2000 Ford Mustang AT base model v6 3.8 - radiator/heater core issue

wolfsmane

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Make
Ford
Model
Mustang
Year
2000
Miles
too many
Engine
3.8L V6
2000 Ford Mustang AT base model v6 3.8 - back in Aug 2019 the car was cooling properly, heater was heating properly, but the antifreeze was nasty looking. Car had the radiator drained, water run through and then refilled with antifreeze. In Oct 2019 antifreeze looked like crap again, added a bottle of radiator flush, run the car for a couple of days and then took it to a garage and let them perform a full flush and fill, plus replaced thermostat and radiator cap, for good luck lol. Everything was running fine with the car - engine temp, heater was heating.
Now, engine temp is where it should be(dash gauge) but no heat from the heater core. Also, hose coming from the thermostat to the radiator is hot, but the radiator cap is just luke warm and the bottom hose is also luke warm. No leaks and engine is not over heating by dash gauge.
My limited mechanic skills says that it should be a clogged radiator since it is going in hot but coming out luke warm. Is this a correct diagnosis or would it be the heater core, or both?
Thanks
 

Mobile Dan

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You need to feel the heater hoses. With a hot engine, and the blower fan turned off (for at least five minutes), both heater hoses should be hot. If you then turn the blower on, one of the hoses should feel noticeably cooler (warm, not hot). But if one of the hoses cools down a lot after the blower has been on for two minutes, the problem is probably a plugged core. If the hoses stay hot with the blower on, it is likely the the blend-air door is stuck at he "Cold" position.
 

wolfsmane

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When you say plugged core, you mean the heater core, correct? So, you don't think there is anything wrong with the radiator, with it being hot going in and luke warm coming out? Thanks for the reply
 

Mobile Dan

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Yes "plugged core" means heater core, in this case. If engine temp guage reads normal (middle?), then heater core should be able to produce lots of heat, no matter what the radiator temp is.
 

billr

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"So, you don't think there is anything wrong with the radiator, with it being hot going in and luke warm coming out?"

There is really no answer for that. The radiator is adequately removing the heat, either because the flow is restricted or... because the radiator is properly sized for the intended purpose. If the coolant was cooled very little going through the radiator, then that would be an unambiguous problem.
 

wolfsmane

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"So, you don't think there is anything wrong with the radiator, with it being hot going in and luke warm coming out?"

There is really no answer for that. The radiator is adequately removing the heat, either because the flow is restricted or... because the radiator is properly sized for the intended purpose. If the coolant was cooled very little going through the radiator, then that would be an unambiguous problem.
That does make sense. I was just expecting the radiator cap and bottom hose too be to hot to handle. I could have grabbed both and held on without it being too uncomfortable. I am now thinking that the car really didn't have enough time to get that hot since she( my daughter drives this car) only drove from her house to mine, about 8 miles @ 35mph.

Thanks for pointing that out.
 

billr

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Lots of other variables, too. What was the engine/coolant temp when she started? What was the ambient temp as she drove? Does the fan operate properly, not come on too soon? Also, rubber and plastic parts, like the hose and maybe cap, don't conduct heat well to your hand. You won't be able to grab a piece of metal much past 130F, but rubber/plastic OK at 175F. (Approximates, let's not burn ourselves trying to nit-pick exact numbers!)
 

wolfsmane

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Ok, so my findings are, at about 50F outside here and it took 30 mins running in the driveway to get to temp. Temp from the thermostat to the radiator was about 170F, coming out of the radiator around 140F.
Temp at the heater core hoses were 170F and 160F with the fan off. Ran the fan on high for about 5 mins, temps at the heater core hoses were 170F and 145F. The air temps at the vents were around 116F with no fan running and around 104F with the fan on high.

The radiator cap and bottom hose are too warm to handle right now.

When she had me check it the other night, the car was only running for about 15 mins and the outside temps were in the 20's and I didn't have a way to check the actual temps.

Maybe the new thermostat is opening too soon, making it take longer to heat up? Normally the vent temps are warm about half way from my house to hers, and now it's taking longer than she is used to.
 

JackC

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Maybe the new thermostat is opening too soon, making it take longer to heat up?
OR? The old thermostat was defective and this new one is operating properly?? But like your diagnosis better. My wild guess is that most vehicles will be warmed up in 2 to 4 miles. So, it should be warmed up half way between your house and hers. 8 miles /2 = 4 miles.
 

Mobile Dan

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So...after complete warm-up with fan off for five minutes...when you turned fan on high...did you get good heat for about 5-10 seconds before the heat faded to mediocre? No = blend air door problem. Yes = heater core is plugged, or flow is restricted, or persistent air pocket, or water pump is doing a poor job at low rpm. Does heater output temp improve a lot if you hold RPM about 3000 for 30 seconds?
 
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