I think that would normally cause the needle to be pushed lower, not higher, so it might not be relevant here.

This resistance chart is from a Fiero, but I assume it would be the same. I've never confirmed if it's accurate for the CTS though, I only used it on a MAT sensor.
[ATTACH=CONFIG]5993[/ATTACH]

Good advice

Also, welcome to the site

[TGP37]

I wouldn't say it's totally worthless, but I would say they are inaccurate. I like watching my temps rise well in advance before a dummy light would come on.

I read GM actually made the temp gauge in the dash offset on purpose. The engine would operate just fine at 195-220 but people brought their cars in for fear of overheating, but their was nothing wrong. Which is partly why there is no 195° point or optimal temp marked on the gauge. The gauge is vague for a reason, because 90% of the drivers are simple people who do not understand the finer details of engine operation.

That temp gauge to me is only worth two things.....1- When the cars is warmed up and 2- When the car is cold

I plan to install 2 temp sensors, one for each head. And have them run to two small diameter gauges. If anything goes wrong, those gauges will register LONG before the stock one does.

I'm a little late but just another suggestion - I'd try hooking up a known resistance to the gauge to confirm whether the gauge is in good calibration. It probably is, but it's worth checking.

Many GM temperature gauges from that time period have a wiring flaw that causes the needle to slam into the peg every time you start the car. It's trying to do a "bulb test" on the gauge instead of the idiot light.
However, I think that would normally cause the needle to be pushed lower, not higher, so it might not be relevant here.

This resistance chart is from a Fiero, but I assume it would be the same. I've never confirmed if it's accurate for the CTS though, I only used it on a MAT sensor.
[ATTACH=CONFIG]5993[/ATTACH]

I would also suggest placing the gauge tip in hot water with a known good thermometer and register the resistance. This may also show if the sensor itself is faulty.