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91 C-1500 Silverado/Heat not great
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partshunter
New User
Dec 18, 2012, 3:16 PM
Post #1 of 3
(1263 views)
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91 C-1500 Silverado/Heat not great
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I have a 91 Chevy Silverado C-1500, 5.7TBI, 700R4 Trans.
The heat takes a long time (very abnormal for chevy in my experience) to get warm.
My heater/blower motor and all controls work fine.
Thermostadt is good
When I was changing the thermostadt I noticed that there was a scale buildup around thermostadt housing neck.
How do I do a "Backflush" to get rid of the scale that must be inside the system? I have thought about pouring a pind of lime and scale remover into the radiator and running the heat wide open till it blows hot, then drain two or three times with cold water to rinse out the lime and scale remover real good. Would this work without damaging the heater core and the radiator? I know that getting the lime and scale remover hot makes it work really well, and that cold water deactivates and rinse it good. Any reason that this wouldn't work to clear all water passages?
I know this heat should blow alot faster. Takes about 15 minutes before warmth comes from vents.
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nickwarner
Veteran
/ Moderator
Dec 18, 2012, 3:30 PM
Post #2 of 3
(1254 views)
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Re: 91 C-1500 Silverado/Heat not great
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Permatex has a coolant system flush chemical that works pretty good to get the junk out of the whole system. If that doesn't clear the heater core, you'll want to backflush it. To do that, unhook the inlet and outlet hoses going to the core. Try pushing water through the outlet hose with a garden hose. Watch the inlet to see how much comes out and how dirty it is. If it doesn't seem to flow out like it should, clear it out with a bit of compressed air (not too much or you build up too much pressure in the core and rupture it.) I've had pretty good success using CLR on the next step where you plug off the outlet hose and use the inlet to fill the core with the CLR. Let it sit for a while and eat at the crap thats clogging it up. After it has had an hour or so soak time, hook the garden hose back onto the outlet hose and flush some more. You know you were successful when you get much more flow than you did prior to adding the chemical. Then rehook the hoses to the engine, fill the coolant up and run it to check for leaks and to eliminate air pockets.
The reason its called a backflush is that you are pushing water through the outlet, not the inlet, so you are going backwards from the normal direction of flow.
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Hammer Time
Ultimate Carjunky
/ Moderator
Dec 18, 2012, 4:02 PM
Post #3 of 3
(1235 views)
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Re: 91 C-1500 Silverado/Heat not great
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Just remember, some of that sludge may be covering up leaks that could show up after flushing. that's not unusual. You may have to dissconnect the heater hoses and backflush the heater core separately.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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