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Pontiac Repair/re:1996 pontiac bonneville - anti-freeze


Hello Mr Puccio- I am having a problem with my car.  The anti-freeze seems to disappear.  Last summer, my husband filled the overfill with what I believe was just water.  a few days later we had a huge spill on garage floor.  mechanics fixed the "plug".  recently at oil change they said they had to put 5 gallons in radiator and I told them I had filled up overflow just night before.  they also said the previous oil change they had to add about a gallon on anti freeze.  My husband took it to a shop that said the plastic part on the right hand side had a crack.........replaced it for $200.   It was fine for a week or 2.  I seem to be able to a noise like a "radiator" and I notice issues seem to happen if the "heat" or "defrost" have been on.  My husband filled up the radiator then took it to the shop next day.......they found no issues but also filled up the anti-freeze.  We just don't know where all this anti-freeze is disappearing to?  Any idea?

Thank you so much,
Natalie Fitzgerald

Hi Natalie:

those 3800 V6 engines were noted for coolant leaks due to the plastic parts the put on the engine. the part you were referring to was an coolant bypass elbow for the heater. very common. the other things that leak on that engine are the intake manifold gaskets (lower) intake the can leak either externally on to the ground or worse into the engine (very bad) the other this that was common for that engine was the upper intake manifold it's self. over time the plastic distorts and it will leak either external or internal to the intake and then it will burn in the engine the issue with this is they uaually leak when the engine is cooling back down from a hot heat cycle. if the leak is bad enough it can actually fill up one of the cylinders in the engine and when you try to crank the car cold it will actually Hydro-lock the engine meaning the cylinder is so full of coolant the starter motor can't turn the engine over because  you can't compress a liquid. that is bad as well. obviously I can't tell you what the issue here is with out seeing it I'm just giving you possible causes. hope that helps. Good luck :-}

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Todd Puccio


General auto repair,electrical issues,driveability issues,anti-lock brakes,SIR systems,HVAC,engine performance,Gm specific. I have worked at my current dealership since the 1990 model year anything much older than that I have limited exposure to. I do not have very much transmission experience so those question you may want to ask of another expert. When you send me a question let me know the exact make/model/engine and year for the car or suv you have it makes it easier to answer the questions that way. If your happy with the answer I gave you please feel free to Donate. This is a free service to you and I am not compensated at all by this web site. I have 22 years of experience to share with you and my knowledge wasn't free to me. I had to pay for my education.


Experience in the area: I have been a technician in GM dealerships for over 22 years and I am a ASE master technician. I work at a Buick and GMC truck store Previously I worked at a Pontiac GMC store for 18 years. I Served a a lead technician when dealership was on a team system. I just recently moved to a Buick,Hummer,Saab Store when my franchise was purchased by this dealership. Organizations: ASE master technician


Education/Credentials:High school diploma,2 year vocational school degree 2 year college degree. Associates degree in applied sciences (auto technology)Awards and Honors: GMC master technician

Awards and Honors
Master GMC truck technician Master ASE technician in 9 categories

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