Definitive results of tests on factors influencing cooling

[steveg]

Testing on Sunbeam Tigers relevant to Healeys:
https://teae.org/cooling-the-sunbeam-tiger-tiger-tom-chuck-king/

Terrific science project.

 

[HealeyRick]

Good read, Steve. Thanks for posting. Would be nice if someone could do the same scientific approach for Healeys. I think it's interesting the article focuses on cooling at idle, where it seems most Healeys have their problems (heavy traffic, parades, etc.) Increasing airflow is problematic without altering the body a great deal. There's not a lot of radiator opening and with the vertical slats in the later grille it must block off a lot of flow. The works style mesh grille with polished aluminum inlets would seem to help, but significantly alter the car's looks. Ray's mods here would seem to help as well: https://drive.google.com/file/d/0Bx4EjcJmfaScY0NLdlB0YjEwRFE/view Getting hot air out of the engine compartment helps, too. I know a "trick" with Tigers was to raise the rear of the hood an inch (you can do it with a Healey, too) to theoretically let heat out, but OTOH, once at speed the base of the windshield becomes a high pressure zone and may hamper flow coming through the radiator. That's where comparative testing would be helpful. Same idea with the popular Rally side vents. They look great, But Geoff didn't put much stock in them. Testing would be great there, too. Inner wheel wells are a low pressure zone and some of the V8 MGB guys have installed vents there to remove heat from the engine compartment (one guy welded in the louvers from an old gym locker, but probably likely to lose a few concours points for that one). Shrouding the fan is a plus, but again it takes away from originality. Electric fans may help and a pusher is easiest to fit in a Healey, but tests show a puller is more effective. Some tests I've read say installing a pusher and leaving the mechanical fan causes them to fight eaach other. The pusher is supposed to restrict air flow. Altogether, there's a lot of confusing and contradictory info.

With 345 hp to cool, I'm having cooling problems. I can keep it in the 190-205 range with a big puller and a fan, but the fan runs almost continuously. I'm biting the bullet with an aluminum radiator from Wizard Cooling with a shroud and my fan installed as a puller. I'll let you know how it works.

 

[Keith_M]

Very interesting article. I like that they approached the problem incrementally and carefully documented the effect of each modification. My healey gets hot in traffic and at idle, particularly after running hard on the highway for a while. I have recored my radiator, added a DW 5-bladed fan, and added a shroud. My own non-scientific assessment of these three mods is that re-cored radiator helped immensely, the 5-bladed fan helped a lot, but the shroud didn't seem to do much. I added a 10 inch pusher this past winter, but it hasn't been very warm in Logan yet this year, so the jury's still out on that one. Based on the amount of air it moves, I think it will help a lot though. I was particularly intrigued that they found it was better to mount the pusher fan about an inch in front of the radiator. That seems totally counter-intuitive to me.

 

[RAC68]

Steve/All,

The doc posted on cooling the Tiger validated a number of things I have been thinking and pointed to some that are quite intriguing. As you know, the things I have added to cool my Healey are both simple and innocuous (unnoticeable). Some of the recommendations in the article do fall in that area and can be easily adopted.

To start with, I was never a proponent of pusher fans as I always thought they blocked air when driving. The article has validated that thought and the benefit of an electric fan with fewer blades. After taking the original air conditioning compressor and supporting components (including the engine-mounted thermostatic radiator fan) from my 1979 TR7, I left the 2 thermostatically-controlled air conditioning 3-blade cooling fans mounted below the radiator. Of significance, mounted low and in front of the radiator, these 2 fans provide no air block at speed and, when at idling, direct an air up to intersect the radiator's fins at an angle. Although these fans were only meant to assist in cooling when the air conditioner was active, they are now functioning as the only provider of cooling air to the radiator and are efficient enough to keep the TR7 cool enough to survive at idle for hours on a 100 degree day.

Now, when considering the potential of hot engine compartment air being re-circulated through the radiator and progressively increasing the environment’s temperature, this is definitely something I believe happens in our Healeys. Again, the TR7’s engine tub with fully enclosed radiator and bulkhead eliminates the forward passage of already-heated engine compartment air. Additionally, with louvers in the bonnet, air is vented out of the engine compartment resulting in the venting and elimination of any high pressure air block that could form.

Our Healeys are definitely plagued by porous radiator bulkheads and, at idle, build pressurized bubbles of hot air in the engine compartments and are constrained by minimal restrictive containment from the radiator bulkhead. Large openings around the steering box, beside the radiator and between the cross member allow large amounts of hot engine compartment air to pass back to the front of the radiator and pulled through again and again. As a result, when at idle, we can often see the temperature slowly increase.

At this point I feel it is not which fan to choose or even what radiator to install but how to improve the air flow within the engine compartment. Sealing the radiator bulkhead is one approach that, I feel, can never be fully achieved. However, it is possible to diminish the present free flow of air through the bulkhead and reduce the effect of hot air re-circulation. But, unless your Healey is partially disassembled, as when Steve addressed the issue, access to many of these openings for remediation would be quite difficult … if not impossible. I wonder if it would be more productive to attempt to reasonably seal the passage to the radiator by completing the closure of the deflector panels and extending this closed path to the grill. Last, I wonder if the installation of 1 or 2 thermostatically controlled Electric assist fans could be embedded within these added panels and out of the radiator’s cool air stream to provide added flow when needed.


Well, that's it for now. What are your thoughts?

Regards,
Ray (64BJ8P1)

 

[HealeyRick]

Ray,

Did you ever try blocking off the area in front of the radiator near the hood locking mechanism? I wonder if air gets to the front of the radiator from the engine compartment over the top of the radiator.

 

[steveg]

Ray,

Did you ever try blocking off the area in front of the radiator near the hood locking mechanism? I wonder if air gets to the front of the radiator from the engine compartment over the top of the radiator.

I've blocked off that and most of the other areas: https://www.pbase.com/stevegerow/healeyaircontrol

The article describes attaching scraps of cassette tape in various places to check the airflow.

 

[steveg]

Ray wrote:

....At this point I feel it is not which fan to choose or even what radiator to install but how to improve the air flow within the engine compartment. Closing the radiator bulkhead is one approach but, as original, will never be completely sealed and will always leaving large unrestricted openings for hot air to escape forward. At this point, I am thinking how viable it would be to partially most bulkhead openings and seal the front radiator deflector panels to and move radiator intake forward to the grill. ...

IMO, the most economical approach would be to figure out the travel of the tie rod mechanism and really seal the deflector panels from the radiator forward to the grille. Incorporate a top cover around the bonnet latch and a scoop at the bottom near the anti-roll bar. A lot of the sealing could be done with waterproof fabric, such as vinyl, providing some sort of "gaiter" around the tie rods.

Also useful to bring the fresh air intake forward to the grille to prevent intake of hot air from the exhaust manifold area.

 

[HealeyRick]

Wow, Steve, it looks like you've covered all the bases/ How does it cool?

 

[HealeyRick]

Maybe we should take Tom Shnerk's approach with his Olds-Healey and Cobra-ize the front end:

 

[CLEAH]

What about using small electric extractor fans mounted behind rally side vents?

 

[steveg]

Wow, Steve, it looks like you've covered all the bases/ How does it cool?

We haven't had really warm weather yet. Will follow up in July. What I can say is the air from the fresh air side is no longer HeaterV2.

 

[shortsguy1]

That is a very impressive study. But I am confused about some of their results. In particular, they say that by shutting off the coolant bypass (and forcing all coolant flow through the radiator), the engine temperature increased at idle. That is unexpected. They go on to say that increasing flow through the radiator does not improve cooling. Heat exchanger design theory would suggest that increasing the flow of coolant through a crossflow heat exchanger will enhance cooling, so their findings are puzzling to me.

 

[RAC68]

Hi All,

First, I want to apologize for my original post as it was sent prematurely and inadvertently. The intended version has since replaced it.

Hugh, I believe that side vents, with or without the addition of fans, could help the air flow within the engine compartment but would require fender modification.

Shorts, although I am also puzzled by their comments on the coolant by-pass, I believe their conclusion that increased coolant flow through the radiator could increase and not decrease operating temperature is correct. My take is, if coolant passes through the exchanger faster then it can sufficiently absorb or expel heat, exiting temperatures will rise. However, if the temperature differential between coolant and exchanger is increased, it is possible that flow can be increased to advantage, provided the efficiency of the exchanger is sufficient. This applies to the heat exchange taking place in the radiator and/or engine.

Ray (64BJ8P1)

 

[Keith_M]

Hi All,

Shorts, although I am also puzzled by their comments on the coolant by-pass, I believe their conclusion that increased coolant flow through the radiator could increase and not decrease operating temperature is correct. My take is, if coolant passes through the exchanger faster then it can sufficiently absorb or expel heat, exiting temperatures will rise. However, if the temperature differential between coolant and exchanger is increased, it is possible that flow can be increased to advantage, provided the efficiency of the exchanger is sufficient. This applies to the heat exchange taking place in the radiator and/or engine.

Ray (64BJ8P1)

This is one of those issues that I've seen discussed in various venues around the web, but I've never seen an answer that completely satisfies me. Ray, I think you are correct in saying that faster coolant flow will not allow the water in the radiator to cool as much, leading to higher radiator-exit temperatures. However, it will also not allow water in the engine to heat as much, leading to cooler engine-exit temperatures. In general, faster flow should mean less difference between the radiator and the engine temperatures, while slower flow should allow the water to cool more in the radiator, but heat more in the engine, and lead to great temperature differences. So, part of the confusion resides in whether you're measuring water temperature in the block or the radiator.

The problem is not quite that simple though. The complete answer depends on the temperature differences between the radiator water and the air, and between the engine water and the engine. To understand this, it helps to think about the extreme situation where you slow flow so much that the water in the radiator approaches air temperature (this probably never happens, but it's a useful thought exercise). Keeping the water in the radiator longer doesn't make the radiator-exit temperature lower, but it will increase the engine-exit temperature because the engine is constantly generating heat. So, you want to keep the water in the radiator long enough to cool it substantially, but not so long that the temperature differential between air and water gets small and limits heat transfer.

I think the complete solution to this requires a heat-transfer computer model of the entire cooling system. Somebody must have done this, but I've looked around the internet for such a thing and never found one.

 

[shortsguy1]

[Warning: boring heat transfer lecture approaching!]

For heat exchangers (like a radiator), q = U*A*DeltaTlm. q is the heat transfer rate in energy per time. U is a heat transfer coefficient that is a function of the flow behavior of both fluids in the radiator. Due to increasing turbulence as flow rate increases, U increases slightly as velocities increase. A is the surface area of metal separating the two fluids (coolant and air) DeltaTlm is called the log mean temperature difference. It is a special type of average of the temperature differences between the coolant and the air. You can calculate it if you know two things: the temp difference between the coolant and air at the inlets, and the temp difference between the coolant and air at the exits. It is not an arithmetic average, but it is typically close to the normal average that most are familiar with.

As a consequence of this expression, to maximize the heat transfer rate (q), you want the temperature difference between the two fluids to be as much as possible throughout the radiator. This probably makes sense to most. The greater the local temp difference somewhere in the radiator, the greater the transfer of energy at that location. So while it is counter-intuitive to some, to maximize q, you want to have the fastest flow rates possible through a heat exchanger. This ensures that the temp difference between the two fluids at the heat exchanger exit is still large enough to help the energy transfer. Obviously at crazy fast velocities, other concerns like cavitation begin to occur. But under normal and common conditions, pushing a fluid through a heat exchanger faster will increase the heat transfer rate (aka cooling capacity).

The idea that the fluid doesn't have time to lose its energy at high flow rates is false logic. Here is one way to think about it. Is our goal to maximize the heat transfer rate (aka the engine cooling)? Or is our goal to maximize the temperature drop of the coolant? These are actually achieved by opposite decisions. To maximize the heat transfer rate, you want to maximize the flow rate. The maximize the temperature drop of the coolant, you want to slow the flow down to a trickle (so it has tons of time to cool off). If you slow the fluid, yes those molecules of fluid in the radiator will cool off significantly, but the other fluid in the system has no opportunity to cool, so the overall operating temperature of the system will increase.

I know it is a bit confusing and I wish I could explain it better. But widely accepted engineering theory says that heat transfer rate (aka radiator cooling capacity) will increase with increase flow rates through the radiator.

 

[steveg]

What they've established is: on a car with a clean cooling system, with increased and more efficient airflow, the Tiger can be made to idle indefinitely in 90 degree weather (as in a parade) without overheating. Using the smaller water pump pulley, they're also moving coolant through the radiator faster as they move more air with a sped-up heavy duty fan.

They also found that some expensive items, such as aluminum radiators and high-volume water pumps make little or no difference in the parade scenario.

Hot air recirculating back through the radiator is a problem on the Tiger as well as the Healey, so reducing that should be a priority.

 

[Keith_M]

[Warning: boring heat transfer lecture approaching!]

Well, I was hoping someone with more knowledge would chime in, so I was glad to see this. What you say seems reasonable, but I have heard people say not to take your thermostat out in the summer because it lets the water circulate too fast and the engine actually runs hotter. I assume that this is just plain wrong? Maybe these people are measuring temperature in the radiator rather than the block. Faster circulation should increase temperatures in the radiator, right?

Based on what you say, the only ways to keep things cooler are to increase water flow rate and increase cooling at the radiator by increasing air flow through the radiator and decreasing air temp through the radiator (preventing air from the engine compartment from recirculating).

I like it. It's simple.

 

[British_Recovery]

Louvres seem to be simple answer to venting under hood heat. How effective are they?
Has anyone driven, or idled in traffic, with the hood off?
Bob

 

[shortsguy1]

Well, I was hoping someone with more knowledge would chime in, so I was glad to see this. What you say seems reasonable, but I have heard people say not to take your thermostat out in the summer because it lets the water circulate too fast and the engine actually runs hotter. I assume that this is just plain wrong? Maybe these people are measuring temperature in the radiator rather than the block. Faster circulation should increase temperatures in the radiator, right?

Based on what you say, the only ways to keep things cooler are to increase water flow rate and increase cooling at the radiator by increasing air flow through the radiator and air temp through the radiator (preventing air from the engine compartment from recirculating).

I like it. It's simple.

I am most familiar with the cooling system on old Mercedes Benzes, but I believe that Healeys are the same as what I am about to say. Some cars (not sure what fraction) have a coolant bypass which allows coolant to circulate (back to the engine) even when the thermostat is closed. When the thermostat opens fully, it simultaneously allows coolant flow to the radiator and closes off the bypass. That is what the moving ring does on a bellows Healey thermostat, and old MBs use a different design but same principle. When you remove the thermostat, now there are two continuously open paths for coolant, to the radiator and directly back to the engine via the bypass. So less coolant flows through the radiator without a thermostat than with one. So if your cooling system is operating correctly, removing the thermostat should reduce cooling and increase the operating temperature of the engine.

In cars with a coolant bypass, occasionally people see the opposite effect (when they remove the thermostat, cooling improves). This is probably because the thermostat was malfunctioning and not fully opening. A second possibility (common in MBs) is that they are able to better purge air out of the cooling system without a thermostat. So they think the affect is due to the thermostat, but it is actually that they got rid of a big air bubble in the system. In these cases, no thermostat could appear to be better than thermostat.

Sorry for repeat what is probably common knowledge, but if a car tends to overheat at idle but not at speed, the problem is likely air flow related. And if a car tends to overheat at speed, but not at idle, the problem is more likely coolant flow related. This is very simplistic and real life is not always that simple. But the Healey I inherited does tend to overheat at idle and slow speeds, so I am going to work on improving the air flow through the radiator first, as suggested by that study that started this entire discussion.

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.

 

[RAC68]

Hi All,

Having just returned, I must say that I have enjoyed andlearned from the discussion and applaud the presentations and comments fromShortsguy1, Keith and others. Thank youfor sharing your knowledge and experiences.

To continue, I agree with Shorts’ comments on the bypass andimportance of the Bellows/Sleeve thermostat:



In the ‘70s, it was a common practice to change the coolantand thermostat annually and in the process I replaced my original thermostatwith the newest and greatest specifically designated for my Healey from one ofthe largest manufacturers. Since thepresence of a bypass within the Healey’s cooling system was unknown to me andnot present in any American Iron, I did not recognize the absence of the bypassblocking cylinder on the replacement and for years attributed the increase inoperating temperature to other issues. Sincelearning of the bypass and replacing and replacing my thermostat with a Sleevetype, I have eliminated the close to 25% cooling lost to recalculated coolantescaping the radiator through the open bypass.



For those wanting to eliminate the thermostat completely,Moss and others can supply a bypass blocking cylinder that will eliminate theissue and loss of cooling capacity.

As far as fender vents and hood louvers are concerned, both allow for more effective elimination of under-bonnet pressure and heat buildup. It is no surprise that the evacuation of large amounts of hot air produced through the use of aggressive fans, without clear exiting paths, is a major factor in the creation of high pressure bubbles that can further encumbers under bonnet air escape. When at idle, this hot air build-up finds an escape through the many openings in the radiator bulkhead and is pulled back through the radiator to further increase the under bonnet air temperature. Bonnet louvers and fender vents, positioned properly, provide a clear and unobstructed escape for this fan motivated hot air stream. Although I believe in the effectiveness of louvers and fender vents, I personally have no desire to modify my fenders and will find alternate ways to evacuate under-bonnet heat air and heat buildup.

Enjoy your Healeys,
Ray (64BJ8P1)