After an engine swap, I'm no longer getting coolant to the heater core of my '80 pickup. The new engine was a lower miles 20R from a '79, though not necessarily the original engine on the '79. Otherwise the cooling system works fine and I've verified the following:

1. The heater inlet valve opens.

2. The heater core is not blocked.

3. The thermostat opens when it's supposed to and coolant starts going to the radiator.

4. The heater outlet hose empties to the bottom of the radiator with no obstruction.

5. The inlet hose goes from a pipe coming out the back of the from timing chain cover then though the control valve to the inlet of the heater core. Blow on it and there's a clear path through the water pump to the radiator But here's the funny thing: this is true even with the engine cranking. Whether the engine's cranking or running, nothing comes out of the hose to the heater core, explaining why there's no heat.

How can the water pump be working and coolant flowing through the engine and radiator but not pumping any water to the heater core? As I say, there are no obstructions to be found anywhere. I have the water pump out now and it looks fine, it's practically new.
Any help would be much appreciated.


-Dave

 

Something busted, simple plumbing, Toyotas are magic, but not the water inside, Gaskets installed correctly?

 

So it doesn't overheat? Everything seems to be working fine, except no flow to the heater core?

I can only figure there's something blocking it. Have you taken that metal pipe off the back of the timing cover to check it out?

 

Sounds like the doors inside the heater box are stuck closed and not allowing enough heat through if outlet hose from heater is hot with good flow?. A cable might have slipped from its bracket perhaps allowing knob to move to heat but not open door? (cable needs to move free within its jacket). Thats all I got unless theres a mouse or some kind of nest in the box I had that when I bought the truck and what a pain picking all the straw and weeds out without removing the whole heater.

If the cables are hard to move like mine was I removed the heater controls as a unit from the top just enough to lube each cable drop by drop to let it flow down. Think I let it set over night with something like WD and did it again with oil or a silicone oil the next day. The levers work well after 10 years but I move the levers at least every couple months to there stops each way. I spray some silicone on that water control valve sometimes also, that would hardly move on mine.

ps. I put a wire mesh screen before are enters heater inlet to help keep leaves and other debris out, think i used 1/8 or 1/4 inch from under dash near firwall?

 

Well he said "The heater outlet hose empties to the bottom of the radiator with no obstruction" but I took that to mean there is nothing obstructing flow...not that he actually has flow.

I mean I'm with you, if there's coolant coming out of the heater outlet, then there's coolant going into the heater inlet, and it's an in-cab heater duct issue.

But it sounds like he isn't actually getting coolant into the heater core.

 

I wonder also if the heater core is plugged with tons of scale but still flows ok ? the scale is like an insulator and wouldn't get much heating perhaps when real cold.

 

Thanks. That was going to be my next step till I discovered that the pipe is really an *inlet* to he pump, going into the pump's upper chamber, where I found a slight buildup of sediment that indicated no flow. The coolant flow diagram below agrees:

Attachment 101880

The diagram shows that the return hose from the choke heater is supposed to go the pipe. Right now the return hose from my choke goes to a second pipe that seems to come out of the cooling jacket. According to he diagram, this is actually where the he inlet hose to the heater should attach. it's possible that on the original ('80") engine, the flow to the heater core was reversed and that what I have now is two inlets to the choke heater and two outlets connected to the heater core.

Note that the diagram, which does exactly fit either engine but looks more like the replacement ('79) engine, doesn't include the heater circuit, only some flow arrows that point in that direction through some kind of vacuum valve, which I've never seen. Origin appears to be the cooling jacket.

Anyway, my tentative plan is to re-install the pump and reverse the choke heater and heater core hoses.

More comments will be welcome and appreciated, especially if you have an actual '79. Does anyone recognize that vacuum control valve?

-Dave

 

That link doesn't work for me.

I looked at the FSM for the early 20Rs to see the coolant flow, but it doesn't show the heater core connections. Only the engine bay stuff.

 

Doesn't work for me either now that it's posted. Let's try this jpeg:



I've also found no diagrams that include the heater core circuit, strange, because it's very much part of the cooling system, in spite of the name.

 

We like pics, don't we?

why ya think I like my Corvairs and VW bus, no water except for windshield washer

 

Not possible to show a pic of the plumbing to the pipes--The intake manifold is in the way, along with a bunch of hoses and vacuum lines. I had to trace the hoses to their connections by feel. We'll know later if my diagnosis correct. I'm pretty sure I know what's wrong, just not quite sure I know what's right.

Funny you mention VW. No water and not much heat, either, through that heat exchanger rig with it's rust-prone flaps. And on the fastback, the windshield washer squirter was actually powered by air pressure from the spare tire!

 

VW's had tons of heat with the gas heater, the one in my 67 Ghia sounded like a jet turbine

 

The no-coolant-heater-core problem is fixed. As per previous posts, I found that the hose connection from the choke heater core and the one from the cooling jacket were reversed. This wasn't my mistake (I outsourced the swap to a friend), but it's one I could easily have made. Both hoses are carefully formed to go the correct pipes, but because the pipes are so close together, this makes it just as easy to get them crossed.

So it wasn't any of the things that were suggested here. other than "simple plumbing" (from Shadowbirdie), but that's ok, the responses gave me things to eliminate and also got me thinking. BTW, I posted this on a site devoted to Toyota minis and got no responses at all. Then I posted them here and got a ton of them, This will be my go-to site from now on.

Thanks, Dave

 

Great.

Yeah, while you definitely get responses here sometimes that are the exact solution to the problem, it's just as often that the responses help you think of things you might not have, and eliminate them as the problem.

We can't diagnose your problem from over here on the internet. It takes being there in person and testing things. We can just throw ideas at you based on experience, and hope you figure it out. And as you'll see if you stick around, the answers people get are only as good as how well they describe the problem, the circumstances surrounding the problem, and what they've already tested. You did a good job of that, luckily.