Motor not heating up... - The 1947 - Present Chevrolet & GMC Truck Message Board Network

prin · 03-17-2017, 11:02 PM

I need some help! My sbc 355 is not warming up. I am getting limited heat as well. I have replace the tstat. I have also noticed that when I drive for several miles, pull over, I can take off the radiator cap(which i replaced) with little to no pressure built up. One side of my radiator is HOT and the other side is only warm to the touch.

I have racked my brain over this. What do yall think????

LongBox · 03-18-2017, 12:23 AM

How do you know the engine is not heating up? Have you used a thermometer to measure the coolant temp, or a remote temp sensor to "shoot" the area around the T'stat housing?

Sounds like you have a coolant circulation issue, or a bad heater core if not much heat from the heater. Could be an airlock (some air left in the cooling system). I would wait till the engine is stone cold, start it, lift the hood, and feel the top rad hose to see if it warms up, but only after the engine gets warm.

So there's a few ideas for ya.

El Dorado Jim · 03-18-2017, 12:31 AM

if you have already replaced the thermostat, I have no idea what could cause this....but I hope someone can help, I am very interested in why it's not warming up

carryall · 03-18-2017, 02:10 AM

Mine did this and my heater core was shot.

**Boog** · 03-18-2017, 07:01 AM

What temp stat you have makes a difference in how much heat it builds. A 180* stat should build plenty of heat. It sounds like the radiator and fan are doing their job just fine. Once you start your engine cold feel each of the heater hoses while it warms up as one will get hotter going to the heater core and the other will be slightly less hot coming out. If one heater hose stays noticeably cooler than the other that's a good indication the heater core is plugged. If so you can remove the hoses at the heater core and back flush it with a garden hose and maybe get more circulation through it but it really will need to be replaced. The lack of pressure in the radiator can be a leak in the system or a bad radiator cap. A 13# cap is about normal.

davepl · 03-18-2017, 12:09 PM

If your T-stat is opening then either your motor is magically not making heat or its not getting to where you're looking - like the heater core.

But if it's not making it elsewhere, maybe the pump is shot?

I think you need a thermal gun to record a bunch of measurements at the heater core outlet and return, radiator outlet and return, and so on, looking for anomalies. The heat is going somewhere!

nightrider388 · 03-18-2017, 02:22 PM

Water pump failure will cause this as well.

cdowns · 03-18-2017, 05:09 PM

or a reverse flow water pump

prin · 03-19-2017, 11:21 PM

Thanks for all of the replies! I dont know what i would do if I didnt have forums like this to go to. LOL. I will be taking a closer look at the core tomorrow to see what i find.

03-17-2017, 11:02 PM	#1
prin Registered User Join Date: Oct 2006 Location: Huntsville, AL Posts: 172	Motor not heating up... I need some help! My sbc 355 is not warming up. I am getting limited heat as well. I have replace the tstat. I have also noticed that when I drive for several miles, pull over, I can take off the radiator cap(which i replaced) with little to no pressure built up. One side of my radiator is HOT and the other side is only warm to the touch. I have racked my brain over this. What do yall think????

03-18-2017, 12:23 AM	#2
LongBox Registered User Join Date: Sep 2016 Location: Vancouver BC Posts: 784	Re: Motor not heating up... How do you know the engine is not heating up? Have you used a thermometer to measure the coolant temp, or a remote temp sensor to "shoot" the area around the T'stat housing? Sounds like you have a coolant circulation issue, or a bad heater core if not much heat from the heater. Could be an airlock (some air left in the cooling system). I would wait till the engine is stone cold, start it, lift the hood, and feel the top rad hose to see if it warms up, but only after the engine gets warm. So there's a few ideas for ya. __________________ Rick -69 GMC 910 Long Box, 350 -98 Chev Silverado 1500, 350 Vortec 4L60e -08 Mustang GT Convertible

03-18-2017, 12:31 AM	#3
El Dorado Jim Registered User Join Date: Dec 2009 Location: El Dorado Ca Posts: 3,374	Re: Motor not heating up... if you have already replaced the thermostat, I have no idea what could cause this....but I hope someone can help, I am very interested in why it's not warming up

03-18-2017, 02:10 AM	#4
carryall Registered User Join Date: Jan 2000 Location: ROMNEY, WV USA Posts: 304	Re: Motor not heating up... Mine did this and my heater core was shot. __________________ 1967 Chevy Truck 1969 Chevy Panel Truck work in progress 1971 GMC 1500 all orginal 1972 Chevy Suburban brought from orignal owner 1984 Dodge Rampage 45,000 original miles 1992 Dodge D150 1994 Buick Roadmaster (LT1 Engine) 2000 Chevy Stepside Z71 2008 Honda Element

03-18-2017, 07:01 AM	#5
Boog laying low Join Date: Mar 2001 Location: Searcy, Ark. USA Posts: 13,109	Re: Motor not heating up... What temp stat you have makes a difference in how much heat it builds. A 180* stat should build plenty of heat. It sounds like the radiator and fan are doing their job just fine. Once you start your engine cold feel each of the heater hoses while it warms up as one will get hotter going to the heater core and the other will be slightly less hot coming out. If one heater hose stays noticeably cooler than the other that's a good indication the heater core is plugged. If so you can remove the hoses at the heater core and back flush it with a garden hose and maybe get more circulation through it but it really will need to be replaced. The lack of pressure in the radiator can be a leak in the system or a bad radiator cap. A 13# cap is about normal. __________________ Boog 69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver primer is finer 91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said. I stand for the flag and kneel at the cross

03-18-2017, 12:09 PM	#6
davepl Registered User Join Date: Aug 2006 Location: Redmond, WA Posts: 6,332	Re: Motor not heating up... If your T-stat is opening then either your motor is magically not making heat or its not getting to where you're looking - like the heater core. But if it's not making it elsewhere, maybe the pump is shot? I think you need a thermal gun to record a bunch of measurements at the heater core outlet and return, radiator outlet and return, and so on, looking for anomalies. The heat is going somewhere! __________________ 1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible

03-18-2017, 02:22 PM	#7
nightrider388 Registered User Join Date: Jul 2016 Location: Arkansas Posts: 147	Re: Motor not heating up... Water pump failure will cause this as well.

03-18-2017, 05:09 PM	#8
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: Motor not heating up... or a reverse flow water pump __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

03-19-2017, 11:21 PM	#9
prin Registered User Join Date: Oct 2006 Location: Huntsville, AL Posts: 172	Re: Motor not heating up... Thanks for all of the replies! I dont know what i would do if I didnt have forums like this to go to. LOL. I will be taking a closer look at the core tomorrow to see what i find.



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.