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RussMasterTech , ASE Certified Technician
Category: Car
Satisfied Customers: 791
Experience:  19 years of GM Dealership experience. ASE Master with L1 and GM Master Certified.
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98 Pontiac: heater Core..Van will not blow out hot air..firewall

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My 98 Pontiac Transport is over heating could a bad heater Core cause this? The Van will not blow out hot air and it will make a gurgle said coming from the firewall. The van has no white milkly look in the oil. There has been a new thermstat, waterpumb and the radiator as been cleaned.

Does the cooling fan work? If you remove the coolant fill cap and let the vehicle run for a bit, do you see a constant flow of air bubbles?

Customer: replied 8 years ago.
After the van runs for about 20 minutes either the reserve fills up. and if you go to take off the cap the raditor antifreezer comes out and this is when the van isn't showing over heating.
Then van will run for fine or not just depends.
And to answer your question no flow or air bubbles that i see
This sounds to me like the common head gasket issue that these engine suffer from. Not normally does a heater core cause for a heating issue. My feeling is that you are getting the gurgling noise and overheating from air in the system. This would be caused by engine compression from within the engine leaking into the cooling system via a faulty head gasket, or cracked cylinder head, or possibly even a cracked engine block. I have seen all 3 of the above cause the exact problem. Not all of the time will you get coolant in the oil. This sometimes happens after time. The only other thing I would take into consideration is if this cooling system was bled properly after the repairs you have performed. If not then you may have air pockets from the prior repairs and I would recommend opening the bleeders at the thermostat and the water pump and making sure the cooling system has been filled properly! Feel free to contact me with any questions or if you would prefer a second opinion! Good luck!
Customer: replied 8 years ago.
Do you know of anything else that could cause it to over heat? Beside the head gasket or cylinder head. There has been a test done saying no.
Can you tell me what kind of test was done? This is one of the most common failures with your particular engine. If the cooling system is clean, the cooling fan is running, and the coolant is flowing there is not much else besides compression stoping the flow that can cause for this. Did you have a chemical test done to see if there was compression in the cooling system?
Customer: replied 8 years ago.
Reply to carhelp4uhere's Post: It was a dye test it took just a few minutes.
Well this is a pretty good test to see if you are getting compression into the cooling system. This really does not help much with what I was figuring. The gurgling noise you are hearing is cause from air in the coolant. this is where I would figure you would be getting it from the compression. If the cooling fan is working and the thermostat is opening and closing you should be getting circulation. I am not sure what else to tell you. I will opt out and see if any other experts can give anymore input! Good luck, sorry I could not help you futher, I am just not sure what else to tell you to look at.

Hello Melissa,

I was just reading through the posts and noticed that it was determined that a dye test was done.

I would recommend a combustion gas analyzer be put on the radiator filler neck when the engine is hot. This tester using "Block Test Fluid" that is blue in color. It is usually put into a tool with one or two chambers and can either have a bulb on one end that the tech can squeeze or it can hook to a vacuum source.

If the the blue fluid turns yellow once the engine starts to overheat, then it is most likely the head gasket that is failing. It can be hard to duplicate because the engine has to be very hot for the combustion gas to start to leak, but by the time it starts leaking, it is already so hot that it will start to spew out of the radiator neck. The tech has to be quick on the draw to get a good and accurate sample.

I've replaced alot of headgaskets on these engines over the years, so I really think this is where this is heading.

Sorry I don't have better news for you.

If this is the information you were looking for, please make sure to click the "Accept" button so I may receive the credit for helping you today. Positive feedback is always appreciated.

Thanks for using Just Answer.


RussMasterTech, ASE Certified Technician
Category: Car
Satisfied Customers: 791
Experience: 19 years of GM Dealership experience. ASE Master with L1 and GM Master Certified.
RussMasterTech and 10 other Car Specialists are ready to help you
Customer: replied 8 years ago.
Would any of this cause the heater not to blow hot air. Or make the check engine light to come on?

It probably is causing the no heat and yes it could cause the check engine light to come on if there were coolant getting into the cylinder and causing a misfire, or contaminated the O2 sensor or even if the temp reading was too high it could set a trouble code that would turn the light on


Customer: replied 8 years ago.
Thank you for your help.

You are very welcome.

I hope everything turns out ok.


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