heat

[OPELFIEND]

I have heat only at idle. Fire the thing up in the morning, nice heat blowing out once it comes to tempature. Jump in, it's warm. Once I get moving, the thing only blows luke warm or totally cold air. Freshly recored radiator, new heater control valve, flushed heater core, adequate coolant, new thermostat. Flushed out heater hoses, etc. Cars runs at the correct temperature. Thoughts?

[wrench459]

Originally Posted by OPELFIEND I have heat only at idle. Fire the thing up in the morning, nice heat blowing out once it comes to tempature. Jump in, it's warm.

Warm.. not hotter than you know what.
I've seen vent temps of over 140 degrees with a good heater core.

[OPELFIEND]

Right. Not hotter than the hubs of hell, just warm. Would it be the heater core? I really have no reason to think that it is; there's no leakage anywhere and I've flushed it well. Car has been well maintained, no rust. As I understand it, it's usually rust with the core. I don't know what else to check out. It's a 70 model. I have a 73 that will cook your a$$.

[yellaopelgt]

Is it possible that the under dash vent hoses have fallen off or rotted and your not getting the full effect? Now that I think about it...not one Opel I've ever been in excactly threw toasty hot air. Enough to keep the windows clear and thats about it. Just a crazy off the wall thought but, are the door and window seals on your car tight?
Joe

[Gary Sullivan]

I had a 69 GT with symptoms which sounded like what you describe and I was getting only a trickle through the heater core. If it is the core which is obstructed I would move heaven and earth to try to flush it in place, as I changed out my core with a new one. If you can avoid going to that length, that is a pretty big job (dropping the steering column....pulling the dash...etc.,etc....lots of fun)
This may sound cockamamie, but I think I would pull off those hose connections....adapt a garden hose to the heater core inlet and gently try to gauge what flow you can get going through the heater core. I say, very gently, as you don't need to discover the Colorado river in your passenger compartment.
Perhaps you could win on this with a careful flushing. Just my thoughts.
Gary

[Itsa '70 GT]

Have you checked your water pump? I had these exact same symptoms on my domestic ride and the water pump was the culprit...the heated coolant is fine as long as you're at idle, however once engine demand comes along, you're left in the cold (no pun intended!), because nothing is cycling and there is enough air flow cooling everything else so that you won't register an overheating problem. Hope this helps....

Best regards,

Bill

[Gary Sullivan]

I don't how stock your hose "plumbing" is, but you could also have air in the system. And sometimes I have forgotten to make certain the radiator was topped off after a cycle of filling it, letting it cool down completely then topping it off a second time, so the system is actually full (And some cars you need to top off a couple times).

[kwilford]

Are you sure the heater control cables are attached properly to the heater box itself? The slide control for the coolant valve has two cables that come from it. One adjusts the valve, the other opens or closes an internal air bypass flap below the heater core. Slide the lever for more heat and the bypass flap closes, forcing all the incoming air through the heater core. Slide the lever for less heat and the bypass flap opens, allowing incoming air to bypass the heater core. The more towards "cold" the lever is, the wider open the flap is. Perhaps the cable broke or fell off the bypass flap lever?

[West Coast GT]

If you're getting warm air at idle and cool air when the car is moving, then it sounds as though your cooling system is too efficient in addition to having minimal flow through your heating circuit.

Double check the temp rating on your new thermostat.

Just for sh_ts & giggles, try placing some cardboard in front of your radiator temporarily and go for a drive. See what happens and get back to us.

[heimue]

Since you mentioned it gets hot (or warm enough) at idle, I don't see the heater core being bad. Two suggestions came up that I can see being the problem: Cold air coming in while driving, and a bad water pump (maybe combined with a thermostat that is frozen in the open position, but that is not too likely). Feel for cold air with your hand while going on the highway.
Maybe it would help to close the windows???

Dieter

[OPELFIEND]

I flushed the heater core as much as possible, until crystal clear water comes out. The heater control cable is broken, however I manually open the valve all the way. And, it's a new valve. Wouldn't the water pump make a noise if it was bad? That's been my experience. I didn't replace it, but it looks fairly new from the PO. Not making any grinding noise or anything. The heat will come out really well for a time, then cool off, then maybe luke warm, then totally cold. I've checked the coolant level several times after driving the car and then letting it cool, and it appears to be full. The best heat is while it's idling. Other than hearing the water pump, how do you tell when it's bad? I mean, the car runs at a good temp, right below the half way mark on the gauge. It's not cold air coming in, it's cool air being blown out. And, the windows are up! Thanks for the help on this. I'm lost.

[BQS4]

a couple of thoughts here, you're right about a water pump not making a noise, but, it can still go bad. The way I tell is with the motor off, grab the center of the fan and see if you can get any movement, radially, out of it. Any movement and your pump is going, but, that may not be your problem. You say it's a new thermostat, what temp is supposed to open at? At idle, it'll be warm, but, at speed, and not at the correct temp, it'll be cool. You can check it by putting it in a pot of water, and heating the water, have a thermometer in the water to check the temp. Also, have you got all the air out of the cooling system? Kinda like your brakes. You can have the thermostat housing top drilled and threaded for a bleeder valve to release the air in your system.
JMTCW

[kwilford]

Originally Posted by OPELFIEND The heater control cable is broken, however I manually open the valve all the way. I'm lost.

There are none so lost as those that will not read...
If the cable to the bypass flap isn't closing it, then the incoming COLD air readily bypasses the heater core. I am at work so can't look at my heater box, but IIRC, the shaft and arm that the bypass cable attaches to is on the passenger side, near the bottom of the heater box. Try sliding the temp lever back and forth to see if the bypass flap is moving. If the shaft doesn't rotate with the cable, try disconnecting the cable and rotating the shaft with a pair of pliers and see it it helps.
HTH

[markandson]

I agree, sounds to me like you have cold air mixing with the hot air when you are moving. The flap valve is probably not closed and allows outside air in which tempers the air coming from the heater core.

[P.J. Romano]

I had identical symptoms (warm air when idling, cold when moving). I fixed it by adjusting the heater valve cable, allowing the valve to fully open. Still, the heating was just a luke warm until I replaced the 160F thermostat with 180F thermostat.
It was a great, dry, sunny but frosty day the other weekend in South Ontario. I decided to pull the car from the garage. Cruised down the Huron Lake beach road with my wife. The heating was excellent. The heater fan was at low speed, never needed full blast.

[OPELFIEND]

I flushed the heater core once more, took off the control valve and cleaned it out as well. There was a bit of crud in it. Put it back together, and PROBLEM SOLVED! Heater is working well. Thanks for all the input on this. Much appreciated.