[thehvacguy]

hey I just bought my first truck and I have a question. when I am driving, the coolant meter goes up and down with the movement of the vehicle. also if I am uphill it goes down to zero. is this normal or is something broken? and if something is broken will that damage my vehicle? thanks for the advise.

 

[95025]

First of all, if it's a GMC Sierra, with the V6, that will be the 4.3 liter engine. It's a good rig!

That said, the first thing I'd check into is the Temp Sending Unit.
http://www.oreillyauto.com/site/c/detail/BWD0/WT3000.oap?keyword=coolant+temperature+sensor!s!sender

It should be located somewhere near the top of the engine, probably near the front.

You'll lose a little anti-freeze when you remove this. Don't do it when the engine is hot!


Again, that's the first thing I'd check. It's cheap & easy. Then, if the problem persists, I'd move on to checking the gauge, etc.

 

[thehvacguy]

lol I wish it was... its a gmc sonoma v6 2.8 liter. how do I check the sensor? I have a muktimeter and know how to use it. is there a standard resistance I should get? or is it pneumatic?

 

[95025]

lol I wish it was... its a gmc sonoma v6 2.8 liter. how do I check the sensor? I have a muktimeter and know how to use it. is there a standard resistance I should get? or is it pneumatic?

Sonoma, not Sierra. Gotcha.

I cannot answer your question about testing. Sorry.

 

[Marty1Mc]

Before you waste money on a new temp sensor. I had seen this once when I was looking for the coolant sensor on my neighbor's 4.3. It took me a while to find the link... This is what a person posted...

"It started out that it would stop working- temp gauge goes to 0 and A/C shut down and then it would come back on its own, now it stays at 0 and A/C off with no particular trigger to make it happen , I just reset the computer and it is good for anywhere from an hour to usually a couple of weeks. I talked to a tech who said it is a common prob and that the computer needs to be updated. This sounds like a defect to me and should be a recall but with the way things are going for Gov Motors I dont see it happening

, anyway I dont have the funds to take it in and pay hour(s) to have the computer dicked with so I just wanted to let you and any one else know what I found out. Easiest way to reset on the go that I have found- motor off key at off position pop hood and disconnect the main fuse box buy pulling up the handles and the lift it up just an inch for about 10 sec lock it back down."

So, based on this and a few other posts, it seems like a GM computer issue. Very strange indeed. I would try to reset the computer first and see if that cures the problem.

Here's the link:
http://www.gmtruckclub.com/forum/showthread.php?38634-Coolant-Temperature-Sensor

 

[95025]

^^ Sure could be. But there is quite a difference between the electronics of a 1992 model, and those of a 2008.

 

[Marty1Mc]

very true, I missed the year on his, duh. If it's a non Vortec engine, I could go check my 85 K10 4.3L and see what the sensor looks like...

Edit: Skip that link, I just looked again. The 92 4.3L has two sensors, one for the computer and one for the gauge, similar to my 85.

 

[thehvacguy]

I dont know why I keep calling it a sierra... I also noticed the gas guage does the same thing when going uphill...

 

[Marty1Mc]

You may want to check the back of your cluster assembly. My year Chevy (1985) has a plastic circuit board. Yes, plastic with copper lands. These tend to give out and cause intermittent errors. My oil pressure goes all over the place. The connections where the wiring clips in tend to be trouble spots as well.

 

[thehvacguy]

hmmm... ok where would that be located?

 

[Marty1Mc]

I would do two things in this order. First test the temp sensor for the gauge. The sensor should have high resistance (over 100k ohms) when cold but can fall to under 100 when hot. I wouldn't focus on the exact readings as much as the high to low resistance when it goes from cold to hot. Since you are looking at the gauge dropping to zero, you should have high resistance when it is hot if the sensor is failing.

If that checks out and I suspect it will, then you need to look at your dash cluster. That means you need to remove the speedometer pod from the dashboard. On the back, to pull out the cluster, you will need to release the speedometer cable from the back. The cluster may come out a little bit and then stop, try pulling gently again. It is usually the speedo cable needing to be pulled out a little and the grommet on the firewall gives resistance. Once you can get your hand behind the cluster, you will feel a tab on the metal part of the cable end, push in on the tab and the cable releases.

On the back of the cluster assembly, you should see the plastic circuit board. It will be on the outside and you will also see the dash lights being plugged through it. These are very flexible (and some would say flimsy) circuit boards. Inspect that for cracks, dirty area where the harness plugs into it.

 

[ukrkoz]

there are NUMEROUS threads in GM forums about issues with instrument clusters. some where under recall. mine, eg, has dancing gas gauge. i just live with it, not worth digging deeper into this.
so yes, make sure temp sensors are fine. just to prevent overheating. otherwise, find out if there was a recall on your cluster.

word of caution: be VERY CAREFUL should you decide to swap out cluster for something else. GM had gazillion of various designs, and it is almost matter of good luck and god's grace to have a matching one found, and everything working fine after swap. GM should be making plows pulled by horses, not getting into electronics. simple stuff.