Old coolant and leaking heater core

[piggy]

Unfortunately I’ve not changed my coolant for about 8 years and I know my heater core is bad because I used bars stop leak on it about 6 years ago. Obviously I need to properly flush and clean the cooling system but I dont want to contaminate the new heater core with the flush. Does anybody know if I should install a heater core bypass and then do a flush /clean of the system. After the flush is done, I would go ahead with the heater core install. It’s a a 1986 GT convertible 5.0 with air conditioning. The green coolant is only good for 3 years so I prey I won’t have other problems. The fluid looks normal and green. There is no oil or rust visibly in the system. You can see gunk on the radiator cap and inside the radiator which I believe may be the bars stop leak I hope. I also did a multimeter voltage test on the fluid which I think the results are ok.
I would appreciate any tips anyone might have.
Cheers
Gareth

[richpet]

Confused a bit. Are you going to flush everything well and then install a new heater core? If so, yes, bypass the core and flush it really well. Or, since you're pulling it out anyway why bypass it?

Do you know it's bad? You used barsleaks - for a heater core leak?

If you flush all really well, repair whatever was leaking, you should be good.

Take a good look at the radiator core(s) for corrosion.

Green coolant can be 'good' for longer than three years.

[piggy]

Hey. Thanks for your insight. I really appreciate your advice. I definitely need the heat here in Canada lol so I was planning on installing a new heater core when the flush is complete. So I would bypass it so it would not leak everywhere when I flush it. Also I dont want all the crap in the system contaminating the new heater core so I thought it’s best to install the heater core after the flush. I had a very experienced mechanic (he is passed away now) put the bars leak in. Unfortunately I dont know how he did it but it worked for the heater core leak. It has never leaked since. Other than oil changes and a few other minor things I have not done much mechanic work but there is so much info on flushes and the heater core replacement online I think I will give it a try since I have the time. I will replace the rad cap, thermostat as well. The hoses seem to be in good shape as well as the water pump. I bought the car 11 years ago with 48000miles on it and it now has 60500 miles so in 11 years I’ve only put about 12000 miles on it.
I suppose I could flush it with the original heater core installed and see if there are no leaks. Or even put more barsleak after the flush but I’m not sure on the side effects of that. I would have to research that. Saves me installing a new heater core which is a big job.
I just thought the flush would remove the bars leak and cause the leak to start again.

[richpet]

Ah. If the core leaked previously I would flush the system and bypass it since you know you have a bad core. No point in the leak possibly reoccurring while you flush. A stepped hose connector is all you need.
When you replace the core buy a flow restrictor that goes on the intake side of the core. It's just a plastic plug with a smaller hole in it that reduces water flow through the core and helps them last longer. And replace those two hoses to/from the heater to ensure they are gunk free.
Flushing is easy and there are differing methods. I drain and refill with only water, run it and drain it again. If I am really feeling anal I will pull the T-Stat first. Some guys like the chemical flushes. If you do use them just read the directions. And do one more fill/drain rinse cycle.
It's a lot of work, but a core that leaked will always leak again at the worst possible time so I would replace it.
Have fun!

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[piggy]

Thanks again. I will give an update on how it goes. There are some good videos by Scotty Kilmer on youtube I've watched over the years-very knowledgeable mechanic.

[richpet]

I have to admit that I am SO glad to have had non-AC Fox bodies. Heater cores are a breeze.

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[piggy]

Very true indeed

[gt4494]

I have to admit that I am SO glad to have had non-AC Fox bodies. Heater cores are a breeze.

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Says someone from Oregon. LOL

[richpet]

Hey now.... It gets chilly in winter. Lol!
Not like Canada.
Fog and fogged up windshields are our main issue.

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[gt4494]

95 degree days with 95% humidity here is why AC is considered a requirement for most.
And yep I've changed several heater cores and all have been a pain in the neck.