The Restoration of PRRROWL
TIGER # B382000221
An Article by John Crawley
February, 2001
Page 9
Cooling
Questions and Answers
If you ask enough knowledgeable people enough questions you will get all the correct answers. The only difficulty is figuring out which ones they were!
Since cooling is always a problem I have spent some time asking questions of all who could give advice on the Tiger's eternal problem of over heating. Be sure to check the work done by others on researching TIGER cooling, there is a lot of it on the TIGER web sites.
Here are some of the questions that I have asked and some of the answers I have received.
To Dennis C. - D.C. has had more sports cars with overheating problems than any one I have ever met. He has become our Club expert on over heating
Q. Dennis what is the "Magic Bullet" that I can bolt on and cure all my over heating problems?
A. There is no such thing. The war on over heating is won little by little, one degree at time.
To the College Automotive Department Head:
Q. Why do our engines over heat after rebuilding with an overbore of 30 thou?
A. The closer the kettle is to the fire, the sooner the water will boil. If you overbore you need to cool more.
New engines are tight. Tight is hot. Break 'em in at night.
To the Physics department:
Q. What fan blade works the best?
A. Try an asymmetrical fan. Symmetrical fan blades set up a vortex (whirlpool of air) that is relatively stable. They move lots of air but they tend to draw the air from only one spot just like the whirlpool of water when you drain your bathtub. An asymmetrical fan tends to set up an unstable vortex that moves around, drawing air from all over the rad. The whirlpool of air from the symmetrical fan will be noisier too, just like a cyclone. The unstable vortex from an asymmetrical fan will not howl as the whirl pool is continually being changed.
TIP: Try a 140 series Volvo 5 blade, it bolts up to the Tiger engine and requires no trimming. I have one on my car and it works great. I got it for $3.00 at "Pick-Your-Part" Dennis has one on his Healey and it is better than the after market "Made for Healey" 6 blade. Get the Volvo aluminum spacer. You will have to have it turned down in thickness but it fits and insures that the fan is centered.
To me:
Q. What do you consider the single greatest cause of over heating?
A. Rads that are plugged. Excess silicon, (widely used in engine rebuilding) tends to flake off in specs and block of the veins in the rad. If a rad has 20 veins and you lose only 4 you loose 20% of your cooling. If it works proportionally 190° + 20% = 228°. I dissected the old rad from a wrecked Tiger and 1/2 of the veins were plugged with silicon from past engine rebuilds.
TIP: Pull the rad and have it boiled. Flushing does nothing.
To an old time Rad man: who "fixes and doesn't just replace "
Q. What else can cause over heating?
A. Stoppage of air flow. Bent fins in the rad. If only one or two small areas are blocked from airflow the result can be one or two degrees of over heating. (Remember how we win this war - one degree at a time). Get a small thin screwdriver and straighten every fin. Don't forget the backside. Even a brand new core can have some damaged fins. Rad men now a days don't like to take the time to do this but it helps.
Also . . . An old rad can have much of the air flow stopped by bits of sand stuck in the fins. This can be removed but plan to spend the weekend with a fine wire hook and use care. Boiling will not get rid of this sand, so if it's bad it may be time for a new core. And remember airflow – airflow - airflow.
TIP: Bugs on the rad stop air. Use a rad screen — clean it often.
To a College Air Conditioning Technology Professor:
Q. What about airflow and how does it relates to cooling.
A. Now you are asking the right questions. Airflow is everything. Air removes heat. Moving air removes more heat. (Ask us Canadians. Minus 40° can be a pleasant day if there is no wind but at minus 20 with a 10 M.P.H. wind, flesh will freeze in 3 minutes.)
Q. So how does a fan move air in the cooling system of a car?
A. Very poorly. The designs are a bit hit and miss - mostly miss. We would never get away with designs like that in the Air Conditioning trade. Especially older cars have poor designs. Look at some of the new cars were they want to save weight by cutting back on the rad size. The engineers compensate for this by proper shrouding. Of course this is much easier and cheaper now that they use plastic rather than metal to build shrouds.
Try This: Hold your hand up to your mouth and blow through your fist. You can feel the air with your other hand even 6 to 8 inches away. Now suck. You can not feel the air move until you almost seal your fist up tight with your other hand. A car's cooling system is the same. The fan sucks, or draws, the air through the rad. If you look at your Tiger's rad shroud you will see that it is open at the bottom. No seal to help the fan suck the air through the rad. Air does not like to go through things — It would rather go around and hence the "reverse" air flow into the engine compartment. The air is being pulled from under the rad and up through the fan. Shrouding the bottom of the engine compartment will work, to a degree, but it would be much more efficient to build a proper rad shroud, allowing the air to be drawn through the rad and then exit, out the bottom, as it should.
An electric fan works because it blows through the rad but to really work it should be shrouded to about one or two feet in front of the rad. Not practical.
Q. What is the proper shroud then for a drawing fan?
A. A proper shroud is one that is sealed up all around the rad. A rubber gasket, between the shroud and the rad, would even help. No leaks. The shroud should surround the fan completely. The fan should be housed with only 2/3 of the blades inside of the shroud. The air must be free to fly away from the tips of the fan blade. This will give you airflow at idle or at any speed.
To an Ex Rootes Automotive Engineer:
Q. Why were automotive cooling systems so poorly designed?
A. Money. Profit in automotive engineering is gained penny at a time, just as you say cooling is achieved one degree at a time. We used to design a rad that would cool an engine anywhere. Then, when the prototypes were being tested, we cut the rad back until it just worked then added a bit. Every inch of rad core or shroud material saved was more profit. Automotive design is one of cost cutting, not one of engineering design excellence. If we had managed to cut the cost of the Tiger cooling system by $10 that would have made a profit of $70,000 more during it's production run. The same $10 cut from the Mustang may have been worth perhaps $20,000,000 to Ford during the car's production life.
Remember the warrantee for most cars back then was 12 months or 12,000 miles. We never designed them to last for 200 to 300,000 miles and 25 years. Modern cars are different. Longer warrantees necessitate better engineering and plastics now allow you to design a good shroud at no more cost or weight than a poor one. It was different when metal and hand labor was used for every shroud built.
We did smoke tests on airflow and when a car is sitting at idle the air is pulled through the rad by the fan. It then hits the pavement under the car and much of it is drawn forward, back up throughout the rad again thus trying to cool with pre-heated air. Shrouds in front of the rad, at the bottom, did stop this on some cars but I am not sure it it would work on the Tiger. I can't remember specifically working on them.
The Magic Bullet
My friend Dennis, had proper shrouds built for all of his "Hot" cars. If there is a "Magic bullet" the shroud seems to be it. Even his MGA, with it's super tuned, 2 liter, done to the nuts, MGB engine, runs cool now when all else had proven to not be a cure.
Additional Overflow tank
The addition of a larger overflow tank is advised in Cat’s "Shop Notes". I gave great credence to this when I built my TIGER. Coolant that spills on the ground is not around to do its job another day! We forget that when these cars were new the Pump Jockey would check the rad and top it up at every gas refill.
Some overflow tanks will hold a full four quarts and still fit behind the headlight of a TIGER. A pipe from the TIGER’s overflow tank exit pipe to the additional overflow tank along with a two-stage pressure cap is all that is required.
If you install an overflow tank behind the headlight drill a hole in the side of the pipe cast into the side of the new tank. Coolant can be siphoned out in the slipstream as the car moves at speed. Drilling the hole will break this siphon effect.
TIP: Before you worry about over heating check the Temp gauge. It may be out.
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