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alum vs brass/copper rad - update

fuzzydog

NAXJA Forum User
Location
BC Canada
I kneel before the wisdom of the engineers....

in another thread i was critical of the alum/plastic rad that was delivered to me when i was told i would get all metal. I mostly object to the plastic as I don't think it has any place in a cooling system....but anyway...
after a frustrating episode with a brand spanking new rad cap that did not seal, i just tried another rad cap and it seals fine and was able to go for a drive....I must say - wow! that alum really does dissipate heat better than copper. I know that I should expect better cooling since its a new rad, but the rate at which that rad cools off is incredible. After a drive and getting up to 100 C +, then shutting down and waiting a few minutes, the rad really cools off quickly.
BTW, I def needed a new rad - after putting in the new one I slogged up the highway doing about 80-90kms/hr up a fairly steep and long hill (5 kms or so) and was able to keep the temp below 100 C with the taurus fan on low. this is with new 33" MTs, 4.10 gears and AW4 in 3rd gear, and outside temps about 24 C. before the rad swap it would have been just below the red part way up that hill.
One thing I did discover is the importance of circulating that coolant - at the top of the hill I slowed to turn around and temp quickly shot up about 5 degrees (C) or so - idle just doesn't move enough coolant to cool properly when it is hot. I think there is a circuit that bumps up the idle when the ac is turned on - since I am getting rid of the ac (pump noisy) I think I will try to tap into that circuit to bump the idle when the fan kicks on.
around town - doesn't even need the fan at all (remember I don't have a mechanical fan anymore). I could drive around town and when I stopped temp would creep up to just over 100 but the rad is so efficient at cooling that when sitting at idle the coolant in the rad really loses a lot of heat. then when you get going again that cooler coolant circulates in the engine and the temp gauge visibly drops and as long as you keep moving it stays around 100.
so - the alum rads definitely do dissipate heat quicker, but you have to put up with sketchy (IMHO) plastic end tanks. Or I guess you could pop for an all-alum rad but that's prob serious $$$ if even anyone makes them for an XJ.
having said that,at the first sign of a prob with my alum rad, i am putting in the new copper brass 2 row that I just bought.
 
I am glad it is all working out for you. Let us know if you do start having problems with the plastic end tanks. My 01 XJ has plastic endf tanks and it has not had a problem yet.
 
the shortcoming of the plastic tanks is pressure. If your system does overheat, it will generate tremendous pressure, such pressure will push the plastic tanks away from the core as it's only attached by simple little crimped tabs all the way around the tank. i had one do that numerous times, you CAN remove the rad and pound the tabs back down effectively sealing the tank back to the core, but that will only get you so far before you see metal fatigue on those tabs. i agree that the plastic tanks have no business on a heat prone, high pressure cooling system like the xj
 
Ha ha, I have all the same impressions when I got rid of the crappy plastic tanked ones for a all copper and brass one. Just think just how much more you would have been impressed had you swapped in a new copper and brass one instead. Old radiators transfer heat badly no matter what they made from. Your impressions would have been more relevant had you swapped from one new one to another new one of a different material construction and then compared the heat difference from one side of the radiator to the other with the same atmospheric conditions..
 
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