Ok, I know that this has been hashed over tons of times on CB.com, and I have found the same answers there or received the same answers when asked previously. So now I am gonna put it to you guys. I freeze my arse off every morning. Here is what I do know...
#1 my heater core is clear, nothing clogging it. I have flushed and refilled several times in the past couple of winters, including this one.
#2 I have a 195 t-stat.
#3 I've got natural A/C going, but it isn't too bad that I can't stand it.
#4 I have done the Chebby motor upgrade
#5 when under load (going up hill), I get some heat, but when I am under light or no load (cruising or at a stop), the heat almost cuts out completely.

Gimme some iders how ta fix'r up fellas. I've been thinking about getting one of those cigar lighter adapter heater do-hickeys. Something to just take the edge off, but I know that my heater should be doing better than what it is right now.

When is the last time you checked/replaced your water pump?

I've had the same problem. My guess is the answer your getting is to cover the radiator?

I can let mine idle and warm up to around 180-190*. As soon as I am headed down the road at 30mph or better, it starts to drop off and when going fast enough, will peg the bottom end of my meter at 130*. If I put some cardboard in front of the radiator, I can get it to stay at temp, but be careful you don't put too much and make sure you take it out when working the motor hard.

I've chased the problem with new t-stats etc to no avail. I figure it's a good problem to have... But I don't drive mine daily either.

J.D.

Make up one of those grill covers like the big rigs have that you can zip up and down to open and close as needed...

I have to use the cardboard in front of the radiator trick in the chebby s-10 company truck (truck? hahaha).

Just have to remember to take it out when it gets warm.

No pictures of the hoses Dan, but I haven't replaced them since I had the engine rebuilt 8 or so years ago.

Mike, water pump was replaced then too & I've never had problems.

JD, yeah, I've got the "cover the radiator" answer before as well, and mine does exactly the same thing yours does, drive down the road and it cools down right nice. Great for the summer, but not so much for the winter.

FWIW, I can cover 1/3 of my radiator and that is fine for driving around town.

Are you certain you are getting coolant flow through the heater core ?

The inline valves are famous for rusting shut but the cable / mechanism still works.

Rox - my valve is rusted open. Summer is a real toe cooker in my rig because the water is always in it. I need to breakdown and get one of those ABS valves that BC sells.

I get it pretty much under load and going up hills. I'll look at the lines and see if there is a high spot in them. I never really thought too much about that.

Air leaks around the heater core can really reduce the temp coming out of the fan. There are seal kits for the air box. Leaves and stuff can also block the airflow through the core. You can take the bad valve out (could be clogged) and get a spigot or ball valve from the hardware store.

Gary, don't take this the wrong way, but are you sure you're working the valves/flaps the right way? I've seen lots of guys (me as well, back in "the day") get it wrong.

A reminder:
The center fan/temp gets pulled out to allow heated water into the heater core so it can work.

The right knob pulls out to allow the heated air to exit the center section around the motor/squirrel cage. I have seen guys that do the Chevy upgrade get this put back in so it doesn't open all the way.

The left knob is a vane that diverts the heated air toward the floor or towards the defroster vents.

If you want a better heater, the Mojave Heater and similar really do work very well, but take some fab to get working well with the defroster vents. The Mojave heater and an electric defroster work pretty well around here.
HTH, Joe

I had one of those "fail safe" thermostats in mine for the last few years. Every so often, the water would really heat up after I turned the engine off and cause the thermostat to lock open. When that happened, it acted just like you're describing. Almost no heat unless I was really working the engine.

The 3rd time this happened I bought a new thermostat (non failsafe) and swapped it out.

Does your engine temp gauge work? What temp do you usually run? Do the heater hoses feel hot after fully warming the engine?

I'm running a standard fan, shroud, standard radiator, etc. Temp guage can get as high as 205 and as low as 180 depending on speed and incline.

I have the natural AC thing going too. It snows inside. But unless we have a -10 day, I stay pretty warm.

I'm having the same issue you are. After replacing my radiator with a 3 row champion, I'm pretty sure my truck isn't getting up to temp. I was toasty warm when snow wheeling with the rad partially blocked, but froze my butt off the rest of the time. I don't trust my temp gauge, but it'll read way low when I'm going down the highway. I get warm air when the gauge gets over 160 or so. My water pump and hoses are replaced in the past year and I rebuilt the heater box with new seals, new core and chevy motor/squirrel cage back in October so I know those aren't the issue. Sounds to me like your rig just isn't getting up to temp. Have you noticed a drop in mileage? Mine has been sucking (worse) all winter.

Has to be a thermostat issue...how many have you put in there?

About 5 years ago I went through 3 of them in as many months until I bought one that worked correctly. Not sure how rigorous their quality control is on a part that cheap...

Also, I have a 97 grand cherokee that had the lower temp thermostat in there and it worked great until I went down the other side of eisenhower tunnel, and then i froze. put in the 10 degree higher one, and haven't had an issue since.

I've put in at least three different ones when I tried to fix my problem.

The way to test them prior to installation is hot water in a pan with a thermometer.

One quick test I did to see that my thermostat wasn't working right.

1) Wait till bronco is completely cold (first thing in the morning)
2) Take off the radiator cap. Lowered level a bit so I could easily see any flow in the coolant
3) Start the bronco
4) Look into radiator and clearly saw a high flow of coolant

Normally you shouldn't see much flow because the thermostat is blocking it. But my thermostat was fully open when cold. This might not help if the thermostat is just opening prematurely. There's a joke in there somewhere.

That's a good test Clay!

Joe, I've thought of the Mohave setup, I just don't want to bite the bullet on it.

Pb, I put 3 or 4 t-stats in with the same result. The EFI system I've got, a speed density system, says that I need a 185 or 192 stat. So I should be fine with the ones I've been getting.

Justin, I've never had a problem with mileage.

I'm at a loss with what the heck is happening. I might have to pull the heater out & reseal everything. I haven't done that in at least 12 years, so that could be my problem, kinda what Viper said.

Not sure if this would work, but maybe a larger inner diameter hose would allow more flow and volume of hot fluid to the core.

It seems like his problem is that the engine isnt getting hot. If that's the problem then passing more Luke warm water through the heater core won't help

I was assuming from the above post that the thermostat is functioning properly...so the engine coolant should be to the correct temperature.

sbolt, is the engine temp gauge showing normal temps? Does it fluctuate?

you could take the termostat and throw it in a pot of boiling water to see if its working...

Pb, yeah, I run right around 180-190 and it reads correct. I have never had it overheat on me, ever. I don't have a long commute, actually it barely has time to heat up by the time I get to work (beauty of a 2 mile commute), but the problem I have is when I go hunting or anything else. And what got me thinking about it and started the thread was I was on a really long trip (20 or so miles ) the other day and it was just cold, and blowing cold air. The temp gauge reads right in the normal area, but it was barely keeping up. I even covered the fresh air intake under the hood to help, but that doesn't seem to work either.

Floor boards are still good, I welded in new metal 10 years ago and then bed lined them. The only holes there are from my old cage. Although it does bring another element into it....Herculiner is NOT an insulator.

Under load, I might get up to around 195-200. If it's in the summer on a really hot day, I might hit 205. What's yours run at?

What does it read when you're just driving along, say at 55 or 60? You might put the sending unit in water of a known temp just to verify that it's reading right. Sounds like it's accurate, though.

If the engine is holding temp well, then the problem has to be in the heater loop.

Plugged outlet, inlet at the ends of the heater hoses.
Plugged hoses
Plugged/malfunctioning inline valve
Plugged heater core
Blocked baffle not allowing air to flow through heater core

Here some tests I might do if it was me. (Assuming engine heat is good).

With engine hot and running

feel the heater hoses. Both should be hot, but return should be slightly cooler.
pull the heater motor and stick your hand in to see if the core feels hot
check airflow (stick a leaf blower down the inlet)


with engine cold

disconnect heater hoses from engine and attach garden hose to one end and run water thorugh. It should flow fairly easily.
which hoses disconnected, see if the inlet/outlet appear unblocked.
Maybe even turn engine over for a few seconds and watch water spew out the ports.


The principles of the Bronco heater are pretty basic.

1) Engine buring gas generates heat
2) Liquid circulates between the engine and radiator to dissipate that heat
3) Some of the liquid is diverted from the engine to heat the core
4) Air is drawn through the core by a fan and disbursed through the cab

Isolate and check each of those elements for function and it should just all work.

(Can you tell I'm sitting in a boring meeting and trying to distract myself before I scream?)

Justin, it stays pretty level right around that 180/190 mark no matter what. It's pretty reliable in that temperature range. I know when it should be higher and when to expect the heat spikes, but this has pretty much got me baffled. I think I'll look at what both Phil & Clay suggested this weekend when I have some time. See if #1 the core is clogged & #2 if I have the hoses on right. Wouldn't that be my luck....I've probably got a clogged core, the box doesn't seal & something else really stupid.

Gary - at least that'd be a means to an end. I am baffled by mine. I get good heat when the temp gauge says the motor is up to temp, but freeze when I am headed down the road and the temp gauge says 140 or lower. If I start my bronco in the winter and drove down the highway, it'll never un-peg the meter at 130*. If I am climbing a pretty hard hill or snow bashing, them temp comes up and I get heat. But even with a warm engine, if I jump back on the highway, it cools back down. It sure seems like a t-stat issue for me, but I have put three in. I have just chalked it up to a good problem to have as opposed to overheating all the time.