Heater Problems

"MasterMario - Keeper of the V8s" (mastermario) 11/16/2016 at 15:46 • Filed to: wrenching

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So I’ve had a heat issue with my truck (1993 F150) since I got it. It blows hot enough, but not really hot like it should. In the winter my cab doesn’t really warm up until I’n half way to work already. So far I’ve replace the thermostat, the heater core, cleaned the ducts and checked door functionality, and flushed the coolant. The only thing I can think of now is that the water pump is weak enough to not get much flow through the heater core, but strong enough to keep coolant flowing through the block. What say you Oppo? Am I on the right track here? Or is there some other mystery I should look into first.

Completely unrelated xkcd for your time.

LongbowMkII > MasterMario - Keeper of the V8s 11/16/2016 at 15:52

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Poor insulation and just old truck problems would be my best assumption. How hard is it to change the water pump?

Urambo Tauro > MasterMario - Keeper of the V8s 11/16/2016 at 15:57

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A friend of mine just bought a ’94 last night. Same problem. Planning to do a coolant flush this weekend. It needs to be done anyway, even if that isn’t the source of the issue.

crowmolly > MasterMario - Keeper of the V8s 11/16/2016 at 16:00

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Thermostat at the stock temp?

I would check the blend door and the blend door actuator again- I think it’s a common issue for Ford trucks around your year.

MasterMario - Keeper of the V8s > LongbowMkII 11/16/2016 at 16:01

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I think fairly easy, but I haven’t really looked at that yet. I’m just trying to figure out what the issue might be right now.

lone_liberal > MasterMario - Keeper of the V8s 11/16/2016 at 16:02

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When you replaced the thermostat did you go to a higher temperature one or stick to what was in there?

MasterMario - Keeper of the V8s > lone_liberal 11/16/2016 at 16:06

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Went to a higher one than stock.

MasterMario - Keeper of the V8s > crowmolly 11/16/2016 at 16:07

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I went with a higher than stock t-stat and the blend door and actuator all seemed to work fine. I checked them when I was replacing the heater core.

crowmolly > MasterMario - Keeper of the V8s 11/16/2016 at 16:08

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When the engine is up to temp, what do the hoses to the core feel like? You probably need to start at the source of the heat and work forwards until things get cold.

MasterMario - Keeper of the V8s > crowmolly 11/16/2016 at 16:13

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I’ll check that later today and see how hot they are compared to the other lines

deekster_caddy > MasterMario - Keeper of the V8s 11/16/2016 at 16:15

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I doubt the water pump is a problem or you would be overheating all over the place. Make sure the thermostat is installed correctly, and test the thermostat if you can or just get another new one. Does the temperature gauge come up to where it should?

deekster_caddy > crowmolly 11/16/2016 at 16:16

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This. If you know anyone with an IR Temp gun it’s a great troubleshooting tool for this. It’s possible you have air trapped in the heater core that never got flushed out thoroughly too.

MasterMario - Keeper of the V8s > deekster_caddy 11/16/2016 at 16:22

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Yea, it warms up to normal operating temp then stays there. It never climbs past that point except on the hottest days

Tristan > MasterMario - Keeper of the V8s 11/16/2016 at 16:39

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How long is your commute? Basically every ‘92-’96 Ford pickup I’ve ever experienced has taken forever to get the cab warm. My dad had a ‘93 he bought in ‘97 that was a creampuff with 45,000 miles. The drive into town from our farm was about 5 miles, and it would just barely start to waft out a bit of lukewarm air when my dad would pull into the parking lot at work. Does it warm up nicely on a longer drive?

lone_liberal > MasterMario - Keeper of the V8s 11/16/2016 at 16:45

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I kind of figured you would have. If the blend door is working normally and the thermostat is good then all I can think of is some kind of blockage in the heater outlet in the water pump. If the radiator had issues it would get hotter faster so that’s kind of out.

deekster_caddy > MasterMario - Keeper of the V8s 11/16/2016 at 17:13

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Hmm. Do you ever hear any gurgling? Could you have an air pocket trapped in the heater core? That happens to some cars/trucks and you end up with no heat. The other thing I saw a few people mention was blend door actuators - that can be a big one.

EngineerWithTools > MasterMario - Keeper of the V8s 11/16/2016 at 17:44

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This is another vote for build up in the lines, but...

Did the previous owner happen to put in a heater bypass valve? It was standard in the Ranger forever (so the part is easy to come by), and a common mod to the larger trucks. It will be an H-shaped plastic thing with hoses connected to each of the H legs, plus a small vacuum actuator. It could easily choke the heater core flow without negatively impacting the rest of the cooling system.

MasterMario - Keeper of the V8s > Tristan 11/16/2016 at 18:14

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It’s about a 20 min drive. It gets warm, but the heat coming out of the vents never feels really hot, just warm

MasterMario - Keeper of the V8s > EngineerWithTools 11/16/2016 at 18:15

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No bypass valve, the lines go straight to the heater core

MasterMario - Keeper of the V8s > deekster_caddy 11/16/2016 at 18:16

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Can’t say I’ve ever heard gurgling. Wouldn’t the pocket work itself out eventually?

Tristan > MasterMario - Keeper of the V8s 11/16/2016 at 19:09

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I’d say pop the glove box off, remove the access panel to the heater core, go for a drive and check to see if the heater core ever gets up to operating temp. Have you ever replaced the hoses? IIRC, there’s a small flow restrictor in one of the hoses that has only about 1/4" of passage. That could easily be blocked by some rust scale.

MasterMario - Keeper of the V8s > Tristan 11/16/2016 at 21:06

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I haven’t replaced the hoses. But that’s interesting about the restrictor. I’ll take those off and check that out.

deekster_caddy > MasterMario - Keeper of the V8s 11/16/2016 at 23:43

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Not always audible, and in some designs you have to actively flush the heater core to get the air pocket out. Not sure if your truck is like that, but it’s possible.

Urambo Tauro > MasterMario - Keeper of the V8s 11/21/2016 at 13:32

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Hey just wanted to let you know, we replaced the coolant on my friends’s ’94 over the weekend, and the heater started working MUCH better afterward. He didn’t flush it though. We just ran tap water through it a few times before switching over to distilled for a couple more run&dump cycles.

Meanwhile, there was a bunch of crud in the surge tank, so we unbolted it and put some chains & water in there and shook it around to make it easier to read. We replaced the thermostat and filled it back up with coolant, and he’s pretty pleased with it.

BTW, that noise that I told you about was indeed the tensioner pulley. SO much quieter now. Despite the dust on the alternator, its bearings spin freely and the pulley doesn’t seem to be out of line with the other pulleys. Weird.

But the truck still needs some more wrenching. I think I’ll write up an Oppo post later after I meet up with him again next weekend to change the transmission (E4OD) fluid.

MasterMario - Keeper of the V8s > Urambo Tauro 11/21/2016 at 13:37

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Good to know. I’m planning on removing the lines to the heater core and checking those. Another opponaut mentioned that he thought one of those lines had a 1/4" orifice in it that might be plugged. I’m hopping that’s it cause I still haven’t seen much improvement and it’s finally starting to get cold around here.

Urambo Tauro > MasterMario - Keeper of the V8s 11/21/2016 at 13:44

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Come to think of it, I did notice that one of the heater hoses has- I don’t know what to call it- kind of a relief line? going to the radiator. Anyway, there’s a tiny little hole where that line enters the radiator, just under the rad-cap. That hole is not 1/4", though. It’s a really small pinhole. With the rad-cap off and the truck running, you should be seeing water squirting into the radiator from that T’d line.