[Bronze66]

In my never ending quest to keep my motor at 180-195 max. I've come to a quandary. My testing so far is: Using a 160 stat the motor will not get above 185 in 85 degree weather. Normally runs 160 to maybe 170 around town and highway in 70/80 degree weather. In 95 degree weather will run 180/185/190max and get to 200 in city stop and stop traffic and will drop to 185/190 once I get moving. Seeing most of the time temps were 160/170 I thought to cool. I put in a 170 stat and the motor runs 170/175 all the time below 85 degree weather temps. Still a tad cool. So I put in a 180 stat. Motors gets to 200 then the stat opens and can't get the temps down below 190 no matter what. Thought I had a bad stat and bought another from a different place. Two different manufactures. Same thing it won't open until 200 and can't get temps below 192 with this one. I can see the temp swing between 192 and 200. Showing me that's the open temp @ 190. I put both 180 stats in a pan of water w/cooking thermometer. (mercury type scale, not dial) and it looks to me as they start to open around 190. Whats that all about? What happened to 180?
Anybody using a 180 stat at 180/185? Or is it time for a Stewart-Shaw stat? Are they that accurate? Anybody using them with good results? I'm going back to the 170 for now. I would really like to keep the temps 180/185 normally at 90 and below. Oh the rest of the cooling system is super. The 160 temps prove that.

[Geoff]

Where is the stat made? I bought two Mr. Gasket [ made in China ] high flow 160 stats, same design as the Stewart-Shaw type. Tested both before using. One opened at 130 & the other opened correctly at 160 but then jammed in the open position! They now reside on the trinket shelf.

[smagnotti]

The robert shaw stats are the only way to go, It also helps alot to make a baffle, that sits under the stat front to rear in the water crossover, and sits about .060" away from the under side of the stat.you can make this out of L stock aluminum, and machine screw it down ( nut and bolt 8-32) thru the bottom of the crossover and sealed with blue silicone.

[george kujanski]

I've seen that also. the way they're manufactured and the method of operation is just not an xact science. It could be, but they make these very cheaply.

On my driver I have a digital temp readout. The original 195 stat would open at 208, this one opens at about 192.

George

[johnsma22]

Just an FYI. There are two basic types of thermostats currently available: You have the balanced sleeve thermostat, and the reverse poppet thermostat. Both types function in the same manner, but have distinct differences. The reverse poppet thermostat opens against the flow of coolant from the water pump. The coolant, being under water pump pressure, is used to help the reverse poppet thermostat stay closed when it is cool so as to prevent leakage.

The balanced sleeve thermostat (Robert Shaw) allows pressurized coolant to circulate around all of it's moving parts, and equalizes the system pressures above and below the thermostat’s moving valve. Therefore the thermostat is pressure balanced and will respond to system temperatures only. It provides a fast temperature response time and increased coolant flow to the radiator. For a performance engine application it is recommended to use the balanced sleeve design for it's added flow capabilities. See photo below:

Also, running a 160˚F t-stat or whatever temp you choose, does not mean that your motor will run at that temp. The t-stat establishes a minimum operating temp. The temp that you motor runs at is determined by the ability of your cooling system to shed heat.

[george kujanski]

Good info, John.

George

[Bronze66]

John thanks for the info. I ordered a Robert Shaw unit last night. I know that the stat doesn't really control temp in all cases. My cooling system is that good that I should be able to use a good stat for temp control most of the time in 85 degree and below outside temperature. I just want something accurate to work with. Funny thing is my 160 stays around 165, the 170 stays around 175. BOTH are marked 160. But the boxes were marked different. Mmmmm wonder if the 170 started as a 160 and they goofed. Making it work at 170. My 180 works at 190. May be another bad one. It is marked as a 180 though.

[Bronze66]

This is a follow up. I put in a Shaw 180 degree stat this morning. It's 82 degrees here w/50% humidity. Motor temps are 182 up to 190 degrees when setting in traffic. I put the stat in a pan with water and thermometer. Looks like it starts to open around 175+ and was fully open at 185. That's a close guesstimate. I've got it where I want it now.

[johnsma22]

That's great news Bronze! I know how frustrating these Pontiac's can be with regard to overheating. To finally get it under control, you must have breathed a sigh of relief. I know I did, after four core radiator, cast impeller water pump, clearanced divider plate, balanced sleeve thermostat, proper temperature sending unit, etc. Now if I can just get this damn Speed Demon carb dialed in I'll be a happy man! But that's a whole other story!

[Formulabruce]

Originally Posted by Bronze66

This is a follow up. I put in a Shaw 180 degree stat this morning. It's 82 degrees here w/50% humidity. Motor temps are 182 up to 190 degrees when setting in traffic. I put the stat in a pan with water and thermometer. Looks like it starts to open around 175+ and was fully open at 185. That's a close guesstimate. I've got it where I want it now.

As you have discovered the T stats have a "static" rating, most 170 are not fully open till 180 roughly. 180 at around 190. This info is huge to me in temp control and this info varies from manufacturer to importer. I used AC T stats and have had good luck, just my 2 cents, Bruce