2004 Chevy Z71 heater core

My heater core went out last July and I had it replaced and it worked fine until the next Feb (7 months) and it went out again. I took it to another shop and had it replaced again. Well last night on the way from an out of town trip it started leaking again and the widow fogged. I know things go out and wear out but is there an unseen problem that would make this keep happening? The shop said they would swap it out for nothing since it has only been 3 months but if there is something else making it happen I would like to fix it also. It’s a pain to have this done every few months. Any help would be great. Thanks

If you need any more info from me just ask.

A few things to check:

Cheap quality heater core: common for them to leak rather quickly.
Using incorrect coolant: must use Dexcool, ONLY.
Flush cooling system regularly every 30,000 miles.
Test for electrolysis:
Remove radiator cap. Engine running at operating temperature. Using a digital volt meter, place the negative test lead to the battery negative terminal, and the positive lead into the coolant in the radiator. A voltage reading above 0.300 volts can cause pin holes in the heater core and radiator. If voltage is excessive, check for loose, missing, or corroded ground connections at the battery and body grounds.

My heater core went out last July and I had it replaced and it worked fine until the next Feb (7 months) and it went out again. I took it to another shop and had it replaced again. Well last night on the way from an out of town trip it started leaking again and the widow fogged. I know things go out and wear out but is there an unseen problem that would make this keep happening? The shop said they would swap it out for nothing since it has only been 3 months but if there is something else making it happen I would like to fix it also. It’s a pain to have this done every few months. Any help would be great. Thanks

If you need any more info from me just ask.


not all heater cores are equal in quality...I have seen this before with other vehicles...

the volts in the radiator testing is a good way to see if electrical currents are eating away your metal..the coolant should be of the proper consentration of at least 50% dexcool...the rest should be distilled water only ...when the coolant becames conductive current flowing in the coolant system eats at the metal..

with this engine you need 2.25 GALLONS OF DEXCOOL COOLANT ...THE TOTAL CAPACITY OF THE COOLANT SYSTEM IS 4.5 GALLONS ..That includes the heater core when you blow out the fluid in it..


REMOVAL INVOLES the removal of the dash ,,this is a big expense..I hope when you replace/ remove the leaking one you determine exactly why it failed..this is important ..

not all heater cores are equal in quality...I have seen this before with other vehicles...

the volts in the radiator testing is a good way to see if electrical currents are eating away your metal..the coolant should be of the proper consentration of at least 50% dexcool...the rest should be distilled water only ...when the coolant becames conductive current flowing in the coolant system eats at the metal..

with this engine you need 2.25 GALLONS OF DEXCOOL COOLANT ...THE TOTAL CAPACITY OF THE COOLANT SYSTEM IS 4.5 GALLONS ..That includes the heater core when you blow out the fluid in it..


REMOVAL INVOLES the removal of the dash ,,this is a big expense..I hope when you replace/ remove the leaking one you determine exactly why it failed..this is important ..

Yes this is the 3rd time in a year it has needed to be replaced.When the shop finishes i'll check all my grounds and maybe make a few more just to be safe. Dose changing over the anti freeze from red to green change anything?

Yes this is the 3rd time in a year it has needed to be replaced.When the shop finishes i'll check all my grounds and maybe make a few more just to be safe. Dose changing over the anti freeze from red to green change anything?


the use of dexcool in these engines is required...this is because of the materials used by GM ...GM does not recommend any non dexcool or compatible coolants used..

If the coolant is changed to another type , this means the complete coolant system including the radiator engine heater core must be drained . then the use of a 15min acid flush with flushing until all the dexcool is removed..

then you should put a tag on the coolant fill to ensure no one screws this up...if you mix dexcool with tap water or other coolants this is how these engine needlessly get damaged..

to drain these engines is not easy ..the drain plugs are difficult to remove on the passenger side side the starter will require removal ..

basicly if this was changed and these proceedures were not followed your screwed...the heater core leaking will be the least of your problems

Thanks for the replys. Can a bad head gasket cause this? I'm going to make sure the grounds and coolaint is correct in this also. I have noticed around 70mph the temp wants to hit 210 but dosen't at lower speeds. this is with no ac turned on.

If the coolant level is low it can cause the temperature to rise. If a head gasket is leaking, it depends where it's leaking; if it leaks combustion into a coolant passage it can cause temp to rise but it most likely would cause a serious external cooling system leak due to the higher pressure in the cooling system. Some shops can test for this, if they have the proper equipment, by checking for exhaust gas in the coolant. It's a quick easy test and not all that expensive, and the results are immediate and 100% accurate.

Update.

I had my heads worked and top end gaskets changed. It did not stop the slight high temps i was getting when a load was put on the truck. The mechanic who worked on my truck offered half the labor back $300 since it did not fix it. I told him I still had a problem he offeres to put a radiator in it for free just to see if it would fix it. He did and it fixed it. so now i have to get the heater core replace again. So here is what me and a few other who know more about this stuff are thinking. the radiator was sligtly stopped up and it would build up a pressure in the motor and heater core when a load was place on the truck and the water temp went up. The heater core was the weak link in the system. so if thats correct when I get the core replace all my troubles should be fixed. any thoughts?

Thanks for all who has helpped on here.

Update.

I had my heads worked and top end gaskets changed. It did not stop the slight high temps i was getting when a load was put on the truck. The mechanic who worked on my truck offered half the labor back $300 since it did not fix it. I told him I still had a problem he offeres to put a radiator in it for free just to see if it would fix it. He did and it fixed it. so now i have to get the heater core replace again. So here is what me and a few other who know more about this stuff are thinking. the radiator was sligtly stopped up and it would build up a pressure in the motor and heater core when a load was place on the truck and the water temp went up. The heater core was the weak link in the system. so if thats correct when I get the core replace all my troubles should be fixed. any thoughts?

Thanks for all who has helpped on here.


if you ACID flushed the coolant system as I stated , and installed dexcool and distilled water you should have no future problems..

the reason you are having these problems is because your coolant system is/has been improperly maintained..



engine/radiator/heatercore all get plugged up. then overheating increases the pressure to destroy gaskets/distort heads etc...

following the advice/proceedures stated here you should be good..