Heaters, coolant temps, and stuff

[curtis73]

I figured I'd post this here since there isn't a specific heater/coolant sub forum, but mods feel free to move it somewhere.

Truck in question is a 94 B4000. When I was test driving the truck, I noticed the coolant was full of a bunch of Barr's Leaks, so I negotiated accordingly. I also noticed that the heat was really weak and only blew luke warm air, so I figured the heater core was probably coated with a healthy dose of coppery sludge. I also noted that the temp gauge only goes up about 1/4 of the way even on the hottest day.

Skip forward a couple months when my intake started leaking. I was in the middle of moving so it went to a shop for the repair and I requested a coolant flush and a new thermostat. Not sure what temp it is, but it was just pulled off the parts shelf from the VIN so I assume it is "correct." It still operates exactly the same; low temp gauge, poor heat. I didn't expect a miracle with the flush and stat, but I was hopeful.

My real question is, where does your temp gauge read? I might understand that the temp sensor is also covered with barrs leaks and would be slow to register, but on a longer trip the heat should eventually soak through it and give an accurate reading. Last month I drove 180 miles on the highway and during a fuel stop and oil check I noticed things didn't feel very hot under the hood. The radiator was just warm. I loosened the radiator cap and it didn't scald me with steam, it just burped a little bit of coolant. I would say the temperature of it was about like drinkable coffee, but certainly not really hot. Ambient temps in the 50s.

-Fan clutch operating normally; stays engaged when the viscous fluid is really cold (the first 1/2 mile or so) and then spins freely and passes the newspaper test. It has never engaged for high heat, even on 90 degree days with the A/C on.
-verified proper heat blend door operation

Normally I would just jump straight to replacing the heater core or trying to flush it out with solvent, but the whole thing has me puzzled. I don't think it is necessarily a heater core problem since the rest of the symptoms all point toward actual low coolant temps.

Theory 1: the whole coolant system is so gunked up with barrs leaks that it doesn't transfer enough heat to the coolant... but if it were that bad I would have such an inefficient cooling system that it would overheat/ping. I would also think that the oil would be taking the majority of the heat, but when I checked the oil I was able to wipe it off with my fingers and it was not that hot.

Theory 2: both the old stat and the new stat are defective in the same exact way.

Theory 3: some other brilliant solution that you will tell me below.

Thoughts?

 

[adsm08]

I would call the shop and ask what temp thermostat they put in it.

If a previous owner put a low-temp unit in they may have pulled it, seen it was marked at 170* or whatever, and gotten one with that rating from their supplier, instead of an OE temp one. That could get you the same set of symptoms without either unit being particularly defective per se.

That's all I got.

 

[curtis73]

I would, but we're not talking about 160 or 170, we're talking like 120 or 130. It's way cooler than a logical thermostat temp should be.

 

[8thTon]

Parts listings can be wrong, and I've dealt with the opposite on another vehicle where the commonly listed thermostat would cause overheating. Still, that would likely be well known here if it were the case.

 

[sgtsandman]

I don’t know if you have the OHV or SOHC, so I may be commenting out of place. My Scangauge II says my 4.0 SOHC runs at about 195 when up to full temp. From what you are describing, it sounds like your thermostat is too cool or stuck open.


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[curtis73]

8thTon... agreed, but nobody makes a 120 degree stat option. It would make sense if I suddenly went from 195 down to 180 or 160, but old stat seemed to keep things around 120 and the new stat keeps them around 120... doesn't matter if it's 70 degrees or 10 degrees.

sgtsandman…. it's an OHV, and it should be running 180-195, but I'm way cooler than that. I would say thermostat stuck open, but I would think it is unlikely that the old stat and a new stat would malfunction in exactly the same way.

After a 180-mile highway jaunt in the mid-50s temps, I was able to take the radiator cap off and the coolant that hit my hand was barely steaming and didn't cause any discomfort. I could lay my hand anywhere on the upper part of the engine and it was just warm.

 

[8thTon]

8thTon... agreed, but nobody makes a 120 degree stat option.

No, but if it doesn't fit correctly and allows coolant to bypass it you might end up there. Is there an O-ring , gasket or seal missing?

 

[curtis73]

Ah... understood.

It should be an o-ring seal, but short of taking it off I'm not sure if it's in there. I can't imagine my seasoned tech forgetting it, but everyone brain farts from time to time.

 

[8thTon]

Ah... understood.

It should be an o-ring seal, but short of taking it off I'm not sure if it's in there. I can't imagine my seasoned tech forgetting it, but everyone brain farts from time to time.

This type of single action thermostat simply blocks the flow of coolant below the set temperature. There are precious few ways to make it run that cool - it's either broken and open or coolant must be flowing around it.

Most such systems have an intentional bypass that allows a small amount of coolant to flow even when the thermostat is closed so that there is some circulation, but that usually doesn't flow through the radiator.

 

[Shran]

Do you have an infrared thermometer? I would be interested in seeing actual temperature readings from various parts of the engine, IE the heads, water pump, etc.

What about the heater hoses? Do they get hot? Upper and lower radiator hoses? The heater hoses in my 92 Explorer are almost too hot to touch after running for just a few minutes.

Several possibilities come to mind here, the radiator could be partially clogged and not letting coolant through. There could be an air pocket trapped in the lower intake (fairly likely if a thermostat with no air bypass was installed.)

The heater issue alone could be caused by a heater plenum plugged up full of leaves and crap, or just a bad heater core.

The heater in my 2 door Explorer does pretty much the same thing, it never, ever gets more than just a little warm but the engine definitely gets up to temp.

 

[19Walt93]

Before you repeat a bunch of stuff try flushing the heater core after backflushing it. I can't explain why but I've seen Rangers with partially obstructed heater cores with poor heat and a low temp gauge reading. Worst case you'll have to replace the core. I know that doesn't make sense but I retired from a Ford dealer after 42 years in service, sometimes weird stuff happens.

 

[curtis73]

This type of single action thermostat simply blocks the flow of coolant below the set temperature. There are precious few ways to make it run that cool - it's either broken and open or coolant must be flowing around it.

Most such systems have an intentional bypass that allows a small amount of coolant to flow even when the thermostat is closed so that there is some circulation, but that usually doesn't flow through the radiator.

I believe the 4.0L is one that doesn't have an internal bypass. It uses the heater core as the bypass like a SBC.

 

[curtis73]

Do you have an infrared thermometer? I would be interested in seeing actual temperature readings from various parts of the engine, IE the heads, water pump, etc.

What about the heater hoses? Do they get hot? Upper and lower radiator hoses? The heater hoses in my 92 Explorer are almost too hot to touch after running for just a few minutes.

Several possibilities come to mind here, the radiator could be partially clogged and not letting coolant through. There could be an air pocket trapped in the lower intake (fairly likely if a thermostat with no air bypass was installed.)

The heater issue alone could be caused by a heater plenum plugged up full of leaves and crap, or just a bad heater core.

The heater in my 2 door Explorer does pretty much the same thing, it never, ever gets more than just a little warm but the engine definitely gets up to temp.

I do have an infrared thermo. But it needs a new battery

I agree that your suggestions would all be valid explanations, but it operates exactly the same for the last 18,000 miles both before and after stat/flush.

If the plenum were full of junk, I would get hot air, but not much of it. I have lots of air flow, but its about 70 degree air.

The heater hoses, radiator hoses, radiator, intake, block, valve covers, water pump... everything under the hood that should be too hot to touch... isn't. After a long highway trip, I could put my tongue on the radiator and not burn it.

 

[alwaysFlOoReD]

Put some cardboard in front of the rad and see if it warms up. Cover half, or maybe 2/3. Temp should come up. If it does then look at thermostat.

 

[8thTon]

I believe the 4.0L is one that doesn't have an internal bypass. It uses the heater core as the bypass like a SBC.

Note that I wrote "intentional", not "internal", but yeah, the heater core is common, and in the days of the carburetor they would often circulate some coolant through the intake and the choke heater. You just can't dead head the pump or the coolant will end up boiling in one spot while the thermostat is still cold.

Anyway, weird stuff like air pockets can happen, but that prevents flow and if it's as you say and everything is cold that can't be it. There is a huge amount of waste heat and if the coolant can't circulate for whatever reason something is going to get hot as hell. The only way that heat energy can get out of the engine compartment is the radiator (and the heater core).

If everything is cold then the thermostat is not blocking the flow into the radiator. If something is actually hot then it could be a whole lot of other things.