SVX Engine cooling "Again & Again"

[Dessertrunner]

Hi all you quite people out there,
Ever wondered what the difference between radiators with top & bottom tanks as opposed to ones with side tanks and which one would be better.
Well as a result of the tests on Steves radiator I can answer that question. One is a mile in front of the other.
Tony

[svxistentialist]

Well, c'mon, c'mon Tony. Don't keep us in suspense.

Which one is better?

Joe

[Dessertrunner]

Hi Joe,
Given that now I see the reason that one is better then the other I feel like a total idot that needs councling.

Side tank radiators on the condiation that the radiator cap is on the same side as the suction. What I learn't with Steve's and it applies to our radiator to a lessor extent was that at around 7,000 rpm our water pumps will pump to 24psi. At that pressure when the coolent hits the radiator there is a head pressure in the top tank, in Steves a case it is above 10 psi so the cap blows and releases the coolant.
What I was trying to do to fix his issue was to drop the pump flow which was wrong instead we need to get his cap on the suction side in that way his radiator is pressurized instead of operating in vacuum.

Think about it with our standard cars we rev the motor above 6k and we suddenly get major head pressure in the top tank which results in the engine blowing all the cooant out the overflow because top tank pressure exceeds cap pressure.

In Steves case he system was cooling the engine it was just that he was blowing coolant out the overflow which ment that in the end (long race) he had none left or the pump could no longer pump due to lack of coolant. If you follow me a bit further, coolant is blown out the overflow which mean an overall vacuum developing in the system where does that vacuum turn up its at the pump suction untill it goes so high the pump can no longer pump and the system dies. That is why I saw -10psi at his suction.

Well Joe hope that answers your question also you should have a look at side tank radiators the majoity have the cap on the out let side.

Have a great day.
Tony

[dynomatt]

If you're measuring 24psi from the pump, then there's big problems.

The cooling system can't deal with those kinds of pressures, hence the stock radiator cap is .9 bar, or 12-13psi. So your comment confirms that in Steves case, the system is just pumping water out the overflow...and eventually drains itself.

Surely you can get the flow without increasing the pressure?

I still am not quite sure why mine has been cured by a pretty simple change yet others (steve) continue to have trouble.

M

[Dessertrunner]

Matt 24psi is the number behind the pump as it enters the block. By the time it gets to the top tank on the radiator it drops to a more reasoniable level.

You and I changed out bottom pipes to improve the flow out of the radiator which resulted in a dropping of the top tank pressure. Also our radiator flows a lot more then Steves interms of litres per minute.
Tony

[Trevor]

Kia ora Joe,

I am confident that you will appreciate that when making a comparison, like must be considered with like. This has become an intrinsic problem throughout this thread.

You will also understand that on a basis of tradition, radiators were developed with top and bottom tanks to take advantage of a thermosyphon effect and the first radiators relied solely on this principle, prior to the introduction of an engine driven pump. Even so this is still effective in assisting flow. Cross flow radiators have been used on the basis of a physical mechanical advantage. Technically, it could be argued that they are less efficient than the original pattern.

Cheers, Trevor.

[Dessertrunner]

Trevor,
I understand you point but the befits of top to bottom flow aren't real when the pump is pushing 200 litres per minute. That is roughly a total change of the coolant in the radiator every sec. Heat current transfers don't work that fast.
Tony

[Trevor]

Originally Posted by Dessertrunner

Trevor,
I understand you point but the befits of top to bottom flow aren't real when the pump is pushing 200 litres per minute. That is roughly a total change of the coolant in the radiator every sec. Heat current transfers don't work that fast.
Tony

Exactly, and part of what I have been indicating throughout this thread.

[Dessertrunner]

Trevor I am talking about the flow of liquids in the radiator not the transfer of heat through the fins.

[Trevor]

Originally Posted by Dessertrunner

Trevor I am talking about the flow of liquids in the radiator not the transfer of heat through the fins.

“Heat current transfers don't work that fast.”

I have been and was talking about, the speed of the transfer of heat during the flow of liquid throughout the cooling system, i.e. how long it takes for heat to be transferred to and from the coolant. I made no reference to the transfer of heat through the fins.

[Dessertrunner]

I understand that is what you were talking about, your argument is that there is such a thing as "the faster you send the coolant around then the less effeicent it will be in transfering heat both to and from".
I don't happen to agree and never have agreed, if what you are saying was true the surface tempreture of a radiator would vary based on coolant flow rates. It justs doesn't happen that way. No were in the thermal transfer calcs for working out the tempreture of the surface of a radiator does it take into account the flow of the liquid behind it.
Tony

[Trevor]

Kia ora Tony,

Sadly we are at cross purposes here, but not to worry as the concept is very difficult to explain and comprehend. The surface temperature of a radiator or calculations for working out the temperature of the radiator is not really involved in what I have in mind.

The efficiency of the radiator and how well it actually works, will depend on the rate of air flow (how much air can get through it) and the conductive area presented to the air flow (the area/surface size of the core). This must be related to (considered together with) coolant flow capacity (how much coolant it can flow). Each radiator will have optimum (correct as designed) air and coolant flow rates. If these are not complied with radiator will not work correctly.

The actual cooling rate (the amount that it cools the coolant passing through it) depends on the rate/speed of the coolant flow. (If the coolant passes through too quickly, or too slowly, the coolant will not be cooled as much.)

Fill a radiator with boiling water, wait one minute, tip out some water and measure the temperature. Repeat but wait five minutes and measure the temperature. Surely it is obvious that time and speed of coolant flow, i.e. flow rate, is a deciding factor, regardless of and quite independent from air flow.

How much heat is transferred within the engine to the coolant (How hot the coolant will get) also depends on the amount of time the coolant remains within the engine. (If the coolant passes through more quickly, the coolant will not be heated as much.)

Much earlier in this thread, in spite of nastily expressed opposition typical of the member involved, I have referred to a ratio of heat transfer between the radiator and engine which makes up the deciding equation.

If the coolant is flowing too fast. ----

a. Radiator. An increased flow/volume of coolant will pass through, but overall the radiator will become less effective (will not cool the increased amount coolant as well as the previous smaller amount was cooled). The temperature of the coolant exiting (coming out of the radiator), will be increased. (It will be hotter as it has not been cooled as well.)

a. Therefore records a definite negative factor, in respect of the cooling achieved as direct result of a flow increased beyond the designed optimum.

b. With an increased flow, there will be less transfer of heat within the engine. (The coolant will not heat up as much.)

b. Therefore records a marginal positive factor, in respect of the amount of heat to be later dissipated. (cooling required).

(*N.B. There is an associated important consideration, in that the engine temperature will rise. Hot spots and boiling pockets are also likely to occur due to any increase in pressure beyond the designed optimum, thus increasing temperature even further.)

Conclusion --- The conductive area within the radiator far exceeds that within the engine. Therefore if flow is excessive (there is too much flow), there may be slightly less heating of the coolant within the engine, but at the same time cooling via the radiator will be reduced very considerably. Result, an overheating system if the pump speed exceeds the optimum due to above normal engine RPM.

Expressed as factor, a. will be greater than b. and therefore there will be an increase in coolant temperature during the cooling process, when optimum flow is exceeded.

*N.B. At the same time engine heat will increase, thus accelerating the problem. The mugwump bird is in free flight.

It may seem strange that increased pressure and therefore flow, does not improve cooling, but when the pressure and flow exceeds the designed limit(optimum), the above scenario applies. The key is to prevent the optimum level being exceeded, e.g. by reducing the efficiency of the existing pump, a method proven in respect of other engines. Granted, cooling at lower RPM could be effected, but for others this has not created a problem. In any event, we are talking about a special application here and the fans should prove adequate to take care of the situation.

The above scenario may or may not represent the problem wrangled about here for so long, but should definitely receive full consideration and testing, especially as all else has failed.

[NeedForSpeed]

Originally Posted by Dessertrunner

Hi all you quite people out there,
Ever wondered what the difference between radiators with top & bottom tanks as opposed to ones with side tanks and which one would be better.
Well as a result of the tests on Steves radiator I can answer that question. One is a mile in front of the other.
Tony

Tony,
I'm reading every post, quitely yes, but appreciatively .
Great work, kudos to you for taking it all on .
Fascinating actually, but with purpose

[Dessertrunner]

Trevor I am not sure I want to go down this path as even if I go to endless effort to support my statement I don't expect that you will accept that I am right? In simple terms and don't reply with a novel, do you agree with the following.

At a given flow of coolant the transfer rate of heat in BTU's per minute is maxium when the tempreture difference is greatest between the coolant and the engine. When the coolant temp approachs Engine temp the system has the lowest transfer rate of BTU per minute. The transfer rate of heat from engine to coolant is non linear when based on time over BTU transfer per minute.
Do you agree Yes or No
Tony

[svxistentialist]

Don't want to muddy the waters or the coolant but the points Trevor made in his lengthy post are correct imo.

A free-er flowing and highly efficient radiator will only be able to dump extra engine generated heat if the coolant is being forced through it at the optimum rate for the whole system.

Too slow and the excess heat from the engine will not be pumped [transferred if you will] fast enough to the highly efficient rad.

Too fast, and the rate of heat transfer in BTUs as Tony notes will not be optimised.

What seems to be happening in our [generalised] case is that high pump speeds are causing higher than acceptable pressures in the system. These high pressures are a direct result of flow restrictions that are more likely to be in the engine block than in the radiator complex, though I have run no tests to prove that. It is just my opinion based on current reports.

Trevor I think is advocating reducing the coolant flow to match what the engine normally runs at, rather than the very high speeds of coolant flow that consistent speeds over 4500 rpm might generate. I see great merit in this approach.

However I will admit I would be happier to see tests identify where the restrictions are in the block, and if possible relieve them to allow a faster flow. Building up pressures so that the rad cap loses coolant is bad news.

I'm not offering answers here, just saying I think Trevor's thinking on the problem is correct as I see it.

Joe