XJ Cooling System Design ... Update/Confirmation

I think it was Ed Stevens who recently postulated that the real problem with the XJ cooling system isn't radiator frontal area so much as proportion -- the tubes are too long, so the downstream end doesn't really do much cooling.

Here's confirmation on that. The author was Greg Freidman, who is (I believe) the founder/"owner" of the Strokers' group on Yahoo:

Well I'm not sure what problem we're trying to solve here. As far as XJs go, I've finally determined conclusively why they have cooling problems. Through a stroke of semi-dumb luck I ran into a guy that's got an aero-thermal engineering and consulting company. He started this after many years of working at AMC/Chrysler/DCX. He was involved in the the XJs cooling system and is friends with the guy that was responsible for the overall XJs cooling system design. The problem is an inefficient radiator design that is the best they could come up with under the circumstances.

The inefficient design is due to the fact that the tubes are so long. The tubes do the bulk of the heat transfer as the coolant travels through the first half of the tubes' length and relatively little in the second half. So while the overall surface area of the radiator is comparable to more typically shaped radiators, a lot of that surface area isn't used efficiently.

The circumstances I refer to are interesting. It turns out that GM would not increase their allotment of 2.8 V6 motors to meet the anticipated demand due to the success of the XJ. It was actually the Mexican stroker motor that was the impetus for creating the 4.0 and putting it in the XJ. But the XJ was never designed for such a long motor and one of the big issues of course was the radiator design and the fact there is so little
vertical space available so far forward. A vertically flowing radiator would have been more efficient, but the upper/lower tanks would have taken up too much valuable vertical space. So the wide but short radiator was determined to be the best bet.

It begs the question why that wasn't resolved in the 1997 model year changeover, but I would presume they determined it wasn't worth the redesign costs and the cooling system was good enough.

So that's the story from one of the horse's mouth.

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So move to ID and we'll design something better. I'm sure an architect and accountant can come up with a better design the some "aero-thermal engineer"

:roll:

Later,
Lincoln

Lincoln said:

So move to ID and we'll design something better. I'm sure an architect and accountant can come up with a better design the some "aero-thermal engineer"

:roll:

Later,
Lincoln

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You probably won't come up with a better design if you stay inside the parameters set by the XJ's overall design. If you allow any of the following, you can probably improve the design:

1. move engine rearward in vehicle (new firewall/footwell design.
2. move radiator FORWARD (new front clip design)
3. make space for rad TALLER (new core support and from frame section redesign
4. make hood taller (new front clip design)
5. make radiator flow vertically, not horizontally (new hose routing, and new core support design.

AZ Jeff said:

You probably won't come up with a better design if you stay inside the parameters set by the XJ's overall design. If you allow any of the following, you can probably improve the design:

1. move engine rearward in vehicle (new firewall/footwell design.
2. move radiator FORWARD (new front clip design)
3. make space for rad TALLER (new core support and from frame section redesign
4. make hood taller (new front clip design)
5. make radiator flow vertically, not horizontally (new hose routing, and new core support design. .

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Amending my statement above, my point is that, given the constraints of not redoing the basic body or platform, the rad design we have now is about as good as it gets

What about a central tank the flows from the center out to 2 side tanks and a Y to a single return?

Rev

Rev Den said:

What about a central tank the flows from the center out to 2 side tanks and a Y to a single return?

Rev

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If you can figure out how to squeeze that into the space available, and include the two return lines to the water pump, that would probably be an improvement, but that's a lot of pipe/hose in a small area.....