thermostat stuck open?

[LAExplorer]

I wonder if someone can help me out... My engine will not heat up much past the low mark on the H2O temp gauge, even when towing. I think the check engine light is probably related to this issue. As far as I can tell, the thermo must be a "fail open" type. Is this the original thermo? I bought the X used so I'm not sure if this is a factory part or not. If I just go to the local parts store will the O.E.M. thermo also be a "fail open"? Do I have to order a special one? I like the safety of not having a $20 part turning into a $2500 problem. Other than guzzling more $2.60 regular gas than normal (and the heater never getting that warm) am I hurting anything? How do I reset the idiot light? I tried to unplug the battery but it didn't change anything. Thanks.

 

[wired_af]

I don't know about the "fail open" or whatever, but when my t-stat was stuck open I didn't get the CEL. If I were you I would just replace the t-stat and see if it fixes it.

 

[Robb]

Your stock t-stat will be a traditional "fail close" t-stat. But it is possible for it to stick open and stay that way. If you have a concern about the stat being to blame, go ahead and replace it. It will only run you about $5 + antifreeze.

To tell you the truth though, I have replaced the stat in my '95 several times, and the gauge always hangs out at the low end of the scale. The gauge just isn't very accurate.

 

[unclemeat]

Are you getting lots of hot air out of the heater? Does the temperature of the air heat up after running the engine? That should tell you if it is the gauge or the termostat.

 

[huskyfan23]

I had one stuck open and my gauge wouldn't move much at all. You could also have a bad sender but I'd think it's the t-stat.

 

[jayhawkexplorer]

Bringing back an old topic. I'm wondering if my thermostat is alright too. The outside temp has been in the mid to high 30's lately, and when driving on highway or in town, my temp gauge doesn't ever move much more then 1/5 of the way up the scale. I know in the '03 Ranger at work with the same gauge cluster, it moves to exactly halfway up and stays there. I've still got plenty of heat, except out of the far left vent, so I don't quite know what to think.

To answer another part of this question, you can buy a "fail safe" thermostat which will stay open when it fails. They cost around $11 but its well worth the investment, in my mind.

 

[LAExplorer]

I just changed the t-stat and found that the small arms that hold the thing together had completely snapped off, fortunately in the open position. I don't think modern t-stats can fail closed and the guy at Auto Zone said the same thing. The difficult thing, other than getting at the damn thing, is that there were 2 different stats spec'd for my year and engine (4.0 sohc, 1997), I know of no way to know which is which, before you have thing taken apart (mine turned out to be the bigger and nominally more expensive one, $8 vs. $15). Also, the idiot light stayed on for a short time after the install, but eventually it went out.

 

[jayhawkexplorer]

Don't trust AutoZone on anything. Those guys are for the most part, idiots. Cheap thermostats can still most definitely get stuck closed. That's why there's products like the "Fail Safe" line, which fail and stay open.

 

[Robb]

ALL thermostats, outside of Fail-Safe (and its couple of clones), ARE fail close thermostats. If it looks like a typical thermostat, it is fail close. The Fail-Safes look quite different.