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Since my vette is down for the engine repairs i figure i might as well try to get a handle on my overheating problem before i get it back on the road It's an 85 vette (naturally), stock as far as i know. I've had it for about 7 years. It has 170,000 miles on it and except fot the latest timing chain-gear incident, the car doesn't smoke nor burn any oil. It also has tremendous power and speed. Go figure? From day one though, it overheated whenever i put the a/c on. Without the a/c on it maintains a temperature of about 180 to 190. When i put the air on it just climbs steadily and will go right over the 250 mark if i dont shut the a/c down. It has the stock aluminum radiator and at one point i even tried an aftermarket metal one but there wasn't any difference. It has 2 electric fans,one in front of the condensor pushing through to the engine compartment and the other behind the radiator pulling into the compartment. Even with both on it still overheats. I've tried with thermostats and without. I've checked for air bubbles. I've used water wetters. My heater core however is bypassed and i'm wondering if the cooling system on this car needs the heater core in the equation to cool the engine. I don't remember when the core was bypassed and when i first noticed the overheating problem. I'm sorry this thread is so long, i wanted to give you guys as much info as possible . thanks rick
 

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Rick,

Just a question, with you having two fans are they mounted one in front of the other?

If they are you may not have enough of the condenser surface exposed to allow for proper cooling.

I would find out about the heater core also. Your system requires a certain amount of coolant to work properly. I don't remember how the return line runs to your radiator.

Just some thoughts.

Pappy
 

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Does the same belt run the a/c and water pump. Maybe with it on, the extra effort involved is causing the belt to slip.................sounds a bit out there, but you never know.
 

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running hot

I have a 79 vette. I took the A/C out of the car and it still runs hot. I took the thermostat out and it dropped 20 deg but still runs hot. I have tried everything to get it to run at a decent temp including new rad. I am now going to cut holes out to the wiper valley for heat to escape.
 

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Try running it at a fast idle, ac on and a box fan sitting in front of it. If it dosn't heat then you haven't got enough air flow.

I don't think the by passed heater will have any affect on a heating problem.

Troy
 

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:smash: i would have to ask first does i do this while driving down the road at 60 mph? or does it only do it in stop and go traffic?is it a auto trans with a external cooler?well first things first. lets check the water pump since the engine is already torn down it will be easy to check,visualy check the impeller for slippadge.second is the pump turning at the proper speed(right pullys for the engine)?thirdly (this is where it gets confrusing).oky doky.a radiator is nothing more than a heat exchanger ,it takes hot water and exposes it to cool air therefore since heat travels to cold the radiator exchanges the hot water to the cold air, the cooler the air the more heat that can be absorbed and carried away.this can only be done if there is adaquate air flow over the radiator.now, you said that you have two fans one pushing one pulling correct?they are most likly mounted directly on the radiator like most aftermarket fans?two problems can occure here.one being that the fans are only pulling air directly in their respected paths leaving a lot of area of the radiator that has no air passing thru it.Or the air is passing thru the radiator so fast that it doesent have time to pick up the heat from the rad.when you are not running the a/c, the only heat that is created is by the radiator,(the cooler the air the more heat that can be absorbed)
when you turn the a/c on the condenser gets realy hot, so now we are blowing already heated air across the radiator,now the radiator cant disburse as much heat causing the heat to go directly back in the engine,with the two fans running the air is passing thru the radiator to fast and since the air is hot it will take longer to absorbe the heat from the radiator.to solve this ,i would say to do away with the double fans on opposing sides and get one of the double fan kits that mount on one side of the radiator and that covers the whole radiator.well hope that helps, and good luck.
 

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Discussion Starter #7
The fans are the stock corvette set up. The one in the engine compartment does not sit against the radiator. It sits suspended by a shroud around it. It is big, big enough to cover the whole area of the radiator. The condensor fan is mounted the same way but up front ahead of the condensor. It doesn't matter if i drive city or highway, it overheats the same. As soon as i shut the air off it drops down quickly to 180. I have 1 serpentine belt that takes care of everything. thanks rick
 

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Thats a tough one. Id get a heat gun and see how hot the front radiator is getting. You have a radiator hooked up to your AC can dont you? Perhaps that is getting hot and as its in front of your coolant radiator, its not allowing your coolant to cool as much as it would previously.

Just a thought.
 

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Discussion Starter #9
Are you asking if i have a condensor for my a/c? If so , yes and it is before the engine radiator and could very well be the problem although i don't SEE any blockage on the outside of it. But that means nothing, it could be plugged anyway. Thanks Siggy, Rick
 

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:smash: just thought of somthing.have you checked your a/c out? there could be somthing wrong with it causing excesive heat in the condenser.if the condenser is hotter thn the rad.then you will have the oppisite affect.insted of cooling the rad.it would be warming it up.just for giggles, what core is the rad.and have you considered trying bigger one.one other thing i have is have you checked to see that the bottem rad hose has a spring in it to keep it from calapsing?i run in to this on a truck at the dealership.it run fine until the a/c was on and then it would get hot,what was happining was the condinser was heating the air over the rad caising the rad not to disapate the heat very well. like i said what doesnt go to the air goes back in the engine which was causing the thermostat to open more reg.till eventualy it stayed open and caused the bottom rad hose to colapse.but on this one it didnt cool off at the a/c was off because after it sucked it shut it would not open back up till the truck was shut off .im still leaning to the air flow to area ratio tho,given the corvets front end and limited space there isnt much room for error.maby try a hotter thermostat (sounds crazy) but a hotter thermo. would cause the water to stay in the rad. longer alowing more time to disapate more heat. maby consider a high volume water pump.
 

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Just a couple of thoughts....I think Engineman is heading in the right direction, and he is definitely right about a hotter thermostat improving the efficiency of the radiator. I went from a 160 thermostat (my idea) to a 195 thermostat (the General's idea); it never gets as cold as it did before, but it never gets as hot either. I also think you need to get the AC checked out. Something is making the condensor heat up too much. You might also check with Hot Rod Air (nice guys who know a LOT) to see if they have run across this problem with older Vettes.

Bracketeer! Do not cut holes in the wiper valley!! That is a high pressure area and may actually increase the air pressure under the hood. Ever notice that most cars have their vent intake in that area? Look at high performance cars and you will see the engine compartments vented to the side or with louvers about midway on the hood. That's why cowl induction hoods are not called cowl vent hoods. Look behind your front wheels and you may find some flaps that can be removed or fastened open (although this may cause problems when driving in the rain).

Keep us posted,

Bluesman
 

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I've seen faulty or near faulty compressors cause the engine to pull hard and over heat.

Troy
 

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I think it has to be something like that, Troy. That is just too big a temperature swing to be coming from a normal AC. Let's face it, the heat in the condensor is mostly the heat from the passenger's compartment plus the general inefficiency of the AC system...and the passenger compartment in a Vette just aint that big!! Since it doesn't overheat when the AC isn't running, the condenser isn't blocked.

Bluesman
 

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back to a basics question, if you turn the temp back to half way can you here the compressor clutch cycling on and off and on and off? If not you have a controls problem.

I can tell you a cure but don't know what will fit to work....(don't know the spec's on your condensor)

Problem:eek:riginal 65 Mustang condensor is single row about 20x20, here in FL, compressor ran 100% of the time, motor gets hot pretty quick, car is not very cool

Solution: I found a 20x20 2row that fit, now the compressor runs 50% and alot colder air (like 42 degrees....we measured it), no motor heat problems

So if you have a 2 row....try a 3 row...so the compressor runs less
 

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I would check...

Have you had your AC checked out for correct charge lately? This might be a good area to focus on.

If your system is low on refrigerant, the hi-side (Condenser coil) is going to show a condition known as "Super-heat". The refrigerant that has removed the heat from inside your vehicle and is now warm is returned to the compressor where it picks up the heat from cooling the compressor AND also picks up additional heat from being compressed.

Think of how warm the head on your compressor gets while running, or how warm a bicycle pump gets from use.

The hot refrigerant will not have enough time in the condenser to shed heat if the charge is low, and "Super-heat" will be excessive. The condenser will run hotter than normal. Depending on the outside temp, humidity & load, it may be close to 200 degrees. I do not have a T&P chart for automotive refrigerants, so I can only guess on the temp.

You may also check out the filter/dryer in the system, as it could be plugged. The check for this is easy, as the temperature should be the same on both the inlet and the outlet sides. Any plugging of the filter/dryer will show as a restriction in the system, and the outlet side will feel noticeably cooler.

Hope this helps.
 
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