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Cooling Modifications

Cooling System for V8

By Andrew Weinberg


There is no doubt that converting an XJ car to Chevy power is a great option to the stock drivetrain. However, unlike the stock configuration, the cooling system for the new engine needs to be more than adequate for the task. That means proper sized radiator, and large fan (in my case, large electric due to the TPI installations).

Until about ten years ago, the only radiator choice for these conversions was the 4-row brass type. Typically, a mid-70's Corvette radiator was used- it had basically the correct overall dimensions, and just needed some small modifications to work in the new application. The lower (coolant pick-up) fitting on the right tank (a 45 degree affair required due to the OE Corvette's angled radiator installation) would be removed and replaced with a straight lower fitting (in the Jag, the new radiator mounts vertically, just as the original Jag radiator did).

Because the OE Jag radiator had no filler cap on the radiator itself (it was on the engine), a remote design was needed on the new radiator to allow filling, etc. The new radiator would be modified by a competent radiator shop to cover over the Corvette filler on the right tank, and then on the car either a remote filler would be added to the middle of the upper radiator hose (ala John's Cars), or a fixed filler "neck" added to the rear of the right tank. The latter was easily accomplished on the new Corvette radiator because the removed lower fitting (from the previous step) could be reused for the filler fitting.

The down side on the brass radiator is that it's heavy, has to be modified to fit the car (and may make getting a replacement a little more difficult, should you ever need one), and that eventually they corrode and leak. Mounting is by sandwiching the radiator and stock Corvette rubber isolators between the stock header plate and the lower radiator support (the isolators are glued to the underside of the header and the top of the support).

This is the radiator I'm running in my '85 XJS (you can see the remote filler with the cap on it).


  The newer style plastic/aluminum radiators that became standard GM equipment in the early-mid 80's are another option for the Jag-V8 conversion. They are light weight, have great cooling capacity (in most cases, better than the 4-row brass types), can be used virtually off-the-shelf with no modifications, are backed (for their original application) with a LIFETIME warranty (wow!), and are about half the cost of the brass type (that's a big savings).

This is the only radiator I use now for my conversions. The model originally designed for 87-90 5.7 L Camaro IROC/Z28/TransAm is a perfect fit for either the XJ6 or XJS. The only modification required is to cut a small 3" x 3" hole in the top of the Jag radiator header plate for access to the filler cap. On the XJS this is no problem; on the XJ6, this mod ends up removing one of the header plate mounting holes (on the right side), but I haven't seen any problem running this way on my own car for the last 3 years.

Take a look at the pictures to see how the "mod" looks. The radiator sits (top and bottom) in standard Camaro rubber isolators that are glued to the top of the lower radiator support, and to the underside of the header plate. The clamping force of the header plate through the isolators holds the radiator in place. Another nice advantage for using this radiator in the Jag is that all of the stock (molded) radiator hoses for the Camaro fit perfectly.

If your engine doesn't have a heater line return fitting (the TPI engines don't- they utilize a return fitting on the right tank), then this radiator is perfect because it has that fitting. For other engines, you can eliminate that goofy heater hose to the water pump. Here are a couple of shots of this radiator type installed in both my daily driver XJ6 and my XJS convert that is under construction. (these shots show the header plate modification on both cars)







  (the lower photo is the XJS before the fan/shroud is installed)

Just FYI- another option, for the heater return hose is to use the radiator hose tee from Stealth conversions. This is simply a special plastic tee spliced into (with hose clamps) the lower radiator hose at a convenient point. The third leg of the tee can accommodate a 5/8" or ¾" heater hose for your return line. Very nice.

Note (winter 2000 Approx).... ed.

For anyone who is in the process of converting their Jag, I recently came across a great deal on these radiators, and bought a few new ones for future projects.

I probably have more than I need, so if you'd like one at a great price, let me know.

Lastly, the Jags always require a "Big Fan", regardless of radiator type. What I have used very successfully so far is the large (nearly 17") electric fan that is standard on 85 and up Corvettes, IROC-Camaros, and Trans Ams. It pulls quite a bit of air, seems to cool the engine perfectly, and comes assembled in a frame that is easy to mount to a flat surface.

The fan is wired both to a thermal switch on the engine, and also such that it turns on whenever the AC compressor is running. I mount it in a (specially made for the swap) fan shroud that is basically a shoebox lid in design, 26" x 19 1/2" x 1 1/2 ". It mounts the fan in the center for even pulling. They're usually made of sheet steel or aluminum, but for the car I'm currently building, I assembled it out of ¼" ABS and glued the pieces together. The fan mounts to the backside of the shroud. It seems pretty sturdy- we'll see how it holds up to the radiator heat.

Here's a photo:


I hope this has been helpful for anyone interested.

If you have any questions, please feel free to E-mail me.




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