Packard Forum Index » Project Blogs

Some thermostats have a small hole or notch to allow air to escape when the system is filled. If no hole is present, it might be a good idea to drill a small hole in the flange, maybe 1/8" or a little less. You don't want air trapped under the thermostat. I don't know if the modern thermostats have the same flow characteristics as what Packard used. A thermostat is supposed to start to open at its rated temperature. It may not fully open until the coolant is a number of degrees above that.

I took another look at the 1937-38 shop manual. It states that 1937 cars used cylinder head thermostats only. But, we know that is not correct for the CDs. It states that for 1938, all Eights (120s) used Sylphon thermostats for the grills. Thermostats in the cylinder head were available to improve performance in heater equipped cars. But, it also states that the cylinder head thermostat should be removed in the Spring.

With that, I will not add a cylinder head thermostat as it seems that Packard was concerned about overheating in the summer time with the cylinder head thermostat being used in addition to the thermostatic controlled grill.

In this snapshot from the shop manual, the first paragraph is for the 1938s and the second for the 1937s. I think the first paragraph (1938) is what is applicable for my 1937 CD since we know the CDs were equipped with the thermostatic controlled grill. So, the parts list including the cylinder head thermostat still makes since as it is listing what could be added in the winter time to improve heater performance.

Unless you use alcohol antifreeze, you can use the 162 F thermostat all year long. The Low temp thermostat was meant to be used with volatile alcohol antifreeze, which was never a good idea anyway. Cold running engines waste gasoline and accumulate combustion chamber carbon and crankcase sludge and rust due to moisture accumulation, especially if they are not driven often and for longer trips. Piston ring wear is increased and gasoline can pollute and degrade the engine oil. Take advantage of modern antifreeze and use the higher temp thermostat. Ideally, a Packard engine would run at 180 to 190 F, and 200 to 210 at the water outlet is no problem. The thermostats originally used in pre-war cars are no longer available, as far as I know, and old ones may not work as they should. Modern type thermostats work on a different principle and probably react differently to coolant temperature than the older types. I suspect that the modern units open more fully and quickly when the correct temperature is reached than the earlier ones did, and do a better job of regulating the coolant temperature. The thermostat in my car appears to be an older one with a coiled bimetal strip that operates the valve. It probably does not work as it should, but it does open and close.

I guess my point is that I see no need for the second thermostat for the following reasons:

1) My car seems to run right at the 180 degree point very consistently until it’s 90 plus degrees outside. Then, it runs a little warmer.
2) My car ran a little e cooler, around 170 when it was 25 degrees outside. Now, I did let it warm up before heading out.
3) I don’t plan on driving the car if it’s less than 25 degrees outside. The only reason I did it the last time was to get my car to the body shop before a big snow storm hit that would have delayed getting it there by a week.
4) Installing the cylinder head thermostat would likely cause the car to run warmer in the summer due to a decrease in flow. It probably isn’t much, possibly not even noticeable, but anything put in the path will at least reduce the flow some.
5) Adding the second thermostat does introduce another point of failure. I know the modern thermostats have a very low failure rate and it likely would never need replaced again in my lifetime.

Anyway, I don’t dispute any of what you’ve mentioned, but it is only applicable if my car were running on the cool side. It isn’t.

If I ever get to a point where I’m driving in very cold weather, I can always add it. In the meantime, it’s in the “if it ain’t broke, don’t fix it” category.

According to the dash gauge, my car runs about 180 F in cool weather, and 190 to 200 F in hotter weather. It has never boiled. I assume it runs hotter in warm weather because the radiator is partially clogged. Removing a properly functioning thermostat will not cure a partly clogged radiator. Systems originally equipped with thermostats are designed to take advantage of the slight restriction offered by the open thermostat which offers several advantages, especially in alow pressure or non pressurized system. A car heater will not perform well without a thermostat. My heater works very well, with quick warmup and plenty of heat.


My car is prone to vapor lock in warmer weather, which I attribute to any or all of several things, including possible fuel line restriction, missing fuel pump heat shield, possible worn fuel pump cam or linkage, and the characteristics of modern fuel blends, which are not designed for atmospheric fuel systems, engine-mounted fuel pumps, and carburetors. A proper heat shield would probably eliminate the nuisance.

Really no dispute and I enjoy the education discussion. You mention “systems originally equipped with thermostats”. Again, my car (as well as all of the 1938s), were not originally equipped with cylinder head thermostats. Those were only installed if requested, and even then, only in the winter time. They were removed in the summer.

Also, I’m not “removing a properly functioning thermostat”. At least from 1960 forward, my car never had the cylinder head thermostat. I don’t know if the owner(s) between 1937 and 1960 ever installed one in the winter time. I do know that Dad drove the car all winter long for five years (1960 to 65) and said the heater always worked well. Now, with my car being a limo, Dad also said “if the people in the back wanted heat, they’d better leave the divider window down”. You also mention that “a car heater will not perform well without a thermostat”. I agree with that, but we also need to remember that I do have a thermostat, just not a cylinder head thermostat. I’m know the cylinder head thermostat would regulate the temperature more quickly, but that doesn’t mean the grill louvers are complete ineffective.

As I’ve mentioned, I really don’t intend to drive in the cold often. Once the engine temp is above the point where the cylinder head thermostat would be open, the heater will perform the same. The only thing the cylinder head thermostat does is get the engine temp up to that point quicker. I suppose, if it was cold enough, the engine might not get to 160 degrees without the thermostat, but I definitely won’t be driving it if it’s that cold out.

When I drove my car in 25 degree weather to get it to the shop (about a 30 minute drive), I was not uncomfortable in the car. That was with no heater or roof. Now, I also didn’t have any of the firewall insulation etc.., which definitely allowed in a little heat from the engine compartment.

I do really appreciate all of the input. I enjoy the discussion. You clearly have a lot of knowledge and experience and I learn a lot from these discussions!

I’m heading out now to go to the shop. They were supposed to be getting my car in to be epoxy primed on Friday. If that happened, I’ll have a nice green car for St. Patrick’s day!

Most of my car has at least made it to the paint booth to be turned green (primer). The rear fenders have already been primered. The front clip has received the needed repairs and is ready for primer. I also brought the grill home to clean and polish. The last picture shows the only wood that needs repair. It’s above the passenger side front door.

Are they going to take the floors down to bare metal and prime them as well?

The one floor panel that is completely rusted out will be replaced. Everything else is very solid. It will get cleaned up and wire brushed really well and then coated with rust encapsulator. I will go help with that since it is something I can do without being in their way. It will also be fun and save me some $$. My labor is a little cheaper than their’s!