To thermostat or not to thermostat

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Wow. I didn't check for a bit and seems like you guys had fun.


Not too sure about how we are going to use protons to figure out this issue. The quote "All models are wrong, some models are useful" comes to mind. With that being said, I'll do my best to work through what the group comments and attempt a logical thought pathway. I fully admit I am a metallurgical engineer and not a mechanical, chemical, or heat transfer engineer and, transport phenomena (heat transfer was a topic) was the only class I didn't pass. But that was because of personal problems with the professor (he was an as hat and I wasn't gonna study that). But I digress...

@Steamer way cool test. To me, this data point confirms running without a thermostat results in more efficient transfer of heat from the engine to the radiator fluid. However, there is one issue with the test and trying to apply it to our engine operation. The issue is that your garden hose is an open system with an infinite heat sink where as my radiator system is closed loop with a maximum heat capacity above which the radiator fluid boils.

Just to clarify for myself, my engineering brain thinks ok we have:
1) heat transfer rate from engine into radiator fluid and
2) heat loss rate from radiator.

Radiator fluid flow rate doesn't effect either, unless we activate another fluid flow regime (laminar vs turbulent flow). check.

Question 1: Does flow variation affect heat gain from the engine? Yes. As @Steamer showed, increased flow increases heat transfer into the fluid.

More support: Looking at the 1F cooling loop schematic (below), looks like there are definitely locations here eddies and "hot spots" locations, such at the rear of the engine. Does anyone have pictures of what the radiator cavity actually looks like? I can't remember too well, but I thought it was fairly convoluted.

Question 2: Does flow variation affect heat loss from the radiator? Unlikely, as radiators are heat exchanges that are already designed to generate as turbulent a flow as possible. Basically, maybe, but I expect the difference to be minimal.

So, high flow results in COOLER ENGINES, but HOTTER FLUID! Hence the overheating.

The next questions:
Does the engine need to be cooler than design? Unlikely given the impressive 1F track record. If I did need more cooling, I would expect to have more aftermarket options for the issue. Others please weigh in here.

Are there other negatives (non-heat transfer issues) associated with high flow due to lack of thermostat? Yes, mainly erosion. I don't know about you guys, but I have small particles in my radiator (even after flushes). I have seen a number of aluminum thermostat housings with pitting, which was likely due to erosion. Additionally, I would expect a slight increase in erosion of the water pump. Are there others that I missed?

Are there negatives associated with putting the thermostat back in? I can't think of any other than that is a couple hours gone and I need a new gasket.

All that being said, I'll put the thermostat back. I'll have a hotter engine, but reduced propensity to overheat (hopefully, unless of course my model is also wrong).


Radiator Flow Overview.jpg
 

Steamer

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there is one issue with the test and trying to apply it to our engine operation. The issue is that your garden hose is an open system

Just to be clear. The bypass blocked off with thermostat removed and the garden hose in the “open” radiator was temporary for flushing purposes only to get the flush chemical flushed out with clean water.

Before I put the T-stat back in and un-blocked the bypass, I saw an opportunity to test the theory of coolant moving too fast. The testing was done with the cap back on and system was not open.

I should also note that after removing the plug and returning the T-stat, the operating temps did not increase. It is my opinion that a wide-open T-stat does not reduce the flow by much if any. I believe the water pump moves about the same amount with it installed or removed with a plugged by-pass.

You should only benefit from installing a T-stat because of the bypass function. If you're still overheating you have other issues. Some good flushing may help.
 

Steamer

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I like to say that unless you've owned your vehicle since new, you have no idea of how the cooling system was cared for or what abuse it may have endured in the past.

One common scenario is a split radiator hose gets a temporary repair with electrical tape and a loose radiator cap so it doesn't build pressure. Fill it up with whatever water is handy and it's good to get you home so you can take care of it right away. Or maybe the coming weekend. Or sometime in the near future. Tap water keeps it topped off each morning and you really are gonna take care of it soon. Then finally when the boil overs get frequent, you finally get on it but discover that an off the shelf radiator flush just doesn't get out the rust and mineral deposits that have built up there. Or maybe you think the flush worked and your new overheating issues must by something else.
 
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Interesting, so (as you and I think others have mentioned) put it in and figure out what else is wrong.

This is a new to me 1971 40, with a 69 engine. God only knows what it has seen.

From my professional life, oxygen corrosion of steel is usually the dominate unless you start talking about strong acids. When I replaced the water pump, I did notice rust, but attributed it to surface rust. I couldn't really get the best view of the inside, but didn't notice significant pitting in the block.
 
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Dizzy

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Here is an experiment:
Garden hose with municipal water, high pressure, low volume, spray into 5 gallon bucket and smell.
Then research what chlorine and chloramine do for contributing to rust? Like stainless steel in swimming pools, etc.
 

Steamer

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Here is an experiment:
Garden hose with municipal water, high pressure, low volume, spray into 5 gallon bucket and smell.
Then research what chlorine and chloramine do for contributing to rust? Like stainless steel in swimming pools, etc.

Yup. And if you have an open system for awhile, it's like a distillery. Clean water evaporates off leaving behind chemicals and minerals where the concentrations keep getting stronger.
 

73FJ40

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I'm happy for the correction - the knowledge is useful and I find the subject interesting.
I stand by my statement that the engine/radiator do not know how fast the coolant is going. They function at a broad range of flow rates.
My point was that there is no correlation between the flow rate and cooling (unless it is standing still or so slow it starts boiling).
So, if a faster flow rate INCREASES the temperature of the hot object, then I've been HEATING my hot soup by blowing on the soup in the spoon instead of COOLING it? :hmm:
 
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73FJ40

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So if there's "no correlation between flow rate and cooling" then wind chill is BS? :hmm:

Somebody should call out the weather service to stop misleading us..
 

3_puppies

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So if there's "no correlation between flow rate and cooling" then wind chill is BS? :hmm:

Somebody should call out the weather service to stop misleading us..


wind chill does not affect non living things, steel at 20F with a 20MPH wind is still only 20F it is not colder
the wind will cool something hot down to ambient temp quicker than with out it, but it won't make it colder than ambient temp
wind chill is the cooling effect that the wind has blowing across bare skin.
 

73FJ40

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wind chill does not affect non living things, steel at 20F with a 20MPH wind is still only 20F it is not colder
the wind will cool something hot down to ambient temp quicker than with out it, but it won't make it colder than ambient temp
wind chill is the cooling effect that the wind has blowing across bare skin.
This entire thread is about heat transfer from hot (engine metal) to cold (coolant). It's not about steel sitting in an equilibrium temperature with ambient air.

Wind chill relates the cooling effect on the body (98 degrees) of air velocity to equivalent terms of still air. Still air at -22 degrees will feel to your exposed skin as 20 mph air at zero degrees. Heat transfer in this case from hot (skin) to cold (air).



So, getting back to your steel in the context of heat transfer, if you had a hot steel rivet ( say 200 degrees) sitting outside, would it cool down quicker in still air at 0 degrees or 20 mph air at 0 degrees?

If the air velocity has no effect on "cooling", then why bother with pesky radiator cooling fans?

It's all about heat transfer, my friend...
 
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Actually, this thread is about heat transfer from the coolant to the air. The OP's problem is that coolant is getting too hot because the cooling system is not dumping heat to the atmosphere fast enough.

Jim, agreed but, does having a thermostat help or hinder? Still not clear to me. For sure it helps getting up to temp, but that was never the problem. Driving around it likes to stay at ~190F, so long as I baby it and try to stay in low rpms. When I am in stop/go traffic in the sun or try to push more than 55-60mph, temperatures climb and I have to be really careful.

Since it sounds like there are too many other potential variables, I’m putting it in this weekend. That is at least one unknown eliminated.
 

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It is probably not an exclusive thermostat, or no thermostat situation. But, what is the pressure on the radiator side of the thermostat, vs, the pressure on the bypass line side of it?

'Shade-tree' folklore says that you can delete a thermostat if you are overheating, but I think those folks were talking about a stuck thermostat?

I'd like to see what it looks like under the radiator cap.
 
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I just read the thread from start to finish....it seems to be screaming restricted flow in the radiator. I'd check for blockages after the thermostat is replaced (water sprayed on a hot radiator looking for cool spots). If you have blockages you may be working with, effectively, half a radiator meaning half the heat transfer from water to air resulting in overheating.
 

FJ40Jim

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Jim, agreed but, does having a thermostat help or hinder? Still not clear to me. For sure it helps getting up to temp, but that was never the problem. Driving around it likes to stay at ~190F, so long as I baby it and try to stay in low rpms. When I am in stop/go traffic in the sun or try to push more than 55-60mph, temperatures climb and I have to be really careful.

Since it sounds like there are too many other potential variables, I’m putting it in this weekend. That is at least one unknown eliminated.
The thermostat helps prevent overheating by blocking the radiator bypass passage when coolant reaches operating temperature.
 

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