Strange Heating Problem

[Pipewrench_Dale]

I have a 1940 Desoto Business coupe. The engine is a 265 industrial Flathead from 1953 or 54. The thing is that all of a sudden this car have started to run really hot.... but only when I use anti-freeze.   If i run it with only pure water in the radiator it  stays cool, but as soon as I put anti-freeze in it it starts to heat up and lingers right on the edge of overheating. This happens when I cruise down the highway or have the car idling on the driveway.

 

Ive compared the temperature in the radiator when using only water or water/anti-freeze mixture. Theres basicly no difference it runs at about 122 F. So I would say that the radiator does its job and the difference is the temperature of the the engine. Looking at the tempgauge on the dash it runs at about 180 with only water and 212 with anti freeze (basicly it bottoms out the temp gauge).

 

Ive tried to solve it but now Im out of ideas. What Ive done so far is this

• Flushed the entire cooling system 4-5 times using both of the shelf radiator cleaners and traditional machine wash tablets. 
• The water pump is new as the old on started to leak o few months back.
• Ive inspected the thermostat and it opens as it should.

[nemo aussie d25]

Dear Dale

I had some issues with coolant with my d25 about five years ago. I think I was running a 50/50 mix of glycol at the time.

I did some research and discovered that the heat transfer characteristics of glycol were something like 10 percent down on straight water. Could be that small difference could be enough in a borderline cooling system of which still works normally with straight water. I've been using straight distilled water and a corrosion inhibitor ever since and with the standard radiator fan idling in traffic on a 40 degree celcius day did not have the temp gauge get anywhere near 212F.The exact details I can't remember but it would be something to check.

[Pipewrench_Dale]

Thanks, Ive had the same thought actually. I think Ill give a few more flushes and put in a lower mixture. Just enough to save the engine if the temperature should drop unexpectedly.

 

 

Another thing is that modern anti freeze increases the boiling point to something like 226 F depending on mixture and pressure in the system. Back then when our engines was born glycol wasnt used (at least what Ive heard) instead alcohol was often used as an anti freeze. Since alcohol boils at 173 F the boiling point is higher in todays mixtures than back then. So, at least in theory, using a modern anti freeze could increase the stresses on the engine when it overheats as the overall temperature is much higher.

Dont know if anyone has given this more thoughts. But the last few days Ive been given it a few thoughts. 

[Young Ed]

Dale I suggest you need to pull the lower frost plugs when you flush and get the cooling jacket really clean.

[greg g]

Water does cool better than coolant and water mix, It also transfers heat in and out better.  Try a different mix.  I run 70 water 30 coolant.  My car is never exposed to outside temps below 20 degrees.  So freeze up is not a concern. Mine is a pretty freshly rebuilt engine consistently runs at 170 degress.  never seen it over 190 even when sitting in traffic at 90 degrees ambient.

[Plymouthy Adams]

I run 50/50 mix in all my vehicles ...I am in the south..it carries the label coolant on it for a reason...I never know if I may have to run to Siberia to rescue William Shatner or not..

[chopt50wgn]

Water is the best dissipater of heat ,but it will still boil at 212F. What happens inside the motor ,as the internal metal temps start building heat, it will turn the water to steam vapors. Those vapors can not remove any heat from the metal, so the motor will start to run hotter.

Using an antifreeze does 2 things, it will help lube the pump and also slow down corrosion within the motor. Not sure what pressure cap you are using but for every pound the cap is it will boost the boiling point by 3 degF ...........example....a 15 lb cap will boost the boiling point of the system by 45 degF, so with water boiling at 212F add 45F and the new boiling point is 257.

[desoto1939]

question do you have a pressurized radiator cap on the car.  Our systems in the early years is a non pressurized system.  I have a 39 Desoto so basically we have the same car.  Did you ever replace the water distibution tube and also pull al lthe welsh plugs on the engine to force out al the crud in the block.

 

Also only use the green antifeeze in your 40 Desoto DO NOT used the yellow extend stuff.  ALso put in a bottle of water pump lube which has  a rust inhibutor.

 

Most Af will last 5+ years but the rusting agents breaks down and the  and the antifees will start to look like a rust color.  Chnage the Af every 4 years  

 

Even thought you put a rad flush on the car and then opening the petcock on the radiator you still might have junk inthe block.

 

Pipewrench where are you located? I live near Valley Forge PA. Contact me.

 

Rich HArtung

Desoto1939@aol.com     

[ptwothree]

The one time I installed a 100% dose of anti-freeze, the car would over heat.  I backed it down to 60% and all was well. 

 

Now...I understand the anti-rust properties of anti-rust because it basically is a soluble oil solution...but what the heck is being lubed in the water pump?  My pump has sealed bearings.

[JBNeal]

on the new NAPA water pumps, the bearings are lubricated by the coolant similar to modern water pumps as there is no grease fitting.  It's my understanding that the original cooling system was non-pressurized to allow air to escape from the lower reaches of the engine block, 'burping' air to the upper radiator tank.  If the system is pressurized, then air gets trapped in the block cooling passages which could lead to hot spots, which might be your elevated temperature readings.  From my experience, running 50/50 mix is more than adequate for these cooling systems; richer on glycol falls into the "some is good, more must be better" logic that isn't always justified.  As for the running temperature of the engine block and how that equates to stress on the casting, I've seen optional 180 & 195 thermostats listed in the parts books for these flathead engines, and considering how much mass the blocks have, I don't think they are under too much stress if they are running in the 200 range...if anything, higher operating temperatures are supposed to help boil out any moisture in the crankcase to help reduce sludge formation.

[TodFitch]

The main reason to pressurize a cooling system is to allow the engine to run hotter. Heat transfer across an exchanger (e.g. radiator) is more efficient if the temperature differences are larger. So a small radiator running under pressure can dissipate as many BTUs as a larger radiator running at atmospheric pressure. It also turns out that running the engine warmer heats the oil enough to help it vaporize out combustion and condensation contaminants so the base oil stays in better shape (might not help the oil additives though).

 

Shouldn't make much, if any difference in getting the air out of the system.

[JBNeal]

if there is air trapped in the block, then coolant is not allowed to pass through that area to allow heat transfer.  This can lead to hot spots in the castings, which may lead to cracking.  I reckon this is similar to a blocked coolant tube.

[DJ194950]

Questions, did you run an antifreeze mix before changing the water pump?

What type of bypass system is on your motor- block type or hose, water pump to thermostat housing?

Do you have a heater? I could not seem to get all the air from the engine cooling system after a motor replacement until I turned the heater on and let the car run till warm with my pressurized cap OFF.

Had your car been changed over to a pressurized system?

 

These experienced pros on this forum may give you some more things to look at depending on you responses.

 

Sure you'll figure it out soon!

 

Doug