P20 overheating problems

[silvio84]

Hello guys 

I have a 218 p20 

I'm already frustrated with my engine, it's overheating ok

the engine was completely repaired 

I have a new radiator

 new water pump 

New water distribution tube

new thermostat already tested 160 and 180 with either one getting hot

and I did the compression test in the coolant and nothing 0

What I have noticed is that when I turn off the car the temperature rises to more than 200 with the engine off. 

I really don't know what to do anymore. It's a frustration because after spending so much money I don't solve the problem.

Any ideas or something similar has happened to someone.

thank you so much

[Woodie]

Do you have a heater in the car - once when I rebuilt and engine I couldn’t get it to cool properly because there was no coolant in the heater core and it provided a place to absorb pressure so water wasn’t pumping properly through engine. If you have a heater connected be sure it is full of coolant and try running your heat to get all the air out of the system.

[silvio84]

No I don't have  heater. 

Is so weird the reason of overheating 

At the beginning I feel on the radiator the thermostat open and close but slowly is the temperature rises up 

[Ivan_B]

First of all, it is ok for the temp to climb up when you idle at the stop light or shut the car off. Second of all, it is damn hot in Florida right know 😅 so running a bit on the high side is to be expected. Third - are you sure that you are actually overheating? Did you measure the engine/coolant temp with the thermometer, or are you just going by the dash?

And lastly - what kind of thermostat did you use? I had the wrong type installed in my car by the PO. When the thermostat was opening, it was actually closing the radiator loop.

[silvio84]

Yes is overheating I have a digital temp gauge I am using the the thermostat from vintage mopar parts 

[desoto1939]

I looked in my Autostat Temp gage catalog

here are screen prints of their thermostats.

 

you should be using the 75-fht or the 95-fht model.

refer to the second and third screen shot.

The 3rd page show what each thermostat looks like.

 

I think you might have an incorrect stat in your car according to the picture you posted versus what this major supplier of thermostats produced from early 1930 - 1950.

 

I would go by his information. Just some FYI for you.

 

This is why i stress the collection of older catalogs to support your hobby of older cars.

 

Hope this solved your heating issue.

Rich hartung

Desoto1939@aol.com

 

 

 

 

 

 

[JerseyHarold]

Check to see that the heat riser valve (sandwiched between the exhaust manifold and exhaust pipe) is open and swiveling freely.  If it's closed, the engine exhaust will be restricted and the car can overheat.

[Loren]

200 degrees is not overheating, especially when the engine is shut down. It is normal for the temperature to rise when the engine is shut down because the coolant isn’t circulating.

The cars I used to work on had a temp gauge that was very accurate, where the red indicated 265 degrees and the green was 264 degrees. As long as the needle remained in the green you were okay as per the factory service information. The combination of 50% anti-freeze, a 16 lbs radiator cap brought the boiling point up to 265.

While the flathead Plymouth has a very minor pressure cap ( what is it 3 lbs? ) with anti-freeze the boiling point is well above 212. Also there should be air space in the top of the radiator, so if you fill it full the excess will leak out the overflow. When it stops leaking, that is the level it should be filled to. Scientific huh?

That said, we should remember once the temp gauge bulb is uncovered by coolant, the gauge will read low.

[sidevalvepete]

Good info above, especially Rich and Loren. Maybe using a laser type gun thermometer that you point to measure temperature at different parts of the block and head may help reassure you that the water distribution tube is working OK and that there aren't residual problems from unremoved sand/slag/rust etc from the water jacket when it was rebuilt.

[Ivan_B]

It sounds like the motor was rebuilt\repaired, so I assume that mostly everything is working according to specs. The correct stat for our engines looks like the 96F at the bottom right corner, on the provided illustration, like this one https://www.ebay.com/itm/375294080332. When the engine is cold, the top radiator outlet is closed and the side bypass is open. When it warms up, the side gets closed and the top is open. Make sure that this is what's happening. I looked at your stat and cannot really determine whether or not this is actually what's happening.

Running without the stat is not a good idea either, because you will have the bypass open at all times (unless you physically plug it).

If I recall correctly, my 201 manual specifies that the temp can get up to 212, since the system is not pressurized and was originally designed for plain water. And, indeed, it used to get this high when I had the wrong thermostat in there. Now, I am running ~180 when the weather is good, and ~190 when it gets a bit hot. You might want to do a test-run early in the morning (when it's a bit cooler) to see what kind of stable temperature you are getting with the engine fully warmed up and the car moving.

 

Later: Here is the stat I am actually using, right now: https://www.ebay.com/itm/315233827198 Seems to be even cheaper than when I bought it. I should probably get a spare 🤔

Edited May 23 by Ivan_B

[keithb7]

If ambient temps are very hot outside, a different thermostat won’t make it run any cooler if the cooling system cannot remove enough heat. You could run no-thermostat, a 140, a 160 or a 190 rated one. Won’t matter much. They’ll all be wide open trying to allow as much coolant to flow as possible. If you like you can run without any thermostat and see what results you get. Just to learn. I always recommend you run with a thermostat in a healthy cooling system. It allows your engine to heat up faster. Reduces carbon build up and oil sludge. Runs at proper efficiency sooner. When it’s 100+ outside, once your thermostat opens its probably not closing again. 
 

“Engine was repaired”. Meaning what? What was done and who did it. I’ve seen people “rebuild” a flathead Mopar and not remove the pounds of scale and sediment in the block.  
 

When new rad, waterpump, hoses etc was installed, did you drive around for a while with the rad cap off? Let the coolant get hot and burp? Get all the air out of the system? 
 

I can drive my flathead and see 180 all day. Then park it and within minutes watch the temp gauge rise to over 200.  It’s totally normal for a fully warmed up engine to do this. Especially noticeable on a hot summer day.  
 

 

[Jerry Roberts]

" the engine was completely repaired " .  A rebuilt engine is usually a little tight and will run a little hot until it loosens up . 

[Sniper]

We aren't even sure it is overheating.  As Loren stated 200 us not overheating,

 

What makes the OP sure he has an issue?  I don;t see any numbers given, other than once shut off and it heat soaks. 

[Ivan_B]

7 hours ago, keithb7 said:

You could run no-thermostat, a 140, a 160 or a 190 rated one. Won’t matter much. They’ll all be wide open trying to allow as much coolant to flow as possible. If you like you can run without any thermostat and see what results you get.

Are we talking about the cooling system with or without bypass, here?

 

7 hours ago, keithb7 said:

When new rad, waterpump, hoses etc was installed, did you drive around for a while with the rad cap off?

Isn't the overflow line on top of the radiator always open to the outside anyway, or is 1950 using a pressurized system?

[keithb7]

I was thinking pressurized cooling system as my ‘38 has pressurized system.  It does need a good burping when coolant is replaced. 
Previous owner added a pressure rad that seems to work well. Its a little undersized for the dog days of summer, up the long steep hill home. 

The pressure is working as it doesn’t boil over. Yet the gauge is up there in the 200 mark under those conditions. 
 

By-pass cooling system or not, I’m thinking the thermostat is wide open when coolant is hot and high ambient air temps. A fan shroud could help. I’m guessing an open fan a couple inches from the rad might be 50% efficient? A guess. 
 

One time I did leave part of a paper shop towel stuffed in the small by-pass tube of my other Mopar. I forgot it in there and reassembled all. It did run hotter. It took a bit of time then it finally flushed through. The pump vane chopped it up. I was scratching my head wondering why it was running hotter, after I put it back together. Soon I found the fibre remnants floating on the top of the rad level.  Don’t do this! Lol. 

 

 

[Ivan_B]

Okay, on the contrary, I was thinking about non-pressurized system with bypass, because this is what I have 😅

We should probably get more info from Silvio, for a more efficient troubleshooting. The reason I asked about these, is that a non-pressurized system is obviously always open to the air, and is using an extra large radiator top as its expansion tank. Also, Chrysler Master Tech specifically does not recommend running a bypass system without the stat because when the stat is fully open, the bypass must be closed. If there is no stat, both the radiator loop and bypass will be open, with part of the rad flow naturally diverting thorough the bypass instead, which will inhibit proper cooling

The same could be the case if an incorrect stat is installed in the bypass system.

 

3 hours ago, Sniper said:

As Loren stated 200 is not overheating,

That is technically correct, but could very likely be running a bit on the hot side depending upon the ambient temperature and the engine operating conditions.

Edited May 23 by Ivan_B

[silvio84]

I have this system I think is the bypass one .

Also I have 16in electric fan front the radiator not much help to cooling 

[Ivan_B]

Yes, this is bypass-type, so let's make sure that your stat is working as intended - rad loop filly open = bypass closed. And, based upon the look of that cap, you are also using a pressurized system, so yes, letting some air from under the cap could be useful if you've recently drained the coolant

Also, please provide more info, such as: what's the ambient temp, what is the gauge showing, fully warmed-up, while in motion; what is it showing while you stop and idle for a minute or two.

[Sniper]

21 minutes ago, Ivan_B said:

That is technically correct, but could very likely be running a bit on the hot side depending upon the ambient temperature and the engine operating conditions.

 

If it's not puking, it's not overheating.  200 degrees after a heat soak, only value given, isn't even running on the hot side to be honest.  An actual value given for the engine running at at temp would sort this out.

 

13 minutes ago, silvio84 said:

Also I have 16in electric fan front the radiator not much help to cooling 

 

All that is doing is blocking airflow and that assumes it's even blowing the correct direction.  Yes, I know, but I have see people wire them up backwards and have it blow towards the grille rather than the engine. 

[D35 Torpedo]

I thought My engine was overheating, evnen made a sweet fan shroud. Turned out the original gauge was faulty. Now, you said you checked it with a temp gun. Did you actually pull the cap and point it at the coolant inside? Your issue could be poor data. Unless something was done wrong in the rebuild.

[greg g]

It is normal for a temp gauge to show a rise in temp when you shut off the engine.  The engine is basically a 700 pound heat sink.  When you shut it down, while you are no longer producing heat, you have shut down the coolant circulation, and the air flow through the heat exchanger.  The heat now has no where go but out through the cast iron and into the now non circulating coolant.  The coolant gauge will show this gain.  Remember, with a 50/50 coolant your boiling point is around 225 degrees, so you have wiggle room.  Also. You might take actual Temps of several places with one of those point shoot and read temp thingies.  Not unusual for the gauge to be inaccurate.   Check the radiator top tank. The thermostat housing, the head where the sender is located.   Compare those to what's on the gauge.  Also if you live where it doesn't get below freezing, you can increase the ratio of water in the coolant mix.  Water is a better heat transfer medium than polypropylene glycol.   I don't drive in winter, and my garage doesn't get much below 40.  I run a 70/30 mix with 70 the water.  This gives me anti rust, freeze protection down to 20 and I think better cooling.  Hardly goes over 170, even driving hills in 80s/90s.

Edited May 23 by greg g

[silvio84]

17 hours ago, JerseyHarold said:

Check to see that the heat riser valve (sandwiched between the exhaust manifold and exhaust pipe) is open and swiveling freely.  If it's closed, the engine exhaust will be restricted and the car can overheat.

That is not in use I put a cap between exhaust and intake. 

Thank you for the information 👍 

[silvio84]

First of all, thank you all very much for helping me and sharing your knowledge.

Today what I did was remove the water pump and flush the block with water and I didn't throw out much, it was clean, I put back the thermostat 180 and I buy alcohol-free antifreeze as recommended here.

The truth is that I don't know what happened but now it maintains the temperature between 174 to 180 and when I turn it off it goes up to 190 ,and outside temp was 93 , tomorrow I'm going to try it on the expressway to see if it doesn't overheat, hopefully not.

[Ivan_B]

Those are the best kind of troubles when you have no idea what you did/did not to fix the issue 😅

For reference, I just checked my own temps today: ambient ~ 90, engine while moving - 180, stopped engine after being parked for ~ 10 minutes - 200. These are very good temps, despite the hot weather, I think.

Edited May 24 by Ivan_B

[greg g]

Remember, the temperature rating on the thermostat is for when it starts to open,  not for how high the operating temp will be. 

 

Rule of thumb if I have it right.  Over heating at low rpm is linked to lack of air flow.  Overheating at high rpm is related to poor coolant circulation.  Others let me know if this is backwards.