We have an '89 6.2L that's been going through a lot of heater cores. We're on the third core this year.

Any suggestions as to what is causing it?

Sounds to me like you have electrolysis problems. Electrolysis can eat up a radiator or heater core very quickly. I would check all your grounds for a good connection. Also make sure to use distilled water in your coolant mix, undistilled water has salts in it which conduct electricity better, which is bad. Other than that there should be no reason that you are going through cores unless the fan is hitting it or something. Also take a look at the cores you take out. You may be able to see some discoloration on the inside of the core which will indicate electrolysis.

does your barbed fitting have a restrictor in it

cricketo99:
It could be electrolysis. I'll check when I get it out. It likely doesn't have distilled water in it right now.

mjd:
I'll have to check on that one. It's been about 3 years since I built that engine.


Thanks for the suggestions. This time, it's really dumping coolant from it. So it looks like I have to make time in the next week or so.

Yeah, especially with over 300,000 miles on it the grounds could be really corroded.

Where has each of the cores failed? Who manufactured the core? What type of coolant are you using?

Got this one out today. It failed in the same place as all the rest. Where the larger aluminum hose swivels on the heater core.


Looked through receipts today as well. This is the 7th failure on this truck in the past 2-3 years.

They're all AC Delco replacement heater cores.

NEVERMIND!

I pressured it up with a garden hose to find where it leaks. I guess your were bang on with your first guess. I believe it is electrolysis. Strange though, I changed all the grounds last time I had the engine out..

This one isn't an AC Delco. No one had any so it's some cheaper brand this time.

My father has great thanks for you!

Jay

Well once you get the new one in I would try this. First drain old coolant and replace with antifreeze and distilled water. With it running take your radiator cap off, and with a multimeter touch the negative to the negative post on the battery and touch the positive to the coolant making sure not to touch the actual radiator. See what the voltages are. I believe the acceptable amount is .1 volt but not 100% on that. Then try turning on various accessories such as the heater fan, etc. to see if the voltage increases. If it does you know you have a grounding problem for that particular accessory. Also read the voltages with the starter cranking. but I am pretty sure that a poorly grounded starter will eat through a rad/heater core pretty quickly. Good luck

I believe there is a ground from the rear bolt on the intake manifold on the passenger side, just opposite the glow plug controller. It grounds between the engine and the firewall. Make sure you check that.

Well the new one is in, and I did the tests you suggested.

Voltage in the old coolant is never greater than 0.1v. Exact same with new coolant in all conditions.

I did reground the heater core though. The tab in the plastic box is damaged from being changed 7-8 times in the past few years. With the new ground the current capacity of the coolant was dropped to about 0.05v. With any luck it's fixed and won't have to worry about it for a while!


Thanks for the help!
Jay