Running hot and cold!

[Guest]

Thoughts please.

60 degrees or 115 degrees. Which is more harmful to your engine as a regular temperature to run at? (Agreed neither is optimal!!!)

Is removal of the thermostat a good idea in either case or a never do that option?

Malcolm

 

[Mike Dozier]

Malcolm

I use to run my Mustang without s stat for fear it would stick in the closed position
(happened once before). Now that they sell
thermostats that fail to the open position,
I don't see any reason not to run a stat.

The best temperature rating to use an open
question. Some swear by 160 degrees...some
say that's too cold and 180 is optimal.
I don't see any reason to run hotter than
180 degree stat.

MikeDD

 

[Guest]

Malcolm, if you only have the two to chose from go with the 115 for sure. You really are better off with a thermostat in place. The bearing and other clearances were speced on the temperature of an engine being at a certain point which means the metal has expanded and put the clearances at an optimum distance. This gap is also where the film of oil that metal parts actually ride on resides. Again, if the gap is not proper the oil will not do it job properly unless you put enough flow behind it to maintain the proper pressure.

An engine also runs better as it gets hotter. Air cooled engines could be the most efficient except that they can't get the temperature even enough across the bore and head or from one cylinder to another to run them at optimal temp. That is why water cooled has become predominant: you can run the engine at a higher temperature and keep it at a more even temperature so that you don't run as much a chance of overheating certain areas like the head around the exhaust port.

Lastly, there is the age old argument about the speed of the water going through the block without the stat. Some say that this is bunk and the only factor in heat transfer is the delta in temperature between the to materials (metal and water here). I don't agree with this. I say there are two other factors: contact area and time. Not too many people would argue with contact area and that is why there is water wetter that supposedly creates more contact on a molecular level. Time is another matter, but I would argue that it takes a finite amount of time for the heat to migrate a certain distance or from one material to another. The rate will depend on the nature of the materials: their conductance, entropy and specific heat. Hence if the water circulates too fast as it might without a stat, it will not spend enough time in contact with the metal to pickup an adequate amount of heat to properly cool the engine. Some say that if you don't run a thermostat, then at least put a restrictor in there to get the engine running at a proper temperature. I agree with Mike though, with our cars, I wouldn't run under 180. If you wait beyond that to open the valve you may be to far behind the curve for your radiator to catch up; especially if you get caught in a stop and go situation. With a thermostat on the radiator or lines just before it you can mitigate the affect of a cooler thermostat. Let the thing open at 160, but let the fans wait until closer to 175. I followed Bill Bayard's lead and used an adjustable thermostat to control the fans. I put the sensor on the aluminum section of pipe immediately before the radiator. So far so good, but as I drive in more and different road conditions, I can tweak it until it will work in all conditions.

[ August 29, 2002: Message edited by: Lynn Larsen ]

 

[Jim Glickenhaus]

For some reason I could never get my MK-IV or my Lola to cool with a thermostat. I kept getting air blockage. I use restrictor plates and they now work fine. My Lola has an extra water radiator in the rear which really helps. It can idle in traffic on a 100 degree day with the AC on and not overheat. The MK-IV can't do that but it can take a bit of in town on route to the highway. In the winter I block the radiator with cardboard. I doubt that the P4 will run as cool and will have to keep stop and go to a minimum.

 

[Steve Toner]

I believe the issue of running with a restrictor has more to do with cavitation than the speed of the water.

Methinks the water will actually move faster with the restriction in place

Let's try an experiment: We'll give Mr. Bernoulli here a garden hose and turn it on, supplying approximately constant pressure. See the water flow. Flow water flow, past the shady tree. Flow water flow, flow to the sea...

Now we'll have Mr. Bernoulli put a restrictor on the hose. His thumb will do just fine. What happens? The water coming out of the hose speeds up, and even though it quickly gets past the restriction, it doesn't just slow down immediately.

The restrictor would cause the water slow down if it reduced the flow rate. Does it? I dunno.

 

The heat transfer (and therefore cooling) is dependent on the temperature differential between the metal and the water (the 'delta' as you call it) and the thermal contact. I don't see the time the water is in contact with the metal as an issue because there is always another molecule along in another microsecond. Furthermore there are imponderables like the effect of flow at the boundary of the water and metal, namely that it will be disturbed and some water will in any case move more slowly at the boundary. The more water flowing through the more heat can be removed from the engine since fresh water is cooler. To take your reasoning to its logical conclusion the water should be static?

With regard to Steve's argument, the increase in water speed on a hose outlet is because the thumb reduces the opening and owing to conservation of the flow the water has to speed up at this point. However if you observe a river, it accelerates at a narrow point (rapids) but round the bend slows again to a meandering pace as the river widens. The reason a hose spray appears to continue fast is that there is relatively no resistance in the air compared to within the hose. Try treading on the hose halfway along, the effect is a slower flow. Basically the stat will cause a restriction which within the closed cooling system will slow the overall rate of flow and cooling - not generally good but I think a necessary evil.

We really have two cases. Firstly in normal driving conditions where the cooling is much greater than the heat produced. Here you must have a device to stop overecooling i.e. a thermostat, I think mine is 76 degrees (not sure) (which is 168 in fahrenheit - I do remember in the UK 'BC', Before Centigrade, but am now used to it!), else the engine will be too cool and not efficient, it was not designed to run at low temperatures.

Secondly when the cooling less adequate e.g. in traffic jams (in track conditions the engine produces a lot of heat but hopefully you are going quickly enough to cool the radiator!) Ideally you could whip out the stat at this time - hardly possible! So you need to maintain the airflow through the radiator with fans. Basically you need a thermostat but also need to get your cooling system up to spec.

I've fitted a more powerful pair of Spal fans (same fittings as GTD and hardly any thicker) which give 50% higher air propulsion. Plus I fitted a extra temparature sensor on the exit side of the radiator. In normal conditions the sensor on the input side switches the fans on in series (i.e. a nominal 6V per fan) which gives a nice breeze (say 75% of originally designed GTD flow) but when the radiator is losing efficiency (stuck in a queue/line up) the second sensor switches the fans to parallel mode (normal 12V each) and I get 150% cooling. I also have override on the dash for both modes. I think both sensors are 85 deg but I need to check. So far no problems with overheating - but after this diatribe I expect to breakdown on the way to the AGM!!!

 

As an addendum, the better fans use about double the current (13A each) so you have to watch your alternator supply (however the highest output needed will be on a rainy night when I expect cooling is not a problem.

Also the effect of pressure of the system has not been mentioned. You need a pressurised radiator cap as water boils at a higher temperature under pressure (PV/T is a constant - Boyle's law?) Which means you can delay dreaded boil up longer!

 

[Guest]

Well I am glad to say that I started this topic without having a problem to resolve, but wanted to see if my thoughts on water systems were in the right area. I am not an engine man but have been given advice over the years and it seems to tie in with most of the thoughts above. Even those fancy words Lynn used!!!!!

I have been of the opinion that it is better to run hot rather than cold given a poor choice between the two. Also I would no longer choose to run without a thermostat. I beleive most engine wear comes when it is getting up to temp. Therefore if you delay getting up to temp by no thermostat then you get more engine wear. The restrictor plate would only marginally change this position. I always thought the restrictor plate was there to slow the water down but also by making the small hole high up in the plate you raised the water level in the manifold to reduce the amount of air in the manifold. By choice I will always have a thermostat. If you are runnning on a cold day at a good constant speed firstly you are not in the south east of England where there is way too much traffic, but secondly you will be at the cold end of the scale if you don't have the thermostat to let the engine control its own temperature. Blocking off the rad is a poor solution, albeit one that may work. It is hit and miss to know just how much to block off and tomorrow may require a different solution to today.

It is good to hear that nowadays you get thermostats that fail to the open position.

I once had an over heating problem on a very hot day in my Citroen every day car. Wound down the windows and opened the sun roof and put the heater on full blast. The engine temp dropped immediately as there was in effect an extra rad now in the system. Got that trick from the film The Gumball Rally. An epic if ever there was one!

I don't beleive in water wetter although I am sure the chemistry theory is correct. It is a bit like fuel catalysts. Don't bother with them either any more!

Rad weld (leak blocker) made no difference to my engine except it did block up the leaks until I put a rock through the rad at Wiscombe. Ran on that for 5 years. Some would never use that stuff. I hope not to have to need to again.

The problem with the 40's is that it is potentially a big overheating problem with rear engine and front rad. Just glad mine is okay for the time being.

Malcolm

 

[Steve Toner]

Thanks, DC, for that clarification. It did occur to me this morning as I was taking a shower that my shower head contains a restrictor that limits the water flow to 3.5 gallons/min or whatever, so the thermostat is probably doing the same thing...

Oh yeah, and a faucet is a variable restriction that controls the flow rate of the water coming out of the tap. Duh. My brain appears to have taken a bit of a holiday last night.

[ August 30, 2002: Message edited by: Steve Toner ]

 

[Guest]

Ok, I think with everyone's help we have the total picture. First the equation for heat transfer: Q=kA(T2-T1)t/d, where:
Q = the total heat transfered
k = the coefficient of thremat conductivity (this is a simplification because iron/alum and coolant have different k's)
A = the surface area
T2-T1/d = the temperature gradient
t = time

Time is in the equation, but since we have a closed system that always has coolant in it, hopefully, this is open ended and doesn't have an affect as I claimed earlier. It will come into play when the engine is producing more heat faster than the radiator can effectively dump to the air: how long until the coolant can no longer be kept liquid.

What bothered me was the fact that, very often, an engine will run hot without some restriction in the system. I think Steve got it right. The excess speed with water flowing over the irregular surfaces of the water jacket cause cavitation (seperation between the coolant and the metal surface) which reduces A and, therefore, the total heat transfered. When it comes to the waterpump, overdriving it can help until you reach the point where the impellers start cavitating which will decrease the flow.

DC is indeed correct in his comment on the increase in velocity of the water through the restrictor that Steve mentioned: this is only a localized affect.

Water alone has much better thermal characteristics (k) than anti-freeze, but steam has a very poor k. So the pressure cap mentioned by DC and the additives combine to maintain the coolant in a liquid state. Note: even a extremely thin layer of steam that exists only at the surface layer of the metal can significantly reduce thermal transfer. It will also inhance cavitation.

The affect of increased coolant flow through the block and air through the radiator is that the temperture gradient is kept as high as possible increasing the quantity of heat transfered.

Everyone agrees on the fact that engines need to be run at design temperatures and that they should reach those temperatures fairly quickly. So, it sounds like your practices have been validated Malcolm ;-)

I have used the windows down, heater on full blast on several occasions. The last time when my Stealth started overheating one eventing. I discovered that my fans were not coming on. So I drove to work sweating and picked up new sensors that go in the base of the radiator (down flow) on my way home and changed them. Next morning, guess what, I drove to work sweating again. Then it dawned on me, the reason the fans weren't coming on was because the thermostat wasn't opening to allow the hot coolant into the radiator to turn them on. My thermo didn't fail to the open! Anyone need a set of sensors for a Stealth or 3000GT? (One sensor turns on the main fan and the second turns on an auxiliary fan when the temp is just a bit higher or the A/C is on.)

PS: I have a 180A alternator so when my fans are on, they are on. They come on when the variable thermostat turns them on, the A/C trianary switch turns them on, the backup temperture switch in the block turns them on or I flip a switch on the dash. I do have an indicator lamp below the temp gauge to tell me when they are on.

[ August 30, 2002: Message edited by: Lynn Larsen ]

 

[Ian K]

Malc,

Was that 60 degrees C and 115 degrees C ?
If so, then 60 deg C = 140 deg F and
115 deg C = 239 deg F! Oi, I'd go with
the 60 deg C in that case.

Ian

 

[Guest]

Hi Ian

Consider that 90% of engine wear occurs in the first 10 minuts of engine running as it gets up to temperature. I would suggest that your engine life will be shorter than a 115 degree engine.

But as stated above neither of these temps are wanted, but the answers are useful to have.

Perhaps we could turn to tricks to ensure your engine doesn't overheat.

In a recent discussion I had, I brought up sparkplug ratings and wonder whether you can effect a noticeable engine temperature change by hardening or softening the plugs.

How can you check for cavitation and just how extra effective is an ali rad? (My ali rad is to be delivered soon).

Electric pumps, water wetter, pure anti freeze, filtered water (!), loads of bleeding points, correct inlet manifold gaskest to get alignment of water tracts, etc etc.

Malcolm

 

[ChrisL]

By removing the thermostat, my experience has been to cause the temperature to fluctuate wildly, finally settling at something higher.

My guess is that we can't strictly assume that we have a "closed" system and predictable temperature gradients in all cases.

For example, the questions that need to be asked, (especially in the case of front engined cars) are...

1) Does the speed of the coolant traveling through the RADIATOR effect the "character" of the energy exchange?

2) What effect does the temperature of the air that flows OUT OF the radiator have on the engine which it surrounds.

My thoughts were... if the coolant enters the radiator at a given temperature, and travels slowly through the radiator, it would exit the radiator at a cooler temperature than it otherwise would if it were to travel quickly. So, initially, although the energy transfer may be similar at both speeds (as per the formula), because you are removing energy from different amounts of coolant per sec, the air temperatures would need to be higher in the fast flow situation.

I suspected that in my case, the air temperatures WERE in fact initially higher, which in turn also caused some sort of a thermal feedback as a result of the resultant higher engine bay temperatures.

Of coarse, all this is theory which depends greatly upon the amount of heat that the engine produces, the energy transfer proporties of the radiator compared to the engine, and the air-flow in the engine bay... not simple to calculate with formulae designed for an ideal controlled situations.

Although it is probably safe to say that, even though your overall energy exchange remains constant with or without a thermostat, it might actually happen at differing temparatures. Change one factor in the OVERALL equation, and your whole system might find a different balance. Is not the primary purpose of the thermostat to introduce some control over this balance?

I have no figures to support my theory... the number crunching would be well beyond my abilities... but it would explain my experience.

Having said all that, thermal feedback does not apply to our GT40s with the radiator in the front and engine in the back.

[ August 31, 2002: Message edited by: Chris L ]

 

Hey guy,

I have an option for you. On my 68 firebird I used an electric waster pump, electric fans and no thermostat. Every thing was on a timer so when the pump was on the fans are off and when the fans are on the pump is off every thing changed at 160 and that was adjustable. It also has a manual over ride that keeps every thing on until you shut it off.

 

Hi all

I agree with Chris L that the volume and speed of flow of water through the radiator is the deciding factor here. If you remove the thermostat then the water speed increases
due to the reduction in resistance to flow. Hence the water spends less time in the
radiator thus reducing the time for heat transfer to occur in the radiator giving rise to over heating and also promoting cavitation.

I also believe that the transducer for the electric fan thermostat should be located in the top hose as close to the engine thermostat outlet as possible in a mid engined cars, this then controls the fans in response to engine temperature and not radiator temperature.

Malcolm you may find that the alloy radiator is so efficient that you may need to
increase the operating temperature of the thermostat by 10 degrees to maintain engine
operating optimum temperatures.

Regards

Chris

 

[Frank Catt]

Why not also consider the source of the heat that you wish transfer. There are two ways which an engine creates heat, one is by the combustion of fuel, the other is by friction. Both can influenced by the engine builder, and are particularly important in such a car as a 40. We all know that a low compression engine running low octane fuel will run cooler than a high compression race engine on fancy fuels, but are most people also aware just how much influence build tolerances and lubrication can also affect internal temparatures. We test all of our engines on a dyno, where sensors check temparatures throughout the assembly,and we have learnt a lot about critical tolerances etc. some of which would quite surprise many people, and are substantialy different to the text book. Lubrication is also not just about choosing which oil to use, and again we have gained a insight into modifications that make a difference. I am constantly surprised to see many cars withour oil coolers, and yet it is demonstrated on the dyno just how essential this is to overall temperatures and oil viscosity. We still have some problems with individual installations, each car is different, but once you know the engine is right, the rest follows easily. I would be interested to follow your lines of thought on this. Frank

 

[Robert Logan]

Malcolm, et all,

The equasions etc are great (I am a graduate Engineer) but you realy have to make the systems WORK !!!!!!!

Here in the land of plenty, Australia, we are very lucky that the most popular racing is our 5 ltr. V8 cars. These beasts are producing almost 650 HP and are restricted to 7500 RPM and can race for 1000 km. with only stops for petrol, tyres and exhausted drivers.

The advantage that I have is that in my opinion one of the series best engineers is the guy who designed my car for me. This over-heating is one of the few things that scream out "kit car" to the deserning public as they laugh at our cars that have had to take a cooling down break because we have been unlucky enough to be cought by two consecitive RED LIGHTS.

The cooling system is closed system designed to disapeat the heat generated by an engine. This heat is dependant on the displacement of the engine and the stage of tune of the engine along with many other things. The system must be designed for the engine it is to be employed to cool. All to often we use a cooling system designed and tested for a 200 HP engine without an A/C condensor fitted to be run in Northern Europe. The system just will not cope with the added strain of the extra ponies, the A/C and the emigration to warmer climes !!!!!

Our system follows the V8 touring cars system that I alluded to earlier. We use very high quality aluminium cores which we import. The cross-section of the cooling passages and fins are a particular shape that has been proven in touring cars. The capacity, fitment and the size of the overflow bottle, the various automatic bleed lines that are fitted and the overall size of all the pipe work together with the size of the water pump pulley have all been calculated (with over 12 years of practical top class racing experience) to produce a cooling system that WORKS.

This thermostat problem is inmy opinion a red herring to the real problem of having a cooling system that is not correctly designed for the conditions.

This experience is available to all. There are many numerous race car engineers that will consult to the manufacturers if they would only ask.

There is an old saying that goes something like this "there is never enough time to do it right the first time but there is always the time to repair it".

Do it once and do it right and expect your manufacturer to have done this for you.

Remember that all the equasions in the world will only work out the cubic capicity of the jar of pickles, you have to open it to eat and live !!!!!!!!!

Best wishes to all,

Long live the FORUM,

Robert

 

[andys]

Robert has hit the nail on the head. The cooling system is just that, a system. It must be designed and configured as a system for it to properly function. It takes a well executed design along with lots of testing to optimize it (as Robert has evidently done). Singling-out one component will not usually cure inherent design deficiencies or problems. The radiator manufacturers will tell you that air flow across the core is fundamental. Leave the thermostat in place. If you're racing, get out the duct tape!

F CATT mentions the motor is setup. Additional to that, a slightly lean fuel mixture (a potentially complex issue when considering the various circuits in a carburetor) will cause the motor to run hot, causing one to chase demons in the cooling system that really aren't there. FWIW

Andy

 

[Robert Logan]

I have just proof read my last post and there are LOTS of errors, SORRY !~!!!!!!

Unfortunately I am dislexic and english in any of its variants was never my strong point.

As a little side :

What does DNA stand for ?

National Deslixia Association.

Best wishes,

Robert