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1977 K5 blowing lukewarm air, Heater core problem or something else?

A

Ancient4X4

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Hi guys. I'm thinking of taking my K5 to the Radiator shop to have the heater core flushed.

In July of 07' my waterpump cracked. I had my mechanic replace it with a new one. The truck seemed to run a bit cooler. But this was in the summertime, so I thought it was great. Then came the winter, well the truck just did not warm up barely above cold. We had a fairly mild winter last year, so I never really got around to looking into it more.

The previous 30 years of its life, it used to warm up to just below the second line on the temperature gauge, now it barely goes above the first line. This morning I had to drive it, so I took it down to the shop. I talked to my mechanic that installed the water pump originally. He said to try a new thermostat. So I installed a new one, but I get the same luke warm air and low temperature. I took it back later this morning after installing the new thermostat. Not really knowing what I'm talking about, I asked him if maybe he installed a "too efficient" water pump. He said that it's gotta be the heater core and that the water pump couldn't have anything to do with the low temperature.

What do you guys think? I trust the mechanic I use, both of them really know their stuff about these old trucks. But I still think somethings not right. Any suggestions? Luke warm air sucks (windows don't defrost properly) and the truck just doesn't seem to be heating up right :doah:

I should add that the heater in this truck use to just about torch me out of there.
 
what temp thermo did you put in? and is the fan blowing good maybe the selector is not opening the hot and cold air diverter properly or all the way. Are the coolant lines on the motor corectly for the heater core or maybe they got switched when the pump was changed?
 
The previous 30 years of its life, it used to warm up to just below the second line on the temperature gauge, now it barely goes above the first line.
Click to expand...

If the temp guage doesn't show the motor warming up, it has nothing to do with the heater core. The thermostat is the only part that can cause this problem. More than likely the mechanic needs to redo it under warranty as you probably got a defective one or it was installed wrong.

When he replaces it, be sure to use a quality brand like Stant or AC. Don't let him use the cheap crap sold at the discount parts places.
 
Guys, I really appreciate your input. That's exactly what I was thinking, that the heater core doesn't have anything to do with engine temperature.

Believe me, there's no warranty, this is a 1977.

My dad used to run a 195 in it. I believe the one I removed was a 195F as well. The one I replaced it with was the one that NAPA sold me two years ago. Probably a 180F. But this made no difference, it heated up just the same, very low.

It still wouldn't heat up with the old thermo (I believe 195F) anyways.
 
Ancient4X4 said:
Guys, I really appreciate your input. That's exactly what I was thinking, that the heater core doesn't have anything to do with engine temperature.

Believe me, there's no warranty, this is a 1977.

My dad used to run a 195 in it. I believe the one I removed was a 195F as well. The one I replaced it with was the one that NAPA sold me two years ago. Probably a 180F. But this made no difference, it heated up just the same, very low.

It still wouldn't heat up with the old thermo (I believe 195F) anyways.
Click to expand...

The warranty he implied was for the work done on your 77. Also, check the cables that adjust the temp from your heater controls, possible they have been stretched or broke, not allowing max heat.
 
Here's a cellphone pic of my temperature gauge at full warmup. Normally it would just about touch the second white line.
Click for a bigger pic:

 
If you did the work, no there wouldn't be a warranty. But you made it sound like a mechanic did the work?

Either way I'd still go back and try a new thermostat again. Be sure you get the 195* Stant or AC. It seems like 50% of the cheapies fail during install :doah:

Another thing to try, put cardboard behind your grill and block 75% of your radiator. See if that makes any difference.
 
kennyw said:
If you did the work, no there wouldn't be a warranty. But you made it sound like a mechanic did the work?

Either way I'd still go back and try a new thermostat again. Be sure you get the 195* Stant or AC. It seems like 50% of the cheapies fail during install :doah:

Another thing to try, put cardboard behind your grill and block 75% of your radiator. See if that makes any difference.
Click to expand...

I installed the new thermostat yesterday morning. A new NAPA part.

My mechanic installed a new water pump in July of 2007.

It used to have a vinyl type radiator shield that could be snapped on in the winter, but the snaps broke last winter. Honestly, it never needed it, it ran plenty warm without it no matter the temperature, -20F whatever, once it warmed up. I only started having this problem since the new water pump was installed.
 
Is the engine itself actually that cold? I know what the gauge says, and what it used to say, but have you verified the engine stays that cold?

At that temp I'd expect the upper radiator hose to be cold enough to hold onto, and little to no pressure if you pop the cap. (be darn careful trying this though, of course) Squeezing the upper hose would give you some idea too.

As already mentioned, in a properly working cooling system, the thermostat governs the engine temp, nothing else. That's why I'd want to verify that the gauge is right, first, so you know to focus on either the heater setup, or the engine itself.
 
hey there im sure u know but i have a topic of NEED MORE HEAT going also but i have a after market gauge so i cant comment on your gauge. but my truck all the hoses are hot to the touch, i did also put a new 195 t-stat in yesterday and not a big differents? is not near as cold here. but going to pull the lower vent out and look over the doors(flaper) maybe i look over something? also like i said the hose are hot! and i have good pressure when the cap is on.
 
replace the temp sensor it may be coroded and not regestering the temp correctly. That might get the gauge to read more accuratly
 
mnstrburbon said:
replace the temp sensor it may be coroded and not regestering the temp correctly. That might get the gauge to read more accuratly
Click to expand...

I'm sure it's displaying the temperature properly as it only began displaying slightly colder temp when I started having a problem getting heat from the vents.

At any rate, the hose and radiator still gets hot to the touch.
 
Are you sure one of your heater hoses didn't colapse? I don't trust stock gauges, so I will stay away from that, but I know when my Blazer gets the hoses hot to the touch, there is plenty of heat coming out of the vents. It won't roast you out of the truck, but it will blow warm air.
 
there is some good points here,I had the same issue with my 77.

First off I did live in Las Vegas and I had to deal with high temps so It had a 180* stat and a 4 core radiator in it I moved to wv 2 years ago and never had heat in my engine that would produce heating the cab .

I had gotten into a thread about this last year and never followed up on it with everyone:doah: Busy I guess

What did was verify that in deed the engine was not hot enough,Although my gauge did tell me this,So I tried a 195* and there was not any difference just took longer to warm up as much as it will,Still no heat.

so my finding is that I ended up covering up 1/2 of the radiator and good to go.It gets around 14* down to -1 at times here.

The only thing is its a pain in the a$$ to cover and uncover so now I got a idea to do this from the cab with out getting out to do this.

As soon as I get time to do it ill post up with pic ect stay tuned.

On another note please make sure the core is not blocked,No water in and out no heat.I had installed a new one because it leaked.

I also want to install a block heater all so to keep it kinda warm in winter.


Mike
 
The hose to the heater core is out, I think that's what the problem is. I've been losing anti-freeze and that's where it's been going.
 
Nope,that would cause it to overheat shortly after it warmed up in most cases..

I'd ensure the engine coolant IS getting up to 195 degrees by using a thermometer or a heat sensing gun ,then if thats OK,feel the two heater hoses ,if one is a lot cooler than the other its a fair bet the heater core is clogged up,or perhaps air is trapped in it...also many tricks wuth A/C have a hot water shutoff valve one of the heater hoses goes onto,that is plumbed into the intake manifold..its contolled by vacuum,ensure it opens and lets hot water flow through it,and its getting vaccum when its turned on (the heater temp control on the dash controls the vacuum to it)..

Sometimes when aftermarket intakes get swapped on,heater hoses end up getting put where they weren't before ,that can lead to problems too--you need one hose to be on one side of the water pump and the other on the intake or on a nipple made into the radiator tank,to get enough flow through the heater core..

I saw one car,a Chevy Citaion,that refused to warm up to normal operating temparature after the owner switched to synthetic oil!..he tried new thermostats,etc,but it never came up over the 1/4 mark on the gauge,and a thermometer test verified it was running at about 165 degrees,with a 195 thermostat..he tried putting conventional 10W-30 oil back in it and his running too cool problem vanished!..but thats the only time I've ever seen or heard of that happening,I suppose its possible the oil lubed it "too good" and reduced friction so much it couldn't heat up..he never found anything else to blame!.
 
I finally got this resolved last spring. Was actually just a bad heater core and a coincidence that it happened when the water pump cracked, just thought I'd update this thread.
 
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