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'71 521 got hot again...


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On the ride home yesterday my temp started climbing again. It hit about 220 or so before I had a chance to pull it over and let her sit for a bit. I'm at a complete loss now on what to do. Heres the laundry list of things I've done to it just about a month ago.

Replaced thermostat, thermostat housing, upper and lower hoses, radiator cap and water pump. I don't have any water in my oil and or oil in my water so I don't know if its my head or not. Whats next? New radiator? Hahahaha, try and find one. Anybody have anything?

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I flushed everything with the hose when it was all open and it looked good. The only thing that was a little slow was the radiator. Filled it up, let it bubble for a few minutes, top it off, wait, top it off one more time and it was good. Should I take the radiator and have it boiled out? I need this truck as its my daily driver, but can't have it blow up on me either.

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if you're using straight water then thats prob you're prob, water has a lower boiling temp then antifreeze.

When you installed a new thermostat, did it have a weep hole in it, if not then take it off and drill a 1/16" hole in it, this will allow all the air out of the block and keep from getting an air lock in the block when you put 50/50 antifreeze in the radiator.

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Sounds like a plugged up radiator core. By the way, to really be complete when back flushing the engine and radiator you really should locate the engine block drain plug, remove it and flush like crazy. You will most likely find a thick film of crud blocking the entry point to the block so may have to tap it out with a screwdriver before being able the flush the block. Installing a flushing Tee [Prestone makes a good one] in the heater line makes this simpler.

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There is a point when it's hot(warm weather), when a radiator that is pluged up won't cool the engine anymore, that is when you have it cleaned professionaly or have it recored. It's not worth ruining an engine by getting it super hot over and over. One day one might say to ones self, it's only one more mile. wayno

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I'm running 50/50 in it. It got hot again on the way to work with the nice cool morning air so I know I'm in trouble this afternoon. Looks like I will be making a nature stop on the way home for a little bit. Will drain it and pull it this weekend and see what my options are.

Thanks everybody.

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If you can find a good 620 rad take that and your 521 rad to a shop and have them swap the lower outlet so that it will still fit in your truck. Look for one out of a 76 and up 620 and make sure its a 3 core.

It should bolt in with little to no modification. Snag the overflow tank and stuff too if you get one from a yard.


I was quoted 40 bucks to swap the lower outlet here in town with out a good buddy deal or anything so it shouldnt cost too much where youre at... could be cheaper.

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if its the stock radiator it should be copper/brass construction


if your trying to by time i would do this borrow a pressure washer from a friend or rent one and cap off the upper hose outlet and just blast away if possible hook it up to hot water and mix in a degreaser in the area for detergent


or plan b get some cans of brake clean and spray them in there then slosh them around (rad cap in place and inlet/outlet facing up) make sure you give it a day to evaporate completely before you try putting it back together


when you get some cash together you can replace the radiator with one out of a vw rabbit or v6 feiro these are popular 510 swaps i dont see why they wont work in a 521 they may be a tad wide for the headlight recesses though

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