Leafy

iTrader: (1)

But that person would have been right, but probably for the wrong reason. The thermostat creates a restriction, even when all the way open, compared to no thermostat. This has the effect of increasing the pressure in the block and decreasing the pressure at the rad cap. What does that mean? Higher pressure in the block minimizes localized boiling and also the size of the nucleates is reduced (in nucleic cooling that happens up in thur). These be good thing yo.

aidandj

iTrader: (5)

The


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Period.

sixshooter

iTrader: (12)

Funny.


Does wood get more dense with age or is it just people? I would think even Helen Keller would understand, "What are your ******* lap times?" after the third query. But then again that deaf, blind bitch would probably be smart enough to run a thermostat, too.

emilio700

iTrader: (3)

Did some more research on this, consulted a friend that's a former HVAC engineer, had an espresso or two. It appears that I'm guilty of propagating a myth, after a fashion. I hate when that happens. Apologies to the community.

Let the coolant haul *** through the system, just like the air through the rad. Looking at our crossflow, I know we have more surface area than a traditional downflow of the same core thickness, but the gains there are modest. What gains there are from any crossflow, are not in any way related to the speed of the slower local flow rate, but the greater surface area of core vs end tank.

sixshooter

iTrader: (12)

Yes, but why are you emilio700 and not emilio949?

JasonC SBB

And the greater turbulence from higher coolant speeds through smaller channels, improves heat transfer to the metal.

emilio700

iTrader: (3)

Not that anyone cares but sure, I'll bite.

When I was in the bicycle business circa 1997, long before I started this business, that was my email address. Road bike wheels are 700c diameter. Became a member of most forums long before starting 949 Racing.

Chooofoojoo

iTrader: (7)

Not emilio622?

nitrodann

I just read the last 2 pages and was wondering how long it would take for leafy to go "Yeah but X". (As an added bonus he is right)

Everything asserted in the last 2 pages, about water flow rate and heat transfer is correct. Its really straight forward and very very many people, even those as experienced as Emilio can be tricked by long held myths.

This forum is awesome. Carry on.

Pestoso

I'm a little, OK very, confused at the apparent contradictions here. I know almost nothing about thermodynamics but what Leafy is saying makes sense about raising the pressure through the block to raise the boiling point. However allowing full flow to achieve greater cooling efficiency makes sense as well. Wouldn't it be more beneficial to raise the pressure throughout the cooling system rather than just the block? In order to create a higher pressure through the block we would need to restrict flow, and that would negatively impact cooling system efficiency. I realize any system contains many trade offs, so perhaps the restriction is one of the necessary evils.

The more I read about these subjects the more confused I get.

I really like the idea of the electric water pump and controller (BMW since ~ 2004), however if the pump is in line without a thermostat we do not see the aforementioned restriction. Is there a built in restriction in beemer systems to replicate what is seen from the t-stat? Or would altering the size of the coolant hoses provide the needed restriction?

Can someone enlighten me, or point me to some information that may answer my questions?

Leafy

iTrader: (1)

We do also increase the pressure throughout when we go to higher rated rad caps, which **** if I remember but that should have been on the first page.

Pestoso

Yes I think it was, my question really is regarding the idea of raising the pressure within the block. If the system is operating at the proper pressure through the use of a good cap, is there any real benefit to raising the pressure specifically within the block? To simplify my question, if someone were to switch the the Pierburg pump what type of restrictions, if any, would be needed to keep engine temperatures stable across the entire block/head?

Leafy

iTrader: (1)

Well within the block there's really only the water pump seal and the head gasket as things that can blow out. You can certainly slap a 3 bar rad cap on the radiator and find out which coolant hose is the weakest.

Madjak

Having a faster flow helps with two parts of the heat transfer equation. First you get more mass flowing over the hot surface, and you also get a larger delta difference in temp inside the engine. If the water is flowing faster the temp is more even across the engine as well as lower.

Here is my example:

Engine A has half the flow rate of Engine B. The engines are both producing the same energy in the form of heat.

Coolant enters at 170F... by the time it exits the block the coolant in Engine A temp has raised 20F, Engine B temp will have raised 10F (with a 'fraction more') as there is twice as much mass to hold the same energy content. The 'fraction more' comes from the greater delta in engine temp to coolant temp across the whole block in Engine B. As that difference is larger there is more total energy pulled from the metal by the coolant in Engine B than Engine A.

The counter to this is that the radiator works in reverse... ie it cools less as the temperature of the coolant is lower. But the coolant is still lower temp than in Engine A. However there is a benefit to faster flow as the coolant maintains a higher delta to the ambient temp and so you get a greater total amount of energy transfer.

All this only has a minor impact on total temp maybe only a few degrees. My reasoning for not running a thermostat was more to do with one less point of failure and more even engine temp than better cooling.

Madjak

Really a race engine should be nowhere near boiling coolant in the block so I don't think the small pressure increase from a restriction point is really that important. If your slapping really high PSI radiator caps on your car to stop it overheating then the cooling as a whole isn't working. If the coolant is instead flowing faster through the engine the localized boiling is less of an issue anyway.

Pestoso

Davies Craig
The "pump too fast lose less heat” notion is very popular and many experienced mechanics are very attached to it but – it is a fallacy. Davies Craig has been carrying out research and development for over a decade on a number of projects and has never been able to pump genuine liquid coolant faster and lose less heat. In all car engines, when the mechanical pump reaches cavitation speed, coolant turns into a gaseous state which is compressible,(liquid is not) and the real flow rate of liquid coolant drops even though the mechanical pump has a higher rpm, and so heat loss drops. The engine temp then rises. And it only seems like the flow rate is too fast, and the coolant is spending too little time in the radiator to lose its heat etc. etc..

I may have finally found the answer, although not very technical, to my question.

slammed200

iTrader: (8)

How did this work out for you? I'm about to change the thermostat on my non-bypass re-route setup (welded mixing manifold and no heater core)

humming

iTrader: (2)

I can't imagine any pressure difference between the rad and block due to the thermostat being very significant... Does anyone have any data on this? If it was half a PSI pressure drop across the Tstat I'd be surprised... Half a PSI raises the boiling point of water by 1.2°C.

NiklasFalk

iTrader: (1)

To get significant pressure difference in a non-compressible medium (water, oil,...) you need a small restrictor.

The Tstat adjust the flow between the different paths.
Remove all alternative flows and you end up with a more uneven flow in the head. A real reason for keeping the heater circuit in a racecar (or place a Laminova in that flow if you never ever see rain).

Just my personal reflections and reasoning for keeping it as-is wit reroute only.

vehicular

iTrader: (3)

I have to agree with this. I would be very surprised if there was more than a fraction of an inch delta P across the thermostat.

I'm not anywhere close to advocating removing it, just saying that increasing pressure in the block is such a miniscule effect as to be lost deep down in the noise.