5th heater core in 8 months

Last August, my heater core went out. I had it replaced.

Then, early October, it went out again. They thought it may have been a bad part, so they replaced it again.

Then, mid December, it went out again. They said it must be a blown gasket head, based on a pressure test on the radiator cap that blew 2 points higher than normal. I said I was taking it somewhere else.

I took it somewhere else, and he ran some compression tests and things, and said they all came back perfect. I don’t remember all of the details now, but I think it was the compression test where he hooked it up to something and left it running for 12 hours and it didn’t lose any pressure, which to him meant there was no way it was a head gasket issue. He spent a day looking it over and said there was absolutely nothing wrong other than the heater core - a side seam was split. He put in a new heater core. He also replaced the radiator cap and thermostat for good measure. (I’ve never seen the temp gauge in the car get above the normal mid range).

Then, in mid January, it went out again. Took it out to that mechanic again, he said he checked it from top to bottom, not a thing wrong - other than again, a split/leak along the seam at the outer edge of the heater core, in the exact same location as last time. He thought maybe it was a run of bad parts because couldn’t find anything else wrong, it went out in the same place again, and he said that if it were a pressure issues then a hose or other older parts would go before the brand new heater core would. He replaced the core again.

And then, this morning, the smell of antifreeze, and then the cloud of thick air that fills the car.

I have no idea what to do. It is an 03 malibu LS with 80,000 miles on it.

OK I’ll guess, bad thermostat and radiator cap causing excess heating and pressure causing the weakest link, heater core to fail.

Hopefully they’re honoring the warranty for the part and work done. I’d see if there’s another manufacturer for this part, or if these are aftermarket parts, maybe pay the extra for a genuine part. It couldn’t hurt to replace the radiator cap, but I’d be surprised if the heater core was the weakest link—I’d think a hose clamp or rubber hose would fail before a brass or aluminum part, but I could be wrong.

as an afterthought, change the thermostat too.

When an aluminum heater core is installed it must sit on it’s insulators freely so the heater core free-floats. This is because the heater core expands in all directions as it heats up. If the heater core is intalled where it’s binding on the insulators this can cause the heater core to crack, because it’s not able to expand freely.


the last time I took it in, before he replaced the heater cap again, he replaced the radiator cap and thermostat as well as a precaution.

parts - GM factory parts. the first time i took it in, they tried a non GM part and it didn’t fit, so then they got the GM - more expensive - part, so they’ve all been GM parts.

He talked about that last time, but said he had checked around everything carefully and there was nothing that he could see that would cause a conflict.

both radiator cap and thermostat were replaced last time - he said they were inexpensive and it couldn’t hurt, so I told him to go ahead.

The first place I had it at was charging me every time I took it in (30 day warranty), and then were about to charge me a trunkful of cash to tear the motor apart without proof of a larger problem, so my dad told me to take it elsewhere. So, I had to pay for the parts and labor again with the second mechanic, but last time it went out he replaced it for free.

I’d attempt to look at the lot number on every heater core (too late for most of them). This is the same failure across multiple parts. The seam should take much more pressure than any rad cap pressure limit. These are defective cores.

Ok, this might sound really naive - but don’t they have to recall defective parts? The first replacement core was installed mid August…could they really have bad parts on the market for so long?

It may be a given lot number. If the end installer doesn’t send it back up the line in complaint/warranty …there’s no initiation of ISO tracing to isolate the lot # line/time it was made. It can take a while for the process to work itself out.

I would do a static air pressure test on the bench with pressure set to 25lbs. Any heat core should withstand this pressure. There may be a thermal component to the failure, but there’s only so much one can do to simulate the condition of failure. Perhaps submerging it in boiling water with air pressure on the core.

This would be a bit much to pay someone to do this, and it would be a bit out of the capability of most consumers.

BMW and VW (maybe Audi also) had a big recall in the early 80’s about heater cores splitting and , get this , dumpimg hot coolant on peoples feet. Well the manufacture came up with what was essentially a weaker link than the heater core and we installed this under the hood.

I have no idea on this one but if these cores are cracking in the same place (and since the odds of getting this many bad cores are near zero) it would seem to me this has to be a stress crack issue.

Core hose nipples overly long, heater hose hardened like a rock or routed incorrectly leading to stress on the seam, etc.? Someone needs to sit on this car for a few days and think this thing through very carefully rather than substitute cores en masse.
They have to be overlooking something.