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Looking through this site's archive, heater cores failing seem to be a common problem.
I already know how to replace it. I'm looking for answers as to why it failed so I can fix that problem.
I've already gathered that a faulty radiator cap and electrolysis may be suspects.
I've also been reading about pressure to the heater core being one possible issue. Would it be safe to install any kind of water control valve inline to the heater core, or would the built-up pressure before the valve be damaging to the water pump?
I've seen so many fail (two in my own Blazer) that when swapping the third in I had the first one that failed done by a radiator repair shop instead of buying another crappy OEM one.
Worked for more than 10 years but ultimately failed again. Seemed cracked. I'm not sure if it is vibration from the hoses or as you suggest corrosion.
During the repairs the heater cores looked just fine inside. Mine always leaked at the lateral casings, never in the heater core itself.
Repaired the one which held for 10 years last year (2019) again. The guy who did the repair also soldered a piece of copper in between the tubes which gave them more stability.
In the future when swapping the engine I will definitively replace it with a custom made heater core. I've been thinking on adding hoses through the firewall and fit them on the heater core instead of the two long pipes.
To that valve question: The heater core needs to resist the full pressure and volume in any case. The location of where it taps into the cylinder head suggests that you could run into local overheat troubles if blocking the flow. When swapping my engine - hopefully next year - I will add a three way valve to bypass the heater core altogether without obstructing the flow from the cylinder head to the water pump.
I'm reviving this heater core thread because I've made significant progress in diagnosing the issue here.
It's been almost a year since this second heater core I installed started leaking (which had been in the truck for about 14 months since the factory one failed). I've just been running the heating system on bypass until I was able to get around gutting out the dashboard. Winter last year was a little brutal going anywhere outside of Florida.
Over the past few weeks, I've been working on this heater core problem by taking things apart, autopsying certain components, and doing an over all deep dive inspection of the cooling system and why a brand new heater core failed in less than 10,000 miles.
Phase 1 - Testing for leaks before disassembly
Since the heater system as been on bypass for nearly a year, first thing I did was to drain and flush as much coolant as I could and refill. Then clean coolant running through the system, I took the heater hoses off bypass and reconnected them to the heater core. This was just to confirm the heater core is still leaking after a year on bypass, and it is after a 30 minute test drive.
When I first bought this Blazer, the first job that was done on it was replacing the leaking water pump. Soon after that was flushing out the clogged OEM heater core. Back then I refilled with the generic green coolant. This time when refilling with coolant, I used the proper DexCool instead of the cheap green stuff. I've been thinking the green coolant has been causing corrosion issues.
Now that I have confirmed a leak and the smell of fresh coolant coming from the AC, next I need to confirm if it's leaking from within (meaning a compromised heater core), or if perhaps a bad hose clamp was causing coolant to run down the heater pipes. The heater hoses are new, so nothing should be wrong with those. I replaced the hose clamps, and I taped off the heater core port for good measure to stop any coolant entering that way. Ran another test drive and confirmed the leak is not from the hoses. Heater core port and hoses were dry. The leak is absolutely coming from inside the AC box, meaning the core is leaking.
New clamps and a water-tight seal around the heater core port.
Phase 2 - Pull out the dash board
Long story short: the interior and dashboard were gutted so I can get access to the AC box (heater box? ... whatever it's called). Pulled out the heater core and confirmed that coolant has been collecting on the inside. Thankfully it's been leaking out of the box towards the firewall and outside the vehicle and never inside the cab staining the carpet. From what I understand, this style AC box is unique to the S10 Blazers that have the center console shifter. So it's the Blazer ZR2, Xtreme, and some LS trims like mine. So far I haven't confirmed if the S10 Pickup ZR2 or ZR5 have the same style AC box.
Dashboard and AC box pulled out. No coolant stains on the carpet.
The AC box itself.
Coolant residue flowing out of the Ac box towards the fire wall.
Phase 3 -- Heater core component test
Next is to confirm what component in the heater is leaking. This will lead me to wether this new aftermaket one I installed was just defective from the beginning or something else happened.
When doing the test drives in Phase 1, I noticed that no visible leak is detected when it's running cold. After the truck gets to operating temperature, then I could see a visible leak and smell a much stronger coolant odor.
Here's the tests I did on the compromised, and brand new heater core I have ready to install. Yes, I'm testing the new one straight from the box just to make sure it's fine.
Presure Test:
Both units held 15 PSI just fine.
Bubble Test:
No bubbles from both units.
Water Flow Test:
No water leaking from both units.
Boiling Water Test:
Compromised heater core started leaking.
New one had no leaks.
Compromised core next to a brand new one. They both look brand new, don't they?
Water seeping up from the bottom and leaking out. Is that brown spot a sign of corrosion?
Compromised core on the left next to a brand new one.
Both heaters cores passed all these leak tests except for the boiling water test where the compromised core started leaking at the bottom when boiling water was poured through it. So I've confirmed where the failure is. The next thing is why did the failure happen.
Is it corrosion? Or is it shoddy construction?
Phase 4 -- Researching heater core failure causes
Before I hook up the third heater core, I want to be 100% sure it's not going to go out like the first and second one did. I've boiled down the reason why heater cores fail to two aspects: pressure or corrosion.
I've confirmed that even the compromised core held pressure (when it was cold), so the only other culprit is corrosion. Now the question is what kind of corrosion is going on here?
Phase 5 -- Researching galvanic corrosion and electrolysis
I began looking into galvanic corrosion and did several tests to confirm electrolysis in the coolant.
Before doing test drives in Phase 1, I mentioned that I flushed the system and added DexCool. When I pulled out the heater core and drained it, pink fluid came out of it.
I also did flush the heater core by itself before taking it off bypass when doing the test drives. I haven't drained the radiator yet. I suspect I might find the same.
Before when I was using the green coolant and I did a drain/flush, the coolant from the radiator would come out somewhat brown. I just thought that was left over residue from the prior DexCool from the factory.
DexCool and Walmart's SuperTech green coolant next to a bottle of the pink coolant poured out from the compromised heater core. Should it be pink?
Tried mixing the orange and green to see if chemical differences turn it pink. It didn't.
I'm failry convinced that electrolysis is happening here if it's turning DexCool pink.
Since electrolysis is happening and galvanic corrosion is highly possible, how badly corroded is my cooling system on the side?
Water pump looking very corroded on the outside. Throught it was just superficial rust at first.
The pipe I used on the heater hoses for the bypass for about a year.
Inside of the bypass pipe is looking very corroded.
I guess I should consider replacing the water pump and radiator if the inside of my bypass is looking like this.
How worried should I be about the water channels in the engine block?
With visible corrosion now confirmed, exactly how much electrical charge is my coolant holding?
Here's how I tested for voltage:
I have the negaive terminal disconnected from the battery, and I've been grounding the black prob on my volt meter to the negative battery wire disconnected from the battery. I've done several tests where I'm grounding my voltmeter to the truck (the negative battery wire), and grounding my voltmeter to the battery itself. This whole time the positive battery wire is still connected. Here's the results.
Positive terminal connected; Meter grounded to truck; 0.07v from radiator coolant
Positive terminal connected; Meter grounded to battery; 11.18v from radiator coolant
Positive terminal disconnected; Meter grounded to battery; 0.00v from radiator coolant
Positive terminal disconnected; Meter grounded to truck; 0.00v from radiator coolant
Other places I pulled voltage from are the transmission oil cooler lines at 0.21 volts, the engine oil cooler lines at 0.18 volts, and random hose clamps reading 0.06 volts to 0.12 volts with the volt meter grounded to the disconnected negative battery cable.
How worried should I be about the 11.18v rating? That seems to suggest there's a direct short somewhere in the wire harness from the positive battery terminal feeding directly into the coolant somehow. If so, well that certainly explains the galvanic corrosion happening here.
Phase 6 -- What's next?
So I've pretty much confirmed galvanic corrioson is the culpirt here. Given the fact that I'm reading a charge 11.18 volts in the radiator when I ground my voltmeter to just the battery means there must be a wire short somewhere coming in contact with the engine block or some other metal pipe running to the radiator. That's going to be a fun puzzle to figure out.
I guess the first place to start in finding the source of this electrical charge is the wire harness that runs across the valve covers. Start from there checking for any bare wires and then whatever runs from it. Maybe something going to the starter is a miss. I just hope there's not a short is something running across the top of the transmission. Then I'm looking at disassembling the whole truck pretty much.
Could a cracked spark plug cause electrolysis? I replced mine not too long ago so I don't have much of a reason to suspect them. There's no misfire.
11-10-2020, 07:21 PM
Second heater core failure; Is corrosion the culprit?
