T stat discussion

[P10crew]

So about a year ago I replaced the stat in my 90 Silverado. Ever since on cold mornings I watch the temp gauge while driving waiting for the stat to open and have noticed the following. Gauge will run up to about 215 before I first start seeing it open. After it opens the gauge will go way down to somewhere near 130 then start to climb again. It will then always over shoot to about 220 before it opens again. The stat is a Standt that was purchased at Oreilly's. Since I am replacing intake gaskets I went to my Chevy dealer and got a GM 12514334. Upon unboxing it I noticed that this new one is a standt as well but everything about the GM piece is different. The pills are different, the stamped parts are different. My question for you pros is are factory stats built to differing quality standards than the aftermarket from the same manufacture?
I sure thought that the old stat should be able to control temps better than this thing has. And I guess I thought I had trust in the Stant name.

 

[demarpaint]

Clearly the two in your picture are different. I'll catch some heat, but here goes. I only use OE when it comes to thermostats. I learned that the hard way by trying aftermarket Stant against my better judgement. Yes Stant might very well make OE thermostats, but that doesn't always meant it is identical to what the OE thermostat in your application is or was. There could be slight differences, just enough to cause problems in some applications.

 

[SwampSurvivor]

I put a stant in my Cherokee back in 2012 and I started to have the same behavior and eventually over heating. The temperature swings were strange. I changed it with another Stant and it got worse! Then I put in a motorad and it got better.

 

[bullwinkle]

I have had fairly good luck with the Stant Superstats, but I actually think the AC Delco ones are better, I've had good luck with the 195F AC Delco one in my GMC (6.2 diesel), and they're usually not much more $.

 

[Dave9]

This is a '90 Silverado. Odds are fair that buying a new, supposed OEM thermostat, you are not getting the same T-stat that came from the factory. Similarly you can buy the same brand and model part and get something from two different factories that don't look alike. It's annoying but one of the reasons many people prefer to shop local and inspect at point of purchase.

As far as your old new t-stat, out of curiosity I would throw it in a pot of boiling water with a candy thermometer and see what temp it takes to open it. One reason for that is that "sometimes" it is not the t-stat but the install that's the problem, an air pocket gets trapped and it takes elevated temp to trigger it.

 

[oldhp]

I always drill 2, 1/8th holes opposite of each other as close to the center as possible. This does 2 things. #1 it bleeds air out. #2 It allows some hot coolant to start mixing with the cold coolant so you don't get the 215° to a lot lower temp then back up to temp. I've done this to every thermostat I've changed. Always a steady cold to operating temperature every time.

 

[Yah-Tah-Hey]

OEM ONLY.

 

[nthach]

The old one on the right looks like a Stant Superstat with a bigger thermowax element. I'd go to the local parts store and take a look at their "heavy duty" thermostats.

GM sources t-stats and caps from Stant or an Indian company called TVS in most cases.

 

[JMJNet]

The Stant made for GM spec is different than a generic Stant from part store.

 

[zzyzzx]

Obligatory:

 

[Chris142]

Originally Posted by oldhp
I always drill 2, 1/8th holes opposite of each other as close to the center as possible. This does 2 things. #1 it bleeds air out. #2 It allows some hot coolant to start mixing with the cold coolant so you don't get the 215° to a lot lower temp then back up to temp. I've done this to every thermostat I've changed. Always a steady cold to operating temperature every time.

Zero reason to do this. Thermostats are already built with a slight bypass. Your holes can trigger a CEL.

 

[edwardh1]

I have also drilled a hole in the stat, it works

 

[Dave9]

I doubt you need as much as 2 x 1/8" holes just to burp it, I've tried 1x 1/16" and it worked fine without a CEL, tho' many do now have a slight bypass gap or check valve. It's better not to do it if you're in a cold climate where you want your windshield to thaw out asap.

 

[zrxkawboy]

I use either OEM or Superstat.

 

[clinebarger]

The proof will be in the way it operates in the vehicle!

To help prevent "Air-Lock"......Fill the coolant through the Intake 'til the coolant is @ 3/4" below the thermostat opening, Install the thermostat & housing, Finish filling it through the radiator neck.

 

[oldhp]

Originally Posted by Chris142
Originally Posted by oldhp
I always drill 2, 1/8th holes opposite of each other as close to the center as possible. This does 2 things. #1 it bleeds air out. #2 It allows some hot coolant to start mixing with the cold coolant so you don't get the 215° to a lot lower temp then back up to temp. I've done this to every thermostat I've changed. Always a steady cold to operating temperature every time.

Zero reason to do this. Thermostats are already built with a slight bypass. Your holes can trigger a CEL.


Not all thermostats have the vent in them. I've never had a problem doing this. Just me.

 

[demarpaint]

Originally Posted by JMJNet
The Stant made for GM spec is different than a generic Stant from part store.

Yes, and that holds true for other brands as well. Which is why I only use OE thermostats now.

 

[Lubener]

Thermostat styles vary with brand. I have found that the only good one made by Stant is their Superstat. When possible, I always use and have best luck with an OEM stat and try to stay away from aftermarket ones. Next time, drill a single 1/16 hole (no bigger) on the flange and position it at 12 oclock if possible to let any trapped air to get by the thermostat to be belched out.

 

[MetalSlug]

I have luck with failsafe t stat and stant superstat . Also drill extra hole cross from other factory hole.

 

[P10crew]

Thanks for sharing your techniques fellas . CLine as I was walking from the house to the shop this morning I had that exact thought about filling this. I didn't install the stat to wait to see what the wealth of knowledge in here had to say. I had to order the heater hose so I should have this on the road this morning.
If you ever need to cross that gates part number to Dayco it's E80418.