302 engine temperature too low?

[DeepC73]

I have a 1973 Bronco with a 302. The motor was rebuilt about 15,000 miles ago. Over the summer here in VB it would heat up when sitting in traffic or a drive-thru to around 220 or more. I replaced the original radiator with an aluminum 3 core about a month ago. I also recently replaced the original 6 inch water pump pulley with a 5” to increase flow for the upcoming Holiday parade. It currently stays around 120-130, no matter what. If am really stuck in stop and go traffic for 20 minutes or more it will creep up to around 150 or so. Is this an issue I should be worried about. I know many say the 302 operates best at around 185 degrees. Thanks in advance.

 

[jerry]

Had a similar issue with my 88 Mustang, after replacing the water pump and upgrading the radiator.
In my case, the thermostat was stuck wide open. If you haven't checked / replaced it, you may want to do so.

 

[BGBronco]

Would be interesting to know if that's an accurate reading. At 130 or so, are you even getting heat inside?

 

[DeepC73]

Would be interesting to know if that's an accurate reading. At 130 or so, are you even getting heat inside?

Yes, I’m getting heat inside. It’s 40 degrees here today and comfy inside. I measured the temps with an infrared thermometer. It’s 131 degrees going into the radiator, 118 coming out. The thermostat housing was 124-130 degrees.

 

[jamesroney]

Yes, I’m getting heat inside. It’s 40 degrees here today and comfy inside. I measured the temps with an infrared thermometer. It’s 131 degrees going into the radiator, 118 coming out. The thermostat housing was 124-130 degrees.

You need to listen to @jerry on this. The purpose of the thermostat is to keep the engine at optimal operating temperature. If the engine is not operating at the specified temperature then something is wrong. The biggest problem with a stuck thermostat is not so much that it is stuck open. It is that it "sticks." Being stuck open is inconvenient. But being stuck closed is terrible. And the same mechanism that allows it to be stuck open is just as likely to keep it stuck closed.

Fix it before you need to.

 

[jerry]

You need to listen to @jerry on this. The purpose of the thermostat is to keep the engine at optimal operating temperature. If the engine is not operating at the specified temperature then something is wrong. The biggest problem with a stuck thermostat is not so much that it is stuck open. It is that it "sticks." Being stuck open is inconvenient. But being stuck closed is terrible. And the same mechanism that allows it to be stuck open is just as likely to keep it stuck closed.

Fix it before you need to.

My symptoms were virtually identical. The radiator swap kept the temps under control here in 100+ heat with my ac on... But in wintertime the car would never warm up to operating temperature...

It's really not that bad of a job on a 302, fortunately.

Let us know what you find out - good luck!

 

[Broncobowsher]

As stated, too cold. I really like to see at least 180°. My latest find is a stock Motorcraft thermostat for a ~'91 mustang. High flow and 192°. Warms up fast, but flows to keep things cool once up to temp.

 

[DeepC73]

My symptoms were virtually identical. The radiator swap kept the temps under control here in 100+ heat with my ac on... But in wintertime the car would never warm up to operating temperature...

It's really not that bad of a job on a 302, fortunately.

Let us know what you find out - good luck!

I just bought a new 185 degree thermostat. I’m wondering if I should wait until “after” the parade to change it. It’s only a week away. I don’t think it will hurt it. I would much rather it be between 120-130 during the stop and go crawling parade pace than 185/190 degrees in case it starts to overheat. The transmission (C4) is known for generating heat. I will let you all know what I decide.

 

[nvrstuk]

My symptoms were virtually identical. The radiator swap kept the temps under control here in 100+ heat with my ac on... But in wintertime the car would never warm up to operating temperature...

It's really not that bad of a job on a 302, fortunately.

Let us know what you find out - good luck!

... and that is what cardboard in front of the radiator from Nov to April is for! Seriously, 30+ yrs ago you would see cardboard in front of almost all pickup trucks and many cars wherever it was cold in the winter. Never overheated doing this for decades.

 

[DeepC73]

Thanks everyone for your help and suggestions. It was raining all day so I went ahead and pulled open the thermostat housing to investigate. I had completely forgotten that I purchased a “failed open” thermostat when I rebuilt the engine last year. As you can see from the link below, it did exactly what it was designed to do. I replaced it and it maintains 180 degrees now. Thanks again everyone.

 

[Steve83]

...many say the 302 operates best at around 185 degrees.

Not Ford, or any engineer. The hotter an internal-combustion (Otto-cycle) engine runs, the more-efficient it is; UP TO the lowest temperature at which any component is damaged. In the case of passenger vehicle engines, that's the oil, which breaks down around 240°F. So the closer you can get to that without going over, the better the engine will run, and the longer it will last.

The purpose of the thermostat is to keep the engine at optimal operating temperature.

Not true. The t'stat has no capability to regulate engine temp. Its only function is to PREVENT the cooling system from working until the engine reaches a temperature at which the PCV system can function. IOW: it's only there to make the engine warm up faster. Once the engine is above the t'stat temp, the t'stat has very little purpose. It's a restriction to the coolant flow which causes SLIGHTLY higher pressure inside the engine than in the radiator, which helps prevent the coolant from boiling and thus carry more heat out. But if everything else is working right, the engine will run fine without the t'stat. The fan clutch has FAR MORE control over the engine's max temperature, and to some degree its minimum temp.

This is the t'stat most of my trucks use:

https://www.amazon.com/dp/B000C5DSKC/?tag=classicbroncos-20

 

[jamesroney]

...Not true. The t'stat has no capability to regulate engine temp.

OK, so normally I would just discount this absurdity out of hand. But being that this is from you, @Steve83 and you have a history of being smarter than most...I am going to have to dig into this deeper.

The notion that the thermostat has no capability to regulate engine temp is an interesting theoretical hypothesis. If the hypothesis were true, then the theory can be proven. The thermostat being a capillary controlled mechanical device that opens an orifice to restrict flow thru the primary heat exchanger. So let's just stress test your theory.

I have a 82 Ford 351W heat engine. Let's assume that it is in it's as-designed configuration. Let's assume that it has a 185 degree thermostat. And for the purpose of destroying your hypothesis...let's assume it is installed in a Mastercraft Boat, floating in a Lake, with a reservoir temperature of 60F, and for the purpose of this analysis...let's assume that the lake is of infinite heat capacity. (Fans, radiators, convection coefficients, thermal transfer, delta T's all go away.) The Tc is established at 60F, with a thermal capacity of infinity. By your theory, the thermostat is not capable of regulating engine temperature. But if you remove the thermostat, the engine temperature will reach a steady state temperature of about 70F. And if you plug the thermostat orifice, the engine will reach an eventual steady state temperature of T(h). But we know that the engine temperature is modulated to reach 185 degrees, and the orifice size is proportionally adjusted to achieve that temperature. There is some hysteresis, and some transients, but fundamentally the coolant temperature is maintained at 185. Therefore the thermostat does control the engine coolant temperature, and therefore your hypothesis fails.

I'm not going to debate the fundamental inaccuracies of the Carnot Cycle efficiency thermodynamic model, except to say that is is also absurd, and like most complex engineering analysis...the solution is constrained to the assumptions. If you assume enough, you can reduce engine efficiency to the classic (Th-Tc) / Tc ratio. But everyone knows that Carnot was French, and the French have been stealing technology and fouling up the world for about 2 centuries. I urge you to visit the Musee des Art's and Metiers if you have the opportunity. It was enlightening for me, and brought home the concept of concurrent invention...but I digress.

I once explained to my Thermodynamics Professor that one cannot reduce an internal combustion engine efficiency to (Th-Tc)/Tc. Because if you do that, you cannot explain how a high performance engine can be more efficient than a low performance engine. They always both have identical Th and Tc. But they have vastly different heat conversion efficiency in both Specific Fuel consumption, and Horsepower per unit displacement. So you might as well "assume" that the answer is "SEVEN" and move on. Back in the 1980's, I actually made a list of my favorite "answers." Those answers include "superman" , "watermelon", "seven", "Napolean," and "his left foot." They are all awesome answers, taken from the back of trivial pursit cards. And they have just as much application to oversimplified engineerig analysis as any other answer.

Gotta run...

 

[nvrstuk]

Dang James- you posted while I was typing!! lol I couldn't let it go either.

There are several caveats in your post above Steve83.

First simple one would be saying that... and I quote: "The fan clutch has FAR MORE control over the engine's max temperature, and to some degree its minimum temp." and ... "the engine will run fine without the t'stat."

So if your statement that the: "if everything else is working right, the engine will run fine without the t'stat."

Maybe your statements would hold true in a controlled environment with a set load and no variables what-so-ever but that's not real life for an automobile engine. HUGE difference between text book conditions and snow/ice in the mountains one day and crossing the desert the next.

Your example (my interpretation of it) would be that once your engine reaches temp you can discard the thermostat because you say the clutch fan takes over because it has more control.

So without a tstat regulating the flow of the water which of course needs to be heated (slowed down) to bring it to operating temps - then how do you build a "clutch fan" and the radiator in front of it to regulate water temps if you are in sub freezing temps or 100 deg temps? You CAN'T because you can't control the over cooling which will occur in the freezing mtn example I just posted even without the clutch fan running and here's why.

The temperature of the water would never reach operating temp because if you designed the radiator to be small enough to allow the water to pass thru quickly enough to NOT COOL below optimum operating temps which you say is barely below oil breakdown temps, then the next day when you drive across the desert you need to CHANGE the size of the radiator so the water WILL have enough time to be cooled either by air travelling thru the radiator because you are travelling at 50 mph or because your clutch fan sensed the temp and now is turning on to help control the water temperature as it's passing thru the radiator.

Explain how the water temperature will be controlled by a clutch fan that will NEVER TURN ON because the water temp passing thru the system never gets above 150 deg F during cold weather because the PASSIVE parts of the cooling system are doing THEIR job (another caveat from your post) and therefore the clutch fan never needs to turn on and can NOT control the water temperature.

There might be parts in my response that are repetitive but I can't believe that you didn't take in to account cold weather operation and passive cooling. I already have cardboard in front of my radiator and my "clutch type cooling fan" is not rotating more than the minimum rpm they all do with viscous couplings.

(I just read your post James and my reponse sounds really "blue collar" compared to yours which is also correct- just more scientific!) lol

 

[Broncobowsher]

James, thanks. Normally I am the one writing the long winded corrections. I didn't have time to deal with that one this morning. I just read it, shook my head, figured I would get to the replay later. Thank you for saving me the work.

 

[bmc69]

I just bought a new 185 degree thermostat. I’m wondering if I should wait until “after” the parade to change it. It’s only a week away. I don’t think it will hurt it. I would much rather it be between 120-130 during the stop and go crawling parade pace than 185/190 degrees in case it starts to overheat. The transmission (C4) is known for generating heat. I will let you all know what I decide.

I run only 192-195 stats in every rig. Even 210 is not "overheating"!..I think you are overly concerned about the temp range you expect to see.

 

[bmc69]

OK, so normally I would just discount this absurdity out of hand. But being that this is from you, @Steve83 and you have a history of being smarter than most...I am going to have to dig into this deeper.

The notion that the thermostat has no capability to regulate engine temp is an interesting theoretical hypothesis. If the hypothesis were true, then the theory can be proven. The thermostat being a capillary controlled mechanical device that opens an orifice to restrict flow thru the primary heat exchanger. So let's just stress test your theory.

I have a 82 Ford 351W heat engine. Let's assume that it is in it's as-designed configuration. Let's assume that it has a 185 degree thermostat. And for the purpose of destroying your hypothesis...let's assume it is installed in a Mastercraft Boat, floating in a Lake, with a reservoir temperature of 60F, and for the purpose of this analysis...let's assume that the lake is of infinite heat capacity. (Fans, radiators, convection coefficients, thermal transfer, delta T's all go away.) The Tc is established at 60F, with a thermal capacity of infinity. By your theory, the thermostat is not capable of regulating engine temperature. But if you remove the thermostat, the engine temperature will reach a steady state temperature of about 70F. And if you plug the thermostat orifice, the engine will reach an eventual steady state temperature of T(h). But we know that the engine temperature is modulated to reach 185 degrees, and the orifice size is proportionally adjusted to achieve that temperature. There is some hysteresis, and some transients, but fundamentally the coolant temperature is maintained at 185. Therefore the thermostat does control the engine coolant temperature, and therefore your hypothesis fails.

I'm not going to debate the fundamental inaccuracies of the Carnot Cycle efficiency thermodynamic model, except to say that is is also absurd, and like most complex engineering analysis...the solution is constrained to the assumptions. If you assume enough, you can reduce engine efficiency to the classic (Th-Tc) / Tc ratio. But everyone knows that Carnot was French, and the French have been stealing technology and fouling up the world for about 2 centuries. I urge you to visit the Musee des Art's and Metiers if you have the opportunity. It was enlightening for me, and brought home the concept of concurrent invention...but I digress.

I once explained to my Thermodynamics Professor that one cannot reduce an internal combustion engine efficiency to (Th-Tc)/Tc. Because if you do that, you cannot explain how a high performance engine can be more efficient than a low performance engine. They always both have identical Th and Tc. But they have vastly different heat conversion efficiency in both Specific Fuel consumption, and Horsepower per unit displacement. So you might as well "assume" that the answer is "SEVEN" and move on. Back in the 1980's, I actually made a list of my favorite "answers." Those answers include "superman" , "watermelon", "seven", "Napolean," and "his left foot." They are all awesome answers, taken from the back of trivial pursit cards. And they have just as much application to oversimplified engineerig analysis as any other answer.

Gotta run...

wuht he ^ said.

Signed: Old Purdue grad that specializes in thermodynamic issues with advanced marine vehicles.

 

[73azbronco]

Not Ford, or any engineer. The hotter an internal-combustion (Otto-cycle) engine runs, the more-efficient it is; UP TO the lowest temperature at which any component is damaged. In the case of passenger vehicle engines, that's the oil, which breaks down around 240°F. So the closer you can get to that without going over, the better the engine will run, and the longer it will last.

Not true. The t'stat has no capability to regulate engine temp. Its only function is to PREVENT the cooling system from working until the engine reaches a temperature at which the PCV system can function. IOW: it's only there to make the engine warm up faster. Once the engine is above the t'stat temp, the t'stat has very little purpose. It's a restriction to the coolant flow which causes SLIGHTLY higher pressure inside the engine than in the radiator, which helps prevent the coolant from boiling and thus carry more heat out. But if everything else is working right, the engine will run fine without the t'stat. The fan clutch has FAR MORE control over the engine's max temperature, and to some degree its minimum temp.

This is the t'stat most of my trucks use:

http://[URL]https://www.amazon.com/dp/B000C5DSKC/?tag=classicbroncos-20

[/URL]

Hmmmm, semantics really, the thermostat will cycle open and closed to maintain it's rated temperature, it does not open and stay open forever, unless cooling capability is exceeded.

 

[nvrstuk]

I read it literally... " The t-stat has no capability to regulate engine temp. It's only function is to ... "

We don't read "engine temp" on our guages, we read water temp.

We didn't even address the oil issue. Running the oil at a temp continually that is only a few degrees below it's actual temp that it "breaks down" at. Some physics happening here also. I have another blue collar example ???

 

[jamesroney]

Hmmmm, semantics really, the thermostat will cycle open and closed to maintain it's rated temperature, it does not open and stay open forever, unless cooling capability is exceeded.

Uhm, I agree with you on the function of the thermostat. But semantics? Maybe on a couple of spoint. But let's look at what @Steve83 said...(and he's usually not wrong...)


"Not true. The t'stat has no capability to regulate engine temp. Its only function is to PREVENT the cooling system from working until the engine reaches a temperature at which the PCV system can function. IOW: it's only there to make the engine warm up faster. Once the engine is above the t'stat temp, the t'stat has very little purpose. It's a restriction to the coolant flow which causes SLIGHTLY higher pressure inside the engine than in the radiator, which helps prevent the coolant from boiling and thus carry more heat out. But if everything else is working right, the engine will run fine without the t'stat. The fan clutch has FAR MORE control over the engine's max temperature, and to some degree its minimum temp."

1. Not true. (we all know what that means...)
2. The t'stat has no capability to regulate engine temp. (False. That is exactly what it does until the cooling system capacity is reached.
3. Its only function is to PREVENT the cooling system from working until the engine reaches a temperature at which the PCV system can function. (Clever, but deceptive. The PCV can function at any temperature. As long as there is vacuum, and combustion, the PCV system is operable. Certainly not the "only" function. It is also quite useful in accelerating coolant warm up in cold climates to facilitate passenger comfort and visibility. But it does this by defeating the cooling system. So I will yield on this as a clever semantic point.) "Its only function is to PREVENT the cooling system from working until always."
4. Once the engine is above the t'stat temp, the t'stat has very little purpose. (Concur, because if the engine is above t'stat temp, then the t'stat is already completely open, AND the thermal transfer of the radiator/ heat exchanger is already inadequate.)
5. It's a restriction to the coolant flow which causes SLIGHTLY higher pressure inside the engine than in the radiator, which helps prevent the coolant from boiling and thus carry more heat out. (Concur.)
6. But if everything else is working right, the engine will run fine without the t'stat. (rebutted previously.)
7. The fan clutch has FAR MORE control over the engine's max temperature. (This is clever, and is correct. But it presumes that the cooling system is at maximum heat rejection capacity due to the thermal fan, and that the heat exchanger is capable of additional cooling with incremental convective flow. Once the fan clutch is at 1:1 ratio, it has no control over max temperature. But OK.
8....and to some degree its minimum temp. (I don't see this.)

Gotta go,

 

[Speedrdr]

I’m wishing now I had paid more attention to the engineering students in my dorm suite as they were discussing (and cussing) the course of Thermodynamics…

Randy