87 Heater Problems

[Rick]

I've got an '87 3/4 ton with a 350 (first year with fuel injection afaik).  The heater doesn't really put out like my '85 did.  One major difference is that on the '85 is that the heater hose came off of the water pump.  On the '87, the supply to the heater core comes off of a pipe on the back of the intake manifold.  The thermostat is about 3 years old, I may consider replacing that.

Water does go in and comes out of the heater core, so I don't think that's the problem.  I don't think there is a lot of water pressure coming out of the back of the block, but I don't know if that matters much.  

I'm not sure of the purpose of the water outlet on the back of the block is for, but I'm considering redoing the heater lines by moving the supply to the heater core from the back of the manifold, directly to the water pump and putting a 'Y' in on the outlet side so the outlet on the back of the block will join up with the outlet from the heater core and return to the radiator.  Or maybe I can just plug that outlet on the back of the block.  

Looking for any advice/suggestions.  

[VileZambonie]

Outlet on the block? You should have a hose nipple on the intake manifold as the inlet to the heater core. The return can go to either the waterpump or radiator (whether it's auto or manual) and yes replace your thermostat.

[DnStClr]

Yes, Rick. The inlet comes out of the intake manifold next to the distributor.

[Rick]

I replaced the thermostat, ran the truck a good 15 miles. Not putting out a lot of heat.  (Later tested the old thermostat in a pot of water - worked fine).

I then proceeded to check the door control to ensure it was moving and determined that it is moving all the way to its limit.

Then I checked the water flow out of the block thru the heater core and into the raidiator - barely a trickle.  Revved the truck up, flow picked up a little bit, but not appreciably. 

I have a tee connection for flushing inline between the heater core and the block.  Connected a hose to that and there wasn't enough pressure to force water from the tee to thru the hose into the radiator filler.  At the time, the upper main radiator hose was hot (thermostat should've been open).

I'm not sure how much water pressure there should be at the back of the block going through the hater core should be, but I'm assuming that it should be more substantial than it is.   So right now, I'm thinking either the metal pipe that comes out of the back of the block is clogged or the water passages are clogged in the intake manifold.   If I'm wrong about how much flow there should be, then it may be the heater core. 

Has anyone ever seen the outlet on the back of the mainfold or the hose get plugged?  I'm not above pulling the parts off and pulling the manifold if needed, but I don't want to waste a lot of time just guessing.

Thanks

Rick

[brownie]

I have seen that outlet rust out the one on the back of the intake that feeds the heater core, you might want to back flush the heater core if you can ,also you can pull the heater hose and see if you can get a coat hanger thru it down near the manifold to see if it is clogged water should be coming out of it at a pretty good pace, is the truck overheating ?

[Rick]

No signs of overheating, except once in summer when it was 90+ and high humidity and I was pulling a heavy trailer.  Main hoses flow pretty well. 

I'll drain down the system and try getting the connection off of the back of the manifold and see if it's filled with gunk. 

[VileZambonie]

If you have no flow out of the bypass side of the circuit and your passages aren't plugged pull the water pump.

[Rick]

If you have no flow out of the bypass side of the circuit and your passages aren't plugged pull the water pump.

I replaced the water pump last winter, truck had same issues last year with heat as well.

[Rick]

Update:  pulled the tube from the back of the manifold, determined that it is somewhat clogged with rust (outside of pipe is bubbled up).  Now it's time to find a new manifold to heater core metal tube.

[Irish_Alley]

metal they should be rubber

[VileZambonie]

TBI engines had metal/rubber pipes and quick connects on the inlet

[brownie]

I think you can still get them at the dealer.

[BigBlue]

FWIW: You can buy the metal quick connect piece that screws into the back of the intake at most auto parts stores now. I know my local Napa has them.

[Irish_Alley]

i wasn't thinking at all last night when i was typing anything forgot all about the "quick" connects at autozone. but i haven't really worked on a tbi for a good bit

[Rick]

Thanks for all the help, I now have good heat in the truck.  As it turns out, the metal pipe was clogged. 

There was indication of internal rusting (outside of pipe was bubbling up).  I tried several local auto parts stores (NAPA, Autozone, etc) as well as some recyclers and nobody had the part.  I couldn't find the part online and I didn't bother with the dealer.

Since the tube was clogged near where the rubber hose was crimped onto it, I decided to cut the pipe before the damaged area and attached a new heater hose with a hose clamp.  There isn't so much pressure on that I'm concerned at all with any leaks.