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Old 05-05-2004, 11:42 AM
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Overheating at Idle

Hi everybody first post here

I have a read alot of threads on here about overheating problems so let me start.

This is a rebuilt 350 CSB 4bolt bored 60 over with 0 miles on it. Car has been timed appropriately. There is an aftermarket universal fan shroud that was purchased from summit. It has a flex fan installed on it. Aluminum Radiator from summit, and a 16lb rad cap. The water/coolant mixture is 60/40% Brand new stock water pump with a 180 t-stat. It has a mechanical temp gauge. There is no overflow tank attached could this be causing the engine to overheat at idle? I have bled the radiator a few times to get rid of any air that maybe trapped in the engine.

Not sure what else I maybe missing but I cant figure out why it maybe overheating??? Was thinking about having him get a 30% more flow water pump but thought I would ask you gentlemen for some more advise.

When the car starts up it will gradually increase in temp. Once it hits 180 you can watch the temp decrease from the t-stat opening. Then the temp drops from the t-stat opening but the engine will continue to climb in temp after this and will not stop climbing. We shut the car off once it reaches 230.

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Old 05-05-2004, 11:56 AM
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Could be air trapped in the system. Also make sure your shroud cover the radiator properly and the fan is half into the shroud. I know this will sound dumb but make sure the fan is spinning in the proper rotation.

Sounds more like a air lock in the coolant system to me though.

Regards
Mark
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Old 05-05-2004, 12:03 PM
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have you double checked to see if the pump is the correct direction. newer engines run reverse flow pumps. the vanes are disigned to propell water when turned a certain direction, if reversed you get a little flow but not much.

when first starting the motor (cold) squeeze the upper rad hose, get an idea how stiff it is. (watch for fan!)
when the thermostat opens, (around 180 in your case) squeeze the upper radiator hose again. (it will be warm to hot, you may want to use a rag) ... you should have enough pressure that it is difficult to squeeze

the overflow tank is there only for instances when you get a little to hot, create steam and pressure exceeds your cap.
when this happens pressure is relieved through the cap, into your resevior. when the pressure drops it will suck it back in.
it will only affect you if you lose enough water to loose circulation.

later,
31
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Old 05-05-2004, 12:16 PM
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ever put in a thermostat in backwards??
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Old 05-05-2004, 12:26 PM
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Once! Learned my lesson on that one.
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Old 05-05-2004, 01:07 PM
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I had left the over flow line off my car when the plastic tank had cracked, it ran hot afterwards, GM uses the burp system, and if it can`t bleed off air it runs hot, reconnect the overflow line and tank and see what happens. also make sure your vacuum advance is connected to a manifold source or one that pulls vacuum all the time, there`s been several cases where this can cause it to run hot at idle.
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Old 05-05-2004, 01:08 PM
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Ok this engine is an older engine I believe in the 70's. Didnt know the fan could turn in a different direction? I will check the hose tonight and see if it will get warm. Its kinda hard to squeeze the hose since its one of those universal flex hose's. I will try to bleed the air from the block again...

I dont have the vacum advanced hooked up could this be an issue?

Is this the correct way to bleed?

1. Let the engine get warm and allow the t-stat to open.
2. when the t-stat opens add water.
3. close rad cap
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Old 05-05-2004, 01:32 PM
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The over flow line must be connected, you can bleed the system all you want and it`ll just create another vacuum lock as soon as the system builds any pressure. if you connect the overflow line to the overflow tank and fill the tank to the correct height, you`ll see it burping air on occasion. what do you have your base timing set at? Unless your running a big cam the vacuum advance is important and needs to be connected, idle mixtures and off idle mixtures in mild street engines are lean, therefore they burn slower, this is where vacuum advance comes in, without a overflow in use and without vacuum advance is asking for it to run hot.
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Old 05-05-2004, 01:56 PM
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This is my buddies "pig" so I will have to get the exact spec for the cam. I know its a high performance cam and the lift is around 486. I think the timing is supposed to be 34* adv. I could be wrong though cuz i dont have the cam card here at work

I'm at work now but when I get off I will connect the vacum advance and try to find a over flow tank. We got rid of his because it was cracked on the bottom and figured we didnt need one right now to break the engine in
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Old 05-05-2004, 02:08 PM
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Sorry double-vision, Never in my life, ever ran a burp tank. It's not needed in order to prevent overheating. It just means you will have to add water a little more often. It's why a lot of manufactures have gone this route. Easier maintenance.



My advice, drain the cooling system by removing the bottom radiator hose until water stops pouring out. Start engine and SLOWLY pour the water back in a little at a time. This will give the system time To warm up and the pressure from the pump will help purge air bubbles that get trapped in and around the heads and intake.

Air lock: Happens when air will not move downward to get to a higher point in a system or to find an escape route.
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Old 05-05-2004, 02:13 PM
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Johnson, not one to argue or disagree, I had replaced everything in my cooling system, from water pump to radiator, the car still ran hot, the only thing I didn`t have was the over flow connected, I came here and did a post on it in fact, when it was pointed out to me it must be in use, I reconnected it and my cooling issues were over. All I had did was run a line off it and placed a bolt in it and left it like that, I didn`t think it would cause it to run hot either, but it did in my case.
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Old 05-05-2004, 03:38 PM
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Make sure the flex fan is on right,and how far is the fan from the radiator?? if all is on right,i would fill the radiator up and unhook a heater hose so it can get any air out of the system. this will help bleed the system. and plus what kinda car is it??? and the new t-stat could be sticking too.

Robbie
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Old 05-05-2004, 04:07 PM
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A good test to see if the fan and shroud are doing their job, is to hold a dollar bill by the corner about 6" in front of the radiator at idle, if the fan/shroud is working correctly the vacuum will pull the bill out of your grasp and onto the radiator. Unless of course your a cheapskate like me and get sucked into the radiator cause you refuse to let go of the money!

Last edited by Pony; 05-05-2004 at 04:18 PM.
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Old 05-05-2004, 04:24 PM
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Double, There are alway's those times things seem to defy all laws. It's happened to me at least a thousand times.

Last night I was trying to get this old jimmy to start after cranking on it for ever. Well, after about another ten minutes I decided the fuel pump must have been weak. I removed the line and cranked it for a split second, the engine started! Why would the thing run with out the fuel line connected!!. Strange things happen all the time.
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Old 05-06-2004, 08:13 AM
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Quote:
Originally posted by Pony
A good test to see if the fan and shroud are doing their job, is to hold a dollar bill by the corner about 6" in front of the radiator at idle, if the fan/shroud is working correctly the vacuum will pull the bill out of your grasp and onto the radiator. Unless of course your a cheapskate like me and get sucked into the radiator cause you refuse to let go of the money!

I did try your test and the dollar ($5 actually) fell on the ground

I also hooked up the vacum advance and still the car overheated. My buddy is ordering the overflow tank from GM today its only $14. Oh btw its a 1983 Oldsmobile Cutlass Supreme.

A buddy of mine told me to jack up the car in front and wait for the t-stat to open and then add water this should help all the air to exit the system...
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