Running too cold with 180 stat?
 

Did a search and didn't find what I was looking for. What thermostat brands are yall using?

I installed a 180F robert shaw knockoff from a parts store over the summer. I had overheating problems, engine would run 210 with a 180 thermostat on the interstate. I flushed and flushed and flushed a lot of gunk out, changed from electric to mechanical fan with a shroud, and threw the parts store thermostat back in. Ever since then, the SOB has been running cold. Like on a 65F day, it's running 150-165F, with a 180 stat in it. I've never had a pontiac run this cold. I can tell it's cold because the idle oil pressure is way higher than normal after a run. My issue is that it's making carb tuning a chore. The AFR a motor wants at 150 is NOT what it wants at 185F.

Is the thermostat likely stuck? I got a moto-rad 180F replacement, but when I made stat soup in the kitchen, it wouldn't open below 190F! What brand are yall using?

I use the Stant Stainless steel thermostat from Napa without any issues for years. Do not push on the bellow with your hand is what I was told. Don't try to open it by hand.

Are you Exh crossovers intentionally blocked in the heads or at the Intake gasket?

Is your water crossover separated from Manifold?

Put a 195 stat in and see what that does for you, it's cheap and takes 25 minutes to swap in.

At any rate this is the better type of cooling system to have to deal with!
Excuse the double listing in the photo!

My LeMans has the same problem. I have the stock 3 core radiator and run a 8.9:1 455 with a 180 T-stat and a Flex-a-lite 7 blade 19" fan. I was using a 160 Tstat and on a 90+F day it would only get to 170 F on the highway. I put a 180 F Tstat in and it only gets to 175 on a 90+ day. I am going to try a 190 F Tstat. I used to run a heavy-duty clutch fan with 7 blades but the car would get over 200 at idle in the summer.

I run a 160. No more over heat issues.

If you have a good cooling system that works like it should and an engine that is happy with it's combo of parts and tune, it's not unusual at all to have an engine run below the rated thermostat temp. Especially if ambient temps are relatively cool outside (90 and below)
Reason being is thermostats open before their rated temps. Sometimes as much as 8-10 degrees earlier as a starting point, and if your engine is happy and the cooling system is up to par, many times just that crack open temp on the stat is enough to keep things cool.

I see this as perfectly normal. If the temps bother you then you may just have to experiment with warmer thermostats and see if their open temps are what you're looking for. They all aren't created equal so it may take a couple tries.

I always recommend double-checking the t-stat in boiling water with a thermometer before installing. I bought the "heavy duty" 180F t-stat from Ames a few years ago. Put maybe 20 miles on it before I tore the car apart for restoration. When putting my engine back together, I had the foresight to check the t-stat before reinstalling, and to my surprise it didn't open even when submerged in fully boiling water (212F). I ended up buying a Murray Ultra 180F t-stat from O'Reilly Auto and it opened pretty much right at 180F when tested and has kept my engine dead-on 180F in the summer when temps are in the 70s and 80s, and also recently when driving in 40F temps.

In short, t-stats aren't always what they advertise. Some open too soon, others open too late. Unfortunately, it's on the user to verify function.

With today`s pump piss, one almost has to run these carb`d engines cooler to avoid fuel boiling problems.

Agree. My brother had constant hot start issues in his '74 GTO w/461, and you could hear the fuel boiling in the carb bowls. After he started using ethanol free gas, the issue went away. Now he and I only use ethanol free gas in our old cars. Even 10% ethanol blended gas (which is what most pumps have) significantly lowers the boiling point.

So if your motor is running at 150-165F for extended periods of time, that means your 180 t-stat must be opening at around 150-ish. The fact that it doesn't get above 165 would suggest that your cooling system is working well overall. Of course, that assumes your sender and gauge are correct. You could verify the temp with a infrared thermometer and test the t-stat in hot water to see where it opens. But if the temps are really 150-165, then no real need to test the stat because the operating temp tells you what you when it's opening.

I had a Robert Shaw 180F a few years back fail the same way. Always ran around 185F . One day it wouldn't run over 160F. Installed a Stant Superstat 180F and it's back at 185F.

Typically good stats are made to fail in the open position. That's what you want it to do honestly. Better for those that don't always pay attention.

Since the op is experiencing cool temps that are more than 10 degrees below the stat rating I suspect that's likely what happened

That's kind of what I was thinking, that this thermostat failed open. When I did a test run with no thermostat, it ran 140-160, so it is like the thermostat is stuck open. As a side-note I did the fan clutch mod to the HD fan clutch, so it locks up at a lower temp. 19" fan and shroud on a Non-AC radiator. Sounds like an airboat when locked up, but it runs cool.

Current stat is a Mr Gasket part, but it looked like the Robert Shaw and was 25 bucks! I remember when a T-stat was about 7 bucks. Before I replace it, should I use the EMP/Stewart (Robert Shaw copy) from Summit Racing, or the Murray Ultra stat from OReilley?

I just learned that Stant was bought out by Moto-Rad in 2019. The plant was shut down and moved to Israel. The Stant I got from Rock-Auto was marked Moto-Rad. It was the 180F that didn't open until above 190F.

You're assuming that it closes, and isn't merely seized open, or partially-open.

It's not possible to make something fail a certain way. "Failure" means you're getting unintended operation.

This is the marketing deception used to good effect (from a profitability standpoint) for the crappy "MotoRad Failsafe" thermostats. Folks think they've been designed to fail "open" when the reality is that they're designed to lock open when SOMETHING ELSE fails and the coolant temp gets high enough.

But the last time I was on the Failsafe web site, their wording was contradictory and somewhat ambiguous; which I suspect is intentional.

Only one way to know for sure...rip off the thermostat housing and look.

I had one of those in my Toronado. Sticky operation--temp went way high, then way low, then way high...took many miles for the temp to stabilize.

But then, I've got a normal-looking 'stat from Motorad that's doing the same thing in my K1500.


I don't trust ANY thermostats any more. Had multiple failures with any brand I'd buy. Now they ALL get tested before installation, and even that doesn't really guarantee a good part, it's not only a matter of when they open, but also how fast they react on both the opening and the closing.

One thing that needs to be talked about here is that any stat is constantly being modulated by the coolant temp out of one head and then the other.

With where the stat is centered in the water cross over and the fact that there’s only one what actually takes place is that the heads switch back & forth with one running hotter then the other for a while.

One head will stop flowing into the crossover as the flow pressure goes up in regard to the temp of that head going above that of the other head.

Once the hotter running head cools down enough and the higher pressure it had gets down to a equilibrium point, then the other head starts to pass out it’s coolant again.

At times of full throttle if you have have a couple of lean running cylinders producing more heat in one bank I think one can see how such a condition can make for a very bad situation that could keep flow output from the other head very limited .

Not everything has to be a saga, jeez

So I go down to the local OReilly and get one of the Murray Ultra T-stats. I open it up and what comes out? A Moto-Rad 180. So I take it home and make soup, and guess what? The SOB stays shut until 195F.

So the Moto-Rad 180s really open at 190-195. Now I gotta take the thing back and play three-thermostat monte with other brands until I get a real 180F unit.

Ridiculous.

That's basically acting just like a 195 stat should act. I wonder if they just boxed or stamped the damn things wrong.
Does it actually say 180 on the bottom of the stat? They are typically stamped with the temp rating.

Or maybe it's a conspiracy and the EPA is involved. They don't want us running cooler stats anymore and they think we don't check them.
LOL

Firstly …Verify your temperature reading! ✌🏼

This! Are you using a factory gauge? Have you checked it with a known good mechanical gauge? Hate to see you chasing a problem if you don’t really have one. Good luck!

Merry Christmas
Murf