For a 64 min A/C Deville - what is the correct temp thermostat. I'm going to replace mine and notice there are several temps offered.

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I think the OEM was 180

The cooler ones let more coolant flow (they open up at a lower temp) and are good for cars with cooling issues (like older cars with the A/C running, in stop and go traffic and the original radiator).  The higher temps allow the heater to work better and faster is cold places. I think you may get somebody telling you the engine runs better hot (better mileage or smoother idle) but generally running cooler is safer for the engine. 

I have a 4 row hi capacity radiator and a 180 degree stat

Here is a repeat in Info I had previously posted:

180 degree thermostat is what was listed in the earlier master Parts books (thru 1967), Later Master parts book (1969) lists both a 180 degree and 195 degree thermostats. I have always used the 180 degree thermostat with excellent results and it goes along with what is stated in the Shop Manual.

The shop manual states: "The thermostat valve should start to open at a temperature between 172 degrees F and 177 degrees F. When the water reaches a temperature of 198 degrees F, the valve should be fully open." 

The stated rating of a thermostat is the temperature at which it starts to open within a few degrees. Per the info on the Stant Thermostat site "The thermostat fully open about 15-20 degrees above its rated temperature", which is consistent with the readings I have taken on the top of my engine of about 195 degrees.  For more info on thermostats click this link to go to the Stant site:

With that,  I think either thermostat would be fine, although for a high mileage engine or one you want to keep a bit cooler in higher temp climates to offset the additional heating, I would tend to run the original spec 180 thermostat. On the converse driving in very cold winter climates I might tend to go for the 195 thermostat if nothing else to keep the water in the heater hoses running through heater core a bit warmer...and keep yours truly a tad more toasty.

As a side note an engine with an over heating problem will not run cooler with a lower temperature thermostat. If a cooling system can't maintain 200 it definitely will not maintain 180 or even 160 degree thermostats. If the cooling system is working properly a lower temp thermostat can help our high compression engines with hot spots in the combustion chamber by lowering internal temps.

Hey, just a quick note, are you sure its overheating? like overflowing radiator or using a thermometer to read the actual temp,  the reason I state this is I have went through two different temp sensors and still have none that will read right, they literally max out my gauge when the motor is at 190 degrees.

Robert is correct. Most of the new temp sending units are mis-calibrated. I sell good used ones for $5 + s/h. I would also suggest a digital IR temp gun. You can get them as low as $20 on sale:

The thermostat controls how cold an engine runs.  If you don't run a thermostat, your engine will take a long time to heat up, and could run too cool, as it will not regulate the coolant flow.

The thermostat has nothing to do with how hot an engine runs. (unless the thermostat is bad, where they usually malfunction in the closed position)

You can get high flow thermostats, but these cars were designed with a very good coolant system. If your engine is running hot, the coolant system needs attention.   Radiator, water pump, coolant passages in the engine may need attention.  

I have installed a temperature gauge in my car. I put the sending unit at the hose that comes out of the thermostat. Normally it runs at just shy of 180 degrees. But in traffic in the middle of summer here in South Florida I've seen it go up to 230. Once I start moving again it goes back to 180. Should I be concerned about this or is this a normal situation?

I have found that coolant that is old and does need replacing will not transfer heat as well as it should and a change will improve that

The ratio of coolant to water ( sb 50/50 ) and  will effect the heat dissipation if not correct

To much coolant to water will reduce heat transfer from my experience  living in a cold climate NY years ago 

I am using a 5 year coolant in my 64  now 

I know they sell additives that will lower the coolant temp by 20 degrees but have never used them 

Depending which fan you have in the car a fan with more blades will improve air flow over the radiator thus lowering the temp 

If your car did not come with a fan shroud installed installing  one has to help air flow 

Owning my car since new I do have to say the stock cooling systems in the 64 when working properly will be all you need as I have been using my car in 80-90 degree weather in Florida for 15 years 

My engine has gone up to 200 degrees ( 1/2 way mark on a stock gauge working well ) but comes right back down 

My 64 —-with A/C  came with a 5 Blade   non- clutch type fan which I think my have been upgraded to a clutch fan at some point in production but it does the cooling job to perfection 

I do know that some models in our years have 7 blade fans ( I think the limos ) stock that could help reduce temps if installed 

If the radiator is clogged with debris it wii have to be replaced

A radiator shop could tell if the rad needs replacing - by its weight 

If the engine water passages are clogged a flush will be required to clear them out 

Sant sells a thermostat that when it fails   It will fail in the open position and not overheat the car leaving you stranded  

I always use the Stant pressure release rad cap on all my cars for years - for safety reasons

The only time I had a problem I broke a fan belt that removed all the belts and the pressure release rad cap can prevent you for being burnt by very hot coolant 

Let’s not FORGET —-I am the recipient of the Golden Thermostat Award ( that is another long story !)

Stay Safe  

I installed an aluminum Radiator a couple years ago. Funny story, I had what I thought was a radiator leak so I replaced my original one with the aluminum one when I got the car home because I heard it runs cooler, not true. Only to find the hose next to it leaked & was squirting on it near the top at the base of the cap. In my defense when it happened it was night time & very dark. I don't have a fan clutch, I do have a fan shroud, which I built side covers for & isolated the top & bottom. So I have a ton of air coming through. I'm leaning towards replacing the after market what pump I put in a few years ago with an original one I found on Rock auto. I am just hoping it makes a difference. As anyone who has replaced a water pump on these cars knows, not a fun & 5 minute job.

Hey Joe D 

Just a quick Hello — my friend 

Be safe 

Hello Buddy :)

Using the 180 degree myself these days 

The 195 has worked well for me as well for many years 

180 degrees on a good working  stock temp  gauge  will be just past the 1/4 mark on the gauge 

Some aftermarket sending units are not calibrated correctly — so buy them from our Web Master Jason Edge or Russ  (  Trust me — they deserves all the business you can do with him ! ) 

Oddly stock factory —was 185 degrees not easily found 

I know Russ has one 

Be safe 



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