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Cadillac Repair/northstar Radiator cap


QUESTION: I have a 99 Deville and am wondering what PSI radiator cap I should have on it?    thanks




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QUESTION: if there is a 16 pound cap on it now and not a 15 pound , will that cause it to overheat    thanks

Hi Doug,

To my knowledge a 15 pound cap is supposed to be in the vehicle and I would. Suggest you confirm at a parts store.
If the wrong pressure cap is installed, many things can happen. If for instance you used a 10 pound cap, the cooling system may not circulate causing the engine to overheat.
If you use a 16 pound cap in place if a 15 pound, you are putting undue pressure on the radiator and other cooling system components and one day you find the radiator split open or a hose fail. As I said, check with a parts store and confirm what pressure cap is designated to be on your vehicle.
The cooling system is designed a certain way. Any divination, problems arise.

As for over heating on these engines, there are far too many variables to be specific, although I did tell you to check the fans and see if they are working.
These engines have very small cooling jackets. What this means is a small piece of debris,like partial remains of a water pump gasket, can either stick in a cooling jacket or even in the overflow and cause overheating.

Blown head gaskets are not ever the cause, but the result of overheating. Many do not understand that.

If the head gaskets are blown, most times you can pretty much give up on the engine, because at that point, heads can warp or crack and other catastrophic damage could have occurred. The worst thing is after all the work of replacing is senseless, if what caused the overheating condition is not addressed,because the gaskets will blow again.

Some may instead decide to get a new engine at a junkyard. Think about that statement once, yet I have heard it many times. Chances are that new engine was overheated or it wouldn't be at the junk yard!
Only option then is to get a crate motor from GM for about $4,000.00 US. That is, if they are still available.

If 16 pound is recommended use, it but if 15 pound like I have always known, get that cap off of there before problems arise.

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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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