How hot is too hot ?

[40desoto]

What do you guys consider water temperature too hot on these flathead six engines?    I hear many opinions ranging from 190 to 220.

Ive never felt comfortable seeing my guage on any car stay too long over 205.

 

Here my situation - I'm running my engine on a stand with a new three core aluminum radiator and just water. Doing so because Im taking care of the head stud leaks before I add coolant to it.  The engine reaches about 210 within 10-12 minutes of starting.  

 

Also, one think I noticed is that the water seems to continiously flow throw the thermostat housing as if its stuck open.  The cap opens at about 185 degrees and gushes water out to the reservoir (9 lb cap).

 

Something just doesn't seem right.  Once I get the leaks fixed I plan on using coolant, moving the radiator closer to the fan in hopes that the motor maintains a good temperature at idle.

 

 

 

 

 

[Doug&Deb]

My 52 Coronet runs between 190-200 all the time. Aluminum radiator and engine rebuild 3000 miles ago. Always seems too hot to me but no problems with overheating as of yet. Hope this helps.

[Jerry Roberts]

Here are my thoughts ;   210 is too high , test with another gauge as your gauge may be wrong .  You can test your thermostat by putting it in a pan of water with a thermometer and heating the water . You can also put a household fan in front of your radiator and see what it does . Allow room in your radiator for the coolant to expand . 

[Los_Control]

43 minutes ago, 40desoto said:

Something just doesn't seem right.  Once I get the leaks fixed I plan on using coolant, moving the radiator closer to the fan in hopes that the motor maintains a good temperature at idle.

Are you sure this is what you want? I think 9 pounds would be too much for my 1949 truck.

And I think they had a 180 degree T-stat back then, although they were swapped out from 160 to 180 for summer to winter use.

Back then they actually swapped the T-stat out for summer and winter use.

But I think there was no pressure on the radiator cap, maybe Desoto was different?

 

I would install a 180 T-stat and a radiator cap with zero pressure, go from there.

If you are still overheating, I would suspect a clogged water distribution tube or other issues.

 

Newer cars do have a 195 T-stat installed, this requires a sealed system and a radiator cap at correct #pound, these older cars did not use pressure in the radiator and larger T-stat.

Just saying, your system does not look right at all  to me.

[Plymouthy Adams]

first off with it running on a stand..you are not drawing your air through the radiator as effectively as you will when installed.   Suggest that you add an aux shop fan in front of the radiator if you wish to continue the bench testing.....IF the engine does not drop a few degrees with the fan blowing on the radiator, then I would suggest looking into actual temps along the cooling system with an infrared thermometer.  Right now...I would not be overly concerned....and as for pressure...if stock you have zero pressure...if you running aftermarket radiator....I would still be careful on what amount of pressure to run as the heater core may or may not yield to the increase...I suggest 180 degree thermostat....160 is a tad low and builds up sludge in an engine fast given you do not get it up to temp and at least a 30 minute plus run at these temps to evaporate the condensates.

[Los_Control]

^^^^ there you go, My biggest point I think, just learn and understand the cooling system you are running. They did change and have different advantages over the years.

 

[40desoto]

I am running a 3 row aluminum Champion  radiator that came with the 9 lb cap.

 

I do have the original non pressurized cap that I can use.  I understand that the original system was non-pressurized.  

Thanks for everyones response.

ill be sealing the remaining head studs. Flush the system, refill will coolant, move the  radiator closer to the fan blades and use a commercial fan in front if radiator to see if it maintains the temperature down.

 

Keep in mind that this is a freshly rebuilt engine with a new radiator.

 

I not quite following on how the engine temperature would vary whether its in the car or on a stand with everything connected? 

 

Im hoping to run the car on idle without an wxternal electric fan and keep under 200.

 

 

[Plymouthy Adams]

tell  me how you control the movement of the air through the radiator and not from the top sides and bottom....granted even in the car you have air coming in from other sources but at least they do try to make it where the most will flow across the radiator...

[40desoto]

1 hour ago, Plymouthy Adams said:

tell  me how you control the movement of the air through the radiator and not from the top sides and bottom....granted even in the car you have air coming in from other sources but at least they do try to make it where the most will flow across the radiator...

Thanks Adams,  I was thinking that in the engine bay that it would somewhat better control the air flow through the radiator.  Since the car did not come with a fan shroud I didn't think it would make that much of  a difference outside or inside the engine compartment. 

I guess every lil bit can make a difference.

 

 

[greg g]

How do you know how hot too hot is?  First thing to do is check the accuracy of your gauge.  Is 190 at the gauge 190?  How hot is the coolant in the radiator when the gauge says 200?  Based on your coolant water mix, what is the boiling point of the mix?  Is it pressurized?  What does the pressure do to the boiling point.  Going down the road my aftermarket gauge says 170.  When I checked it in a pan of water before I installed it, it agreed with my kitchen thermometer.  So I am fairly sure when it says 170 it is within a couple degrees of that.

[Bbdakota]

1 hour ago, greg g said:

When I checked it in a pan of water before I installed it, it agreed with my kitchen thermometer.

What a great idea! Wish I'd done that before installing mine. 

Someone else on the forum pointed out the temperature probe location in the back of the head would read hotter than up near the thermostat housing like most v8 engines 

[greg g]

Think that's why the heater tap is at the rear corner...

[Don Coatney]

[40desoto]

Don is that small return tube on top of the radiator critical on a non-pressurized system

 

hope I dont regret purchasing an aluminum radiator instead of rebuilding my original

[greg g]

Here is a note about that tube.  It's location independent of the radiator cap is an indicator of a non pressurized cooling system.  So regardless of what the radiator cap indicated for psi, no pressure will build in this system.  Most modern radiators have the overflow incorporated into the filler and cap area, usually above where the cap gasket seals to the filler neck.  These will allow pressure to build till it forces the gasket up against the spring and allows pressure and coolant to be expelled.  Keep 8n mind your Welsh plugs and heater core were not designed to be pressurized.  So the modern system for you car should have the lowest pressure rating you can find look for 2 to 2 1/2 pounds.

 

[Don Coatney]

I used a 4# cap with an aluminum radiator. Even with that low pressure there were welsh plug failures.

 

[Bbdakota]

7psi cap with my aluminum radiator, so far, so good. 

Don, how long did it take for the failure to occur? 

Did you just replace the plugs to fix the problem? 

Edited October 5, 2019 by Bbdakota

[Sam Buchanan]

Is there an easy way to modify an aluminum radiator or a cap so it won't develop any pressure? Maybe install a bulkhead fitting in the top of the radiator so a vent hose can be attached? Will a non-pressure cap like we use on our old radiators fit on an aluminum radiator so the overflow can be used as a vent? Just thinking ahead in case a new radiator is ever needed on my P15.

Edited October 5, 2019 by Sam Buchanan

[Bbdakota]

3 hours ago, Sam Buchanan said:

Is there an easy way to modify an aluminum radiator or a cap so it won't develop any pressure? Maybe install a bulkhead fitting in the top of the radiator so a vent hose can be attached? Will a non-pressure cap like we use on our old radiators fit on an aluminum radiator so the overflow can be used as a vent? Just thinking ahead in case a new radiator is ever needed on my P15.

The cap from my original radiator fits the new aluminum radiator fine and has a seal for the top lip so a simple cap swap is all that's needed to make it non-pressurized but I would run a recovery tank so you could fill it to the top and not have to leave room for expansion. Another option would be to modify a cap to not seal on the bottom lip and run a recovery tank for expansion. Or, one could weld a overflow fitting to the top of the tank and run a line from the new fitting to a recovery tank along with a line from the filter neck (or plug it) since the pressure type cap will try to suck coolant back in when the system cools down but that seems to be the hard way to get a non-pressurized system. Myself, I like the idea of a pressurized system. No problems so far. 

Edited October 5, 2019 by Bbdakota

[Sam Buchanan]

The manual for the P15 says to not fill the radiator any more than an inch or so of the top so coolant won't slosh out the vent during a hard turn. So it looks like a non-pressure cap and a vent hose connected to the neck would give us a non-pressure system like the original. 

 

Thanks for the feedback, I'll keep this in mind if I need to replace the original radiator at some point. I like the non-pressure system because it doesn't put any stress on fittings, hoses, heater core, etc.

 

By the way, Scott, the Plymouth runs with just a subdued hum now with the fresh exhaust gaskets! Fuel pump is almost as loud as the engine.     

Edited October 5, 2019 by Sam Buchanan

[Bbdakota]

1 hour ago, Sam Buchanan said:

By the way, Scott, the Plymouth runs with just a subdued hum now with the fresh exhaust gaskets! Fuel pump is almost as loud as the engine

Nice! Glad you got thru it without too much trouble. 

You are correct about leaving the coolant an inch low. The only reason I  suggested an expansion tank is volume of coolant old radiator vs new. I haven't measured but I  don't think (at least my aluminum radiator) holds as much coolant as the original. Of course, that may not be an issue with the plymouth, I believe you can buy a direct replacement so it may have as much volume. Then again, with a  more efficient aluminum radiator, still might not be a problem. 

[Don Coatney]

6 hours ago, Bbdakota said:

 

Don, how long did it take for the failure to occur? 

Did you just replace the plugs to fix the problem? 

 

 

You will have to ask the new owner of my car. (Hotrodtractor) Failure occurred after I sold the car.

[1951plymouth]

Hi, I have a 51 Plymouth w a 165 thermostat and a 4 lb cap, which I believe is proper for my year.  This cap is consistent w the then new style radiators with a pressurized system with the overfill tube in the neck of the radiator cap.  9lb is too much even for the latest 1959 plymouth, those expansion plugs seem like a weak spot for too much pressure. The higher pressure caps allow for hotter temps before boiling.  With my setup on a stock 218 with dual carbs and headers my car rarely gets near 200 degrees in california.   Sometimes if my radiator level is too high it will puke just a little fluid, which right sizes the coolant level in the radiator for coolant expansion.  

 

You might check for the proper type of thermostat, fitment and water distribution tube condition as they wrought rust away and cause hot spots evidently.  I like the idea previously mentioned of using an infrared temp gun to check temps around the engine for clues on why your temp is so high. 

  

[normanpitkin]

If steam comes out of the radiator it is too hot.If there isn't any  steam its fine. Easy to overthink these issues.

[40desoto]

So heres my latest. Installed a non pressurized cap on my aluminum radiator and filled radiator with water  leaving about 1 inch space on top for water expansion.

once the temperature at guage reached 175 water started flowing out if the  radiator relief tube.  It reached 210 and water started pouring out of the tube consistently.

 

When the temp reached 180 I turned on a  household fan that I had mounted to the front of the  radiator and it didnt change the temperature at all.

 

on the positive side, there are no more water leaks on the head studs.

 

I plan on flushing the system and refilling with distilled water  and testing again.

hoping the distilled water and coolant will

make a difference.