Definitive results of tests on factors influencing cooling

[Bob_Spidell]

I have an OEM sleeve-type thermostat as pictured sitting in my parts cabinet. It appears there is a possible issue with these being 'fail closed' which, of course, means that if the thermostat quits working you will overheat. I've heard there are some newer versions that are 'fail open,' but offhand don't recall where I saw the info or source.

 

[steveg]

I experimented with several solutions. Left - Moss sleeve cut down to cover the bypass port only. This was briefly used with a Moss 180 degree fail-open thermostat and modified double green gaskets.

Also shown, two Robertshaw thermostats. The upper is the 160 degree one I bought from BCS which had the movable sleeve soldered to it. I unsoldered that and moved it to a 180 Robertshaw purchased elsewhere on the internet, which is what I'm currently running. The lower one is the spare 180 Robertshaw I bought as a fallback if my soldering job went pear-shaped.

I think the fail-open with modified bypass port sleeve might work equally well in warm climates.

 

[RAC68]

Bob, when you mentioned the fail close issue, I also remember that being a major issue a number of years ago. Not remembering which sleeve thermostat I have in the car, I probably chose the one from BCS for that reason but just don't remember. I took a look at the one offered by Moss Motors and can't believe they are charging $114 rather then around $11.

Steve, based upon the cost of a replacement, I would appreciate more detail on how you constructed a more cost effective replacement unit.

All the best,
Ray (64BJ8P1)

 

[steveg]

Bob, when you mentioned the fail close issue, I also remember that being a major issue a number of years ago. Not remembering which sleeve thermostat I have in the car, I probably chose the one from BCS for that reason but just don't remember. I took a look at the one offered by Moss Motors and can't believe they are charging $114 rather then around $11.

Steve, based upon the cost of a replacement, I would appreciate more detail on how you constructed a more cost effective replacement unit.

All the best,
Ray (64BJ8P1)

Ray,
I bought the BCS thermostat, which is a 160 degree Robertshaw with a sleeve soldered onto it via three little tabs. See the solder marks on the side of the upper Robertshaw in my picture for where the tabs attached to the body of the Robertshaw. I used a propane torch and unsoldered this ring, then soldered it onto a 180 degree Robertshaw.

I'm not going with the Moss $114 one because I trust the Robertshaw ones or the Moss fail-open more because they are real thermostats made by companies that do that for a living.

 

[Bob_Spidell]

Ray,
I bought the BCS thermostat, which is a 160 degree Robertshaw with a sleeve soldered onto it via three little tabs. See the solder marks on the side of the upper Robertshaw in my picture for where the tabs attached to the body of the Robertshaw. I used a propane torch and unsoldered this ring, then soldered it onto a 180 degree Robertshaw.

...

Exactly what I did. Been running it for many years.

 

[Keith_M]

One last point of clarification, faster coolant circulation will ensure a smaller change in temperature of the coolant, which means that the heat transfer is better between the coolant and the air. It won't "increase temperatures in the radiator", but it will allow the system to be better controlled by the thermostat and operate at a more constant temperature.

This is a really interesting thread, and I feel like I've learned a lot about cooling system problems, but one thing still bothers me a little. You say that faster coolant flow means a smaller change in temperature of the coolant. I understand that, but doesn't that mean that the radiator water will stay warmer? i.e., it won't cool as much in the radiator because it moves too fast.

I don't mean to be anal about this, I'm just trying to understand what the ramifications of measuring temperature in the head vs the radiator might be for people who increase the coolant flow and then report that the engine runs hotter. The whole thermostat bypass thing is another wrinkle in the problem.

 

[steveg]

This is a really interesting thread, and I feel like I've learned a lot about cooling system problems, but one thing still bothers me a little. You say that faster coolant flow means a smaller change in temperature of the coolant. I understand that, but doesn't that mean that the radiator water will stay warmer? i.e., it won't cool as much in the radiator because it moves too fast.

I don't mean to be anal about this, I'm just trying to understand what the ramifications of measuring temperature in the head vs the radiator might be for people who increase the coolant flow and then report that the engine runs hotter. The whole thermostat bypass thing is another wrinkle in the problem.

I'm not an engineer, but it seems to me the factory could have easily sped up the coolant flow if they wanted to - there must be some tradeoffs here such as noise, power draw, etc. Maybe when we consider how egregious the airflow management is, the coolant flow is relatively insignificant by comparison.

 

[HealeyRick]

Steve,

One might think the engineers were totally unfamiliar with U.S. weather extremes as the cars don't handle high temps well and heaters, defrosters and windshield wipers aren't well suited for cold and snow. I would've though DMH and Geoff would have picked up on that during their cross country trips. The cars do seem better suited for UK weather than US conditions.

 

[shortsguy1]

This is a really interesting thread, and I feel like I've learned a lot about cooling system problems, but one thing still bothers me a little. You say that faster coolant flow means a smaller change in temperature of the coolant. I understand that, but doesn't that mean that the radiator water will stay warmer? i.e., it won't cool as much in the radiator because it moves too fast.

I don't mean to be anal about this, I'm just trying to understand what the ramifications of measuring temperature in the head vs the radiator might be for people who increase the coolant flow and then report that the engine runs hotter. The whole thermostat bypass thing is another wrinkle in the problem.

Hi Keith-
I think it is important to remember that the radiator is just one component of a system. If you increase fluid flow through the radiator, you are also increasing fluid flow through the engine. A faster moving fluid will not increase in temperature as much as it travels through the engine, and a faster moving fluid will not drop in temperature as much as it travels through the radiator. This will enhance heat transfer in both the engine and radiator.

So you asked whether water in the radiator will stay warmer. Yes, its temperature will not drop as much, but it will have rejected more energy into the air, so the overall cooling ability is better. Think about the coolant passing through the engine. Do you think it is better to have a slow flow of fluid which will then experience a very large change in temperature as it flows? No, this would be a bad situation. A large fluid temperature change does not reflect that a large amount of heat transfer has occurred. At maximum engine loads, it is best to have high coolant flow through both the engine and the radiator. The temperature of the coolant won't change as much as it travels through either, but it will be taking in more heat transfer from the engine, and rejecting more heat transfer to the air. I guess another way to think about is that, with higher coolant flows, the water should be less likely to ever reach extremely high temps (assuming a well operating system). So the fact that the coolant temp doesn't drop as much in the radiator isn't a problem, as long as overall cooling capacity is adequate.

Or maybe think about the air going through the radiator. To maximize cooling, most of us would say that more airflow is better than less airflow. I don't think anyone has the intuition that a slow air flow is better because it will achieve a larger change in temperature, which indicates more energy was removed (This again is false logic). At conditions when overheating is a possibility, you want to be sure that both the coolant flow and air flow are sufficiently high to facilitate the required amount of heat transfer between the fluids.

 

[steveg]

See new thread about the modified Robertshaw thermostat.

 

[Patrick67BJ8]

I'm not an engineer, but it seems to me the factory could have easily sped up the coolant flow if they wanted to - there must be some tradeoffs here such as noise, power draw, etc. Maybe when we consider how egregious the airflow management is, the coolant flow is relatively insignificant by comparison.

Coolant just not flow through the radiator too fast. Race cars, NASCAR, use restricters instead of thermostats because if they didn't the water would not get cooled. I had a NASCAR engine builder tell me this.

 

[shortsguy1]

Coolant just not flow through the radiator too fast. Race cars, NASCAR, use restricters instead of thermostats because if they didn't the water would not get cooled. I had a NASCAR engine builder tell me this.

That does not match accepted engineering practice, but no doubt in some special cases, there might be exceptions to the rule. For instance, at very high flow rates, cavitation could occur which could damage the water pump or some other component. If cavitation is occurring, a restrictor could be beneficial. Also, if the water pump impeller is designed to produce a certain flow rate (based on rpm), and you greatly exceed that range the intended rpm, you could have flow separation. If the flow path through a pump does not remain attached to the impeller blades (i.e., if the path traveled by the coolant is no longer parallel to the edge of the impeller blade), you can end up with low flow even thought pump is spinning like crazy. There are also cases in our cooling systems where high flow rates could exceed the pressure of the radiator cap. If 7 psi is created by the water pump, it could possibly cause the radiator cap to release pressure, even at temps below the boiling point of water. So in these limited cases, a coolant restrictor could be beneficial.

But in the vast majority of cases, increasing coolant flow rate will improve overall performance of a car's cooling system. Here is one companies explanation:
https://stewartcomponents.com/index.php?route=information/information&information_id=11

 

[Lotuswins]

For those of you doubting that coolant flow increases enhance heat rejection capability, here is a paper reviewing radiator performance: https://www.ijeat.org/attachments/File/v2i3/C1204022313.pdf . Note that to obtain significant changes in cooling capacity, sufficient air and water flow must be provided.

Thanks Steve, for providing access to the Tiger study on cooling. Great work, and it really helps to define what a good fan and shroud arrangement can accomplish, as well as other items. The only note I can add is that something was going on with the upgraded pump to increase flow that was not understood by the testers. As shortsguy1 explained (and very well thank you) and the paper above illustrates, increased flow carries away more heat, adding cooling capacity. It has to do with boundry layer theory, laminar flow versus turbulent flow, and temperature differential. Any contaminants that interupt the efficiency of the heat transfer, like air entrainment caused by flow separation at the pump, can significantly affect capacity. Also note that they had better cooling capacity with the vaned versus paddle pump impellers, and if I'm not mistaken, the vaned impeller should flow slightly better than a paddle version. Also the reduced pulley diameter, which added capacity, was not an air over coolant increase 'fight' but both contributed to the capacity increase.

Thermostat restriction plates are installed mostly to keep the cylinder head at higher pressures so spot boiling doesn't occur, and with high performance engines that is critical to keeping them cool.

Thanks shortsguy1 for keeping us on the straight and narrow!....

 

[Keoke]

Note that to obtain significant changes in cooling capacity, sufficient air and water flow must be provided.

YEP just make sure it is sufficient but do not over do water flow rate or your engine will heat.

Yep we drill small holes in our standard thermostat flanges so if the thermostat fails closed we minimize overheating TOO

 

[RAC68]

Hi All,

I have really enjoyed this as high temperature, whether in the cooling system or cabin, represents one of the greatest issues of the Healey. I have appreciated the comments of Keith, Shortsguy1, and Jerry which have addressed specific components reinforced with some background theory. I must say that when considering the coolant as the heat transport from exchange 1 (engine Heat to coolant) to exchange 2 (coolant to ambient air), it becomes obvious that within the objective of expelling excess engine heat to ambient air, we are subject to a number of components and conditions within a not so simplistic cooling system. Yes, a faster transport (cooling flow rate) can carry heat from exchange to exchange and, as Shortsguy1 has properly well stated, will contribute to the potential for greater cooling. However, this efficiency is easily thwarted if heated air continues to recirculate through the radiator of if the engine bypass is left open to recirculate 25% of its heated coolant, or a number of other conditions as Jerry has well considered.

As I see it, we are addressing the improvement of the cooling system and therefore must address individual issues as components of that system. Although the improvement in coolant flow will contribute, it is a component and must be balanced to the requirements of other interfacing components to lend its improved contribution. It makes no sense to me to push for a faster coolant transport that can't eliminate its heat or have the best radiator when cooling air is blocked. When looking at our objective (Idle at 800-1000 RPMs for 2 hours on a 90 degree day without overheating) where are the problems and, with the elimination of the problems, how can we make it better. Yes, a faster coolant transport is a benefit but only after other well observed conditions are addressed. Additionally, any change I would consider would require that it is as close to incognito as possible, conservatively priced, reasonably reversible, and above all retains the character (from my perspective) of my Healey.

All the best and thank you for this thread,
Ray (64BJ8P1)

 

[Keoke]

The cars do seem better suited for UK weather than US conditions..

Yep that is what they were designed for.

 

[Patrick67BJ8]

The cars do seem better suited for UK weather than US conditions..

Yep that is what they were designed for.

I respectfully disagree. They were designed for "export", namely the USA, since we has enough people who liked sports cars and had the money to buy them.
I believe I've read articles/quotes, that 95% of the Healeys were exported from the UK or was it 95% ended up "new" to the USA?

 

[Keoke]

I respectfully disagree OK

But:
DMH had no history of exporting cars, thats why the healey has such lousy metal in it.
The Crown gave all the good metal to those with car exporting track records.
consequently, and economically the Healy production relied on available home grown out of the bin parts

 

[blueskies]

Somewhere in this thread, someone mentioned adding an aluminum radiator to a Healey. Possibly other design elements of the Healey defeat the possible advantage of an aluminum radiator, but in other vintage cars, an aluminum radiator can make a huge difference. In a big block Chevelle, for example, an aluminum rad provides a simple, although pricey, solution to overheating.

 

[steveg]

Somewhere in this thread, someone mentioned adding an aluminum radiator to a Healey. Possibly other design elements of the Healey defeat the possible advantage of an aluminum radiator, but in other vintage cars, an aluminum radiator can make a huge difference. In a big block Chevelle, for example, an aluminum rad provides a simple, although pricey, solution to overheating.

I've always wondered why. They don't even paint them black. Copper is a better heat exchanger than aluminum.

Here's a good discussion of the relative merits of each:
https://www.caparadiator.com/aluminumvscopper.html