Question about 1999 Chevrolet Silverado 1500

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No heat, replaced thermostat,water pump,heater core, all hose ok

No blockage found. Someone says there is a switch but the hose goes straight to cor and back to engine. Door flaps work god. I Am lost now. Was a mechanic for 6 years this one has me buffalowed

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  • majesty711 Mar 05, 2009

    Wow! That's crazy! Cause i have the same problem. Changed every thing radiator all of it. And i been working for gm as a master tech for over 15 years. But the only thing i can think of is that it the engine passages in the block are clooged and the coolant is not flowing properly cause. Its moving really slow. GM had a bulition about 10 years ago on dexcool. Not good! Cloging everything up. They came out with a cleaner that worked great back in the day but there was an acid in there that ate through alumn so they stoped making it. Now your on your own! Thanks GM! Im trying to find a cleaner thats safe. But these safe cleaners are not effective. I will fix my truck! Just not wanting to pull the heads, freeze plugs and clean the block with a tooth brush. It's gonna get ugly! LoL! Mechanic's car is always the last to get fixed. I'll get back to you if i find a cleaner that works. Cause we need Heat! :)



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When you put your hand on the inlet & outlet heater hoses are they both hot to the touch ? I mean 'ouch' hot, not just warm.
You might have an 'air lock' in the system if they are only warm, or temp feels quite different between them.
If possible, leave the return heater hose loose, start engine, let it warm up then bleed the system using return hose for a minute or so.
KEEP rad full while bleeding.
tighten hose, then watch the radiator fill hole for signs of air bubbles or frothing coming up thru antifreeze.
If either are present, you may have compression leak !
Another check for compression leak, is put rad cap on, drive around the block twice, let vehicle cool down then slowly remove rad cap & smell at filler hole as cap comes off.
compression leak will smell strong & burn eyes.. & we both know there is only one cure for that situation !!

Posted on Mar 02, 2009

  • plato_101 Mar 02, 2009

    I should have asked...

    Have you or has anyone put anti leak products in the radiator ?

    these vehicles have crossflow rads, with just enough tubes to do the job.

    those stop leak compounds can and will accumulate at the bottom of the inlet rad tank & block off two or three rows of tubes.

    While this may not cause a hot running condition, it can cause a low heat condition, & can partially block a heater core in short order!

    I have Auto Body Licence for 36 years, & 6 years rad shop experience, so, don't pull your hair out !

    Start at the rad, & work your way back to it.

    You may have to remove Rad & take inlet tank off to clean it out.

    naturally, if that is the culprit, the heater core may be partially blocked also. but that should have been noticable when touching hoses on hot system.



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