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Old 03-02-2016, 09:06 PM   #1
Join Date: Feb 2016
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85 GMC Vandura 3500 not fully heating up

Hey guys!

I recently purchased a 1985 GMC Vandura 3500 4 window shorty. It has the 5.7l Vortec V8 w/auto tranny. The bus does not appear to be warming up all the way resulting in it running lean. The first thing that I would normally assume is that it has a faulty thermostat, but I do not have experience with buses and after looking under the hood briefly there is some stuff that I am not familiar with.

Please see the attached pictures and let me know if you have any ideas.

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Thanks much!
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Old 03-07-2016, 07:48 PM   #2
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Be careful as you do any of the following.....if you have access to an IR thermometer use it to make sure anything is safe to touch before proceeding.
With the gauge reading that low, I would get a thermometer (like one for cooking meat or candy) and check the temp of the water in the radiator. This will eliminate a faulty gauge as a culprit.
Also check for coolant flow at the radiator when the cap is removed.
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Old 03-07-2016, 10:50 PM   #3
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That not too bad. Unless I was up on the hiway on a hot day, my 85 GMC cube van would read about there. And there would be no reason that would make it run lean.
Don't make a fuss-just get on the bus!

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Old 03-09-2016, 12:13 PM   #4
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Well, the other reason other than the temp gauge that I feel that it is not reaching full operating temperature is that the heat is barely even luke warm.

In regards to the pictures, does anyone know whats up with the red garden hose looking knob that runs into the box there on the passenger side firewall?
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Old 03-09-2016, 01:04 PM   #5
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Looks like it adjust the water flow to the heater. Do you have a rear floor heater?
I was looking at a bus the other day that had a valve like that right under the dash
And it controlled the under seat heater in the rear.
Could be that your thermostat is ok but has been changed sometime in the past.
It might be a 180 degree and should be a 210, or the other way around. there are always ???? When you buy used..
I always try to document what I do to a vehicle like a maintance record to keep in the glove box for me and to pass on, makes my vehicles a lot easier to sale, and gives them better trade in value.
Don and Ellen
Plus one fuzzy faced kid (Poopcee)
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Old 03-09-2016, 01:11 PM   #6
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There is not currently a rear heater. I don't really see any traces of there being one either. Granted I do not really know what I am looking for completely, but the subfloor has already been replaced previously and all the factory seats removed.

Does anyone know what the temp should read when it is fully warmed up if I take a read at the radiator as Old'Skool suggested?
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Old 03-09-2016, 04:30 PM   #7
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Upon further investigation, the red knob is set up as a bleed point. Also, there used to be rear heat at some point. There was a switch with white out on it, I scrapped the white out off and it read passenger heat. Ill experiment with the function of those switches at a later point.
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