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Replacing a radiator in a classic car

Radiators can fail in any car, even one with absurdly low miles — such as my 1974 Plymouth Valiant, which has yet to see 20,000 (but has 41 years behind it). Years ago, a pinhole leak developed on a long 100° trip; it disappeared when the system pressure dropped to normal levels.


Suddenly, five years later, it came back with a vengeance, as a large hole that sprayed coolant onto the engine when it was barely warm. In the 1980s, I would have taken it to any mechanic to have the hole closed; now only specialty shops will do it, it costs more, and they tend to be more conservative about what they will and will not patch.

In short, I had to take the radiator out to take it to a shop, because it was too far to drive as it was. The first step, as you probably guessed, is taking the antifreeze out of the radiator.

First, get a large antifreeze holding pan. Antifreeze is toxic and it’s usually against the law to drain it into the gutter, and it’ll raise your taxes (or poison your well) by making the water harder to clean and more toxic. Letting it soak into the ground is a bad idea for the same reason. I was surprised that the pan held all the antifreeze and was easy to handle, thanks to a spout on one side and a handle on the other.

coolant reserve tank

To get the antifreeze out, you open a valve on the bottom of the radiator — in our car, about a third of the way over on the driver’s side. In the past, I always opened it from below, which is not particularly easy and can be messy.

The easiest and cleanest way to open the valve is to take off the shroud first, assuming you have one (the black plastic thing that covers the blades). The shroud directs more air from the fan onto the radiator; not all cars have them, but most cars with air conditioning or a V8 do. If you don’t have one, get one for more effective cooling.

The shroud is held on by four bolts, at least on my car, and was very easy to remove. Push it back, once the bolts are off — it should not be stuck to the radiator — to see the valve at the bottom. It’s much easier to reach this way than from underneath, which is how I have usually attacked it. Put the pan underneath, being aware that the antifreeze comes out from the end but some dribbles onto the ledge below and comes out through the holes and off the edge — not a terribly good design, especially since the holes were not underneath the valve. If the valve sticks, use penetrating oil, then if needed, a large pliers — very gently. Only the handle turns, not the center part.

Not all cars of the 1970s have antifreeze overflow tanks, but they are a fine idea; when the fluid expands, it goes into the tank, and when it contracts, it goes into the radiator. Every car made after the early 1970s has them. The tanks are usually white plastic, next to the radiator itself. The hose is very small.

Once the valve was open, and antifreeze had been coming out for ten seconds, I opened the radiator cap, then clipped the thin overflow antifreeze hose (only used in relatively recent cars) at the crimped clamp, which couldn’t be reasonably taken off, and gently took off the antifreeze temperature sensor from on top of the radiator (not all cars have this). (I did not open the radiator cap first because antifreeze tends to spill out of the top before the radiator’s been drained down a bit.)

Why does the radiator even have transmission fluid pipes? The transmission fluid cooler is part of the radiator. Better-spec cars, including taxis, police cars, and anything with a towing package, have a separate transmission cooler, in addition to the radiator.

I left the radiator overnight to finish draining, because it just kept dripping, Then I took off the upper and lower radiator hoses, tackling the difficult lower one first. Brian Kapral recommended using large dental picks for this, to help peel back the hose gently from the pipe, a bit at a time, freeing up any stuck bits, before rotating and pulling it off. Too much muscle, and you can break the radiator or water pump. (The clamp has to come off first; screw type clamps are easy, factory clamps with two thick wires sticking out are easy if you have the right tool, and much harder if you have a vice-grips and “walk them” onto the pipe. Don’t “walk” them onto the hose.) I personally used a flat-bladed screwdriver, not having picks, but that’s not really a good idea, and I am getting the picks for next time.

cooling system

Now, it was time to attack the transmission fluid pipes (if you have a manual transmission, pat yourself on the back, this is unnecessary for you). A sensible person will get rubber stoppers to both hold as much fluid in as possible, and prevent anything from contaminating the system while it’s open. You will need to know the size of the pipe to do this.

Be gentle and careful with the transmission fluid pipes. Pete Doll recommended starting with penetrating oil, then using a flare wrench, not an ordinary open-ended wrench, to avoid stripping the bolts. They may be on very tight, and in my case, one came right off with no problem, and the other wanted to take the radiator fitting with it. The problem is movement in the metal pipe on one end can cause an expensive, hard to fix leak on the other. Eventually I called Pete in to help, and in the end he pretty much did it himself — I held one wrench on top to keep the fitting in place and he turned the other on bottom. It was a hard, dirty job with a few false starts. Again, when I did this in 1985, it was pretty easy, but this car has not seen the lines taken apart in 41 years.

transmission fittings

Finally, that was done, and we could lift the radiator out; it, too, was held on by just four bolts. Pete Doll pointed out that you only have to loosen the lower two bolts; the top two come out, but the bottom two stay on. That makes it easier to get the radiator back in.

The only radiator shop in my area came highly recommended: Auto Cool in Hackensack, New Jersey (as Billy Joel sang, Hackensack ack ack ack). I brought the unit in to have it cleaned and pressure tested for $25, or, if he did the work / supplied a replacement, free. He called up later the same day to say that the radiator was unrecoverable; the damage was too great and there were too many other holes, some of which appeared to have been patched in the long distant past (probably none too well). I could have it re-cored for $500, or I could get a new radiator for $400. In both cases, the guts would be made in China; if it was re-cored, the labor would be done in Hackensack.

radiator top

I wanted to see how much a replacement would cost, and found that while it’s not common anywhere else, that Rock Auto had a plastic-tank, brass-bodied radiator for $280, including shipping; if I didn’t have air conditioning, it would have been $50 cheaper. $120 (or $220) isn’t chicken feed, and RockAuto has a fine reputation, so I opted for an APDI/PRO unit, crossing my fingers as I did so. All modern radiators have plastic tanks, so that didn’t worry me, though the connection of the plastic tank to the brass does. When we got it, it seemed to be all brass — the description might be somewhat generic. The fit seemed perfect, in every way except the stamped Mopar logo and part number to be identical to the original. (Which I did pick up from the shop, paying the $25. It was now beautiful in its brass color, shorn of its black paint and grime, and showing not only the original brazing but some repairs done here and there since.)

radiator valve

Now, we had three people at work: Pete Doll, TJ Lang, and me. We moved the transmission line adapters from the old radiator to the new one, which came without them; this was relatively easy, with teflon tape helping seal them up. Then the shroud went back into place, and the radiator went into the car, resting on the bottom two bolts; the top two were fastened. We had snipped off the end of the overflow tube, which was longer than it needed to be, and attached the new one without a clamp, since it’s held in place by friction; using a clamp is probably a good idea, though (it doesn’t have one on the other end). Finally, we attached the hoses.

radiatorThis is a good time to replace the large hoses that go into the water pump and the engine with new, high quality ones. They usually have springs inside, to prevent the hoses from collapsing. First, make sure you got the right ones. Then put the clamps in place on the pipes or the hose (loosely and not where they attach), wiggle them on until they are fully in place, and tighten the clamps over the pipe, leaving some hose over the pipe on both sides.

You may want to use a turkey baster (that you will never use again), siphon, etc. to remove any leftover old antifreeze and gunk from the overflow bottle. Some people also drain the heater core so they can flush out all the antifreeze. If you’ve been maintaining your car, this probably isn’t needed.

Finally, once all this is done, and the radiator tap is closed, and you’ve checked everything twice, refill the transmission fluid from the awkwardly placed pipe, in our car near the bulkhead by the passenger side. This is a good time to have a long funnel. I have used portable funnels sometimes because transmission fluid is nasty stuff.

Now, put about a gallon of distilled water into the system. Start the engine and let it run with the radiator cap off, for a little bit, while you check for leaks; then slowly pour in antifreeze. After that, pour in a 50/50 mix of antifreeze and water, antifreeze first, then distilled water. (I am assuming you bought concentrated antifreeze rather than pre-mixed solution, which costs the same but gives you half as much actual antifreeze. If you bought the mixture, just put it in from the start.)

Starting out with distilled water helps you check for gross leaks. As you empty the jugs of antifreeze and water, pour the old antifreeze into it from the big collecting thing. Hopefully there will be no leaks.

What will happen as the engine runs and warms up is that the level of antifreeze, after you get it near (but not up to) the top, will drop down from time to time, usually with a lot of bubbling. If you will up the radiator to the brim, it will go over the side a few times before it settles down.

radiator replacement

In the picture, you can see Pete Doll with his hand on the upper radiator hose; he put it there from time to time to see if the thermostat had opened. When that happens, suddenly the antifreeze will be allowed to return to the radiator, going through the heater core, and the upper hose will get hot. While you’re waiting for this, check the antifreeze with one of those glass testers that has beads in it, to make sure it’s going to protect your engine well enough against both heat and cold weather.

What kind of transmission fluid to use? I would suggest ATF+4 or Dexron 6 rather than the old Dexron III these cars were designed for. Both claim to be good in Dexron III cars, but are better than the old fluids in cold-weather viscosity, long-term durability, and other traits.

Eventually, the hose you see under Pete’s hand heated up, the antifreeze bubbled a few more times, and it was time to top it off, put the cap on, and drive around for five minutes, coming back to make sure there were no leaks. Fortunately, all was good and tight.

It was a shame to loose a perfectly good radiator; the car had never overheated. But 41 years is not bad for a brass unit, and I was fortunate to have friends who were willing and able to help fill in for my own gaps. It was probably a two person job from the start, but a skilled mechanic could likely have done most of it, aside from removing that one transmission fluid pipe, on their own. Thanks again, Pete and T.J.

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