Repairing Your Imperial's Thermostat


Imperial Home Page -> Repair -> Cooling System -> Thermostat

How To Locate and Replace Your Thermostat:

Replacing a thermostat is a relatively easy task. If your temperature gauge is running way down on the low side and your heater isn't putting out much heat, it's time to replace the thermostat. Here is a description of how to change a thermostat. The exact location of your thermostat may be slightly different but most of them are near the top radiator hose in the top of the engine.

The thermostat is normally in a housing which is at the engine end of the top radiator hose. Drain the coolant into a drain pan - toss it down the john - it's the correct way to dispose of it. Take a screwdriver and remove the hose clamp from the top hose where it meets the top of the engine. Get a flashlight and see if you can peek down the hole and see the thermostat. If it is faulty it will be open.

Not all thermostat housings are identical but typically it will be held on with two bolts. Remove them. Tap the thermostat housing with a wooden block or a soft faced hammer. It should pop off easily. You can then see the thermostat. Lift it out. Don't sweat the gasket - you are going to replace it anyway. Use a new gasket. Scrape EVERYTHING off both mating surfaces. Use a single edged razor blade. Apply some blue rubber sealant to both sides of the gasket. Then grab it between your fingers and "squeegee" any excess off. You don't need a lot of sealant.

Make sure you put the gasket on the right side of the thermostat. The stat will normally fit into a recess in the engine, the gasket goes on top and the housing on top of that. Wipe a bit of blue rubber sealant inside the hose, put it back onto the housing nipple and clamp it back in place.

You should probably drain all of the coolant by draining the block but if you can't find the small plug it the side of the engine don't sweat it. You should mix antifreeze and water in a ratio of 50-50 and replace what you drained out with the fresh mix. If you can't get all the replacement mix in while it's cold just warm it up a bit and watch the level drop as the thermostat opens up. Then add mix until it is totally filled. Replace the radiator cap and put a quart or so in the overflow bottle (which you should have drained previously).

How to test a thermostat and the correct temperature for a thermostat:

Microwave a bowl of water, and drop the thermostat in.   If it opens, it works.   If not,  it needs to be replaced.  The correct temperature thermostat for the Imperial is 180-195 degrees...for all engines.


Is it necessary to run a car with a thermostat?


From Carmine:

I would advise against running any car without a thermostat. Part of a thermostat's job is to keep coolant in the radiator long enough for it to "cool". Taking out the thermostat is for guys in primered-up Chevy Novas. Let me assure you, that as long as everything is "up to snuff", you'll have no overheating problems. My '61 LeBaron is 100% stock, the engine has never been rebuilt, it still uses points, the carburetor is original, etc. I have replaced the water pump (not from failure, just maintenance) and all belts/hoses. The original radiator still flows well, so it hasn't been re-cored. Also keep in mind that my '61 probably has the smallest grille opening of the whole '57-'63 series. (Horizontal bars are very close). I drove the car from Detroit to Auburn, Indiana at the end of August 1997. Dual A/C on the whole way. Trust me, I don't drive slow. Not only did the car not overheat, but even at 5 MPH "parade speeds", the temp gauge never went past 1/2. I've also driven the car in several local cruise nights, including Woodward Ave, which is nothing but a 90 degree, asphalt parking-lot. I wish I had a dime for each newer model car that had to be pushed off the road in a cloud of steam. (I glided by silently, except when a late model piece of foreign junk was being towed away. Then I yelled "Get a horse!") (That's one of my favorite put-downs, because it has historical/educational value). Anyway, before you re-engineer what was properly designed in the first place, fix the PROBLEM. I've re-cored several radiators on my cars, never at a cost of more than $200. I think this, and a pressurized flush should be your first step.

From Norm:

Taking the thermostat out completely eliminates increased pressure and the engine will never reach proper operating temperature and the will cause premature sludge build-up and other unwanted side effects-like no heat in your heater. Of course, if you do not 
drive the car very often , it really won't matter. 

As an opposite point of reference, I always put in the proper thermostat and radiator cap , 50/50 antifreeze to water mixture and regularly drive my cars all year round.  In the winter I have heat and in the summer I have air conditioning with NO overheating-even at idle with the air on in any of my current or former cars-even on a summer day in the desert.

If the cooling system is clean, the water pump is good, the fan belts and fan clutch( if so equipped) are in proper working order and the timing is properly set, I have found no reason to bypass the way the car was originally designed to run. No pinging, no overheating-ever.

From Gregg:

I definitely agree with keeping a thermostat in the car but for a different reason. I ran my Chrysler without a thermostat for a while, but my car was running hot. I guess it depends on the motor, but in my case I was running hot because the coolant was flowing so fast it didn't have time to cool. This stopped when I installed the thermostat. For good measure I also drilled an 1/8" hole in the side to allow some water to flow through no matter what. I have heard even race cars will install a restrictor plate to slow the flow of coolant just enough to allow it to cool down.

From Steve:

You really need a thermostat. The thermostat acts as a restrictor as well as regulating the temperature. Without the thermostat the water can travel faster than it should through the engine. When the water goes to fast it doesn't stay in the radiator long enough to cool properly and can cause also cause the heads to run hotter than normal. This might be a good time to have the radiator rodded out and flush the engine block. I would probably go ahead and replace the water pump as well and check for rust in the water pump housing when you pull the water pump.

Tip from Brad:

To preface this saga, I had the radiator cleaned, flushed and pressure tested earlier this spring. I had installed a new thermostat along with water pump, hoses, rebuilt heater core, etc.; the whole system is "new". The first time I started the car after that the thermostat stuck and took a rap with a screwdriver to open. I believe that I got a bad thermostat and that it stuck again yesterday. After the car cooled down (after work) i drove it with no problem for almost an hour making several stops around town. Anyway, I bought and installed another new thermostat and arranged to have the radiator shop re-flush the system. The car is there now and I'll pick it up later. Once again it's a $2 part that keeps most of us off the road! AAArrrrgh! By the way....those little 4-inch Craftsman wrenches are perfect for getting out and in those water inlet housing (water-neck) bolts. 9/16 on these bolts.

Question from Zan:

While I was (literally) crawling around in the engine this weekend I was reminded that my previous mechanic suggested when I had the radiator replaced I probably needed to replace my thermostat. What's involved in doing this? Now that I'm feeling empowered I thought I might give this a whirl if it's not to hard :)


From John:

The thermostat is very easy on a 62.  It is located in the housing at the bottom end of the upper radiator hose.  Drain the radiator first.  If you're car has a/c the bolt on the right side as your looking from front to back is a little difficult to remove & you'll also find this bolt to be shorter then the other.  After getting the bolts out, remove thermostat & note which way it is facing as it has a definite up & down position.  If you put it in upside down, it won't work.  Clean off any old material that are on both surfaces.  Install the gasket & I like to use a small amount of the green Permatex sealer on both sides of the gasket.  Reassemble, fill coolant and check for leaks.

From Norm:

It is very straight forward.  Two bolts or nuts hold it on . It is easier to get to if you remove the upper radiator hose where it goes in to the engine.  The thermostat is right in that ball shaped housing that the hose attaches to.  Just make sure you observe the way the original is set in there-set the new one in the same way( hoping that the original was positioned correctly).

Question from Chris:

I have decided to tackle the cooling system on my 65 LeBaron. I have successfully replaced the heater control valve (thanks to Bob Hoffmeister), removed the radiator and have sent it out to be fixed (small leak at the top tank seam). I will soon be replacing the thermostat, water pump and all hoses to be finished by a spanky refurbished radiator. The question you say? There is a sensor between the two heater hoses on the engine, near the thermostat housing. Am I correct in assuming that this is the temp gauge sensor? If so, how many wires should be attached? Mine has two attaching points but only one wire running to it. My temp gauge seems to work but is a bit lazy, rarely going to the normal range. Should I be looking for another wire or should I just try cleaning the contact on the one and see if the gauge is more accurate? I am deferring once again to those who have encountered this before.  

Reply from Bob:

My '66 only has one wire for the temp gauge to the thermostat housing and it connects to the "point" on the top. I had no special burping problems when I drained and flushed my radiator. I used Havoline Dex-Cool, which is a new "long life" coolant that claims to be less corrosive and abrasive than other coolants. It's about the same price as other major brands and the orangeade color is a nice change of pace.

Tip from Gary:

If you have replaced your thermostat and you feel that you are still having problems in that area of your cooling system, you may want to add a restrictor plate.   If you have too much water flow, you may have to fit a restrictor plate to slow down the water and give it a chance to absorb the heat while flowing through the radiator when driving on the highway. 

Question from Gregg:

Where can we purchase a restrictor plate?

Follow-up from Gary:

The restrictor plate can be made out of any non corroding metal, usually brass, I have in the past sometimes cut out the center of a thermostat and used that, this was while working out optimum flow rate, a hit and miss affair if watching the water flow in the radiator cap hole isn't your specialty, thin sheet brass cut out with tins snips is what I use, one really has to experiment on the road until you get the right flow, I know this sounds a bit iffy, but with older cars and radiators being changed and cores having different replacement types, water pumps changed and maybe even the pulley sometimes, the original Chrysler setup isn't always going to work, I live in a temperate climate where one actually doesn't need the thermostat and when it would fail I would simply give it the flick, on the odd occasion the car would overheat as the flow was too fast, hence the plate. I'm not sure if there are commercial products of this type available.

Question from Tim (1962): 

Can anyone tell me what the correct thermostat temperature setting is for a '62 413cui.  The one in the car is 180 but the car is running really hot. Car also has a 15lb radiator cap. 


From John:

It sounds like you need a real good engine flush and or radiator rebuild--- after that many years those radiators and heater cores can get really plugged up....

From John (different respondent):

On the 413 which was made from '59 thru '64 (I think) the factory thermostat was 180 -- that's what I run in mine with good results.

Question from Mark: 

 I was going to replace the thermostat, but then I started looking at the housing, or cover, for it, and I noticed that the paint had flaked off almost completely.  I was wondering if it would be better to paint this thing again before installing it (the thermostat housing or cover), and if so, does it require a primer or can I just spray some correct color engine paint on there and be done with it?  My goal is to reduce corrosion & rust (yes, even aluminum will rust out).


From Dick:

residual antifreeze left in the block to protect it overnight. I think the thermostat housing was aluminum, anyway if it isn't cracked a coat of paint can't hurt I don't think Chrysler bothered with any primer Matt

Follow-up from John:

An easier way to purge air out of the cooling system is to let the engine warm up with the radiator cap removed & as the coolant circulates the air will move into the radiator & bubble out.

From Peter:

I'd suspect the radiator, even though the problem came on so suddenly. I had a 66 Fury wagon (383) that my parents had purchased new and the dealer always serviced it. I can't remember exactly how it began, but it suddenly started to overheat. They took it to the the dealer who told them the block was obstructed and quoted them some horrendous price for pulling the heads and rodding out the block. They took it to a local garage for that work and he didn't find anything wrong. It still over heated so he replaced the thermostat and water pump. Still overheated (violent radiator eruptions and nasty churning noises from the block). They gave up, bought a 76 Fury wagon, and gave the 66 to me: "If you can fix it, you can drive it." I discovered that I could extend my driving range by turning the heater up full blast and opening all the windows. Partial success in hand, I suspected that the radiator was at fault. After all, isn't the heater core just a miniature radiator? I took the radiator to a specialty shop where they offered flow testing. My radiator, which was supposed to flow either 20 or 22 gallons per minute, was flowing only two gpm. Problem solved. For 80 bucks (1978 prices) I got the radiator recored and the car ran great. Check radiator shops in your area for a shop that offers flow testing. It's a pain to pull the radiator but you'll be able to positively eliminate it as the source of the problem. 

Question from Mike:

Where can I find a thermostat housing for a 413?


From Dick:

They are the same as on the 440s and they are still in stock at NAPA.

From Brad:

I agree with Dick and can testify to the truth of the matter. I bought a thermostat housing (water neck) for my '66 from NAPA last week. About $13.00. They listed both the A/C and non-A/C parts. I had it the next day. You might get lucky at a bigger store and find it in stock.

Tip from Dick (1981 -1983):

Readings for the correct resistance for the EFI Coolant sensor: I just remeasured 4 of them that I have easy access too, and they are remarkably consistent for this type of device. They all measure right about 970 Ohms at 70 degrees F, and 1310 Ohms at 180 degrees F. It is possible that wider tolerance is not a problem, but since these are so closely grouped in value, I suspect that the specifications were held very tight.

Second, the size of the socket required to remove this device is 15/16th", deep, 6 point, at least for the factory part.

The NAPA EFI Coolant Temperature Sensor Number is TS5008. I am looking at one now, so it is certain.


Tip from Joe:


As a safety precaution against getting hot when the stat sticks, I will always put three (3) 3/16s holes in the plate of the thermostat. It is a back up trick we used to use years ago. I personally do not use thermostats here in Palm Desert. My 61 Crown with its 22 inch radiator runs 170 without the stat and the air on when it is 100 degrees. My 61 LeBaron runs 160 with the air on when it is 100, with its 28 inch radiator and dual air. 

Follow-up from John:

This may work for the "older" cars, but when you get into the 70's cars with the spark control system it won't, I had a 77 NYB that ran good for the first couple of minutes after startup, but after that, the performance just fell right off. It was hard to get the car past 50mph; The problem turned out to be that the thermostat was stuck open & the sensor was telling the computer that the car was still cold. Replacing the thermostat solved the problem.

Follow-up from Joe:

I would assume that you all would have a radiator rodded out or replace the core. Then do your driving. At that point is where I will not use a thermostat as I can get away with no problem pinging as I always want them to run as cool as possible here in the desert. If you are going to drive an Imperial, do not think that you can assume all is well when it sat for so many years. I run a coolant filter so it will NEVER get plugged up. If you are going to drive an Imperial, spend real money to get them in the shape they deserve or you will be sitting on the side of the road. Remember, a customer buying a new Imperial back when, had real money and could afford anything to be done to keep them representing the upper class people that bought them. So, do not think you can cut corners or get it cheap as these are not cheap cars. They demand the best, so give them the best. I base all my answers on giving the car all the new or perfect used items they need if you are going to drive them like they used to be driven. If you bought a new one, it did not have used or defective parts so you could make long trips in. When I talk about an Imperial, I am relating to being able to do the proper and most likely expensive way to do it perfect. You cut corners or can't afford to do something, then maybe a Chevy should be in your driveway. Some of you will take this wrong, but they are not understanding where an Imperial went. These people who bought them new, had lots of money and probably would have not paid attention to you in your Ford or Chevy, or for that matter even a Cadillac. So, give that Imperial your very best as it represents all of us on the road. Keep them in the upper class that they deserve. That is my Imperialist answer. Remember, good parts are not cheap and cheap parts are not good. A serious investment now will give you many happy returns.  

This page last updated October 10, 2003.  Send us your feedback, and come join the Imperial Mailing List - Online Car Club