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**hatzie** · 01-20-2015, 12:16 AM

First thing I'd look at is the heater box blend door seal.
Are you leaking air around the kick panel vent flaps or the heater box intake on the passenger kick panel? Rust holes in the plenum under the wipers?
Your vent temp at 120F should warm up the cab unless you are leaking in cold air.

I'd look at the fan clutch and change the thermostat.
The next thing I'd look into is moving the heater return from the radiator to the water pump like the earlier trucks.
A 350 or 305 with a massive radiator should have no trouble driving you right out of the cab using the heater in the dead of winter. I've had several of them do just that.

01-20-2015, 12:16 AM	#4
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 5,022	Re: lack of temp First thing I'd look at is the heater box blend door seal. Are you leaking air around the kick panel vent flaps or the heater box intake on the passenger kick panel? Rust holes in the plenum under the wipers? Your vent temp at 120F should warm up the cab unless you are leaking in cold air. I'd look at the fan clutch and change the thermostat. The next thing I'd look into is moving the heater return from the radiator to the water pump like the earlier trucks. A 350 or 305 with a massive radiator should have no trouble driving you right out of the cab using the heater in the dead of winter. I've had several of them do just that. __________________ 1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials... 1973-1991 GM Light Truck Service, Unit/Overhaul, Wiring Manuals, Parts Books and Some 1968-1999 GM Service Training textbooks in PDF 1988-1998 GMT400 CK service manual project 1988-1993 GMT400 CK parts books. 1967-1972 GM Light, Medium, & Heavy Truck Service Manuals in PDF Please include at least the year and model in your threads. It'll be easier to answer your questions. And please let us know if and how your repairs were successful.