DrDyno

Hi All,

I'm old school. By way of introduction, my first Corvette was a '56, some 51 years ago. Between then and now I've had a dozen more and spent six years in the 70's as a wrench and proprietor of a Mobil Oil full service gas station (in the days when we had lifts in the bays rather than delis and beer coolers). All of the above is to say I should know what to expect when a thermostat is changed out.

My '96 LT1 (which has a DeWitts dual-row radiator and Delco 180° thermostat) idles around 201° with the fans on and runs around 197° on the highway. Occasionally the idle (with fans running) will climb up to 205° or so and up to 215°-220° with the fans off. I know what the LT1 specs are but to my old school way of thinking, that's just too damn hot!

I've read some interesting posts about guys who moved down to 160° thermostats. Some of their claims were beyond belief... 20°-30° temperature drops, others with 3°-4° temperature drops. Anyway, today I changed out my Delco 180° thermostat for a Hypertech 160° thermostat (from Summit Racing). As the coolant was practically new, I put the same coolant back in and went for a ride. My car now idles between 186° and 190° with the fans on and 198°-200° with the fans off and cruises down the highway at 184°! HOW CAN THIS BE??

Everything I've ever known or been taught about thermostats says they don't regulate engine temps... they just allow coolant to start flowing earlier or later. Once opened, the engine temps depend upon the engine's thermodynamics, not the thermostat. Given my results, I must believe the Hypertech thermostat has different component dimensions than the Delco, allowing more water to circulate past it. It looks a little different in terms of the piston diameter and placement but WOW! what a difference. I'm sorry I didn't do this years ago!

Hot Rod Roy

Are you of the opinion that thermostats are digital, that they snap all the way open when they reach their operating temperature? They do not.

Watching a thermostat in a pan of water on the kitchen stove will convince you that they are linear, and open further as the temperature increases beyond their initial opening temperature. This should convince you that they do allow more coolant to flow in the cooling system as the engine gets hotter, thereby regulating the temperature of the engine.

A full boil on the kitchen stove will only be about 212* F., so you might not see the thermostat fully open. That might only happen in a pressurized system.

enventr

That is normal temps with the 180 stat. You live in Florida like I do. I also have a Dewitt's radiator. I always have the a/c on so the cooling fans are always on. I am keeping the system close to stock except the Dewitt's rad. Your car has a reverse cooling system

DrDyno

Hi Roy,

Thank you for your response. I am fully aware of how a thermostat regulates engine temperature on a limited basis. That's why the second sentence of my final paragraph starts with, "Once opened..."

I test all my thermostats on the stove before installation. The 180° Delco started to open at 188° and was full opened around 198°. The Hypertech started to open at 172° and was full opened around 184°. They both appeared to be fully closed at their stated temps: 180° for the Delco and 160° for the Hypertech.

DrDyno

Enventr, thank you for your response. yes, here in Florida our cooling systems are subjected to higher ambient temps. Allow me to suggest a Hypertech 160° thermostat with your next coolant change.

GREGGPENN

Your pretest appears to answer your own questions since the car runs in the range where each thermostat is fully open. Why does that surprise you? Is it because the stats don't perform WHERE they are supposed to? Or...that the car is running at a lower temp now (and hasn't risen to those higher-than-static-system 215-220 temps like it did before the stat swap)?

If the later, I'm betting you will still see those higher temps (215-220) when it gets really hot in the summer. You know...once ambient temps made it HARDER to "pull" heat from the coolant as it passes through the radiator. Mine did the same thing but it takes longer to get there.

Tom400CFI

You've been on ths forum long enough to see that posted many, many times. You've probably been here long enough to see me challenge that -at least with greater explanation.


I hope that by "thermodynamics" you mean the capacity of the cooling system, and the heat generated by the engine.

ALL stock cooling systems are better than good enough. To be validated, they need to cool the car under most imaginable driving conditions, in the worst heat available for testing: Death Valley, Davis Dam, in the summer. Most of us aren't towing trailers up hill in Death Valley in the summer, so since we're not operating in those extreme conditions, there is quite a margine in our properly maintained cooling systems. You've taken that margin and increased it quite a bit with your DeWitts radiator.

What does this mean? It means that with more cooling capacity than is necessary for most conditions, your cooling system, with decent air flow, should be able to drive your coolant temps right down "against" the thermostat....at which point, the stat IS regulating the coolant temps. By lowering the T-stat opening temp...and with that excess cooling capacity, you've just lowered your operating temp.

Most of the people who have experienced no change in operating temps w/a lower stat/change -especially at cruising speeds, I'd submit that they don't have a properly maintained cooling system. All my cars have nearly always run "down against the T-stat" and changing, removing or lowering the stat would , or has resulted in lower running temps, in nearly all cases. Exception would be something like climbing 3000' over 13 miles in 95*+ temps. That is one condition where the heat generated would exceed the stock radiator's ability to shed heat as low as, or lower than the T-stat opening point.

Your results are precisely what I'd expect.

mtwoolford

Not another thermostat thread

Okay let me add my opinion, based on more years in a ship's engine room than I care to admit, and continually monitoring oil coolers and various heat exchangers.

first off EVERYBODIES RIGHT to a point. If your cooling system is capable of holding the system at a lower temp (this depends on a lot of variables, condition of the system, volume of the system, ambient air (or water in a marine system) temp), then a cooler thermostat will allow it to operate at that lower temp while a higher temperature thermostat will force the system to function at the higher temp.

If the system is undersize, inadequate, in poor shape, or there are high ambient temps, the lower temperature thermostat will open earlier and the temperature of the coolant will continue to rise to the point that the higher temperature thermostat would open. At some point above the temperature rating of the higher temperature thermostat the system will stabilize at an elevated temperature... (the amount of heat removed becomes greater as the difference between the temperature of the coolant and the temperature of the ultimate cooling medium, here the outside air, becomes greater).....if it doesn't stabilize at an acceptable temperature (but too hot by old school standards), well that's when overheating occurs.

I think Dr. Dyno has a very efficient system in good condition and it's capable of operating (discharging or expelling the engine heat) at a relatively lower temp and the quicker opening 160 degree stat allows this to happen; of course a higher temperature thermostat would delay opening until a higher temperature was reached, in essence, forcing the engine to operate at a higher temperature, which was something the factory apparently desired for reduced emissions .

and yes, all this will be on the quiz

DrDyno

Tom... what took you so long to respond? I probably should have just PM'd you for the answer. In any case, you and MT have, obviously, provided the answer I was looking for.

Moral of the story... regardless how old you are or the experience you've had, there are always folks who can teach you a thing or to!

Many thanks!

vetteLT193

A lower T stat also gives you a lower starting point when you hit traffic. If you are running a 160 degree stat it is possible to run as low as 160 which gives you a better starting point.

In reference to how yours is running... both your stats seem way off. When I ran a 180 I ran about 185-186 highway with the AC on in summer. When I ran a 160 it ran the same mid 180's in the same conditions. I could get the car to run cooler than that with the 160 on cool days, AC off, slower speeds (i.e. less load... think 45 mph just cruising). There were some nights I was running just higher than 160. When I had a 195 degree stat the car would run 196 when going a sustained 35 mph and above regardless of conditions.

DrDyno

Well, I certainly can't account for your results. Hard to imagine running 160° with a 160° thermostat considering they don't start to open until they pass 170°. Was it very cold when you experienced that? Your cooling system and engine internals must be squeaky clean.

Are your temps from your analog gauge or are you reading it from the digital display? Mine are from the digital display which are supposed to be more accurate than the gauge.

2HIP4U

When I lived in Dallas, I solved the alarming temperatures by installing a fan relay switch which turns on both my radiator fans at about 200. They are supposed to turn off when the temp returns to 180, but that rarely happens -- even here in the north east.

Hot Rod Roy

If your fan turn-on temperature is too low, you'll end up with the fan running all the time, because the fan CTS and the thermostat are battling for control!
As the engine temp increases, the thermostat opens to control the engine temperature. If the thermostat hasn't opened all the way, and the fan comes on in an attempt to cool the engine, the thermostat will close somewhat, trying to raise the temperature of the engine!

GREGGPENN

Another way to put this is the aftermarket aux fan switches have too low of a turn OFF temp. If the thermostat holds temps above or near the turn-off temp (and the ones sold in Corvette catalogs do), the aux fan will run all the time. I posted a thread on this a few years back...and included a better option that comes on near 215 and shuts off at 200.

GREGGPENN

Tom and mtwoolford: Thanks for taking the time to better explain what I was getting at in post #6.

enventr

DrDyno,
Let me know how the temps are in June while in traffic. I would be interested in those results. I have thought about the 160 for some years but now I'm living in Florida and may try it. As many mentioned above it will take longer to get to those temps. In traffic the 160 may be the same temps as I have on the 180 stat. thanks To you and everyone else on this post for the above information.

DrDyno

For VetteLT193 and enventr...

I had my '96 out two evenings before I changed the thermostat, fifteen miles in each direction to our local club meeting. It was 7 or 8 degrees cooler that evening than the afternoon after the thermostat switch.

With the A/C off, my car easily reached 200° in traffic. I also have a manual fan switch on a relay which I switch on during such occasions and, that evening, was able to keep my temps from exceeding 201°. In the summer with the 180° thermostat, I usually stayed below 205° in traffic, with the fans on. Two days later with ambient 7-8° higher, my car never exceeded 191° with the fans on.

The point I'm making is there is no doubt in my mind that my temps will be lower all year round with the 160° thermostat compared to where they were with the 180° thermostat.

enventr

Thank you for your reply. I just ordered the 160 hypertech and will try it. I'm leaving the stock fan settings. This is not a daily driver. Majority of the time the a/c will be on which will activate the fans. I also have a tranny cooler so the trans temps will go down a few degrees as well. I do not have any annual emissions testing in Florida like I had in NY. So I do not have to worry about emissions. Do you notice any difference with the a/c running in traffic Vs. fans on without a/c in traffic as there is more of a load on the engine

Thanks again

DrDyno

DGXR

First, I don't understand why a 160F thermostat would just begin to open at 172F. Wouldn't that be called a 172F thermostat?

One of my past cars would run erratic cold/hot/cold in the summertime (according to temp gauge) and in diagnosing, I found a previous owner installed a thermostat that is cooler than factory spec. SO I learned that coolant needs to spend a bit of time in the radiator to be effectively cooled before being returned to the engine. A lower temp thermostat will sometimes stay open, depending on conditions. An open thermostat allows coolant to flow constantly through the system, in which case the coolant might not spend enough time in the radiator to cool off, so it's returned to the engine too warm, which was causing my hot/cold issues. A factory spec thermostat cured the problem, the gauge stayed rock solid no matter the outside temps. This story might or might not be helpful to anyone.