99 Sierra has no heat

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fine409
Posts: 2
Joined: Sat Feb 09, 2013 1:06 pm

GMC Sierra Intake Manifold coolant leak

Unread post by fine409 » Sat Feb 09, 2013 1:11 pm

i have a 96 GMC Sierra p/u. i have a coolant leak on my intake manifold, driver side towards the front. i can see coolant bubbles when i put pressure on my coolant system. it is coming out above the #2 cylinderjust below where the valve cover attaches. i have no coolant in my oil, or in that cylider. could i have a bad intake gasket?, or bad intake? how common is this?

scotty
Posts: 19
Joined: Sun Oct 14, 2012 11:52 am

Re: coolant leak

Unread post by scotty » Sat Feb 09, 2013 5:43 pm

Yes this is a very common problem on the older GM V8 engines.
The intake gaskets are leaking coolant.
The coolant passages are on all four corners of the manifold where it meets the cylinder heads. Over time the gasket deteriorates.

Depending on how long it has been leaking, the alluminum intake manifold may have some damage. Antifreeze will eat at the manifold causing pits. If they are not too bad, you can swipe a thin layer of RTV sealer on it before bolting it back down.

If it is badly damaged, you would need to replace it.

fine409
Posts: 2
Joined: Sat Feb 09, 2013 1:06 pm

Re: coolant leak

Unread post by fine409 » Sat Feb 09, 2013 9:45 pm

thank you for the info. hopefully will not be too bad of a job :)

Dan
Posts: 3
Joined: Wed Jul 01, 2015 8:35 pm

99 Sierra has no heat

Unread post by Dan » Thu Aug 27, 2015 10:47 pm

99 Sierra pickup has no heat.
I flushed the heater coil and have hot water both sides.
Fuse is ok.
Blower and control for vents, defrost works ok.
Turning the cold to hot control, temp stays the same, although it sounds like something is moving, but not certain what the noise may be.
Just for info, the instrument cluster needs to be replaced, but I can't see where that could be related.

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carriedi
Posts: 2573
Joined: Wed Apr 10, 2013 12:42 pm

Re: 99 Sierra has no heat

Unread post by carriedi » Fri Aug 28, 2015 8:50 am

you should take off the air temp door motor and see if you can change the temperature by moving the door manually.the motor could be bad, the door could be stuck or the door could be broken.
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air temp door motor.jpg
GMC Sierra A/C temp door motor location
air temp door motor.jpg (74.85 KiB) Viewed 4519 times
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