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Discussion Starter · #1 ·
Did a coolant flush on my 2001 chevy Silverado,also change the surge tank.put in antifreeze idle with the heat on high to get the bubbles out. Heat works fine when the surge tank cap is off but when I tighten the cap an drive the truck for a bit Im getting cold air. Not shore why?

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Need some information. What caused the need for a system flush? The coolant should never need to be replaced unless it was contaminated in some unusual manner.

Operating the system with the heat on would not have any effect on air pockets in the rest of the system, only the heater system. I suspect you have an air lock in the system because the system was drained of coolant and improperly refilled.
 

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Discussion Starter · #3 ·
I flush the system and changed the coolant surge tank because the dexcool harden in the reservoir tank and the coolant was very dirt,also when I would drive the truck coolant would leak from the cap on the surge tank and also come out off the the hose out of the side of the surge tank.

I suspect that the harden coolant was blocking the flow of coolant so I replaced the reservoir also flush the coolant because I looked really dirty by removing the lower radiator hose and putting a garden hose in the reservoir and cycling the engine to remove the coolant from the block till it ran clear.

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To break the air lock take the cap off when cool. Turn on the heat, idle the truck and slowly raise the rpms to 3000 and hold for a couple seconds. Very very slowly go back down to idle. If you don't slowly go back to idle the radiator will purge antifreeze out of the cap. Do this 2 or 3 times and then let idle for few minutes. That should do it if it's an air lock.
 

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Discussion Starter · #8 ·
apcnc said:
Did you get solid chucks out of it? Did you run a flush or just water? The heater core may be stopped up. You may want to back flush the core.
Ran 2 bottle of Preston flush and drove it for 2 days then flush removed the lower radiator hose put the garden hose in the surge tank and turn on the car with the water running through it till clear water did see and big solid chuck just a rusty looking orange coolant.

I back flushed the core samething happen I bleed the the system with the heat and the cap off the surge tank rev the truck from time to time the heat blows really hot with the cap off just when I tight the cap on the surge tank to drive I loose heat feels like ac coming through the vent after 5-10min driving.

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Discussion Starter · #9 ·
Jasen said:
Were you having issues before the flush, although a chunk of deathcool could have moved and is blocked up somewhere.
Like apcnc is suggesting, a chem flush might be needed.
Idk because the problem now is when the cap is sealed on the surge tank I loose heat.before with the old surge tank the cap wasn't sealing properly and antifreeze escaped pass the seal but I had heat and now the only time I have heat is if I loosen the cap on the surge tank. I'm not sure if it's because of the flush or its another problem.

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Did water flow through the core ok when you backflushed it? Are you sure its the cap or driving down the road. Your thermostat may be stuck open and just cools a lot going down the road. If you can check the temp through the diagnostic port while driving. The gauge lies to you. It shows 210 by 165 or so degrees. The only thing the cap should do is seal and pressurize the system. but that's only after it gets hot. Not sure why that would stop the flow to the core.
 
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