No Heat

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Dec 13, 2021 | 07:18 AM

idealtrucks

Thread Starter

Fleet Mechanic

Joined: Jul 2002

Posts: 1,297

Likes: 34

From: S/W Virginia

No Heat

So this morning on the way to work, the heat was not working in my truck. Engine temperature was good, just blowing cold air. I moved the temperature control **** back to cold and back to hot, no change. I believe that it is actuating the door since I can hear it squeaking just a little bit when moving. It's done that for years. I turned max AC on to test that since I've seen some vehicles with a vaccum valve on the heater line, thinking that might be stuck. No change. Then 30 seconds or so after I cycled max AC, the heat started blowing hot.
Thoughts?

Dec 13, 2021 | 09:34 AM

alloro

Fleet Owner

Joined: Apr 2008

Posts: 24,316

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From: 0,0,1

To me it sounds like a blend door issue. Just because it squeaks doesn't mean it's moving all the way over.

Dec 13, 2021 | 09:39 AM

idealtrucks

Thread Starter

Fleet Mechanic

Joined: Jul 2002

Posts: 1,297

Likes: 34

From: S/W Virginia

That would certainly be easier than a heater core.

Dec 13, 2021 | 10:23 AM

projectSHO89

Hotshot

Joined: Jan 2004

Posts: 19,760

Likes: 1,079

From: St Louis

You need to determine whether or not hot coolant is circulating through the core when you have a "no heat" condition. Without that information, it's pointless to dive into ANYTHING else.

Open the hood and CHECK THE HOSES next time you have that issue.

Dec 13, 2021 | 07:57 PM

steve(ill)

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Joined: Jul 2005

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FIRST... make sure the tank is FULL of antifreeze to the upper mark...... Low level will cause COLD air when asking for heat.

Dec 14, 2021 | 08:58 AM

idealtrucks

Thread Starter

Fleet Mechanic

Joined: Jul 2002

Posts: 1,297

Likes: 34

From: S/W Virginia

I was low on antifreeze. Over a gallon low.
So...it's going somewhere. I have never noticed a leak under the truck or in the truck. Any other explanations beside head gasket?

Dec 14, 2021 | 07:39 PM

steve(ill)

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Joined: Jul 2005

Posts: 11,931

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I have had a couple older 5.4 motors that had "internal" leaks.... I used BARS COPPER HEAD GASKET SEALER and that seemed to FIX the problem for a year or better... Then i did it again.....The stuff i used, you had to drain and add to clean water.. I think these days they have something you can add to the antifreeze... NEW STUFF is not like the old aluminum flakes or the black GOO from 20 years ago......... No problems with blocking heater core or thermostat..

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