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Topic: Heating problem

in Forum: C3 Cooling and Heating Systems


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Heating problem (2/12)
 12/31/10 11:54am
Gunslinger
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Frederick, MD - USA

Vette(s):
1969 convertible L71 427/435 4-speed black interior


Joined: 9/8/2003
Posts: 3398

It could be one of several things, but my first inclination is to look at the lower radiator hose.  If the internal spring is missing or rusted away, the hose can collapse under vacuum pressure, thus creating a restriction.  When you slow or stop the hose goes back to normal shape and allows coolant to flow normally.

To check the fan clutch, have the car idling at normal operating temperature and shut the engine off.  If the fan clutch is OK, it should stop rotating almost immediately with the engine.  If it keeps spinning for several rotations it's bad.  Usually with a bad fan clutch you'll find overheating at idle when it should be locking up with engine rpm...just the opposite of what you're experiencing.  At speed the fan clutch should be free wheeling anyway.

Other things to check...tightness of belts, seals properly installed around the radiator and air deflector in place under the front end.

Start with the easiest and most basic...belts then work up to more complex.  You should be able to squeeze the lower hose and feel whether the spring is present.  Visual check of the fan clutch and whether seals are present.  It could be as simple as slipping belts.
Heating problem (3/12)
 12/31/10 12:45pm
yostusota
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York, PA - USA

Vette(s):
1969 daytona conv. all original 350 350 380 4 sp w/air..and hard top


Joined: 5/18/2010
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Replace the thermostat. and run a flush thru the radiator. I would bet it's stuck open and the radiator is a little clogeed..mine did the same thing too.
Rich
yostusota2010-12-31 09:47:42

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Heating problem (4/12)
 12/31/10 1:51pm
aceintheholeLifetime Member
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Manteca, CA - USA

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1978,two tone,Metalic Rootbeer & gold 1975 L48 4 speed


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..and, of course, if it's an older motor, the temp. will increase as the load increases until it's over 200, and can run that way all day without harm. Just makes you feel a little uncomfortable.

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Heating problem (5/12)
 12/31/10 2:24pm
Adams' AppleLifetime Member
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Duncanville, TX - USA

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#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


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The fan clutch really shouldn't be doing anything(much) while driving except just going along for the ride. At speed, there should be enough air flowing thru the rad to keep the temps in check. Bruce is prolly in the right area when mentioning the lower raditator hose. I don't know about being able to squeeze it tho, unless yours is easier to get to than mine!
I'd have to go with a restriction in the system, most likely a hose, but possibly the thermostat....might even be a smidge low on coolant.


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Heating problem (6/12)
 12/31/10 2:33pm
yostusota
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York, PA - USA

Vette(s):
1969 daytona conv. all original 350 350 380 4 sp w/air..and hard top


Joined: 5/18/2010
Posts: 1518

That's funny..I could grab the lower hose on mine..just haven't..that spring thing inside the hose is that a stock thing..mine was a completely open thermostat and a clogged radiator..temp went up while driving and back down once at idle..unless I sat for to long then the temp would go up yet very slowly..I didn't even think that I had a thermostat untill I removed it..
Rich

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Heating problem (7/12)
 12/31/10 5:06pm
ranger3Lifetime Member
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North Charleston, SC - USA

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1975 L48 AT AC T-top


Joined: 3/20/2004
Posts: 4176

I agree with Gunslinger regarding the lower rad hose. I have had that problem on three different Vettes.
 
Scott
Heating problem (8/12)
 12/31/10 5:50pm
Gunslinger
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Frederick, MD - USA

Vette(s):
1969 convertible L71 427/435 4-speed black interior


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Posts: 3398

The spring inside the lower hose is stock, unless you have a replacement that's a flex hose. There are some new replacement hoses that don't come with springs anymore...either they're stiff enough or have a spring wound inside the rubber...don't know which.  That might be fine for a new hose, but what happens when the hose material softens with age?  Maybe I'm old school, but I find the presence of an internal spring comforting.

The problem could be a combination of several things due to age...hose, coolant level, sending unit or gauge, belts, radiator seals, radiator fins or tubes clogged...any combination could be playing a minor part but together could make it happen to the degree you're noticing.  
Heating problem (9/12)
 12/31/10 5:59pm
yostusota
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York, PA - USA

Vette(s):
1969 daytona conv. all original 350 350 380 4 sp w/air..and hard top


Joined: 5/18/2010
Posts: 1518

Ok so the lower hose should have some sort of spring in it..ok..makes sense how that would make for some real wierd cooling problems..it isn't all that hard to check on these cars either..probably the easiest thing next to fluid level..I will put that in the data bank..
Rich
 


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Heating problem (10/12)
 12/31/10 6:59pm
lukesvetteLifetime Member
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HOWELL, NJ - USA

Vette(s):
1979, Targa Blue (72 Color), Pace Car rear spoiler, L88 hood, Dark blue factory interior, 525HP 406, HD 700R4, 370 gears,Steeroids, composite rear spring, TT IIs wrapped in T/A Radials.


Joined: 5/18/2004
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Same darn thing was happening to my car after I swapped in the 406. The lower rad hose with the spring was the fix!! Get ready for the price!! I think I paid a little over $40 for one. All the parts counter hoses had no spring...had to get it from a Vette parts place.
Heating problem (11/12)
 12/31/10 7:33pm
yostusota
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York, PA - USA

Vette(s):
1969 daytona conv. all original 350 350 380 4 sp w/air..and hard top


Joined: 5/18/2010
Posts: 1518

Ok so now you guys got me real curious..I had to check..I got a spring in mine..it's not the stock hose and I know it's pretty old..looks like a real PITA to change..looks like you can get it from underneath..so how does one know if the hose IS the problem or so you just do it or do you see if the hose is collapsed after driving..I think making sure the fluid level and the condition of the radiator and thermostat would be first..if you can't see the hose collapse..there is one other thing I have seen although rare..the water pump impeller can be rusted away..making flow the issue..not a fun thing to figure out but it can be a concern..
Rich

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Heating problem (12/12)
 12/31/10 11:16pm
ossw1
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Rocklin, CA - USA

Vette(s):
1970 T-Top350/350hp numbers matching 4 speed. It's a mess and 1970 Convertible 4 speed.


Joined: 4/2/2005
Posts: 484

Thanks guys lots of info. 3 months ago I took out the radiator and  radiator frame. I clean up the frame and put in a new radiator with new seals. When I bought the lower hose I did ask about the spring and I was told that this hose did not need it. So I have not check the thermostat and I will. The engine is old I am hoping when I take off the thermostat it will tell me something. Now I did not have this problem before I change everything. I will start the process of the elimination and see where it will lead.     
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