@racsan Guys here gave me great instructions about poor heat. I had no thermostat at all in mine when I got it. Put in 190-195 thermostat w/ new gasket per instructions, to start off, and did back flushing with hot vinegar, also, reverse the heater core hoses after. Mine was under 100F before I started and after the work it was topping 130F. Measurement depends on having the engine fully warm also depends on ambient temp, but absent any specific figure, it should feel quite warm and should warm up the cab pretty quickly. I think the spec is 130-135, but the main thing is you should feel it really warm as there's a big difference between 100 and 130.
Changing the thermostat in mine didn't help that much (got like 110) and that's when I did the flush, which really worked.
Can also be other things wrong but from what you said, you have to start with the right thermostat and get the system clean. Take off radiator hose at bottom and flush the engine and radiator too. Do enough flush that you see basically clean water coming out.
Test the coolant with bulb tester after, some water remains in the system so you might want to top off with non-diluted antifreeze.
Get 5/8" hoses from store or you can use scrap garden hose if i.d. is ok. I run a piece from the core down under the truck then I can see what is coming out. Get white vinegar at the grocery store and heat it up in the microwave. I flushed reverse and forwards a couple times and I could see all kind of crap coming out.
When engine is warm it should read, I believe, almost half in the bracketed range.
There are a bunch of posts on this you can find, but I think I covered most of it there. Oh, you probably want a rubber cork so you can stop up one side of the core so you can leave the hot vinegar in there like fifteen minutes to work, then put on the hose and flush. Drain hose to under truck not necessary but really nice so stuff doesn't go all over the place.
Other really good thing to have is a hose clamp pliers, that will speed things up, the ones that have the ratchet, it makes it super easy to manipulate the clamps on/off and they don't slip off the clamps like slip joint pliers do. Also have a funnel to pour the vinegar in a short hose connected to the core.
When it's working right you should feel a noticeable difference in temp between the in side and the out side of the core, otherwise, it's not pulling heat out. Core is non-directional so flushing reverse is what you want to do... I flushed both ways... then connect them up reversed.
I also had to replace heater fan resistors as I had only high speed but that's easy to do, though I did have to replace the pigtail as connectors were shot to h. Nothing to do with the heater core, but it's nice to not have fan always on high.
If your core is clean/working and your thermostat is good you should then have heat. If not, check heater mix door operation and that valve that allows hot water to core is working. Chances are all that stuff is good on yours (we hope) and if you get the thermostat in and the core clean, I bet you'll have nice heat.
With things off you can actually hear the mix door moving, also, when running, you should feel it make a difference hot/cold in it. But first, I'd do the thermostat and good flush before worrying about anything else.
Hope that helps, and like I said there's a bunch of posts on it from the guys that gave me the good instructions that worked great.
Also, some settings of the vents cause the a/c to dry the air first, but if you put it on dash vents only I think that does not go thru a/c first. Just mentioning that as it might affect the output temp somewhat.
Other guys here know more about it... but following what they told me to do, mine works great now.
Probably you want to take off air tube when you change thermostat, might not be necessary, but makes it easier. Clean off any old Permatex-type stuff someone may have put on it. New gasket should seal fine, of course, check it for leaks... I changed that out and tested for leaks prior to doing the flush so I wouldn't waste good coolant, though, you really don't lose a whole lot in the changing of it, I think.
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