Coolant Leak/Radiator Drain Petcock Spinning

After getting an oil change, the place I went to mentioned I need some coolant service. I searched around to get another price and opinion. The mechanic I went to told me that I have a coolant leak and that I would need a new radiator. Thing is, everything else is fine, the hoses and the radiator itself are all in good condition. The problem is that theres a small leak coming out of the radiator drain petcock and when the mechanic went to take it out, it was stuck and kind of just kept spinning around without loosening or tightening.

Is it possible to just replace the petcock or is a entire radiator replacement necessary?

With the labor charge to remove the radiator and repair will be almost as much as new radiator plus you will have a warranty. You did not give age of vehicle but it might be worth while to have new hoses at the same time.

I’d see if I could find a new petcock and hope that fixes the issue if there are no other leaks. Someone has may have boogered up the threads on the petcock (hopefully) or the radiator. There’s probably a rubber o-ring on the petcock. It could be out of position or damaged as well.

It’s worth a try getting a new petcock vs springing for a new radiator, in my opinion.

You might be able to find one in the “help” section at your local parts store.

I’m assuming it’s a plastic petcock, not a steel one like on older brass radiators.

Maybe you should get a can of radiator stop leak. Don’t know if it would work since I never had the opportunity to use them.

I’d buy a new radiator instead of using stop leak, if a new petcock doesn’t work. Heck, I’d change the coolant and epoxy the petcock in there.

I’ve never used stopleak. I don’t trust it myself. Could be unfounded fear, but if it’ll plug a leak, it could plug other stuff too IMO.

@VOLVO_V70 sorry its a 2006, 111,000 miles.

Yeah I stop leak doesn’t seem like the best route, its might clog up some other stuff and im not willing to put too much $$ into this should it mess with other parts.

@Scrapyard_John have you personally replaced a petcock before? How would you suggest taking it out if it just keeps spinning?

I had a slight leak from a Chrysler minivan’s petcock. IIRC it was a bayonet mounted nylon petcock, and took a surprising amount of force to pull it out - that’s after determining at which position it could be pulled out. So, just unscrewing or screwing it, it could give the impression that its or the radiator’s mating surface was stripped.

The underlying problem was a broken rubber o-ring.

This is not a place for stop-leak!

You should be able to twist it and pull it out, on most radiators I’ve replaced. It may take gripping the petcock with pliers. Again, I’m assuming it’s the plastic style.

There is a possibility you’ll break the threads / locking tabs on the radiator that mate with the petcock and hold it in. This of course will make the leak worse… But, if the other option is buying a new radiator anyway, I’d give it a shot.

I have replaced one petcock - rather I took it out and reinstalled it. I bought an aftermarket radiator that leaked at the petcock when new, but pulling it out and reinstalling it stopped the leak.

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Danielle, did you mention the make and model? I saw you mentioned it was a 2006.

If you search Dorman products for radiator drain cocks, you should be able to find the style that is on your make / model car and see what you’re dealing with. Some are held in differently - some just thread in, others twist, unlock, and pull out.

@shanonia interesting, ill have to see whats up when i work on this

@Scrapyard_John its a hyundai elantra 2006…i found the petcock online already, they are super cheap and will try that route before replacing the whole thing. it doesnt make sense that what could be replaced for like 30 minutes worth of work and a $3 piece would cost $380 if i go full on radiator replacement.

Anyway, thanks everyone for your advice, to be continued when the part i ordered gets here

Yeah you can get replacement petcocks provided the threads that it mounts to in the radiator aren’t messed up. It’s mostly plastic now. Part of the issue though will be access to get the old one out and the new one in. If the radiator has to come out to repair it, might as well replace it, but if there is decent access, then it can be replaced but the car has to be up in the air a little at least.

A few months ago, I was working on a Freightliner with a leak from the radiator.

Turns out the head of the plastic radiator drain cock was broken off AND the o-ring was split

There was nothing wrong with the rest of the radiator, and it would have been a bear to replace it, in any case. An apt choice of words, since the radiator was literally a Behr :bear:

None of our suppliers could get the plastic drain cock in a reasonable amount of time, so I said I’d check my stash of parts in my garage when I got home, after work

Sure enough, I had a correct spare drain cock at home, and the o-ring was in excellent condition. Still pliable, and not flattened or split

The next morning at work, I had to use a reverse drill bit to get started. Once the drill bit got a bite, the drain cock started to slowly back out. Soon enough, there was enough protruding, for me to grab it with needle nose pliers and unscrew the rest of it. Then for good measure, I chased the female threads in the radiator, before installing the new drain cock

Some of the guys at work had been telling me I should just order a new radiator. But I said I can get this truck going without any expensive new parts.


It’s not necessary to have a drain cock on the radiator. If necessary it can be drained easily enough just by removing the lower hose. It’s probably possible to just completely block off that hole and live w/out a drain cock.

The best way to block off that hole, depends on the configuration. But it is likely quite possible to do. I’ve repaired cracked plastic home water heater drain valves by chiseling them out and installing a new one. Takes very little time at all, 1/2 hour max.

Agreed. I’d drain the radiator and seal the petcock with 2 part epoxy before buying new.

People may scoff at the epoxy, but it’s holding a plastic piece in our dishwasher fine for the last several years. Worth a shot. However; I feel like a new petcock will fix op’s problem in a less redneck fashion than the epoxy. It’s ok for me to say “redneck”. I live in Mississippi.

But what if you’re being less than truthful, and you live in New York City . . . ?

Then it would be wrong to use that term, as per your logic?


That’s right. It’s politically correct if you’re making fun of your own. Ha

You gave me your explanation, but that doesn’t necessarily make anything correct :wink:

Where I have lived I get to say cracker or hillbilly, but the 2 part clay like epoxy for drains is some incredible stuff as is the old slow cure jbweld, not a fan of the new fast jbweld, shoe goo is another favorite sealer n not sure about the heat of a radiator, but have added locktite plastic binder for hard plastics to my list of possibilities for plastic repair along with the old formula of liquid nails. Now I was really impressed with the plastic binder I used on a locating wand, but it got ran over by a big old truck and broke in the same place, so I did a shoe goo repair, funny thing they were wanting the piece and I always give a 2 day cure time, not ready yet I said, needs to cure another day, next day it was gone, then Hey this is not working, duh, I had not reconnected the 16 pin connector back on to the circuit board, and yes on a different piece the 32 pin lcd screen was a pain to replace as it was broken, and I am even surprised the replacement display worked. Boss says it is not worth your time to do for a $700 replacemet, bean counter says you get paid either way, I like fixing things and sneak it under the radar.

Like this drain? this is my broke hex and my replacement plug. there is nothing to easily grab as it is inside the radiator. an easy out or drill might be able to tug it. but its not leaking so i am not going to try it just yet