Heater Not so Hot / Consistent
 

Resolved on Post #25


I read a few older threads on this but thought I'd start my own.

My heater can get warm, though I wouldn't say hot. Then as I am driving it can actually be cool to ever so slightly warm.

72 C10 with 2 Port Vacuum control 4 Seasons - Heater is Stock

1. Vacuum controls are tested as good, Inside door closed tight and cowl opens in Heat mode (for the record the reverse in AC mode perfectly).
2. No Vacuum to AC Type Vacuum Water valve in Heat mode- I do have a manual cut off valve inline, before the Vacuum Water valve for summer time and it is fully opened.
3. Hot Water comes from intake and returns to the radiator (just below radiator cap).

I disconnected heater holes from intake, push water through with my homes water holes and water freely moves out of disconnect heater hose at the radiator.

Just to be sure there isn't a restriction in the heater core, I am running some CLR in it now, just to be sure.

Engine is running right at 1st line on my temp gauge, if sometime slightly before this 1st line. Water temp after AC Type Vacuum Water valve is 150~160. Water temp on hose coming out of Heater Core hardly reaches 100, most times 80~90 (using laser temp gun). I do have a new-ish water pump (about a year old). I disconnected heater water hose from radiator while engine is running and I get maybe a trickle stream of water or none at all.

So, what should I be seeing (water wise) coming out of the heater core to the radiator return line? My only test I haven't done is see how the water is coming directly out of the intake. BTW, when I say water I actually mean 50~50 Antifreeze/Water that is full up.

Re: Heater Not so Hot / Consistent
 

Do you have a thermostat installed ? With out a thermostat installed water won't get hot enough to made the heater get hot and work.

Re: Heater Not so Hot / Consistent
 

Do I know for a fact, no. That would be an epic fail on my brother's part when he put everything back together after the engine rebuild.

The water that gets to the Vacuum Water valve is 150~160. I just put everything back together after the CLR flush. Which didn't help but I didn't expect it to since water was cycling through the core just fine with my water hose before the flush.

Would the thermostat effect the water flow to the heater core? I'd get that if the water wasn't getting hot enough then you'll get little to no heat but 150~165 seems ample. Right now I just don't think water is getting pushed out of the engine with enough pressure.

Re: Heater Not so Hot / Consistent
 

Well, there is one and it's a 190 one. Might as well put in a new one in there.

Re: Heater Not so Hot / Consistent
 

New thermostat installed and far as I can tell I have the engine burped from having bits apart. No change.

From the Chevy manual, water going into the heater core is the bottom (from intake) and return is the top of the core going to the radiator. I got that right, yes?

Re: Heater Not so Hot / Consistent
 

Where on the intake are you getting the supply from? There should be way more than a trickle coming out of the return hose at the radiator. 150-160 should produce some heat but isn’t going to be really hot. With the 190 thermostat in my K20, it will roast you out in no time unless it’s way below freezing out. Sounds to me like you may have the heater hose on the intake plumbed in the wrong place. It should be supplied with coolant from the passenger side front pipe bung of the intake.

Re: Heater Not so Hot / Consistent
 

Well, been burping more and I ended up just shooting my water hose up into the return line to force water up into the core and then waited for water to pop up out of my cap hole in the radiator.

Sitting idle in the drive way my laser light says I am getting 105~110 at the floor vents now.

Photos attached, red is hot from intake to core and the teal color is water from core to radiator.

Edit: I did go with a 180 thermostat, read that is what our SBC are suppose to be, 190 was for later on? I haven't fought any over heating and my temp gauge has happily been at the 1st mark, some time just past it.

Re: Heater Not so Hot / Consistent
 

Maybe check the vacuum line routing and type of valve. A 72 truck would typically have heat/ac control with the three port vacuum switch and a normally open heater hose shut off. Normally open vavle, one with the bracket.
67-70 was two port and normally closed valve. Normally closed valve does not have bracket.
There are threads that have the hose routing diagrams. See if I can dig one up.

Re: Heater Not so Hot / Consistent
 

I have seen those and I have a two port, all that checks out. The water valve is normally open and will close under vacuum (when AC is turned on). I have also tested this today with a vacuum pump - that is all good.

This also tested good when engine off and I shot water up into the return line from my water hose, which forced water up into my core, into my engine, and out my radiator cap hole.

Oh, this is also why I have a manual cutoff valve for summer time - I really don't trust that hot water valve to be completely closed under vacuum (thought it tests pretty well with a vacuum pump).

Re: Heater Not so Hot / Consistent
 

Okay. Guessing you understand the hose routing must be modified from the factory two port diagram to use the n/c valve with the 2 port control.

Re: Heater Not so Hot / Consistent
 

Will this help?

Re: Heater Not so Hot / Consistent
 

I am not sure what you are saying there. This part of the truck (heater / cab controls) came to me like this.

1. two port vacuum dash controls
2. Inside Passenger Vent, Cowl Vent, and Heater valve actuate under vacuum (triple checked as operational).

Far as I know that is factory operation for a 2 port vacuum port controller. Now is that how my 72 C10 came from the factory? No idea but it is what I have :-)

This is my Truck's setup, Two Port Vacuum Dash Control
http://67-72chevytrucks.com/vboard/a...1&d=1448761541

Re: Heater Not so Hot / Consistent
 

Hi Accelo - thank you but I have that, basically beginning of the manual. Though I only scratched my head wondering if there is any difference with AC (since the diagram examples seem to be a Heater Truck only). Anyways, for the heater water holes, that is my routing :-)

Re: Heater Not so Hot / Consistent
 

I have seen ( most rare ) an impeller that slips on the water pump shaft so you don't get a water flow that is up to par.

Re: Heater Not so Hot / Consistent
 

Well, that would suck if I had that problem- hardly a year old water pump. Though I'd image I would have over heating problems too with that problem?

So did a test drive, same one I did this morning that is mix 30~70 mph. More than 2/3 of the drive I pretty much maintained 105~110 temp with my laser gun coming out of the bottom duck. Then when I was getting close to home my heat dropped to the 80s.

Makes me wonder if there is something flaky with the vacuum valve or trash in it. When I got back in the drive way, I cycled back and forth between AC to Heater a few times and got back up to over 100.

For the record, my dash Temp gauge doesn't much past 1st mark of "C". It just kind of hovers there at that 1st mark moving back/forth on that mark.

Re: Heater Not so Hot / Consistent
 

Dumb question (sorry) but I'll ask anyway. The manual shut-off valve in your supply hose from the intake manifold (your post #7). As pictured, the handle is perpendicular (90 degrees) compared to the hose. *If* that's a ball valve, that would likely be the 'off' or closed position. 'On' or open, the handle would be in line with the hose. Don't shoot me, I had to ask. :chevy:

Re: Heater Not so Hot / Consistent
 

Do you think there is any chance you might have a mouse nest or leaves down inside your heater box that could be interfering with the heater door? There have been multiple threads about that issue. It wouldn't explain the lethargic water flow through your heater core though.

Re: Heater Not so Hot / Consistent
 

I don't think that would apply to this valve, close up is like the photo attached. But I don't know.

All nice, clean, tidy - no obstructions at all from cowl on down into the box and through the passages in the cab.

Re: Heater Not so Hot / Consistent
 

In that last pic it appears to have a threaded shaft so probably not a ball valve. Just make sure it's open (handle turned all the way counter-clockwise) so I can stop thinking about it. :lol:

Re: Heater Not so Hot / Consistent
 

100% threaded and fully opened. Also today I have cycled closing / opening many times.

I did have a lever/ball valve and it was horizontal but I had someone comment it looked out of place. So I replaced it with this type of valve, which I believe was in earlier chevy trucks for a heater cut off (no vacuum control shut off I think).

Re: Heater Not so Hot / Consistent
 

This isn't exactly scientific but maybe worth a try. With everything warmed up and heater on, grab the water hose where it leaves the intake manifold. If water is flowing it should feel fairly hot. Next, feel the hose between the manual shutoff valve and the lower nipple of the heater core. Should feel about the same temp. Now the hose between the upper heater core nipple and the radiator. It should also feel pretty hot. Any of those hoses feeling cooler would indicate a probable restriction.

Re: Heater Not so Hot / Consistent
 

Well something has dawned on me thinking about the heater throughout the night and letting it sink in that the stock heater valve is normally opened (no vacuum needed to open it). When I cycle the dash controls and go into AC and back to Heat, I start to get heat at the floor again (sometimes it takes a few cycles).

@Stocker - I did some feel testing earlier (lines get hot / read 150+ via laser), which is why I thought I needed to flush the core out (did with just water, then CLR) and then moved on to seeing if I had air trapped (burping the radiator).

Perhaps something is going sideways inside this doodad that lets various amounts of water through but always enough to read a hot line going into heater core. Assuming O'Riley's is telling me the truth, I'll have one tomorrow late morning. I needed to use a $5 awards anyway before loosing it.

Re: Heater Not so Hot / Consistent
 

It's a puzzler for sure. Gonna be interesting to see what the culprit finally turns out to be!

Re: Heater Not so Hot / Consistent
 

Yay, forums are up again, been down all morning!

I took off the vacuum heater control valve.... it's dodgy.

1. No Vacuum ~ 4 hg partially obstructed, around 20~30%
2. 5~7hg 100% opened.
3. 8~9 hg Completely Closes

I put in my ball valve for a valve bypass, laser temp is 140~160 and steady at ~150 whilst driving around at speed.

This is why I'd get some good heat whilst moving the AC/Heater controls, as vacuum was being applied I'd get some water flowing. When testing with a water hose yesterday, I guess it is pushing so much pressure it would seem there wasn't any obstruction. Hopefully O'Riley's will have my part on time and I suppose I'll know how a new one operates. Though the one on my truck now was supposed to be new when the AC was upgraded to 134r after the Engine rebuild.

Re: Heater Not so Hot / Consistent
 

Okay, the new O'Riley's Murray MRY-74610 Valve is working and keeping me at the same temp as my bypass. During my test drive I'd say average was 155-ish.

Though it is also slight restricted too and is completely open/without resistance to be blowing through it at 5~7hg vacuum. I am not really impressed with this little valve at all. Perhaps GM's was 100% opened at 0hg vacuum... I have a feeling this thing is going to crap out again like the one I replaced....