2000 Silverado-Can vac. leak cause rough running and no heater?

Old 01-04-14, 09:03 AM
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2000 Silverado-Can vac. leak cause rough running and no heater?

I have a 2000 Silverado, 4.8 V8, this past week my truck seems to be running a little rough and I noticed 2 days ago that the heater isn't putting out any warm air either. I am working 12hr shifts this week and I only drive 4 miles each way to work so I haven't had a chance to look into it nor is the lack of heat unbearable. I live in SC and it isn't too cold.

I was just thinking on the way in this morning that maybe a vac. leak could be causing this, accounting for the rough running (which in only slightly noticable, nothing drastic) and maybe not allowing the control to shift on the dash from cold to hot.

Doesn't the cold to hot contol knob just move some dampers by using vacuum?

Your input is appreciated.
Old 01-04-14, 10:00 AM
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Some dampers are vacuum operated and some are electrically controlled.

Put your function control to defrost..... the air should just come out up top.
Put the function control to floor.....the air should now come out the bottom and no longer from the top.
Put the function control in AC ..... the air should come out the front of the dash.

If the air is coming out the correct locations, it's not likely a vacuum leak as the same vacuum source would also control the heater water valve if the vehicle had one.

Your problem is more likely a temperature blend door.
Old 01-04-14, 04:22 PM
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Check coolant temp if it is low suspect thermostat. If it is hot then feel heater hoses, they should both be hot. If one is cold suspect clogged heater core. If they are hot suspect temp door motor or dash control.
Old 01-05-14, 09:51 PM
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vacuum leak

I would be more worried about the ruff idle being a vacuum leak. I drove my truck to work about 25 miles with a vacuum leak and burnt a hole in the number 5 piston. The engine didn't show it was overheating because the only hot spot was at the vacuum leak. I had repaired the leak and it wasn't until another 2 weeks went by when it gave out. It's hard keeping a dipstick and oil in the oil pan with that kind of compression or blow by going into the crank case. One thing for sure unless your the kind of guy that hands out 100 dollar bills at WalMart you don't want to buy a piston from a dealer.

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