thermostats . . . .yes, no ?

[zefarelly]

do you use them in race engines ?

just built me engne got it running and I was wondering whether I should take it out or not . . . .will it restrict water flow once I get hot ? or will it stop the engine running too cool ? or is it a case of test'n'see ?

its a 1500 precrossflow, in a MK1 Cortina . . . .

[Tim Falce]

Without the thermostat there can be a problem of the water not having any restriction in the engine and flowing round the rad too quickly and not cooling enough. If you remove the thermostat you may need to put a restrictor disc in place of it to slow the water down.

[zefarelly]

ok, thanks Falcemob . . .I'll leave it in for now . . . .Ive never had a problem thrashing road cars . . . but racing is another matter!

[JimW]

Interesting. What Falcemob says seems contrary to the basic physics of the situation. Since I have no racing experience I have to defer to his knowledge but can I explain why I am surprised? :confused:

A given radiator and air flow will transfer an amount of heat from the radiator (including the water in it at the time) to the air. The amount of heat is proportional to the temperature. There are three principle mechanisms of heat transfer (from radiator surface to air stream and surroundings):

Conduction. Transfer rate is proportional to the temperature difference.
Convection. Transfer rate is proportional to temperature difference to the power of 3/2 (Newton’s law?)

Radiation. Transfer rate is proportional to the fourth power of the temperature difference.

Ignore the detail; the point I am interested in is that the hotter the radiator, the more heat is removed and this increases faster than the temperature difference.

Now consider the objective; we are trying to cool the engine block/head or “the whole engine” and not just the radiator.

So the faster we get the hottest water from block to rad., the greater the heat removed from the “whole engine” and the lower the temperature in the block/head.

If this is correct (and I agree entirely that it is simplistic) then remove all obstructions to water flow.

Factors I have ignored include:

Turbulent water flow in the wrong places
Increased pressure in the rad.
Cavitation in the water pump
That I may have forgotten my basic physics


Easy enough to check I would have thought. What are all these Formula Student teams doing?

Regards

Jim

[MikeM]

Oh dear, I cannot do physics but - I've always understood that, within reason, the slower the flow through the radiator - the greater the amount of heat lost. If the flow is too quick and the heat loss insufficient then the engine will end up overheating. Again, if the flow is too low the water will heat up and reduce the heat loss to the system. Does this make sense?

[JimW]

Originally posted by MikeM
Oh dear, I cannot do physics but - I've always understood that, within reason, the slower the flow through the radiator - the greater the amount of heat lost. . . .

I think I would argue that heat and temperature are being confused here.

You are not primarily interested in the temperature of the radiator exit water but in the temperature of the "engine". So it is heat you want to remove from the engine by supplying lots of cooled water. I have suggested above that the hotter the water in the rad. the greater the loss of heat.

(I recall that one of my "Oh I understand now" moments during my physics education was when the difference between heat and temperature was made clear. It can be somewhat confusing.)

Regards

Jim

[Tim Falce]

Er.......right. I would never argue with someone who can quote facts and figures like JimW has, so he must be right.
Time for another cold beer me thinks.

[275 GTB-4]

Originally posted by MikeM
Oh dear, I cannot do physics but - I've always understood that, within reason, the slower the flow through the radiator - the greater the amount of heat lost. If the flow is too quick and the heat loss insufficient then the engine will end up overheating. Again, if the flow is too low the water will heat up and reduce the heat loss to the system. Does this make sense?

A few racers in touring cars have told me that you often need some restriction to allow the radiator time to cool the water. They just cut out the thermo part from its plate or disk and put the big "washer" thats left over back in place.

Sometimes things work despite physics??.....

[JimW]

Originally posted by 275 GTB-4
A few racers in touring cars have told me that you often need some restriction to allow the radiator time to cool the water. They just cut out the thermo part from its plate or disk and put the big "washer" thats left over back in place.

Sometimes things work despite physics??.....

Hmm. Sorry but without this becoming tedious I don't buy that either. You don't want a "small" quantity of "cool" water; you want a large quantity of slightly less cool water. Again heat versus temperature.


If it helps understand my point Heat equals energy and temperature equals (corresponds to) that energy spread over the amount of substance it is in.

I can only suggest that someone tries it out and reports back.

Regards

Jim

[shiny side up!]

OK, it has been years since I have taken a thermodynamics course, so I would be hard pressed to build a valid mathematical arguement off the top of my head. (Don't make me get into mass flow rates and thermal conductivities, please... ) Anyway, from the common sense point of view:

How does a thermostat in a car work? Engine too hot: thermostat opens, more water flows through. Engine too cold: thermostat closes, less water flows through. Since the designer of the car doesn't know how much heat you are going to make the engine produce (whether it will be 67.893% of the maximum or 100% of the maximum), the cooling system must be designed to allow enough cooling if you are one of the 100% customers. On top of that, they throw in a safety factor and design the cooling system to actually be able to cope with more than 100% of the theoretical maximum amount of energy the engine will put out (in the form of heat to the water). This would make sure that leaves or snow stuck in your grill or some other unforeseen circumstance would cause your car to overheat.

So, moral of the story, whether it is intuitive to the physics mind or not, is that if you have typical production automotive engine and cooling system and take out the thermostat, the engine is going to run too cool. To compensate, a restrictor can be used to control the water flow in the system and thus control the amount of heat transfer (conduction, convection, radiation) and thus the operating temperature of the engine.

Phew, sorry to be so long winded with no maths to back it up!

[JimW]

Ah, now you're talking. I'll buy the argument that you can overcool the engine. And that you therefore might need to throttle the flow of coolant to control this.

Regards

Jim

[Onlooker]

You will never get the engine up to temperature.What you can do is run no thermostat,a restrictor in the radiator inlet and then put tape over the grill if you are running first thing in the morning and remove it fro the afternoon.This is a ver common thing to do in racing.
BTW I think you will find that most engines make peak power at a certian temperature thus running below of above that will lose power,equally by putting a higher pressure cap on the radiator it will run cooler as is the case with most road cars now.,as will the addition of "Redline ,Water Wetter".

[mmciau]

From years of speedway experience (speedcars using methanol), if the thermostat is not used, then a restrictor must be intoduced/developed. If the coolant moves too quickly through the radiator, it will not "cool" properly, get hotter and then finally dump coolant through excessive expansion.

In a related matter, some people "bore out" their engines thereby reducing water jacket thickness. This "thinwall" can drastically effect engine heat transfer characteristics too.

Mike

[tzei]

I understand that water have to flow slowly due to it's basic physical nature: it takes time to absorb the heat and/or let it go (like no other liquid on the earth). so if it flows too fast thru block it doesn't have enough time to take heat away from the block. same goes for radiator but opposite direction.

[KC]

We run a closed loop water system on the drag boat big block Chevy instead of too cold and dirty lake or river water. We do not use a thermostat because we are looking for lots of flow. The radiator doesn't just cool the motor, it's job is to keep the motor at its nominal operating temperature. Too cool reduces efficiency just as too hot.

[Dave Brand]

Has anybody actually tested flow rates with & without a thermostat? I suspect that thermostats don't obstruct the flow as much as people seem to think they do. When a thermostat is fully open, the cross-sectional area (csa) of the gap is pretty big - bigger in most cases than the csa of the top hose - & the thermostat housing is designed to provide a large water passage. In many systems there's probably a smaller restriction somewhere else which will limit water flow more than the thermostat will.

Is it just me, or is there a flaw in the logic which removes the thermostat because it causes a restriction & then places a restrictor in its place to balance the system? Why not use a restrictor which autmatically adjusts the flow rate to maintain the optimum working temperature?

I wouldn't worry too much about a Mk1 GT running hot - the standard cooling system, with the proper GT radiator (5-row, if I remember correctly!) is well up to the job. The biggest problem I had with my road car was getting it to run hot enough, & on the rally car we never had any problems with keeping the water temperature down......with a full sump guard & no oil cooler we saw some pretty impressive oil temperatures! Of course, when I was running Mk1 GTs 'global warming' hadn't been invented!

[Tim Falce]

Originally posted by Dave Brand
Is it just me, or is there a flaw in the logic which removes the thermostat because it causes a restriction & then places a restrictor in its place to balance the system

Who mentioned removing it because it causes retrictions?
Nobody seems to have noticed the bold italics in the word 'MAY' in my post. The reason I would remove a thermostat is because they sometimes go wrong or don't open/close at the temp I want them to, not for any restriction reasons. The area of the gap of the thermostat (when open) in my car is far greater than the smallest area of my rad hoses.

[BugEyed]

I'm not sure that you guys are as far apart as it appears.

Fact: all engines have an optimum running temperature - too cool saps power and too hot runs the risk of detonation.

Most engines run bypass water systems whereby the pump circulates water around the block bypassing the radiator when the water is cold. This avoid the waterpump stalling and no flow at all causing local pockets of vapourisation and extreme heat within the engine (eg around the valve seats). In theory if a thermostat is present then as the water temperature rises it both opens up flow to the radiator and blocks flow from the bypass loop. If you just remove (without replacement) the thermostat then not just will you have no temperature regulation but also you will have less flow going through the radiator as quite a bit will take the easy option of the bypass loop. For this reason, if you remove the thermostat you either need to remove the bypass loop or place a restrictor in it to prevent too much of the flow taking the easy option.

Personally, I prefer to see thermostats left in place as getting the temperature correct by blanking the radiator is very difficult, leaves the car prone to changing conditions, and is unable to cope if the radiator become partly obscured by debris or the effect of slipstreaming the car in front.

HTH

Duncan

[StephenRae]

"In the good old days" thermostats used to fail in the open position modern ones fail closed. The fail open ones are still available at a price. There is a Ford part (a disc with a 5mm hole for the twin-cam, same block as a non crossflow.
All of the previous points are valid but given the chance water will circulate the easiest way, not via No 4 cylinder. I have run FF1600 for years with the cheap thermostat (with a 3mm hole for my peace of mind) and as free flow a water system as possible. I can watch the temp gauge rising and falling as the thermostat opens and closes.

[Dave Brand]

Originally posted by falcemob
Who mentioned removing it because it causes retrictions?

Read the first post in the thread......

"will it restrict water flow once I get hot ?"

[Red Dog]

Zefarelly

I run with out a thermostat. I use a restrictor plate slightly larger than the original thermostat aperture. You need to have a restrictor as without it the water flow can be upset/reduced through the head which is a very bad thing. Detonation leading to piston meltdown and generally a very expensive bang!
You are racing so you want maximum power - so you want your water jacket at a cool 70 to 80 degrees. Road engine thermostats are usually over 90 degrees and modern engines even hotter for maximum fuel economy which is bad for power. I see no reason why you should not have one if you can find one for your optimum temperature.

The bit that seems to be missing from all these posts is the swirl pot. It is vital. Air bubbles in the water must be removed as far as possible as aerated water is not a very efficient coolant. Also the water pump needs to be run a bit slower than standard as you will be running at constant high revs. The swirl pot's job is to remove the bubbles. It is always a good thing to have more cooling efficiency than you need as it is so simple to blank part of the rad to raise the temperature. It some times necessary to add a steam bleed off at one end of the head to make sure that water surround all the combustion chambers. This bleed is led back to the swirl pot for any air to be removed.

[Tim Falce]

zefarelly..............What Red Dog said

[Richy_Rich]

I run a thermostat with the gubbins cut out, the reason (at least on our cars) being that you need the restriction is because without it the mechanical water pump doesn't get enough back pressure and thrashes around causing cavitation (which is bad).

I doubt this applies to the electric pumps some of the modified cars run, but then the pump is thermostat controlled (or at least can be) so overcooling isn't a problem.

Again, I race a triumph spitfire where over-cooling is almost always the least of your worries...

[thebear]

Originally posted by falcemob
Without the thermostat there can be a problem of the water not having any restriction in the engine and flowing round the rad too quickly and not cooling enough. If you remove the thermostat you may need to put a restrictor disc in place of it to slow the water down.

One thing that has been missing in all the discussions is "TIME" as in dwell time. Heat transfer is not instantaneous. One of the properties of a cooling system is it's limited surface area. Should one produce sufficient heat that can not be removed during the coolant's flow the result is overheating. Obviously on a cool day, the temperature across the radiator fins will be suficient to remove a large part of the heat. If one's motor is producing a large(er) quantity of heat that can be distributed, high temperature readings will be observed.

There are two basic types of flow, Laminar and Viscous. Laminar flow is a result of low velocity in the system and results in poor cooling. Laminar flow will have a boundry layer along the walls of the system (pipes) that effectively insulates the periphery from the fluid in the center. Visous flow, on the other hand is brisk and results in a `tumbling' action from the exterior to the interior of the pipe which effectively mixes all the contents of the flow medium.

As relates to dwell time, if the fluid is not present along the passage long enough for the heat transfer to occur, there will be a "hot time in the old town tonight". If one's thermostat removal provides unrestricted flow it is possible for the engine to overheat due to the coolant passing thru the radiator too fast.

[graham bahr]

most of you seemed to of missed the point here, the thermostat does cause a small flow restriction when its open but you need it, with out the thermostat the coolant takes the path of least restriction, so without one the coolant will only circulate round the rad, thermostat housing and water pump, starving the rear of the engine of vital cooled water.

as for modifying the stat i prefer to just drill 6 or so 8th inch holes around its outer circumferance, this allows a little more flow through it and does provide some flow if the stat fails giving you a greater safty margin