Engine temperature gauge problem?

[bowtiefreak]

So all of a sudden the temperature gauge is showing a lower than usual temperature. Like from one day to the next and it has remained that way for a week.

Usually indicated about 200-210
this day 175ish (we all now these gauges suck and are a reference point but still)

I replaced the thermostat (195) and temperature sensor. No difference.

I am worried the ECU thinks it is running cold and is going to play with fuel / air ratio

Why is the gauge indicating lower than usual? is it bad?

I have plenty of heat, it makes me feel like I am melting.

I'm stumped, ideas?

 

[laredo1307]

That's a good question. My Tahoe has always run at around 160F. When I changed out my radiator and waterpump I put a 180F T-stat in but still the dial reads the same. Maybe it is at 180 but the dial is slightly off. Anyways, I've never seen my gauge fluctuate except when I had a crack in my radiator.

 

[bowtiefreak]

my gauge does move, just not to where it used to. It spiked up once to the 210 range but right after I swapped the t-stat and sensor. then never again. The sudden change is why I worry

 

[bowtiefreak]

There is a temp SWITCH on the drivers side head...feeds to the gauge. New switch just went in. need to drive ans see what happens

 

[bowtiefreak]

The temp switch didn't do the trick either.

What's next?

 

[SouthernHoe]

All the Vortec V-8s and V-6's have run where you are describing normally. If mine gets to 210 something is wrong. It did just recently and I realized I had a leak and it was low.

 

[bowtiefreak]

both my trucks have always run about 200...t-stat is 195*...when it dips too low there is an issue. Last time it did this was a bad thermostat.

This was a sudden change from one day to the next is why it is in question. I've owned my one truck for 14 years and I know it pretty well. this is a weird problem.

Where is sunlit?

 

[SunlitComet]

The dash guage and the pcm use two different sensors. What does the pcm see, by means of a scanner, as it's reading when you see the dash guage dip as well?

Sent from my SPH-L720 using Tapatalk

---------- Post added at 02:53 PM ---------- Previous post was at 02:50 PM ----------

You can test the guage as well with a variable resistor with a range of 90 ohms I think it was.

Sent from my SPH-L720 using Tapatalk

 

[bowtiefreak]

Both sensors are new. Going to try to get a scanner on it tomorrow.

Thanks

 

[Tbruz]

Sunlit,
Can you post the procedure to test the temp gauge using the resistor?
Thanks
Tbruz

 

[96redsport]

Mine always ran right with the thermostat temps until I had a intake gasket break resulting in a big over heat which ended up spinning a main bearing... When the engine was rebuilt I had a new temp sender put in and ever since my temp readings have been lower than the thermostat temp. Even changed clusters to the esky style but the readings still remain the same. So i wondered if it is the temp sender I had put in but never got around to changing it. I guess I should get the scan temp values first before I go replacing stuff...

 

[bowtiefreak]

I finally scanned it and the ECU reads the temp at 194 so that is good. What are the chances the switch is bad? The gauge seems to work, a quick test taking the negative side of the battery to the input line allowed the gauge to reach past max. I am happy the truck is running at correct temp. I'd just like to see this accurately. I did try another temp switch...no better

 

[Tbruz]

Bowtie,
I had(have) the same issue with my 97.
Scanner reads 195 but the dash temp gauge reads lower.
I too replaced the temp sender on the head and on the thermostat housing.
Changed T stats twice and tried my spare dash as well.
All this with no luck.

I finally decided to "recalibrate" the temp gauge by removing the temp needle and re-installing it at the 195 mark once the truck was up to temp and validated at 195 by the scanner temp.
Downside is the temp gauge doesn't sit at the 100 mark when stone cold.


What I think is going on is that the temp gauge itself is a variable resistor that wears out over time. I haven't been able to locate a temp gauge calibration procedure against a known standard(specific value resistors indicate a specific temp readings) so I cant be sure.

I figured I need the hot temp indication to be accurate not the cold side.
Tbruz

 

[bowtiefreak]

Not a bad option.

 

[SunlitComet]

104° 1200-1350 ohms
125° 53-55 ohms.

that is ohming the sensor itself. if out of specs, replace it. also ohm your sensor connector, harness side to cavity 13 dark green wire on plug behind cluster to ensure you have no resistance issues. a few ohms would be expected but not like say double digits probably.

---------- Post added at 01:06 AM ---------- Previous post was at 01:04 AM ----------

and fix it, don't "recalibrate", there is no such thing in these vehicles for that gauge.

 

[My99Yukon]

Both sensors are new. Going to try to get a scanner on it tomorrow.

Thanks

This is an older thread but I just started to have the same issue. I am "mostly confident" that the Yukon was running much hotter on average than the 160ish that it tops out at.

1. The heater cranks out lots of heat.
2. Even when it is 110 deg and I am idling around the temperature gauge never gets above this mark. I believe it used to be much more centered.
3. I flushed and filled the radiator 8 months ago. Replaced items with the following parts: Duralast Radiator Cap 7616; Fail-Safe Thermostat 7228-195
4. There was an initial spike like you had but it was because I had air in the system still. I pulled over, released the vacuum, topped it off and cleared any remaining air. I have run the truck for 8 months without an issue so I don't think this affected any of the sensors or engine.
5. Now to the sensors:

There is a good video on how to test the driver side sensor and wires here. But since you swapped out those parts that is not an issue.

It is possible that a bad ground somewhere could be affecting the electricals. I am about to upgrade some of my wires next weekend and I will let you know if that magically fixes the issue. I will post the upgrades in my Project 99 Yukon thread.

Did you figure out the issue? Any help on this issue would be great.

 

[My99Yukon]

As an update, I was able to get a scan today and my temp was 195-199 and functioning as designed. I will see if any of the electrical work on upgrading the grounds helps with this and update if this is part of the problem. I will try to check each ground before I replace it with my DMM and see if I can pinpoint the culprit, if any.