2001 slow to heat - The 1947 - Present Chevrolet & GMC Truck Message Board Network

67swb72klb · 11-22-2021, 10:23 PM

My 2001 RCSB with the 5.3 just does not build heat fast in the colder months even if its just in the 40s let alone when we get to the sub zero temps that are around the corner.
Takes forever to get up to just under the 210 mark
Replaced the T stat once and the water pump got replaced when it started leaking neither one made any difference

Any ideas?
Thanks!

**hatzie** · 11-23-2021, 12:27 PM

Are you sure the thermostat is the correct temp and it's opening when it's supposed to?

Do you have an air pocket in the cooling system or low coolant level?

Are you getting heat or is the heater blowing colder than it should with the engine warmed up?
I've had heater cores rot out internally between the intake and outflow ports on 1978 Dodge W200 Power Wagon and one of my mid 80's Subaru Brats. There's a separator panel in some heater cores to force the coolant to flow through half of the heat exchanger and back through the other half that rotted through in those rigs. The coolant was almost completely bypassing the failed heat exchangers through the rusted out separator panel. A replacement heater core made them heat too well.

Last but not least is the temp gauge actually reflecting the real engine temp?
Failing Engine Coolant Temp senders can read lower than actual and react slowly to temp changes.

67swb72klb · 11-24-2021, 09:00 PM

Thanks...
I put a standard thermostat in it about a year before the water pump started leaking and also played around with the coolant level without any change
The gauge is pretty much saying what the heater is putting out.
This truck has been like this since I bought it three years ago.
City driving this thing takes forever to get close to 210

It is a Ca. truck I guess they don't need much heat anyway..

**hatzie** · 11-25-2021, 10:57 AM

You can get 165°, 180°, & 195° thermostats.
I always specify the temperature. I've had the parts guys hand me 180° stats because they didn't have the 195
I believe the stock stat in the 2001 4.8/5.3L is 195°.

Vacuum cooling system fillers are almost a must have tool anymore.

**Accelo** · 12-12-2021, 08:48 PM

These trucks tend to plug the water side of the heater core. I am not sure why it happens but it does. Just helped my friend do his, night and day difference in the cab heat.
Just pull the heater hoses and back flush with a hose. No high pressured needed.
Hook it back up and enjoy. Be careful as the plastic quick disconnects get fragile with age. It takes a special tool to get them off.
Stainless steel replacement are available but not necessary. Just be aware of the possibility of them braking one off. I recommend replacing them to avoid issues later.
I had to do mine about once a year till three years ago I flushed the system and replaced the antifreeze. Been good since then.

11-22-2021, 10:23 PM	#1
67swb72klb Registered User Join Date: Dec 2010 Location: livingston co.mi Posts: 2,470	2001 slow to heat My 2001 RCSB with the 5.3 just does not build heat fast in the colder months even if its just in the 40s let alone when we get to the sub zero temps that are around the corner. Takes forever to get up to just under the 210 mark Replaced the T stat once and the water pump got replaced when it started leaking neither one made any difference Any ideas? Thanks! __________________ California 65 GTO---Texas 64 burb 283 ---Oklahoma 67 CST SWB BBW wood bed 327 2004r---New Mexico 72 k10 350 350 auto---Georga 72 short step project

11-23-2021, 12:27 PM	#2
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,977	Re: 2001 slow to heat Are you sure the thermostat is the correct temp and it's opening when it's supposed to? Do you have an air pocket in the cooling system or low coolant level? Are you getting heat or is the heater blowing colder than it should with the engine warmed up? I've had heater cores rot out internally between the intake and outflow ports on 1978 Dodge W200 Power Wagon and one of my mid 80's Subaru Brats. There's a separator panel in some heater cores to force the coolant to flow through half of the heat exchanger and back through the other half that rotted through in those rigs. The coolant was almost completely bypassing the failed heat exchangers through the rusted out separator panel. A replacement heater core made them heat too well. Last but not least is the temp gauge actually reflecting the real engine temp? Failing Engine Coolant Temp senders can read lower than actual and react slowly to temp changes. __________________ 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.

11-24-2021, 09:00 PM	#3
67swb72klb Registered User Join Date: Dec 2010 Location: livingston co.mi Posts: 2,470	Re: 2001 slow to heat Thanks... I put a standard thermostat in it about a year before the water pump started leaking and also played around with the coolant level without any change The gauge is pretty much saying what the heater is putting out. This truck has been like this since I bought it three years ago. City driving this thing takes forever to get close to 210 It is a Ca. truck I guess they don't need much heat anyway.. __________________ California 65 GTO---Texas 64 burb 283 ---Oklahoma 67 CST SWB BBW wood bed 327 2004r---New Mexico 72 k10 350 350 auto---Georga 72 short step project

11-25-2021, 10:57 AM	#4
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,977	Re: 2001 slow to heat You can get 165°, 180°, & 195° thermostats. I always specify the temperature. I've had the parts guys hand me 180° stats because they didn't have the 195 I believe the stock stat in the 2001 4.8/5.3L is 195°. Vacuum cooling system fillers are almost a must have tool anymore. __________________ 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.

12-12-2021, 08:48 PM	#5
Accelo Senior Member Join Date: Mar 2015 Location: washington Posts: 2,295	Re: 2001 slow to heat These trucks tend to plug the water side of the heater core. I am not sure why it happens but it does. Just helped my friend do his, night and day difference in the cab heat. Just pull the heater hoses and back flush with a hose. No high pressured needed. Hook it back up and enjoy. Be careful as the plastic quick disconnects get fragile with age. It takes a special tool to get them off. Stainless steel replacement are available but not necessary. Just be aware of the possibility of them braking one off. I recommend replacing them to avoid issues later. I had to do mine about once a year till three years ago I flushed the system and replaced the antifreeze. Been good since then.



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