Cadillac Repair: air in cooling system, arc forensics, tim romine

Question
i have replaced a bad radiator.  At the time the car was running fine provided I kept water in it.   I was careful to not let it get too hot.....as I did not want a cracked head.  When I got it back from the shop.....I did not get 3 miles before it began to overheat(temp gauge going up)  When pulling over (did not get over 235, and unscrewing the cap....I notice the water was not hot but bubbling out anyway.  I waited for cool down and took it back to shop.  They said it was my cap only holding 12lbs of pressure when it should hold 16 and they replace it and thermostat or so they said.  The car did absolutely fine for 1 week with the gage staying at 201.  Then one day...the gauge begain climbing again.  I took it back to shop and he piddled around with it and told me to take it down the road and see how it did.  It worked fine for another week then the same problem began only this time....I would take the cap off and it would have coolant up to the brim so I could not add any.  I really don't think my head is cracked...power level is fine and at times it will run fine.  At times the gage will start to go up and then I will hear this funny noise behind the dashboard and the temp gauge will drop 20 degrees to normal....everytime.....but then immediately start to climb again.  The water bubble and pressure is there to make it spew but it is not hot.  Please help.  Without this car I may very well become homeless....   Thank you so very much.  Amber Sewell

Answer
Hello,

You did not state the year, make, model of Cadillac, and unfortunately these aluminum engines are filled with so many potential over heating problems, it hard to nail down just one cause.

Considering your description, it sounds like some sort of circulation issue. Once the thermostat opens, temp should be 195 degrees at the radiator. If not hot, the system is not circulating properly. These engines have very small cooling jackets that can be prone to plug just by left over used gasket material, when a water pump is changed. I only tell you to give you an idea of how critical for the cooling system is to flow.

I am guessing, but the noise you hear behind the dash could possibly be the cooling fans under the hood coming on and they would bring the temperature down. The cooling fans operate when a sensor in the engine or the radiator gets to a certain temperature and the fans come on to cool the engine.

The easiest way to eliminate a blown head gasket is something you can easily do.

Check the engine oil, if white and milky, one or two head gaskets is blown.

If you have the engine warmed up and white smoke is coming out of the exhaust, you have blown head gaskets(s) or a cracked engine block.

Cracks in the block can also occur on the outside of the block and will leave dripping coolant.

Blown head gaskets are not the cause of the over heating, but the after effect of an overheated aluminum engine.


In your situation, coolant does not appear to be getting from one side of the thermostat to the other. I would be considering a plugged radiator. Is the coolness you say is at the cap, the same at the lower hose? In other words, with a warm engine, is the entire radiator cool?

If the thermostat is open and engine is warm, upper hose should be warm as well as lower hose. If not, you need to consider a restriction in the radiator.

You should never be opening the cap and instead check level in overflow bottle. That is also where you ad coolant.

Now you have your home work and we will go from there.

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