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Cadillac Repair/Radiator Petcock


I have a 1990 Cadillac Brougham, 5.7 liter TBI, and recently the petcock failed (I think). The Cadillac dealership said that the "correct" petcock for it is a brass one, whereas the one in it is plastic. Also, are there any tricks or tips I should know before changing this out? I can find one very similar online, but again, not through Cadillac.

And again, why I think it's the petcock, is that that is where it appears where the leaking is coming from, and it was a very fast failure, i.e. when it went, it took less than a minute to empty the radiator.

Thanks again for any assistance.



In all honesty with over 30 years of working on vehicles, I have never seen a petcock fail. I have seen where it had been removed and reinstalled stripped causing a leak.
I suppose a plastic one could crack, or if the tank is made of plastic instead of metal, it could crack around the threads. I have never seen one blow out or cause an instantaneous leak!
They are seldom.used. The only time used is to drain the radiator.
Are you sure the tank of the radiator is not leaking in that area, or the threads let loose and sent the petcock sailing out of the radiator?
Normally, you would loosen the handle two ears) and coolant will flow out slowly. The more you open, the more coolant comes out. Even pressurized, with the peacock wide open, I cannot picture that much fluid coming out as you describe short of the petcock missing or a crack in the tank.
I am not saying the petcock can't fail. I have never seen it.
If it calls for steel, then you have to use steel. If it calls for plastic, then you need to use plastic.
To replace, make sure the radiator is drained. There is a nut that holds the assembly into the radiator. Remove by turning counter clockwise. Before installing, go to the hardware store and get thread tape. Install one wrap of thread tape on new petcock assy.tighten with attaching nut. (Not to tight). Take your fingers to the ears any turn clockwise until tight. Fill radiator with 2 gallons of premised coolnt/anti freeze.
Make sure you don't have any leaks.
If you have animals and it spilled in driveway, flush the driveway very good with water. Anti freeze/coolant will destroy a cat's or dogs kidneys and will kill them! They are attracted to it because it is sweet tasting.


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Rob Painter


Alarm system questions cannot be answered on this forum. These systems are not what I can answer. Without being physically at the vehicle and not knowing what kind of electrical service has been done on the vehicle, there is no possible way to give an accurate answer over the internet. My expertise is in Ignition/key based anti-theft systems. These issues include GM VATS (resistor chip in key blade) PASSLOCK (MRD)-ignition lock rotation based, no special ignition key and the PKIII Transponder (computer chip in key) systems. These systems are not alarm based and are integral with the starting of the engine. This is why I cannot diagnose alarm problems without physically looking at the vehicle: Alarm systems are a completely different annimal than ignition key/lock based anti-theft system. Many alarm questions come from vehicles 10 years old, and since older, many hands that had been involved over the years.I am an expert in all GM factory (ignition/key based)systems. Alarm system questions pose to many situations beyond my knowledge as to what has been done to the vehicle over the years. Some guy may have actually wired the stereo into the alarm system. Who knows? Over my past 30 years in vehicle wiring repair, I have seen unbelievable wiring disaters done by guys that consider themselves "mechanics." I have seen stereos and alarms intalled using surgical tape. I have seen modules burn up, un-fused circuits, wiring jambed between the doors and even lamp cord used for a starter kill. To answer alarm questions over the internet without examining the vehicle is like asking; What does it take to remove a dent?


Education/Credentials-ASE certified. 11 years with a GM dealer and 17 years with a repair facility dealing with only the repair of theft recovered vehicles.

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