60deg ambient 95deg vent heat? 91 3fe (1 Viewer)

Joined
Dec 5, 2010
Messages
614
Location
Northeast PA
I decided to get prepared for our upcoming long PA winter by doing some PM work to my '91 FJ80.

Last winter I remember the heat was far from adequate, so I decided to dig into getting more heat out of her.

I replaced the thermostat with OEM (including the top gasket) - no change in heat.
I flushed both the front and rear cores with water and compressed air. I flushed them independently, nothing unusual came out of the line. (I assume the top firewall ports are for the front heater core)
My flow control valve operates correctly.

When the truck is warmed up, and the temp gauge sits at half (where it normally does for my truck) I get 95degree vent temperatures when measured with my IR thermometer, that's with an ambient temperature of 60degrees. I read in other threads that people were getting 135degree vent temperatures. I don't lose any antifreeze to speak of.

I have not tried the CLR method yet.

I don't think my heater core is clogged in the heater box because I get good airflow. (meaning there's probably not a squirrel nest in my heater box)

I haven't checked the outlet temperature of the rear heater.

Is this vent temperature normal? Any ideas what I should try next?
 
Joined
Apr 20, 2011
Messages
456
Location
Nevada City, Ca
I have the same issue with my 91. I did use CLR to soak the front core, and it did not help. I also flushed it several times both normal and reverse flow. The rear heater blows really hot air, but it just isn't enough to warm the entire rig. I hope you figure out a solution, because i need help too.
 
Joined
Dec 5, 2010
Messages
614
Location
Northeast PA
I guess I need to shoot the discharge temp at my rear heat to narrow down the problem.

If the rear temp is also 95degrees, then the issue has to be near the 'stat housing (where the supply comes from)
If the rear temp is hot, then the issue has to be at the front core, or the supply tubing to the front core. (perhaps the Tee is clogged? I didn't look, and flushed past the tee)

We can safely assume the heater box is not clogged, as it would impede airflow.
We can safely assume the front core itself is not clogged, as we get good water flow, and you did CLR.
 

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