1948 Desoto radiator cap presure

The cap that you should be using on your radiator is an R-3 Radiator cap. You can find them for sale on Ebay.  Your system is a non pressurized system so not install a pressured radiator cap.

Rich HArtung

desoto1939@aol.com

Thanks Rich, I restored a 1948 7 pass long wheel base sedan about two years ago, the original radiator leaked like crazy so I replaced it with an after market aluminum one as temporary fix , the new radiator came with a 16 pound cap , I have been running the car all this time and I had coolant leaks, water pump , freeze plugs etc . I dug my old radiator out of the attic and found that it has a overflow tube at the highest point and a solid cap with no spring. I guess I will try to run the car with the old cap? I may loose coolant out the overflow as it is in the filler neck  and not at the high point of the radiator, I would guess that there is some kind of baffle in the original  overflow? Need to find a good original radiator. Thanks for the info Bill.

@billcypher

Bill: Yes you had a non pressurized system and then by adding a pressure cap it had caused you the issues that you mentioned.  Yes the neck of the radiator has the overflow tube just like on my 39 Desoto.  So when the  amount of water has expaned in the top of the rad then it will seek its own level and permit the excess to flow out and down the overflow tube Do not refile the radiato it should be about an 1/2 below the bottom of the radiator neck.  It will seek its own level.

As another point of interest is that since you have a cast iron block every year you should put in some Radiator anti rusting fluid. It is a milky white color and is about 11 oz. I got might at NAPA made by GUNK.  This product helps keep the antirusting agents active in your green antifreeze. Over time the rusting agents break down. When you check your AF and it has turned brown of milky chocolate color then rusting agents have gone away. Then its time to flush and install new AF and the old GREN stuff not the newer stuff.

Rich Hartung

Desoto1939@aol.com

Thanks Rich , I think I have everything worked out, I made a baffle out of a short piece of 1 1/2" brass pipe and placed it under the oriental cap I drilled 4 very mall holes in the top of the pipe.so there can never be pressure but coolant wont splash out .I also replaced my water pump , thermostat , and two lower freeze plugs, when I removed the old plugs from the engine nothing came out! the bottom of the engine was plugged up with rusty mud. Hence a good idea that treatment you mention, Funny how things work out, If I had not messed up by putting a pressure cap on and caused all the leaks I would be running the car with the engine full of mud. My car did sit in a barn for 35 years before I saved it from certain death . No pun intended but it did start its life as a funeral coach in home PA. Now all I have to do is wait for spring to give it a good test run. Thanks for all the insight Bill.   

Bill:  yes a lot of people do not know that the early cars up to 48 ran anon pressurized cooling system since most of the current cr owners grew up in the mid 50 and that is when we started to use a pressurized system. So that is all they know and they think that th e older cars should have the same style cap.

By putting on a pressured cap as you noted then this can cause leaking issues because of the pressure that is building up in the engine and radiator.

So one problem forced you to correct the issue that probably started the leaking.

These car the kinds of articles that need to go into the newsletter to let people know these small points because most of us do not have the information told to us.  Or even some of the members that attend the convention should have a tech seminar schedule to talk about these topics.  I did one at the Maryland convention.

There is so much information out in cross reference catalogs that article could be written for each publication of the NDC newsletter.

If you replaced the freeze plugs did you find the brass flat plugs or the galvanized flat plugs?

Rich Hartung

desoto1939@aol.com

I used steel plugs not brass , I read somewhere that brass was not a good idea . I am a plumber by trade and I do know that brass and steel do not get along. It was interesting installing them ,I had to take the front wheel of the car and fabricate a 3 foot long chisel , my son held the chisel center from under the hood while I wacked the the other end , There is just enough room to send a chisel threw between the frame and the inner wheel well. As for the convention ,I wish there was something nearby I would love to attend one But I am a local yokel .I have to much of a mechanical mind to drive very far in a 70 year old car . I do attend most of the local car shows. Thanks Bill. 

Bill:  I have heard the same thing about brass with a steel engine block.  But I have to throw out that theory becsue all of the early cars and I have a 39 desoto has the brass thermostat in the top of the head.  This was original to the car and I even remember changing the thermostats  in the cars from the 50-60s and they used antifreeze with brass thermostats.

So if there ever was an issue I would have thought that the car manufacturers engineers would not have used a brass but a steel thermostat. But the steel would rust away because of the water and antifreeze.  Yes there might be a chemical reaction but my 39 is 81 year old and the engine block has no issues. so I think the brass frezze plugs and also water distribution tube can be used without any issue.  Yes there are brass water distrubution tubes. I have one for my 39 Desoto.

Rich

Good point Rich the heater valve, temp sensor, and heater elbows are also brass. I hope my distribution is intact? When I replaced my water pump I did not take the radiator out of the car, I just kind of felt inside and I think its ok. They seem way over priced for what they are, The car is running around 170 degrees with the new thermostat, There was no thermostat in it before that, someone just removed it. 

Bill I am assuming that you put in either a 160 or 180 degree thermostat.  The 170 is a good number.  Remember these cars like to have air movement to keep the temp down so in the summer whenthe temp is high and you are stopped the engine temp wil rise but when you get moving agin the temp wil lower because of the movement of the air going past the radiator and over the engine block.

Keep the inner engine block clean and keep the anti0freeze up to ar. Use distrilled water in the rad not tap water.

Rich Hartung

Hi Rich , I honestly don't know what temp the thermostat is , but my wife and I drove the car about 20 miles today and everything seems fine. the temp gauge reading around 170 .Have to also take into consideration that the gauge is 70 years old and may not be totally accurate , as for the antifreeze I bought a 50/50 mix so no need to add water . So far So good, Thanks Bill.

Bill:  If you have a harbor freight store near you they sell  a hand held temp thermometer like a gun that you canpin point to sections on the head at each cylinder to get a more accurate reading on the temp of the engine.  They are not to expensive.

Also this fall go to a napa store or automotive store and get a 12 oz bottle of Waterpump anti rust inhibitor and waterpump bearing lubricate.  Just pour it into the top of the radiator then start the car and let it come up to temp.  This keeps the antirusting agent active in the cooling system. Ocer the years the antirusting agents break down.  This chemical was a yearly maintenance item that everyone that had cast iron blocks would add to their cars.  Mopar even sold cans of these you can find the Mopar cans on Ebay but why buy them just get the new plastic bottle ones.  I do this every fall before my last run of the year around Thanksgiving. Also this is the best time to recheck the strength of the AF to make sure you are covered to a specific point and to make sure that the AF is still green  and not a brown color. If the AF has turned brown then the antirusting agents have broken down and its time to flush the block.  This is why I use the antirusting liquid every year.

Rich HArtung

desoto1939@aol.com

Thanks Rich,  I have thought about doing just that ,I am also thinking of taking the thermostat out of the car because the temp gauge is reading around 200 at times , before I put a thermostat in it was running 165 on the gauge even in a slow hot parade, We have a local car club here that has been doing covid nuns (drives at hospitals and nursing homes ).Last week I participated in a run in Goshen , about 10 miles from my house ,It was not very hot out maybe 70 , and when I got home the car smelled like gas, My carb was wet and very hot to the touch. I believe the main purpose of the thermostat is to keep the engine hot so you have heat? But I will say the car behaved itself much better before I added the thermostat .I also need to hunt down a replacement distributor , it seems to have a lot of play in the point cam and the vacuum advance is leaking threw , Its like a never ending battle for truth justice and the American way LOL.