Need help troubleshooting a temp issue.

MoparFlores

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How's it going all. I really need some help with a cooling issue I have and I would really appreciate any and all help. A few weeks ago I was driving home from work and noticed my temp gauge alittle higher than normal. This is a 1973 plymouth fury with a 360 btw. So I noticed my gauge alittle bit high and kept an eye on it, the scary part was after a few minutes I had a very sharp and sudden temp spike. My gauge went through the roof and slowly dropped back down. So I thought the worst (blown headgasket even though I wasnt driving it hard) and pulled over. Checked my coolant level, it was alittle bit low and alot of air escaped when I released pressure from my cooling system. Topped it off and checked my oil. I didn't have coolant or oil mixing. So I babied the car home (keep in mind I daily drive my fury 180 miles every day) I noticed my temps would drop when going down hill and would randomly spike and then go back to normal. So anyways long story short I replaced the thermostat and the car was fine for a few weeks. Tonight on my drive home the car did the same thing again. I live in northern nevada its winter right now, we have snow, we are lucky to get above 40 degrees Fahrenheit right now. I've been driving this car daily for over a year now and never had an issue with it even in the hot nevada summer. So why am I having cooling issues now when its colder than hell. I havent changed much recently besides the belts and an alternator and changed the oil. Idk what my issue is, another thermostat? Should I run no thermostat? The first time I had this issue I put in a 160 degree fail safe thermostat and it did fine until tonight. :( I'm so bummed right now
 

Davea Lux

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You should run a 180 degree thermostat. The 160 will often cause the coolant to circulate too fast to where it does not get a chance to cool properly. Is the coolant level full? you may have a small leak someplace. If you bought one of the china crap t-stats from Autobone or Carcrap it might have failed that quickly. Check your timing, if it has changed for no obvious reason , the timing chain may have excessive slack which can cause overheating. If the car runs normally except when pulling hills also check the clutch fan if the car has one.

If you have not done so already find a quality T-stat such as a Stant brand unit. Also check the fins on the radiator for debris as that can cause a reduction in air flow and result in overheating under load. See of the fan has any play from loose water pump bushings, if the impeller in the pump is rocking from loose bearings, that can cause cavitation resulting in overheating.

Dave
 

MoparFlores

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You should run a 180 degree thermostat. The 160 will often cause the coolant to circulate too fast to where it does not get a chance to cool properly. Is the coolant level full? you may have a small leak someplace. If you bought one of the china crap t-stats from Autobone or Carcrap it might have failed that quickly. Check your timing, if it has changed for no obvious reason , the timing chain may have excessive slack which can cause overheating. If the car runs normally except when pulling hills also check the clutch fan if the car has one.

If you have not done so already find a quality T-stat such as a Stant brand unit. Also check the fins on the radiator for debris as that can cause a reduction in air flow and result in overheating under load. See of the fan has any play from loose water pump bushings, if the impeller in the pump is rocking from loose bearings, that can cause cavitation resulting in overheating.

Dave
The t-stat in it now is a Stant fail safe 160 degree. Heater core has a very small leak. It only has the temp spike going downhill, Not under a heavy load I have to climb a very steep grade to get to work and it never has a temp spike going up hill only down the other side.
 

Davea Lux

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The t-stat in it now is a Stant fail safe 160 degree. Heater core has a very small leak. It only has the temp spike going downhill, Not under a heavy load I have to climb a very steep grade to get to work and it never has a temp spike going up hill only down the other side.

Check the clutch fan. Going down hill with no load it may be disengaging to where the fan is not turning fast enough.

Dave
 

MoparFlores

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Check the clutch fan. Going down hill with no load it may be disengaging to where the fan is not turning fast enough.

Dave
How would I go about checking the fan clutch. I'm only familiar with air actuated fan clutches on semis idk how exactly to troubleshoot this.
 

Davea Lux

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How would I go about checking the fan clutch. I'm only familiar with air actuated fan clutches on semis idk how exactly to troubleshoot this.

The fan clutch is temperature actuated, warm air coming off the radiator causes it to engage. A quick test is to start the car and let it run until it warms up. Have a helper turn the car off, the fan should stop turning with the engine. If it spins freely after the engine is off, the unit needs to be replaced. How many miles are on this engine? If it is 80k or more, it is due for a timing chain unless it has already been replaced. Have a helper put a socket on the harmonic balancer pulley and rotate the crank until you get to TDC. Remove the distributor cap and have the helper rock the crank back and forth and note how many degrees of crank rotation it takes to get the distributor shaft to move. If it is more that 10-12 degrees, the chain needs to be replaced.

Dave
 

CBODY67

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The fan clutch locks up due to the temp of the air coming through the radiatoer. IF that part of the radiator is clogged, it'll have cooler air coming through those fins, so the fan clutch thinks "no load" and will not work as designed, no matter what the temp gauge indicates.

Just because the radiator tubes might look good under where the radiator cap might be does not mean they look that way on the bottom of the core. Which is where an IR heat gun comes in handy to check for reasonably-consistent temps across the whole radiator core.

What about the trans fluid level? When cold in cold weather, a normal level (when checked on a cold engine) can be at the ADD mark, but will rise toward FULL as the engine and trans warm up with driving.

To me, the temp spikes might tend to indicate a coolant flow issue. A flow that, for some reason, is not constant and consistent. Use the coolant overflow jug to check the coolant levels, rather than removing the radiator cap on a hot engine.

In that cold weather, how is the heater operating? Does it seem to get hotter when the temp gauge spikes happen?

Just curious,
CBODY67
 

Big_John

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Did the engine really get hot or did the gauge just malfunction?

Generally, they don't spike like that. A bit of bad insulation could be shorting the gauge wire to ground, the voltage limiter failing, or even the gauge or sender is failing.

Some sort of other failure, like a head gasket, might drive the temp up fast, but not really "spike" the gauge. If something drove it up high fast, I wouldn't expect it to just come down on its own either.
 

cbarge

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Get a laser gun and compare its reading to the gauge. I bet they read differently...either the sending unit or gauge or gauge volt limiter is ready to take a shit.

Also the cooling system needs to be under pressure in order to function properly. The heater core leak is not helping in that department.

Pressure test the rad cap while you are at it.
I had seen people pull cylinder heads for no reason when they discovered after the fact a 30 year old $10.00 rad cap failed.
 

1970FuryConv

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I agree with Big John: intermittent short to ground in temperature sending unit TSU wire.
You could bypass the wire in the engine compartment harness, by butt connecting in a new wire from your bulkhead connector to your TSU connector. If the problem goes away, you've found your problem.
With no steam, smoke, boil over, I doubt you're really overheating.
 
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I've had a bad radiator cap cause overheating. Also, I think 160 thermostat is too low, 195 is probably recommended. Fan clutch usually causes engine to heat up when sitting in traffic idling, usually engine starts to cool down when going fast, especially coasting down hill. You say it heats up going down hill but is cool going up hill?? That is puzzling. Sorry if I missed this but are just going by the factory dash gauge? Maybe try installing a new aftermarket temp gauge so you have a better idea of the actual temp the engine is running.
 
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Oh just to add a comment about the temp "spiking". I had a new thermostat installed in my work car (03 Mercury Sable) and shortly thereafter on 2 separate occasions going up a long steep hill the temp went almost to the top of the gauge, then dropped to normal suddenly and quickly. It's almost like the thermostat was stuck. That was 5 years ago and that car hasn't done that since.
 

MoparFlores

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The fan clutch locks up due to the temp of the air coming through the radiatoer. IF that part of the radiator is clogged, it'll have cooler air coming through those fins, so the fan clutch thinks "no load" and will not work as designed, no matter what the temp gauge indicates.

Just because the radiator tubes might look good under where the radiator cap might be does not mean they look that way on the bottom of the core. Which is where an IR heat gun comes in handy to check for reasonably-consistent temps across the whole radiator core.

What about the trans fluid level? When cold in cold weather, a normal level (when checked on a cold engine) can be at the ADD mark, but will rise toward FULL as the engine and trans warm up with driving.

To me, the temp spikes might tend to indicate a coolant flow issue. A flow that, for some reason, is not constant and consistent. Use the coolant overflow jug to check the coolant levels, rather than removing the radiator cap on a hot engine.

In that cold weather, how is the heater operating? Does it seem to get hotter when the temp gauge spikes happen?

Just curious,
CBODY67
AC and heater are both inop since I got the car. Honestly dont plan on fixing it in fact I may remove what I can without doing any permanent mods. I want the car to be able to be restored at some point but not right now. My heater core leak I think is the main contributor on my drive to work this morning I noticed my leak has gotten bigger.
 

MoparFlores

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Did the engine really get hot or did the gauge just malfunction?

Generally, they don't spike like that. A bit of bad insulation could be shorting the gauge wire to ground, the voltage limiter failing, or even the gauge or sender is failing.

Some sort of other failure, like a head gasket, might drive the temp up fast, but not really "spike" the gauge. If something drove it up high fast, I wouldn't expect it to just come down on its own either.
I thought the same the first time I had this issue and I replaced the temp sensor and checked my wiring for any damage. Didn't find any but I know something is still wrong because my gauge has always read extremely low since i got the car. I drive 90 miles to work every morning this is my temp after about 60 miles of my commute, it's not actually low. Something is wrong with the gauge or wiring, but it does respond to temp change. I changed my radiator cap last night just because I had one and topped off my coolant. Didn't have any spikes this morning.

20210129_055300.jpg
 

CBODY67

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Then either loop the heater water outlet and inlet (on the engine) or get rubber some caps (and hose clamps) to close them at the auto supply. Before you end up with a coolant-fogged windshield and leaks in the floor.

CBODY67
 

CBODY67

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AC and heater are both inop since I got the car. Honestly dont plan on fixing it in fact I may remove what I can without doing any permanent mods.

If you go to the trouble to remove the hvac system, you'll have about 1/2 the work done to replace the heater core. Plus removing the hvac will also affect air circulation in the car that does not come from the cowl floor vents. Need to have some air circulation to the windshield to help keep it clear!

CBODY67
 
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mopar440

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The t-stat in it now is a Stant fail safe 160 degree. Heater core has a very small leak. It only has the temp spike going downhill, Not under a heavy load I have to climb a very steep grade to get to work and it never has a temp spike going up hill only down the other side.
Check all that was said, of course

But this sounds like air to me. I bet when it's cooling down, it's sucking through the hole in the heater core. Bypass to test. Also, test the cap, and make sure you got the right one. Different caps for tank and no tank.
 
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traintech55

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One thing not mentioned already, Chrysler radiators have a tendency to clog at the bottom because of their design. This would also show up at highway speeds, but be good in slower traffic. First thing block off the heater core as suggested, top off the coolant level, and drive it to see what happens. It is not uncommon for a couple of things to go wrong with a cooling system at the same time on an older vehicle.
 

MoparFlores

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My plan is to bypass the heater core, as far as possible removal of HVAC components. I plan on only removing AC components under the hood. My glass has never had an issue fogging up but I definitely dont want it to start now. Plus winter is almost over. I did test the new cap I threw on her and it's working fine. I'll most likely bring my car into the shop and work on it before I go home today. Got a whole lot of parts and tools here so it shouldnt be a big deal.
 
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