Temp light comes on and off

[Sgt Thor]

Hey everyone, newbie here. I bought my first Comanche 2 weeks ago from a local dealership. 1986, 4x2, base model, v6 automatic in red. It's the 4th truck I've owned and already my favorite by far. However yesterday started something really weird and I'm stumped. 

 

While taking my daughter to school the temp light came on for about 30 seconds and then went out for about 10 seconds. It continued this until I got it home. 4 hours later I started her up and saw the light was off, so I drove it to work - approx 10 miles away. Halfway through the trip it started doing it again, all the way to work. I popped the hood and the rad cap was steaming and the reservoir was empty (which was weird because I distinctly remember it being full 2 weeks ago at the dealership). I figured I had a leak and asked my wife to bring me some antifreeze.  A little before leaving work I filled it up with the antifreeze and the same thing happened at about the same amount of time.

 

Today I was using it around the property and she was fine - multiple starts and stops, multiple trips from one end of the property to the other with no prob. When I was done I drove it to the gas station 1 mile down the road and the darn thing started doing it again. 

 

It's not a fluid issue - the reservoir is still full and there were no signs of leaking in the driveway. 

 

Anyone know what it could be? Thanks in advance.

- Will

 

[eaglescout526]

I bet you anything it might have the gauge sensor instead of the one for the light. 

[Sgt Thor]

 

1 minute ago, eaglescout526 said:

I bet you anything it might have the gauge sensor instead of the one for the light. 

 

What do you mean?

[eaglescout526]

There’s two types of the temp and oil sensors. One is a sensor that is for the gauges and the other is a sender for the light. 

[Sgt Thor]

Gotcha. Do you think it's ok to drive until I get it fixed this weekend? If it's just a sensor I wouldn't think that would mess with the engine. She's running just fine...

4 minutes ago, eaglescout526 said:

I bet you anything it might have the gauge sensor instead of the one for the light. 

 

What do you mean?

[acfortier]

If you've had it for 2 weeks, and it just started doing this (assuming you were driving it in a similar fashion when the issue occurred), not sure if it'll be because you have the temp. sender (for an actual gauge) vs. temp. switch (for the light on the cluster). I'm not sure what symptoms they exhibit when they go bad, though, and they're probably cheap enough to replace.

[jpnjake]

Ok so your confusion is in the clusters, there’s 2 basic styles with different variations one has a bunch of “Idiot lights” that just tell you when something is wrong, it sounds like that’s the one you have

The other has actual gauges for everything, Here’s an example of each one. 

and to answer your question if it’s just the wrong sensor you should be ok to drive it, I’d just keep an eye out for steam or other signs of overheating 

[Sgt Thor]

9 minutes ago, jpnjake said:

Ok so your confusion is in the clusters, there’s 2 basic styles with different variations one has a bunch of “Idiot lights” that just tell you when something is wrong, it sounds like that’s the one you have

The other has actual gauges for everything, Here’s an example of each one. 

and to answer your question if it’s just the wrong sensor you should be ok to drive it, I’d just keep an eye out for steam or other signs of overheating 

Yep- I've got the top one. And the light just comes on and off intermittently after a few miles. Thanks for the help!

[Sgt Thor]

1 hour ago, acfortier said:

If you've had it for 2 weeks, and it just started doing this (assuming you were driving it in a similar fashion when the issue occurred), not sure if it'll be because you have the temp. sender (for an actual gauge) vs. temp. switch (for the light on the cluster). I'm not sure what symptoms they exhibit when they go bad, though, and they're probably cheap enough to replace.

 

What exactly would be the parts I'd need if I were to go to AutoZone? Just in case they're as clueless as I am...

[Ωhm]

Disconnect the wire from your Coolant Temperature Switch (CTS) and leave it disconnected. Drive it. If dash lamp still lights, then your problem is NOT with the CTS.

[Sgt Thor]

34 minutes ago, Ωhm said:

Disconnect the wire from your Coolant Temperature Switch (CTS) and leave it disconnected. Drive it. If dash lamp still lights, then your problem is NOT with the CTS.

Thanks. I honestly have no idea what to do here. 

[Ωhm]

Location

The Motor Manual Guy_Cooling 3_5 pg139.pdf

[Sgt Thor]

1 minute ago, Ωhm said:

Location

The Motor Manual Guy_Cooling 3_5 pg139.pdf

That's awesome! Thank you so much!

[Sgt Thor]

Just to give you all some closure on the situation, I found out that I got a cracked head. Now I have to decide if I want to rebuild, put in a new engine or sell this thing. 

 

If it weren't for bad luck I'd have none at all.

[howeitsdone]

I know what you mean! Found out my head was cracked in Jan when rebuilding. Felt defeated, but bought another head and went on with the rebuild. Yesterday I was tearing down another motor from my XJ and found it had a hole in it. Rather than let it get me down, I found a guy 40min from me selling a block that needs rebuilt. Called him last night and he said come on out Saturday and get it. It'll be business as usual in a few days. Both my motors with issues, yet here I am because a good vehicle is hard to come by these days. Plus I enjoy it 

 

Fortunately, a cracked head is much simpler than a hole in the block. Just need to swap in another! Of course, it'll take some time if you wanna do it right, but at least the truck didn't catch fire or anything! You can look at it as a large maintenance item that you can check off the list.