Chevy 350 SB Running Hot

[Built in America]

Every day driver is a 1941 GMC truck. We call it a little mule and it has been turning over and running as good as it probably did the day it was pulled off the lot 80 years ago. Only swap out was the flathead 6 for a 71 350SB (done by prior owner), and 6 to 12 volt system.

 

The issue:

Overheats (never use to)

 

Details:

Warms up nicely to 180° within 16 to 20 minutes - with the electric fan running during idle. At roughly 25 minutes weather pressing the  excelerator to force some more coolant into the block or hitting the road and driving, it creeps up to 190 (we know 190 to 200 is often said as a healthier engine temperature BUT it is always ran at 180 and never went beyond that until recently) my 25-30min.  
 

Prior to 35 minutes when driving or tapping the accelerator when at idle  the temperature gauge will drop down to 180, then back up to 190, then back to 185 when tapping  excelerator, then up to 195, and then after 35 to 40 minutes tops it slowly continues to rise to 200, 220 and keeps going up beyond 230 (we have course back off and work on calling it down once it starts creeping beyond 200).

 

What we have done during diagnosis:

Replaced hoses, replaced thermostat, drilled two small holes inside of thermostat before installing to allow ongoing circulation (the old thermostat had this done as well by prior owner), replaced radiator cap, replaced water pump, flushed radiator and block with radiator flush (twice), burped of course after replenishing coolant, and remedied any minor leaks.

 

When running top coolant hose is hot as it should be. Bottom coolant hose is very warm but not hot (as I believe it should be given it personally called fluid into the water pump and block).  As we see the temperature gauge start to climb above 190° we realize that the bottom coolant hose seems to be almost as hot (based on from touch) as the top coolant hose. ***Is this a possible sign that the radiator is not cooling the fluid well enough once reaching higher temperatures?

 

Signs:

No white smoke is coming out of tail pipes, motor turns over nicely at cold start, no traditional signs of a blown head gasket (although we’re not narrowing out anything at this point), not seeing any leaks in the colon system.  The 350 just doesn’t want to stay below 190 as mentioned above.

 

Where the trouble started:

Was on the road on a hot day and overheated. We’ve been in these conditions before and it stayed strong at 185. When we pulled over and checked under the hood the lower coolant line popped off the bottom of the radiator.  Not sure if that was just due to a loose bracket, for too much pressure built up somewhere in the corn system due to blockage and forced it off.

 

At this point we allowed at the cool, reconnected the lower coolant hose, checked all other hoses and fittings, refilled with coolant, burped, and everything was running nicely for about two weeks; thereafter  the overheating begin we begin our attempted diagnosis in changing out basic parts to eliminate possibilities.

 

Many thanks,

Jason and the AOA team 

Edited February 1, 2023 by Built in America

[Los_Control]

My first thoughts is possibly some crud got knocked loose in the radiator from overheating when the rad hose came off?

Possible the T-stat is now malfunctioning getting ready to stick open or closed????

 

What I would do at this point I call the shotgun approach. I figure if the lower radiator hose needs attention, so does the rest of the cooling system.

I would pull the radiator & flush it with a garden hose in both directions .... meaning turn it upside down and insert hose in lower so it comes out the radiator cap.

I figure the water should come out just as fast as you pit it in .... or it is plugged. I would repeat this until the water comes out clean.

 

I would check the water pump. If I can get the slightest wiggle from the front bearing, I would replace it. They are cheap & would piss me off if it starts leaking 2 months from now.

 

I would replace heater hoses, radiator hoses, T-stat .... I would install a flushing T in the heater hoses while at it.

With it all back together I would fill it with vinegar and run it through a few heat cycles to flush out the block & heater core using the flushing T.

 

May be over kill, now you can cruise trouble free for years knowing your cooling system is in good condition. When I give this treatment to my daily drivers, I also replace the serpentine belt, pvc & vacuum hoses .... the things we normally forget about.

[kencombs]

Electric fan?   Have you verified that it is running at full speed, charging system keeping battery at full charge?   I suspect something going on with the fan, voltage available, or possibly the thermo switch that controls it.

No electric fan, ignore me.

[Built in America]

On 11/4/2022 at 10:00 AM, Los_Control said:

My first thoughts is possibly some crud got knocked loose in the radiator from overheating when the rad hose came off?

Possible the T-stat is now malfunctioning getting ready to stick open or closed????

 

What I would do at this point I call the shotgun approach. I figure if the lower radiator hose needs attention, so does the rest of the cooling system.

I would pull the radiator & flush it with a garden hose in both directions .... meaning turn it upside down and insert hose in lower so it comes out the radiator cap.

I figure the water should come out just as fast as you pit it in .... or it is plugged. I would repeat this until the water comes out clean.

 

I would check the water pump. If I can get the slightest wiggle from the front bearing, I would replace it. They are cheap & would piss me off if it starts leaking 2 months from now.

 

I would replace heater hoses, radiator hoses, T-stat .... I would install a flushing T in the heater hoses while at it.

With it all back together I would fill it with vinegar and run it through a few heat cycles to flush out the block & heater core using the flushing T.

 

May be over kill, now you can cruise trouble free for years knowing your cooling system is in good condition. When I give this treatment to my daily drivers, I also replace the serpentine belt, pvc & vacuum hoses .... the things we normally forget about.

Hi Los Control! 
when you initially responded I sent a grateful response but it seems as though maybe it never posted.

 

Anyhow thank you so much for the help. Turns out to be a pretty wicked radiator clog likely due to a past effort that the prior owner may have taken to use a chemical treatment to fix a minor head gasket seal.

 

After going through a traditional flush, water and baking soda, and then a two day vinegar soak 98% the clog was worked out. The SB still wasn’t running as well as I knew it should after a couple hours on the road so I tried a bit of a MacGyver approach and it actually work marvelously = picked up a commercial auto detailing steamer that will use on other projects and used the extension rod (carefully bent it in a bit of an S shape to reach properly) to reach down into the top reservoir of the radiator and steamed the top of the vents at about 230°.
 

That evaporated the clogging at the top forcing the steam (used a rag to plug the top of radiator while the steamer Extention was manicured in) and everything that was dissolved flowed down through the bottom valve (took a gallon of water/steam over about 60min).  Our 41 GMC is back on the road running like a lion. ?

Edited February 1, 2023 by Built in America

[Built in America]

On 11/4/2022 at 11:00 AM, kencombs said:

Electric fan?   Have you verified that it is running at full speed, charging system keeping battery at full charge?   I suspect something going on with the fan, voltage available, or possibly the thermo switch that controls it.

No electric fan, ignore me.

Hi there KenCombs!

 

thank you for your response. I apologize for the delay. Our first posting on this forum we apparently did not submit our response properly back in November.

 

Your guidance definitely helped us eliminate other possibilities. Fan and electrical system is working well.

 

Turns out to be a pretty wicked radiator clog likely due to a past effort that the prior owner may have taken to use a chemical treatment to fix a minor head gasket seal = solidified gasket sealer was clogging and someone not fully out of the coolant system.

 

After going through a traditional flush, water and baking soda, and then a two day vinegar soak 98% the clog was worked out. The SB still wasn’t running as well as I knew it should after a couple hours on the road so I tried a bit of a MacGyver approach and it actually work marvelously = picked up a commercial auto detailing steamer that will use on other projects and used the extension rod (carefully bent it in a bit of an S shape to reach properly) to reach down into the top reservoir of the radiator and steamed the top of the vents at about 230°.
 

That evaporated the clogging at the top forcing the steam (used a rag to plug the top of radiator while the steamer Extention was manicured in) and everything that was dissolved flowed down through the bottom valve (took a gallon of water/steam over about 60min).  Our 41 GMC is back on the road running like a lion. ?

[Built in America]

On 11/4/2022 at 10:00 AM, Los_Control said:

My first thoughts is possibly some crud got knocked loose in the radiator from overheating when the rad hose came off?

Possible the T-stat is now malfunctioning getting ready to stick open or closed????

 

What I would do at this point I call the shotgun approach. I figure if the lower radiator hose needs attention, so does the rest of the cooling system.

I would pull the radiator & flush it with a garden hose in both directions .... meaning turn it upside down and insert hose in lower so it comes out the radiator cap.

I figure the water should come out just as fast as you pit it in .... or it is plugged. I would repeat this until the water comes out clean.

 

I would check the water pump. If I can get the slightest wiggle from the front bearing, I would replace it. They are cheap & would piss me off if it starts leaking 2 months from now.

 

I would replace heater hoses, radiator hoses, T-stat .... I would install a flushing T in the heater hoses while at it.

With it all back together I would fill it with vinegar and run it through a few heat cycles to flush out the block & heater core using the flushing T.

 

May be over kill, now you can cruise trouble free for years knowing your cooling system is in good condition. When I give this treatment to my daily drivers, I also replace the serpentine belt, pvc & vacuum hoses .... the things we normally forget about.

Hi Los Control! 
when you initially responded I sent a grateful response but it seems as though maybe it never posted.

 

Anyhow thank you so much for the help. Turns out to be a pretty wicked radiator clog likely due to a past effort that the prior owner may have taken to use a chemical treatment to fix a minor head gasket seal.

 

After going through a traditional flush, water and baking soda, and then a two day vinegar soak 98% the clog was worked out. The SB still wasn’t running as well as I knew it should after a couple hours on the road so I tried a bit of a MacGyver approach and it actually work marvelously = picked up a commercial auto detailing steamer that will use on other projects and used the extension rod (carefully bent it in a bit of an S shape to reach properly) to reach down into the top reservoir of the radiator and steamed the top of the vents at about 230°.
 

That evaporated the clogging at the top forcing the steam (used a rag to plug the top of radiator while the steamer Extention was manicured in) and everything that was dissolved flowed down through the bottom valve (took a gallon of water/steam over about 60min).  Our 41 GMC is back on the road running like a lion. ?

Edited February 1, 2023 by Built in America

[Built in America]

On 1/29/2023 at 8:41 PM, Built in America said:

Hi there KenCombs!

 

thank you for your response. I apologize for the delay. Our first posting on this forum we apparently did not submit our response properly back in November.

 

Your guidance definitely helped us eliminate other possibilities. Fan and electrical system is working well.

 

Turns out to be a pretty wicked radiator clog likely due to a past effort that the prior owner may have taken to use a chemical treatment to fix a minor head gasket seal = solidified gasket sealer was clogging and someone not fully out of the coolant system.

 

After going through a traditional flush, water and baking soda, and then a two day vinegar soak 98% the clog was worked out. The SB still wasn’t running as well as I knew it should after a couple hours on the road so I tried a bit of a MacGyver approach and it actually work marvelously = picked up a commercial auto detailing steamer that will use on other projects and used the extension rod (carefully bent it in a bit of an S shape to reach properly) to reach down into the top reservoir of the radiator and steamed the top of the vents at about 230°.
 

That evaporated the clogging at the top forcing the steam (used a rag to plug the top of radiator while the steamer Extention was manicured in) and everything that was dissolved flowed down through the bottom valve (took a gallon of water/steam over about 60min).  Our 41 GMC is back on the road running like a lion. ?

[Built in America]

On 2/1/2023 at 11:57 AM, Built in America said:

Hi Los Control! 
when you initially responded I sent a grateful response but it seems as though maybe it never posted.

 

Anyhow thank you so much for the help. Turns out to be a pretty wicked radiator clog likely due to a past effort that the prior owner may have taken to use a chemical treatment to fix a minor head gasket seal.

 

After going through a traditional flush, water and baking soda, and then a two day vinegar soak 98% the clog was worked out. The SB still wasn’t running as well as I knew it should after a couple hours on the road so I tried a bit of a MacGyver approach and it actually work marvelously = picked up a commercial auto detailing steamer that will use on other projects and used the extension rod (carefully bent it in a bit of an S shape to reach properly) to reach down into the top reservoir of the radiator and steamed the top of the vents at about 230°.
 

That evaporated the clogging at the top forcing the steam (used a rag to plug the top of radiator while the steamer Extention was manicured in) and everything that was dissolved flowed down through the bottom valve (took a gallon of water/steam over about 60min).  Our 41 GMC is back on the road running like a lion. ?

[Built in America]

On 11/4/2022 at 10:00 AM, Los_Control said:

My first thoughts is possibly some crud got knocked loose in the radiator from overheating when the rad hose came off?

Possible the T-stat is now malfunctioning getting ready to stick open or closed????

 

What I would do at this point I call the shotgun approach. I figure if the lower radiator hose needs attention, so does the rest of the cooling system.

I would pull the radiator & flush it with a garden hose in both directions .... meaning turn it upside down and insert hose in lower so it comes out the radiator cap.

I figure the water should come out just as fast as you pit it in .... or it is plugged. I would repeat this until the water comes out clean.

 

I would check the water pump. If I can get the slightest wiggle from the front bearing, I would replace it. They are cheap & would piss me off if it starts leaking 2 months from now.

 

I would replace heater hoses, radiator hoses, T-stat .... I would install a flushing T in the heater hoses while at it.

With it all back together I would fill it with vinegar and run it through a few heat cycles to flush out the block & heater core using the flushing T.

 

May be over kill, now you can cruise trouble free for years knowing your cooling system is in good condition. When I give this treatment to my daily drivers, I also replace the serpentine belt, pvc & vacuum hoses .... the things we normally forget about.

Thank you again for your help with the previous trouble we’re having with our 41 GMC that has a Chevy small block under the hood.

 

Hopefully you receive the response below but realized that we didn’t respond to the post properly.

 

Rendering into the hot season here in California and I believe the mistake that we made causing the radiator to clog has been corrected by using the hot steaming method rather than having to rebuild the core or replace the radiator overall.

 

Many thanks,

jason

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