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Coolant system opinions please

Coolant system opinions please

Coolant system opinions please

(OP)
Given this is a hobby, I did not want to post this in any of the automotive forums

The attached illustration is of a 70’s design deTomaso Pantera that had a reputation of having cooling problems. The rear mounted engine is a Ford Cleveland that utilizes a special design thermostat for a high flow bypass during warm up (to sweep the block and prevent hot spots)

The original design used a swirl tank on the thermostat discharge that was fitted with venting pressure cap and a recovery tank. The original radiator was baffled for front/rear pass. A high point vent tube was on the rear pass outlet tank and routed to the radiator outlet pipe. The heater core flow is taken before the thermostat and returns to the pump suction. A throttling valve would control its flow. (The upper illustration)

Later revisions were to re baffle the radiator for a lower/upper pass and to add a vent to the upper reversing tank and route it back to the swirl (not shown). A recommendation was to remove the pressure cap from the swirl tank and place it on the recovery tank. Add a vent from the swirl to the recovery and drain recovery tank to pump suction, thus converting the recover tank into a surge tank. The radiator vent is then rerouted to the new surge tank. (The center illustration)

My proposed reversion would be to add a 4 port heater control valve to limit coolant in the passenger cabin and it having the ability to maintain flow for the heater bypass. The heater return would then be routed to an educator supply. The radiator vent would be rerouted to educator suction, with the educator discharge into the surge tank. The surge tank will be partially filled to allow for the coolant’s thermal expansion. I am thinking there will be about 5% increase in volume. If filled proper, the compressed air volume from cold to hot should provide the 13 psig of the cap relief setting.

So is my proposed over engineering or would there be any benefit to having the heater core by pass flow going to the surge tank to degas the coolant (like a deaerator)? I have heard that entrained air reduces the coolant’s efficiency.
Any discussion or comments?
http://files.engineering.com/getfile.aspx?folder=8...

RE: Coolant system opinions please

An educator is a teacher.

The word you seek is 'eductor'. It may not work as you expect here; at low motive flows it becomes an inefficient tee. ... but at least it has no moving mechanical parts.

It appears that the factory never got the cooling really sorted out, but they had more resources than you do, and more engines to kill in experiments.

Start with what the factory did, proceed with caution, instrument the hell out of the installation, and pay attention to what's going on. At least instrumentation is cheaper and more flexible than it used to be...

Mike Halloran
Pembroke Pines, FL, USA

RE: Coolant system opinions please

Pardon my questions here, but I think you need to back up a step or two and identify what part of the heat transfer problem with this particular engine/placement/radiator/coolant tank/overflow tank/cylinder block is the problem.

When was the overheating the problem?

Hot engine - running wide open at full speed on a desert track on hot days?
Hot engine - idely for a long period of time at 0.0 speed ? On hot days? Or on cold days?
Cold engine - but just at startup, when the full-sized radiator is "too much" coolant area so the engine doesn't warm up fast enough?
Cold engine - but when trying to immediately rev up to full speed with cold coolant and a cold block so the emissions and heat are not balanced as they are when running for a while?

RE: Coolant system opinions please

(OP)
I am just returning to this hobby after 30 plus years of working on the road (sort of retired) so bear with the vaugness of the "problem". From historical documentation, the major problem was the factory did not impliment the design. the configuration,sizing of the components and comments from engineers of that time the layout should have been surge instead of the recovery tank. (should have been more like the GT40 configuration).

the other historical errors noted from dealer bulllitens was the inadaquate filling resulting in air pockets in the radator and rear engine. factory production was stopped shortly after the revisons to add the radiator vent to the swirl. the latter non Ford produced cars and earlier models that were plumbed as per the second illustration have operated acceptably. my pieces are as per the original configuration.

an intersting discovery for me was that my revison was something I mulled over just in though for years and after I made the illustrations and wrote the question for here, even to me, the ideal seems pretty much unjustified. Going back to the need to isolate cabin coolant to the heater core, just simple manual double isolation valves worked prior

thanks for the replies as sitting around the house just thinking can lead to trouble

RE: Coolant system opinions please

I think you are asking great questions, but having heard about a few cooling system/ HVAC problems at second hand, I seriously doubt that you, or we, could redesign the cooling system to perform properly.

But of course these days we can do three things that De Tomaso didn't have available for production

a) instrumentation - thermocouples and thermistors are cheap, and you can use an Arduino or the like to monitor them

b) electric water pump.

c) electric cooling fans

Good luck.

War story: once upon a time we were offered PWM motors for our prototype electric cooling fans. We spent many happy days testing these variable speed fans, logging which speeds caused resonant issues, and generally refining them. We put in predictive algorithms, so that the engine coolant temperature did not vary as the a/c cut in, and so on. Then the bean counters struck. Out went PWM. In came 2 speed +freewheel. Well, as it turned out, we had already logged the variable rpm we needed for the fans, so picking the fixed speeds we could live with was dead easy. The most interesting result from all the logging was that most of the time the fans were just ticking over, pushing the air the right way through the rad.

Cheers

Greg Locock


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RE: Coolant system opinions please

(OP)
thanks Greg. I didn't mention, but I want to maintain the original appearance and just refine. As for my recolection from back when I did drive the car, the major coolant problem I had was blowing off a heater hose showing off before thermostat opened AND the trouble I had trying to get the air out of the system following repairs. the owners manual had recomendations of filling with the rear of the car jacked X inches, runnning and then jacking front first then back again etc

As for monitering, the engineer in me wants a massive instrument cluster, but the automotive entusiest wants only the orginal minimal provided.

RE: Coolant system opinions please

Well, maybe an aux electronic display for the extras?
It can be blank when you don't need it or serve as sound system or climate control display.


Jay Maechtlen
http://www.laserpubs.com/techcomm

RE: Coolant system opinions please

Based on what I've seen, the first step for such cooling issues is often to install a new aftermarket or custom-built radiator with an improved design.

This might be something that your local radiator shop could fabricate, putting a much-improved core into the existing radiator. Drop in installation.

RE: Coolant system opinions please

(OP)
I had studied the article MintJulep linked. One of the points I noted was the excessive system flow head losses do to the lenght/diameter of the tubing, the number of turns and the two pass radiator. Making similair modifications like that owner did radically changes the original configuration even though it greatly optimized the system.

I have not measured and determined the lenghts and transitions, but the basic turbing size is 1 1/4" both for radiator inlet and return.

the radiator vent tube I was planing on added would be about 3/8 to 1/2" with the thought it would possibly have some scavanging flow not just air venting, hoping I could get a little suction from the eductor. another option would be have the radiator vent on the turning tank so there would be the second pass head to produce the venting flow.

RE: Coolant system opinions please

In theory, the factory had more resources than we do.
In practice, it depends a lot on the people...
and resources.
We've all seen examples of someone who has an idea, and the power to make it happen - but they're wrong.
And it goes into production with <maybe> enough patches to make it kind of work.

Jay Maechtlen
http://www.laserpubs.com/techcomm

RE: Coolant system opinions please

(OP)
I have a specific automotive question about this discussion.

will a radiator cap provided the function of an accurate pressure relief valve given there will be an air volume under it as per my proposed configuration. I am thinking radiator caps may be designed expecting coolant fluid to be appled, not hot air and vapour.

RE: Coolant system opinions please

Radiator caps were invented long before recovery tanks.
The cap should work fine.

Mike Halloran
Pembroke Pines, FL, USA

RE: Coolant system opinions please

(OP)
again, I am asking for discussion/opinions as there is no specific problem needing an answer.
is there any advantage of a coolant system with a recover tank versus expansion tank.

with recovery tank the system is filled "solid" under the relieving radiator cap, there fore as soon as any heat causes thermal expansion of the coolant, the pressure builds quickly to relief pressure.

with an expansion tank filled with an air volume greater than the coolant expansion at rated temp, the pressure of the coolant gradually builds with temperture and the water expansion compresses the air. if the initial fill volume was 2X air volume cold, the pressure would be ~15 psig at rated ( the cap relief)

so is one better than the other? the "solid" or the "soft" pressure?

AND on the use of an eductor to assist the venting of the remote radiator, the manufactors of 1/2" eductors are very proud of them! over $200. but their expected performance with the system conditions did indicate a sufficient suction would be generated

RE: Coolant system opinions please

Attached is a CAD cutaway of the assembly and an example of the core of an eductor I made. Six lasercut flat shapes interlock to form the nozzle and diffuser of an end-suction adapter. They are assembled around a short piece of tubing which forms the mixing zone, wired together for temporary retention, and welded into a 1" nipple about 7" long. The actual suction end comprises a washer and a short piece of 1/4" NPT pipe. The nipple's side is cut out for a side entry branch for the motive fluid. It could just as easily use a tee and a couple of short nipples for the housing.

The lasercut flats are exactly as they came from the lasercutter, with no beveling and no deburring done by me. There exist a lot of internal leak paths where the edges don't quite seal to each other, e.g. at the six flat surfaces that form each of the hexaplanar cones.

The eductor was designed to suck condensation from the inner bore of a jacketed exhaust pipe, which also contains hot exhaust from turbochargers.

It worked just fine, certainly well enough to drain a basement.

My point is that the commercial eductor manufacturers' products perform very, very well, but you can make an eductor that performs less well, but adequately for government work, from, well almost anything. Just eyeball the internal dimensions of the commercial units from their marketing illustrations, scale them to the size you need, and start hacking from there.

Mike Halloran
Pembroke Pines, FL, USA

RE: Coolant system opinions please

Oh, and 'solid' is way better.

There are millions of examples of cars with recovery tanks on the road today.

Their ancestors all had expansion tanks, which were a constant headache, with corrosion above and below the air/water interface, and all manner of gooey sludge at the interface and in the radiator cap.

Moving the air/water interface outside of the pressure boundary was a _huge_ improvement. Don't waste your time by learning that the hard way.




Mike Halloran
Pembroke Pines, FL, USA

RE: Coolant system opinions please

Quote (MikeHalloran)

You can make and eductor out of ... almost anything

This is true. I once made one using a pool noodle and a blow-off nozzle.

RE: Coolant system opinions please

(OP)
I feel I still need to qualify this is a hobby that I am slowly get back into.
For some reason the majority of the online info I keep finding discusses going with the seperate expansion tank, some even have a schader valve for "precharging" the air volume. I wonder if the air volume is not in the proximity of the radiator core would lessen the generation of sludge and initation of corrosion

RE: Coolant system opinions please

The presence of air within the pressure boundary, not its location, is what matters most.


If you want to use an expansion tank as a recovery tank, go ahead, and even call it an expansion tank when you brag to the folks on the Internet. Just vent it like a recovery tank, try to put the radiator cap near the top of the car, e.g. by putting it in an expansion tank that you keep full of cooant, make sure to get all the air out from the system, and keep it out.

Mike Halloran
Pembroke Pines, FL, USA

RE: Coolant system opinions please

If you really really wanted to I suppose that you could use a bladder type expansion tank to separate the coolant from the air.

But I can't see why you would want to.

As Mike notes, there are millions and millions of cars on the road demonstrating the efficacy of a recovery tank design.

RE: Coolant system opinions please

(OP)
I have not been keeping up with the engineering under the hood of my three current drivers so I just looked.

two out of three have are expansion tank design, 2001 yukon & 2004 silverado, but the 2004 monte carlo SSSC did have a recovery. I don't know all the details of those two with expansion tanks but I did see the upper radiator vent and the tank hose back to pump suction.

RE: Coolant system opinions please

My '01 Sierra(GMC badged Silverado) and my wife's '07 Yukon both have recovery tanks as does my daughter's '97 Lumina.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Coolant system opinions please

(OP)
here is a parts house hose schematic showing the coolant hoses for yukon (forgot what year I searched for) showing the "expansion tank". several google hits refer to it as a "pressurized recovery tank". the tank's coolant exchange is probably low, but it does have the coolant surface subject to pressuzed air and allows for a gradual pressurization with heat up.

RE: Coolant system opinions please

Thank you for the information. I stand corrected.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Coolant system opinions please

(OP)
I am not saying yours is a Pressurized recover like I referanced for my truck and suv because it seems a vented recover design is still being used along with the other. .

RE: Coolant system opinions please

Thanks for the schematic. Still my mistake.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Coolant system opinions please

Seems to me, with either an expansion tank or recovery tank, it would be important to have enough volume.
You want to avoid air bubbles in the engine, the radiator, and in the main cooling lines.

Since the Pantera has long hoses/pipes going to/from the radiator, it would have a greater change in volume than a car with the radiator right next to the engine.
It should be much easier to provide that large volume as a recovery tank than as a pressurized expansion tank.
However, a pressurized expansion tank might be less sensitive to small leaks in the cooling system which might keep an expansion tank from doing its job.

In the previous article about Pantera cooling, there was a referenced link which is obsolete.
this is may be what was referenced:
http://stewartcomponents.com/index.php?route=information/information&information_id=14

Jay Maechtlen
http://www.laserpubs.com/techcomm

RE: Coolant system opinions please

(OP)
I have though about the expansion and have gotten feedback from an owner that approxiamates the calculated value (they sort of guess how much went into a catch bottle.
the coolant volume is 6.4 gallons.
I figured if all the coolant went from 70 to 195F the expansion would be 47 in^3, the original resovior tank is 14" tall X 4" diameter so a rise of 3.7". if the cold filled volume leaves 7.4" (halve full) the resulting expansion would result in 15 psig. being cold filled between 4 and 7" should result in a 15 psig cap relieving, but no coolant being expelled.

If the original resevior tank is plumbed as a "solid" dearition tank with cap relief, a quart resevior would work.

the big installation differance between going with an expansion tank with >4" air space cold and dearetion tank with resevior would be raising the 14X4 tank the >4"

an interesting observation I have made while persuing this "hobby"...the manufactors of water pumps throw out claims of increased flow, BUT they never provide a flow/rpm curve! the same is true of radiators, they do not provide pressure/flow information

RE: Coolant system opinions please

Good point re the pump curves and radiator restrictions.
You know- after reading the info on the Stewart site, seems to me that four instruments would tell most of the story:
Pressure and temperature coming out of the motor.
Pressure and temperature returning to the motor.
(or psig at either point and delta-P across the motor)
You wouldn't need the pressure gauges once the system was debugged, but might tell you a lot while testing.

Regards
Jay

Jay Maechtlen
http://www.laserpubs.com/techcomm

RE: Coolant system opinions please

(OP)
I am still trying to understand the advantage/disadvantage of a "solid" system or one with the expansion tank (an accumulator)

consider the following situation;
having a solid system with a 15psig cap. this would have the boiling temp about 250F. the car is pushed hard and as the coolant expands, the cap keeps the pressure at 15 psig. the temp increases to 240F and then the driver backs off and the temp drops to 210F. Given the cool off from 240 to 210F will result in a coolant contration, would the system pressure drop for 15psig (to a vacuum) and cause the coolant to flash?

RE: Coolant system opinions please

Vacuum in an engine cooling system is not desirable. Boiling will create vapor lock in engine passages, collapse hoses, and cause cavitation in the water pump. Oxygen is also more likely to enter the system and cause corrosion.

RE: Coolant system opinions please

The temp isn't going to drop instantly to 210. As it cools down, the really hot bits of the motor should be getting cooled down, too. As it drops to/below 210, it seems the pressure would drop.
All the hoses relax a bit (the flex hoses do expand a bit, don't they?)and when the gage pressure drops a skosh below zero it will start pulling from the recovery tank.
Presuming the cap and recovery tank are functioning correctly, the pressure in the coolant system would only drop enough to suck from the recovery tank.
Anyone know the required pressure delta to pull from a typical coolant recovery tank?

Jay Maechtlen
http://www.laserpubs.com/techcomm

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