The Stovebolt Site Forums The Shop Area Engine Shop Correct thermostat for 235?

Is a 180° thermostat correct for a 1955 235 or should I get one that opens up a little sooner? Gets hot here in south Texas during the summer and I don’t want to over heat.

A thermostat sets the minimum operating temperature- - - - - -the condition of the radiator and the volume of air across it determines how much hotter, if any, that the coolant will get once the thermostat opens. The only exception to that rule might be if the engine idles for a long period of time in very hot weather. Are you running an original radiator, or an aftermarket one that's rated for higher pressure? Ditto for the heater core. A 1955 truck probably had a 7 pound radiator cap that allowed the coolant to reach 233 degrees F. before it boils.
Jerry

Jerry, I’ve still got the original Harrison radiator and original heater core in my 1950 1/2 ton. The newly acquired 235 is a 1955 model.

OK- - - -I believe the 1950 models had either a "zero-pressure" radiator, or no more than a 4 PSI rating. Does the overflow line come from the filler neck above the radiator cap gasket, or is it incorporated into a canister high up on the top radiator tank? With a low or "no pressure" system, it might be wise to use a 160 degree stat. The only downside will be poor heater performance in cold weather. Be very sure the cooling system is clean and leak-free.
Jerry

This brings up a question in my mind. I purchased the copper/brass “direct replacement” radiator from Jim Carter several years ago. I always assumed it was a a low/no pressure unit just like the original Harrison it replaced. So I just re-used the cap from the Harrison.

Now I’m wondering what the replacement is rated for. How would I tell?

Call Jim Harrison and ask him.

My 1950 216 has the original radiator and a 4 lb cap.

Have you been having over heating problems that can be traced to your thermostat? If not, I'd leave it alone and keep an eye on things. If it acts up and the thermostat is to blame you can always change it later.

I once overthought a similar situation and thought I had a problem when I didn't. I reduced the T stat from a 195 to a 180 on 1972 Monte Carlo. The temp gauge was showing 230-240 under normal operation. I thought that was bad. (car ran fine)

I put in the lower temp T stat and the car ran like total crap! It never got hot enough to run right until I put the 195 back in and let the engine get hot.

This is for a 54. They don't have 55 truck listed. It should be the same.
http://chevy.oldcarmanualproject.com/chevyresto/54151.htm

You guys are over engineering this.
If you put in a 160 thermostat a 235 will run at 180 F
If you put in a 180 thermostat a 235 will run at 180 F
It is the design of the engine.
I have tried both and each runs at 180 F.
Doug

You are undoubtedly correct however the OP asked what is "correct", not what will work. The "correct" thermostat is listed in the link Tim posted above.

I'd suggest calling the supplier and asking what the pressure rating is. Be aware that if the radiator is built to handle a higher pressure, then the heater core becomes the limiting factor. It would need to be upgraded as well.

Any engine that routinely runs 20 degrees over the thermostat setting either doesn't have enough radiator, or the cooling system is terribly dirty.
Jerry

That is exactly the balancing act. Most motors run best at around 170-180. There are exceptions of course. The thermostat stays closed until the water comes up to temperature, whatever the therm is rated at. So If you have a 160 thermostat, that is not the temp the motor will stay at, that specification is the tempreature the therm opens at. At that point, the speed of the water through the engine, fan efficienty and radiator capacity now take over to keep the temperature at or about operating tempreature. If you have an over efficient system, when the therm opens, the system is so efficeint that the motor looses too much heat and cannot maintain operating tempreature. If the system is underefficient, it does not matter when the therm opens, 160, 180, 120, lol, if the system is undersized or mismatched, it can't maintain operating temperature, and runs hot to some degree. The trick is to get the system matched up so that it maintains a good operating temperature at all speeds, but especially at idle.

So your water pump has to run at an appropriate speed, like goldilocks, not too fast, not too slow. The radiator has to be of sufficient capacity and the fan has to be able to move an appropriate amount of air through the radiator, especially at idle.

Two sort of examples, big rig trucks with diesel motors tend to have a very, if not over efficient, cooling system. In the wintertime, this leads to some trucks not being able to maintain temperature which is why you sometimes see a truck with a big piece of cardboard in front of the grill to cut down on air flow. The other, at one time I was invlved with a super comp NHRA dragster that ran on a pair of alcohol fueled holley carbs. The alcohol caused the motor to run cool, really cool. So in order to get the motor to180 at the starting line, we had to let a race motor, with a teeny tiny radiator, sit and idle in the staging lanes just to get sufficient heat in the motor. What we learned was that the motor did not run as well at 160, 170 as it did at 180-190.

So maybe try installing a 180 thermostat and a 4 lb cap and see where you are at. You will need an accurate guage. I chuckle over the number of folks that use the original guages as the ultimate arbitar of accuracy. Don't fall for that. Install a good name brand electric or mechanical temp guage and get some accurate readings. If the motor is running hot, you can start to fiddle with fan shrouds, 5 and 6 blade fans, larger capacity radiator. Last year I got my hands on a five blade 348 Chevy with AC fan and installed it on my 261 motor. Finally, the motor ran at 190 in 90 degree plus heat. The extra blade and more aggresive pitch made a huge difference with air movement through the radiator at idle, as an example.

You should also confirm that you are using the pullys for the year motor. If not, you should consider doing a little math and see if that may be part of the issue, too slow or too fast on the water pump.

Always exceptions, you might get lucky and be one fo the few that can regulate operating temperature by changing the thermostat, but if you are not, you may have to tinker a bit to dial it in.

This! The other thing to keep in mind is that "engine temp" is not a uniform thing. The coolant enters the engine at its lowest temp, then picks up energy (and raises temp) as it goes through the coolant passages and comes out at its max temp. Because of that, some caution needs to be used when talking about "normal" engine temps because that will be affected by your measurement location.

As a specific example, an LS has the coolant temp port on the front driver corner, in the head. The heads are symmetric so you can add an additional one at the rear, passenger corner. It is fairly common to use the driver (stock) one for the ECU and put in an aux-sender for an aftermarket gauge in the passenger one. These two locations will read temperatures 15F-ish apart because the passenger side port is only about halfway through the coolant flow. I have seen plenty of people spend an inordinate amount of time trying to "fix" the operating temperatures from measuring it at a different place.

Another "old mechanic's tale" (That's an old wives' tale about fixing cars) is that an engine is "overheating" when the coolant isn't boiling. The clearances built into the rotating assembly, valve guides, and other oil-lubricated parts determines the point where an engine is running "too hot". If you want a higher operating temp for whatever reason, install the appropriate thermostat to keep the coolant at the minimum temp you want, clearance the moving parts to be happy at that temp, use a lube oil that works at your target temp, and build a cooling system that will transfer enough heat to keep the whole works at your pre-selected temperature. Use enough cooling system pressure to keep the coolant from boiling. Every pound of pressure on a 50/50 mix of water and antifreeze raises the boiling point at sea level by 3 degrees F. A 15 lb. cap keeps the coolant from boiling below 257 degrees at Daytona Beach- - - - -the "boil over" temp is a little lower at the top of Sonora pass at 10K+ feet elevation.

Like a lot of other things stovebolt-related, making very generalized statements about engine cooling is rarely doing anything more than stirring up a bunch of hot air!
Jerry

Tim’s link to the 1955 data says the correct thermostat begins opening at 148-156 F. and fully opens at 176 F. Does this describe a 160 or a 180 F. thermostat? If it makes any difference, I’m more concerned about overheating in the summer than I am about having a hot heater.

Thank you all for all the detailed comments to my question! I’ve learned much more than I thought I would. You guys are awesome!

I'm going to assume (yes, I know what that makes you and me!) that those specs are for a 180 stat. 176 is 16 degrees ABOVE a 160, which doesn't make good nonsense!
Jerry

Maybe it's a typo and should say 166 degrees?

My understanding is the 'start' temp is the rating of the thermostat. Since it starts at ~160 I'd say it would be a 160 thermostat. It's handier to call it a 160 instead of a 148-156 thermostat. A quote from the Motor Trend article linked below: "If a thermostat is advertised as "195 degrees," that means the thermostat is designed to start opening (thus allowing coolant to flow through the radiator and cool the engine) when engine coolant temperature reaches 195 degrees."

https://www.motortrend.com/how-to/how-to-choose-a-thermostat-for-your-classic-car/

Thanks for sharing the MotorTrend article with us Tiny. It really does make sense if you think about it…… the thermostat will start to open at either 160 or 180 F.
Based on the Chevy stat sheet it looks like I need a 160 F. thermostat.