Cadillac Repair: 93 Eldo throwing up coolant...?, cylinder head gasket, head gasket leak

Question
Hello Mr. Cherniwchan,

I am the proud owner of a 1993 Cadillac Eldorado the car is equiped with the NorthStar Engine, and has about 84,000 miles on it.  It NEVER overheats,
no matter how much I drive it. infact the highest temperature it ever reaches is about 234 degrees maximun, however, every now and then, I notice some coolant comming out of the reservoir over-fill hose, it doesnt do it all the time, but I cant help but to think its not supposed to do that, since I usually have to re-fill the reservoir about once a month.  Could this be just a bad radiator cap? or somthing more complex?
any and all help is greatly appreciated.

Thanks
Manny

Answer
Hi Manny, You are right. With a Northstar engine the computor is designed to shut off fuel to 2 cylinders at a time and up to 4 total so the engine is pumping air to try a cool the engine down. 234 degrees is on the higher end of normal but should still not be cause for concern. However the fact that coolant is comming out of the overflow hose has me alittle concerned. Some things that could cause that would be a weak consentration of antifreeze i.e. does it protect to -34? If -20 to a positive number that could cause overheating. If the cap can't hold 15 psi. If there is a leak somewhere in the system. If the cooling fans don't turn on when they are supposed to. If the thermostat is faulty and doesn't open soon enough or wide enough. something is plugging the radiator and it can't cool. And the last thing is the start of a cylinder head gasket leak. As you can see there are alot of possabilities and you just need to start from simpelest to hardest. Hope those suggestions helps find a cure to your problem. Bill