"1990 Buick Lesabre: Radiator Fluid Overflowing Problems"

White 1990 Buick Lesabre Left Side View

My 1990 Buick Lesabre, radiator fluid overflowing out of cap? I thought I had a radiator leak but the mechanic tested my car and it doesn’t have one. But what I noticed is I’m still losing fluid. And I opened the hood and it’s coming out of the spout. We just replaced the cap and the mechanic said he overfilled it. Now it’s not leaking anymore but when I opened the cap I can see the coils (I think that’s what they are) in the radiator. The fluid is about 3-4 inches below the spout. Is that too low?
What can be making the fluid do this? Is it the thermostat? Also, the check engine light comes on when I’m on the interstate after about 10 minutes. I noticed that now that I put the heater on heat the engine light hasn’t come on. is this all related? Please help me.

Answer: There should be enough fluid in the radiator to cover the coils, if you can see the coils the fluid is too low. I would have the thermostat changed and the system flushed out and see if that helps and if it doesn’t I would be looking at the radiator as being plugged up or possibly the water pump. My bet would be the radiator as old as the car is.