88 k5 heater not hot - The 1947 - Present Chevrolet & GMC Truck Message Board Network

65truckowner · 11-11-2018, 04:11 PM

On my sons 88 k5 the heater is not blowing hot only warm. The coolant is full the engine temp is just under 210. What I dont understand is there is a hose coming from the intake to the heater core then from there to the radiator. The return hose is larger than the intake heater hose. Is this not backwards? But the heater hose coming from the intake has a fitting on it that screws into the intake.I thought the larger hose was the one going into the core not coming out. What else could be causing it to not blow hot. Also the heater core is new.

**hatzie** · 11-11-2018, 06:52 PM

Your 88 K5 Blazer is a squarebody not a T400. The 88-91 Suburban and Blazers were all RV series squares.
There's a lot more traffic on the 73-87 squarebody area. You should probably ask a mod to move your post to that area.

IIRC 5/8" hose goes from the bottom of the heater core to the intake and 3/4" goes to the water pump or the radiator depending on the truck but it's always the larger hose on the intake manifold. If you have a 3/4" hose barb on the intake someone re-assembled it incorrectly.
My 85 C10 was 3/4 on the radiator and my 75, 77, 78, & 79 C20 & C30 trucks all ran to the water pump.
Can't remember what the 350 in the 76 was plumbed like and it's not even close to any 1976 stock driveline now.

65truckowner · 11-11-2018, 10:19 PM

Ok i was going by the year. If someone could move it that would be great

**hatzie** · 11-11-2018, 11:45 PM

The suv and some 3/4 & 1-ton year splits get obnoxious. GM made both T400 CK & RV squarebody 3/4 & full tons in the 88-91 years.
My 2000 GMC is an 88-98 T400 body truc and IIRC the 2001 Suburban was a T400....

They're likely going to do it with the K2 & T1 next year

11-11-2018, 04:11 PM	#1
65truckowner Registered User Join Date: Oct 2012 Location: mountain view arkansas Posts: 1,299	88 k5 heater not hot On my sons 88 k5 the heater is not blowing hot only warm. The coolant is full the engine temp is just under 210. What I dont understand is there is a hose coming from the intake to the heater core then from there to the radiator. The return hose is larger than the intake heater hose. Is this not backwards? But the heater hose coming from the intake has a fitting on it that screws into the intake.I thought the larger hose was the one going into the core not coming out. What else could be causing it to not blow hot. Also the heater core is new. __________________ http://67-72chevytrucks.com/vboard/s...d.php?t=548705

11-11-2018, 06:52 PM	#2
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,913	Re: 88 k5 heater not hot Your 88 K5 Blazer is a squarebody not a T400. The 88-91 Suburban and Blazers were all RV series squares. There's a lot more traffic on the 73-87 squarebody area. You should probably ask a mod to move your post to that area. IIRC 5/8" hose goes from the bottom of the heater core to the intake and 3/4" goes to the water pump or the radiator depending on the truck but it's always the larger hose on the intake manifold. If you have a 3/4" hose barb on the intake someone re-assembled it incorrectly. My 85 C10 was 3/4 on the radiator and my 75, 77, 78, & 79 C20 & C30 trucks all ran to the water pump. Can't remember what the 350 in the 76 was plumbed like and it's not even close to any 1976 stock driveline now. __________________ 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.

11-11-2018, 10:19 PM	#3
65truckowner Registered User Join Date: Oct 2012 Location: mountain view arkansas Posts: 1,299	Re: 88 k5 heater not hot Ok i was going by the year. If someone could move it that would be great __________________ http://67-72chevytrucks.com/vboard/s...d.php?t=548705

11-11-2018, 11:45 PM	#4
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,913	Re: 88 k5 heater not hot The suv and some 3/4 & 1-ton year splits get obnoxious. GM made both T400 CK & RV squarebody 3/4 & full tons in the 88-91 years. My 2000 GMC is an 88-98 T400 body truc and IIRC the 2001 Suburban was a T400.... They're likely going to do it with the K2 & T1 next year __________________ 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.



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.