The heater had been working fine. Then I changed my intake manifold gasket. Everything else is good, but my heater no longer works. I have driven it about 200 miles, and I have checked the coolant level multiple times. The upper radiator hose gets hot after driving, but the heater hoses feel pretty cool. The weird thing is, if I jack up the front end and run it, the heater will start working, but the next time I drive it it will not work again.

Its a 1995 Camaro with a 3.4

Any ideas? Thanks in advance.

I tried flushing the heater core both ways. It did not make any difference.

Update—

I backflushed the heater core again, this time using a LOT of pressure from the garden hose. A BUNCH of nasty looking stuff came out of it. I think the previous owner may have put stop leak in it at some point. I’m guessing the core is still 3/4 plugged up, but the heater is now working, at least good enough for a Florida car! ��