Truck heater litte or no heat

old · Jan 2, 2010

My 1986 Isuzu pup with the 1.9 engine does not want to get very warm as in the heater does not put out air that is very warm. I changed the thermostat today and put in a 192 in place of the 180 and it still does not heat up well. It will sit and put out warm air for a few then cold then back to warm and it keeps doing that. Temp gauge says it is running right where it should is in about the middle of the gauge and the water in the radiator is warm enough that you do not want to hold your finger in it long.
So what am I missing on this any ideas guys??
Thanks

Zachary Hoyt · Jan 2, 2010

Does the truck have vacuum operated blend doors to control the air temp? I have heard that a collapsed vacuum hose or a loose connection can make the blend doors not work right. I've never had this problem on a vehicle that I was looking at, so I don't know the details, just what I've heard.
Zach

440roadrunner · Jan 2, 2010

Feel both heater hoses---what do THEY feel like

I once had a Dodge (64 426) on which the stamped pump impeller broke loose from the shaft---it was cooling on "convection."

Not knowing the valving (if any) in the heater hoses, follow the hoses, try to determine if a mechanical/ thermostatic/ vaccum valve in the heater line is shut

As said above, "doors" problem, either mechanical or vacuum

CCer · Jan 2, 2010

I've had vehicles that had an air bubble in the hose. With engine running. loosen the highest heater hose clamp and slowly begin to remove the hose, allow it to burp out air and some coolant. Re-assemble hose and tighten the clamp. I hope that cures it.

Bob Bancroft · Jan 2, 2010

Friend just got an older used Dodge 4x4 diesel for plowing snow. Everything worked but the heater. He removed hoses and went after the heater core with both air and water under pressure and flushed a lot of crap out. It's not 100%, but he can use it now without freezing. Seems like any garbage in there wants to settle in the heater core. Not to mention the crap, mouse nests, chaff, leaves, etc. that wants to settle in and around the fins.

Dean · Jan 2, 2010

When did you last flush the cooling system and change the coolant?

If it has been neglected, quite likely the heater core is (at least partially) clogged, resulting in little or no heating of the air therethrough.

Dean

Lou from Wi. · Jan 2, 2010

440 roadrunner said to feel both lines, If the in-put hose is hot, but cold on the return, it's almost a sure bet the core is plugged.He is correct! We took out the heater core on a 79 Dodge W/318 and used CALCI-SOL (strong acid cleaner)then used baking soda solution to neutralize the acid,blew out the core, now the heater will run ya out of the cab in short order,even at -20 o below. Hope you find the problem,I know all about freezing ones astericks off.
LOU

Anonymous-0 · Jan 2, 2010

The problem is coolant flow. Either there's a blockage in the heater core, or in the heater hoses, or there's air in the cooling system. Either way, you're not getting a constant flow of heated coolant through the heater core.

JMS/.MN · Jan 2, 2010

Had a bubble and no flow in a "65 Mustang convertible. Got out in the open, punched it to 80mph, popped the bubble loose....heat was nice.

Anonymous-0 · Jan 2, 2010

don't know what that 1.9 engine is gas or diesel/ if it is a diesel put some of that pipe insulateing form over the heater hoses, can't think of the name, but you can get it at the hardware store, about 5' long 1.5 around black tube made out of styroform 'spelling' what I had to use on my home built diesel chevy pick up.get

old · Jan 2, 2010

What gets me on this one is it comes and goes sort of like you turn it on and off. It will be warm for a few minutes then go cold then go back to warm. Now granted I did not drive it all that far and only let it run for say 15 minutes or so. So maybe when it does get driven into town it might do better

old · Jan 2, 2010

Ya I was thinking about taking the heater hoses off and switching them around so the flow would go back wards of what it does now and see if that would help. I had a car years ago that we would do that about one a year and when we did the heater would always burn you out of that car, but if you didn't switch the hoses around it would freeze you

old · Jan 2, 2010

In the last year it has had 2 different heads on it so the coolant has been changed and the head has been changed. First head had a crack so got another head and put it on just a couple months ago. What is funny is that it will put out heat then go cool then go back to putting out heat.

olgentdc · Jan 2, 2010

had a 302 ford that played that trick , ended up blowing head gasket ,,, i think something was left in the block from rbuilding the motor , ended up trading it ,,so i never did find out,..back flush heater cores by going from hot to cold ShOCK TREATMENT from the house hot water heater ...

olgentdc · Jan 2, 2010

had a 302 ford that played that trick , ended up blowing head gasket ,,, i think something was left in the block from rbuilding the motor , ended up trading it ,,so i never did find out,..back flush heater cores by going from hot to cold ShOCK TREATMENT from the house hot water heater ...

kyhayman · Jan 2, 2010

I'd bet dollars to donuts that there's an air bubble in there somewhere. My Dodge did that after I put a heat core in it. Before the heater core it would run you out, after, nothing. I burped the head twice and couldn't get it to clear. Finally it cleared itself and now it will run you out.

msb · Jan 2, 2010

Have had several farm trucks that I had to blow out the heater core that was plugged up with dirt,mouse crap and bees wings.Might not be your solution, but it can't hurt.

sammydwm · Jan 3, 2010

What gets me on this one is it comes and goes sort of like you turn it on and off. It will be warm for a few minutes then go cold then go back to warm. Now granted I did not drive it all that far and only let it run for say 15 minutes or so. So maybe when it does get driven into town it might do better

let it warm up a bit longer. get all the fluid around the same temp.
Sounds like the temps drops when the tstat opens.......
problems with the cooling fan? On all the time?
Cold ambient temps?

MarkB_MI · Jan 3, 2010

Heater switching from hot to cold is a symptom of a blown head gasket. When the thermostat closes, air gets trapped in the heater core. When the thermostat opens, it blows out the radiator.

old · Jan 3, 2010

This is a new head gasket and a good used head and has only been on the truck for a couple months. I do not get any water out the exhaust like I was with the old head, it was cracked. Also no coolant in the oil or the other way around. Water flow seems good also when you have the radiator cap off

old · Jan 3, 2010

Cooling fan on this one if belt drive so yep spins all the time. Yep it is cold out as in lower then 20 degrees so that may have something to do with it. I do have card board over the radiator also so it should warm up real well but who knows as old as this truck is and the number of miles on it the heater core may need to be flushed or the hoses switched this thing has 186,000 plus mile on it. I say plus because the speedometer stopped working a few months ago

MarkB_MI · Jan 3, 2010

Yes, but what happens when you do a pressure test?

Bill(Wis) · Jan 3, 2010

After hearing about a new head gasket, etc., I think kyhayman has the right answer to your problem. Had that happen myself, maybe 20 or 30 years ago but can't remember the make.

old · Jan 3, 2010

Not set up to do a pressure test but the cap is a 14lbs cap and it holds well and if you open it then hot it will spray you real good LOL

MarkB_MI · Jan 3, 2010

Borrow a pressure tester. Mount it on the radiator and start the engine up. If the pressure gage takes off immediately, you have a bad head gasket. If it runs for a minute and the pressure rises only slightly, the head gasket is good and you can look elsewhere.

Owen Aaland · Jan 3, 2010

(quoted from post at 13:02:43 01/03/10) Borrow a pressure tester. Mount it on the radiator and start the engine up. If the pressure gage takes off immediately, you have a bad head gasket. If it runs for a minute and the pressure rises only slightly, the head gasket is good and you can look elsewhere.

If you put the pressure tester on the radiator after running the engine enough to stabilize the temperature, any rise in pressure is a good indication of combustion gasses entering the cooling system.

The fact that the heat comes and goes with the cooling system full is almost always an indication of a combustion leak into the cooling system.

Billy Shafer · Jan 3, 2010

I just worked on a 2003 F550 with about the same problem. Blender door was stuck and control module was messed up. Replaced module and now I get hot air when I should.

Truck heater litte or no heat

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