Heater output is lacking, brrrrrrrr!

TDS 854X4 · January 7, 2002

Hey all!

I'm in need of some help troubleshooting my heater in the '85 pickup.

I'm not getting much heat, but there is a little. I have replaced the heater core a couple weeks ago, and this past weekend, put in a 180 deg. thermostat, new coolant, and decided to put new upper and lower rad. hoses while I was into it.

Even after all that, I'm only getting semi-warm air coming out of the vent. I drive 30-45 minutes to work in the morning, and running the heater on high the whole way, it only gets up to 58 in the cab. I don't have any leaks or the windows open ;) .

I simply drained the fluid from the rad., and the hoses when I replaced it, I did not power flush anything. I don't have a temp gauge in my truck, (just a helpful light ), so I don't have any idea what temp the engine is running at, but the upper hose feels nice and warm, and I feel the heat on the radiator cap for what that's worth.

Any ideas??????

Torque Junkie · January 8, 2002

What's your engine temp doing? Is it staying cold too or is it warming up to normal operating temp?

If it's not warming up, then, well DUH, it's the thermstat sticking open again.

If the engine is warming up, then I wonder if it's a clog in the core preventing warm coolent from flowing thru it........ Anyone else?

-Mike

95Yukon · January 8, 2002

Once its up to temperature, feel the hoses going in and out of the heater core. Since you just changed it, that should be flowing fine (both hoses roughly the same temperature would indicate good flow) If they are both hot, theres good flow and its just a matter of air not being directed through the core. Check that they are at least warm.. if not you may have a weak water pump, which is moving enough through the radiator, but not enough through the heater core or a restriction. Check if you have one of those restrictors for the waterflow on the heater hose. That may be not working or restricted. Assuming the coolant is actually coming up to temperature, which is seems to be, as indicated by the top hose getting hot, (you can check for sure by putting a suitable thermometer in the coolant as it come up to temperature..) If its okay, theres either a flow problem to the core, or..

The flap which directs the hot/cold air mixture isn't shutting all the way, allowing cold air to mix with the warm. (just like if you had the hot/cold control in the center setting) Iv'e gotten into heater problems before and totally overlooked the obvious.. Now you say its an 85..did that year still have the cable type slider going from hot to cold control? If so, I've seen these go out of whack and never go to full hot mode. If that's the case, theres a little metal clamp at the remote end of the cable which connects it to a small lever. Have someone slide it from hot to cold while looking under the dash to locate it, then when its in the hot position on the control, continue the movement of the lever to see if it is traveling the full distance. If not, you can simply adjust the clip where it goes on the steel cable and slide it over to where it belongs. Sometimes you can tell if its out of whack if you slide it to cold and you can hear the little flap door closing at the other end. Sorry for the long post, but if you check that and the flow through the heater hoses by feeling their temperature, you should be able to hopefully get it working again.

95Yukon · January 8, 2002

Oh..and also, if the heater hoses seem cooler than they should be, you may also want to check for a blockage at the nipple of where the heater hose connects to either the intake or the water pump. Iv'e seen a lot of those get a little bit of crud in them and it causes a restriction, since the internal opening isn't very large, and they tend to rust out from the inside. If there isn't a mechanical steel cable connecting the hot/cold flap, it may be vacuum controlled so check for a small vacuum hose not connected or it may sound like a hissing sound under the dash. If it's one of those, there will be a small round black vacuum reserve under the hood on the passenger side on or near the firewall. There will (should) be a single small vacuum line connected to it. I've seen these crack and/or fall off and the hot/cold flap ends up in whatever position it was in when the vacuum hose fell off. From what I can tell, that one small hose runs all the vacuum actuators for the heater/AC system. (one of which may also have ripped or failed, if you have that type system)

Good luck..let us know what you find

TDS 854X4 · January 9, 2002

My system is controlled by the cables instead of the vacuum, that was only if you had AC. I feel good warmth on both hoses to the core, however from another board I frequent, there is some thought that the hose routing might be incorrect. I find that possible, but not really likely. I do get cooler air as I move the lever to the "cool" side, and it is warmer as I slide it to "hot", but I was thinking the same, that maybe it doesn't go FAR enough?? I checked the door operation while I had that cover off changing the core. I'm hoping to get back at it this coming weekend.

Thanks for your posts.

95Yukon · January 9, 2002

It's got to be that little flap door. If both heater hoses are hot, that would mean theres hot water flowing through your heater core, so its just a matter of getting all the air to flow through the core now.

Adjusting the clip on the end of the cable should hopefully fix it.

76BBSub · January 10, 2002

One other possibility, though doubtful, is that there's one of those vacuum operated shutoff valves inline somewhere on the heater hoses. These are common on '70-'82 Corvettes, don't know about the trucks. What they do is shut-off the water flow into the heater core unless the selector is on "heater", thus opening the vacuum operated valve. Something to look for...although I tend to agree it's probably the little flapper door.

Jeff

TDS 854X4 · January 15, 2002

Nope, definitely no vacuum operated anything in the heater hose. I haven't had a chance to get back under the dash yet. ( I really hate working halfway upside-down and hanging out the door of the truck) ( and I can't even fit the thing in my garage all the way) :angry:

Actually, I had a friend along for a ride the other day, and he said there was a pretty good draft coming in around the weatherstrip on the pass. side door. Well, I never go over to that side, so I haven't felt it "first-hand", but that might also have been a factor. I'm going to start with the operating cables, and work from there.

Thanks for all your replies!!!

Luckily, the weather has been warmer than a usual MN winter. I've just been dealing with it so far.