The Heating & Cooling Circuit

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Heater Unit
August 16, 2002 -- As part of the assembly process, I needed to find a good radiator and heating unit. The project car, when I purchased it, had been stripped bare and the gent I bought it from kept all of the ancillaries to sell off at his leisure. The project actually came with a blown out radiator sitting in the boot (trunk), but it was not repairable, so into the trash it went.

I wound up finding what I needed on eBay, for terrific prices. First, I found what was being marketed as either a Spitfire or GT6 heater unit, complete with core and fan. I opted to use the seller's "buy it now" feature and may have paid too much at $45, but it looked to be a good restoration prospect. When it arrived, I was mildly dismayed to note a bit of rust on the box near the bottom. Oh-oh. Leaky core? After dismantling, a trip to my local radiator shop brought releif after pressure checking the core. The manager knew immediately what the cause of corrosion had been. "Sombody didn't tighten the hose properly, and water shot back into the housing along the outside of the pipe at some point." This radiator man is good. He had correctly diagnosed the bit of rust he had found before he even checked the core for pressure, declaring the core healthy and ready to go.

The above photo shows the heater unit after I had cleaned, painted and reassembled it. As it turns out, this unit was built for use in a GT6 Mk1. The only difference between it and the Spitfire unit, is that this one has a two-speed fan motor, and the baffling which routes the airflow between the demisters and the floor is a more sophisticated cable operated affair, instead of the manually adjustable flaps on the Spitfire units. I had considered selling this one in order to search for the "correct" Spitfire heater, but opted to keep this upgraded version instead, after determining that it mounts perfectly in place of the Spitfire heater. I'll just need to route the cable controller to an inconspicuous location. I'm thinking under the dash top, above the driver or passenger side parcel tray, or perhaps on the dash via a push-pull knob somewhere, provided I can make it look like it "belongs".

Note: I learned a very important distinction between GT6 heater boxes and early Spitfire heater boxes. While they are identical in size and mount exactly the same way, since ALL GT6's had the tach and speedometer located in front of the driver, versus early Spitfires that mounted these gauges in the center, there are no holes for the tach and speedo cables drilled through the heater box on either side of the fan motor! Naturally, I only discovered this dismaying fact after fitting the heater box. The remedy was easy, however. With the box still in place, I simply marked off the center of where the holes would be, removed the heater box, drilled the holes (which are located a bit higher on the instrument side of the heater box to prevent a sharp bend in the cable from the heater box exit to the gauges) and installed rubber grommets on both sides of the heater box, routing the cables through them before re-installing the box to the bulkhead. Careful not to crimp one of your cables between the box and the bulkhead like I did! I managed to ruin a new speedometer cable, which led to the purchase of a replacement -- which turned out to be a few inches shorter than the first!! Since routing the cable sheath through the grommets was the most difficult part of this project, I opted to simply leave the sheath in place and replace just the inner cable itself. Rather than remove the heater box for the 2nd or 3rd time and wrestling with the grommets again, I was simply going to lube the new cable with graphite and slip it through the sheath. Upon discovering the difference in cable length, I opted to cut down the length of the sheath rather than purchase yet another cable... This was possible with a pair of tin snips, a crimping tool and patience. I'd pull the cable out on the gauge side so as not to accidentally cut it, clip off a bit of the sheath on the transmission side, and then refit the inner cable. When I finally had just enough cable emerging from the sheath, I refit the end cap, crimped it down and that was that.

The Radiator
Now this has been a satisfying and fun adventure for me... I've seen a lot of radiators offered for sale on eBay and I was hoping to find a good, used radiator that if need be, could be recored, rather than option for an expensive, new reproduction. For no particular reason, I was leaning towards an original Mk3 radiator despite it's smaller size, for two reasons. First, one must remember that the original, wider radiator was replaced with a narrower version in the Mk3, reportedly to correct "over cooling" problems in earlier model Spitfires. I find that one a bit hard to swallow, but the fact is that my last Spitfire Mk3 radiator did a very good job of cooling on all but the hottest days while sitting in traffic. Even then, it never went past more than 3/4 on the gauge. The following shows the radiator I wound up with. The thing that drew me to this radiator, aside from the fact that it was being sold by a reputable eBay dealer with whom I've done business before, were the relative straightness of the fins, indicating a recent recore. The clincher was the assertion by the seller in writing that the radiator was pressure tested for 3 hours and didn't lose a pound of pressure. Hey, for $9.95 plus shipping, I was willing to take a chance!

After removing the mounting panels and sending them off with a bunch of other engine compartment brackets for sandblasting and powder coating, I ran water from the hose through the core and was pleased to see a fast rush of clean water coming out. My hunch was confirmed and the seller's assurances verified. This is actually a "newer" radiator. I spent about 20 minutes straightening any bent fins with a single edged razor blade. After painting, the radiator looked like this:

What appears to be scratches down the left side of the radiator are not. It's just the sunlight reflecting off two of the capillaries.

After purchasing an early, metal fan blade for a Mk1 or Mk2 Spitfire, and spending another hour or two sanding it down and painting it with silver Hammerite, then installing it on the engine, I awoke the next morning and remembered a very interesting message thread on the TTN regarding electric fan conversions. After revisiting this thread, I realized that it made little sense to install the stock, heavy fan blade, when more efficient, quieter, power-enhancing electric cooling was available.

After deciding on the type of fan I wanted, I set out to find the best price. As fate would have it, the gent who sold me my engine had a nearly new electric fan and mounting kit that he offered me for $40. The PermaCool fan is actually better than the one that I had researched, drawing in considerably more CFM than the one I had planned to purchase. It can be set up either as a pusher (for use in addition with the mechanical blade) or a puller, which is how I opted to set it up. The 10" PermaCool actually measures out at 9.5" in height, which perfectly fits the space on the radiator. From the aforementioned message thread, the prevailing wisdom states that some sort of a shroud is essential for maximum cooling efficiency. I opted to fashion my own shroud using aluminum sheet metal, simply mounting it to the outside flanges of the radiator with two sheetmetal screws on each side. I created a template using cardboard, to trace around the fan perimeter.

I chose sheet aluminum over galvanized sheetmetal for two reasons. Primarily cosmetic, but aluminum is certainly superior for heat dissipation as well. After mounting, I polished the metal with a small buffing wheel attached to my die grinder.

Buffing out the panels didn't take long at all, and yielded a very nice shine.

Once I was satisfied with the finish, I mounted the spacers...

...and installed onto the radiator cradle.


This project is compete! Well, except for the adjustable thermostat wiring... Note in the photo immediately above how nicely the grommet on the wiring harness for the fan fits into an existing hole in the radiator mounting panel.

8/19/02 -- One step forward, two very big steps back. Only when I had trouble fitting my radiator hoses this afternoon, did I realize that I mounted the radiator in the wrong position, bolting it to the front of the radiator cradle instead of the rear. No wonder the hoses seemed too short! I need to close the gap by placing the radiator where it belongs, only guess what? My electric fan won't clear the water pump! In order to do that, I'll need to offset the shroud slightly meaning -- you guessed it -- I have to create a new shroud. Arghhhh!!! I picked up a piece of zinc coated sheetmetal this evening while shopping for new clothes washer flexible hoses to replace the one that burst and flooded the house today. Yeesh!

2/7/03 -- I should have updated this page a long time ago and regret not doing so. I tried to create a new shroud that would offset the fan to clear the water pump housing, but no luck. The only way to make this a "puller" setup is to install a full-width radiator and offset the fan to the far left side, but I'd rather make the installation a "pusher" setup than bother with that. For now, I've removed the electric fan entirely and have just decided to stay with the mechanical fan for the time being. However, I do plan on fitting the electric fan at a later date to reclaim those marginal horsepower gains and to improve cooling at idle during the hot summer months. I've poured in a 90/10 mixture of distilled water and Xerex racing coolant for now.

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Please. Always wear your seatbelt while driving -- and that goes double for your children if you have any.