Author Topic: Overheating problem  (Read 5515 times)

Offline bobcooter

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Overheating problem
« on: June 27, 2010, 04:29:01 PM »
My 79 C-20 with a 350 is starting to work on my mind. I was driving to work Friday and it ran hot. I found a busted bottom radiator hose. No biggie Right? I replaced the hose and changed from a 195 thermostat to a 180 degree since it's been crazy hot down here.  The hose was cut right along where the hose clamp goes on the radiator neck. The thing is it's still giving me problems. About a year ago when I rebuilt the engine I put all new hoses, water pump, thermostat and not quite a year ago I replaced the radiator. I have about 19000 miles on the engine with no problems until now.  With the 195 thermostat, on a rally hot dayith the ACon, it would run around 200 to 205 degrees.The radiator has around 17000 miles. It is a cheap looking plastic and aluminum thing from a major parts chain.
 So far i have: Changed the bottom hose
Replaced the fan clutch set up with a mechanical drive flex fan off of a 78 parts truck of mine.
 Checked the new 180 thermostat for operation and reinstalled.
Changed the water pump
Checked to make sure the new bottom hose isn't getting sucked flat.
It was still acting up so I even flushed the radiator with radiator flush. From looking in the top of the radiator it was very clean inside. For some reason it just doesn't seem like enough water is flowing through the radiator when you look inside the fill neck with it running.
 You can start it up and it will run at about 182 to 185 degrees while driving with the AC on. Right now it is 86 degrees with 76% humidity. Yesterday the heat index was 116. If you stop for a redlight the temp creeps up to around 190 or so. As soon as you give it gas to take off it it drops back to around 182 or so. Just drove it about 15 miles with no problem except it pushed water out into the overflow jug. Nearly full. I had lowered the level in the jug to the cool mark and the radiator full before driving it today.
Now for the really weird part. Once you shut it off, the temp creeps up to around 215 degrees.  ???
'79 C-20, 350/400, 3:73 gears, 9 leafs and a headache rack
Favorite Quote, "Good judgement comes from experience. Experience comes from poor judgement."

Offline Layne

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Re: Overheating problem
« Reply #1 on: June 27, 2010, 05:01:41 PM »
It'll heat soak when you shut it off. My 77 runs at 215 and my sierra will do 220 all day. they both have 195 stats in them.
77 c-10 - 77 400 86 700r4 "Emmy"
83 citation - 2.5L Four on the Floor!
88 sierra - reman 350 700r4 "Eleanor"
All normal practicality and rational money handling goes out of the window when it comes to my truck.

Offline bobcooter

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Re: Overheating problem
« Reply #2 on: June 27, 2010, 05:37:12 PM »
Matbe it was doing it all along and I just did not look so closely. The thing that bothers me is it doesn't suck the coolant back out of the overflow jug into the radiator as it cools down. It let it idle in the driveway today and let it get up tp temp and run there for a while . I had run the overflow hose into a gallon milk jug so I could see beter. I shut it down and went insdie for about an hour? It had sucked the coolant back into the jug.
'79 C-20, 350/400, 3:73 gears, 9 leafs and a headache rack
Favorite Quote, "Good judgement comes from experience. Experience comes from poor judgement."

Offline bobcooter

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Re: Overheating problem
« Reply #3 on: June 27, 2010, 06:46:42 PM »
One more thing: I had my radiator cap tested. Tested fine. Went ahead and replaced it anyway with a new 16psi cap.
'79 C-20, 350/400, 3:73 gears, 9 leafs and a headache rack
Favorite Quote, "Good judgement comes from experience. Experience comes from poor judgement."

Offline Layne

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Re: Overheating problem
« Reply #4 on: June 27, 2010, 07:38:43 PM »
I had run the overflow hose into a gallon milk jug so I could see beter. I shut it down and went insdie for about an hour? It had sucked the coolant back into the jug.
I'm confused? Do you mean the radiator?
77 c-10 - 77 400 86 700r4 "Emmy"
83 citation - 2.5L Four on the Floor!
88 sierra - reman 350 700r4 "Eleanor"
All normal practicality and rational money handling goes out of the window when it comes to my truck.

Offline bobcooter

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Re: Overheating problem
« Reply #5 on: June 27, 2010, 07:48:57 PM »
Uh... yea, the radiator sorry...
'79 C-20, 350/400, 3:73 gears, 9 leafs and a headache rack
Favorite Quote, "Good judgement comes from experience. Experience comes from poor judgement."

Offline Irish_Alley

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Re: Overheating problem
« Reply #6 on: June 28, 2010, 01:16:51 AM »
Everything sounds fine. But are you saying with the overflow jug the coolent won't be sucked back to the rad even after changing the cap? What happens if you over tighten a cap won't that do the same thing
If you can’t tell yourself the truth, who can you tell it to?~Irish_Alley

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Offline bobcooter

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Re: Overheating problem
« Reply #7 on: June 28, 2010, 07:47:51 AM »
I don't think I overtightened the cap and yes, it is brand new. The amount of coolant that stays in the overflow jug after it cools down is the same amount it takes to fill the radiator back up. I had the rdiator filled up and then I marked my overflow jug. I have one of those "Louisiana Credit Cards" to siphon (pump) the coolant back into the radiator.
 I'm praying someone has a simple soulution and it's not a bad head gasket. :-[
'79 C-20, 350/400, 3:73 gears, 9 leafs and a headache rack
Favorite Quote, "Good judgement comes from experience. Experience comes from poor judgement."

Offline topp

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Re: Overheating problem
« Reply #8 on: June 28, 2010, 08:22:40 AM »
I don't think I overtightened the cap and yes, it is brand new. The amount of coolant that stays in the overflow jug after it cools down is the same amount it takes to fill the radiator back up. I had the rdiator filled up and then I marked my overflow jug. I have one of those "Louisiana Credit Cards" to siphon (pump) the coolant back into the radiator.
 I'm praying someone has a simple soulution and it's not a bad head gasket. :-[

If the Coolant goes INTO the overflow, and does not get sucked back in, there is a leak in the system somewhere.
If there is no coolant under the vehicle, smell your exhaust when it's hot.  If it smells sweet, you prolly have a head gasket or intake manifold leak
'90 Suburban TBI 350

Offline bobcooter

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Re: Overheating problem
« Reply #9 on: June 28, 2010, 08:34:55 AM »
Thanks topp. I'll check that when I get home this afternoon.
'79 C-20, 350/400, 3:73 gears, 9 leafs and a headache rack
Favorite Quote, "Good judgement comes from experience. Experience comes from poor judgement."

Offline bobcooter

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Re: Overheating problem
« Reply #10 on: June 28, 2010, 01:30:05 PM »
One more question.  I have a set of 882 heads on the engine. I hear they are notorious for cracking when hot. Where do they usually crack so I can check them?
'79 C-20, 350/400, 3:73 gears, 9 leafs and a headache rack
Favorite Quote, "Good judgement comes from experience. Experience comes from poor judgement."