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Overheating big block - could use some suggestions...?

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Overheating big block - could use some suggestions...?

 
Old 05-18-2019, 02:58 PM
  #21  
BigBill94
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Originally Posted by Gunfighter13 View Post
That radiator is not made to run with a surge tank. Made to use a overflow tank. I did not see you list the temp the fans come on and off. may be another issue.
I have the Dakota set to spin up the first fan at 185 and the second at 195. Both fans on full blast the temperature still climbs. Said another way, once it hits 185 the first fan comes on (5 degrees over the thermostat) then the second one comes on 10 degrees later..... It still easily passes 210 with both fans running full blast.

The radiator doesn't "know" it has a surge tank or an overflow tank, can you explain?

What I've noticed is that the heater outlet on the intake manifold "pressurizes" the surge tank, and then coolant is forced into the radiator via the small overflow hose on the surge. The radiator cap does act as a "one way" until it opens, meaning coolant can flow into the radiator via the small discharge tube on the surge tank but not out of the radiator discharge until the cap opens.

Am I missing something?
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Old 05-18-2019, 04:47 PM
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Originally Posted by derekderek View Post
first, double check the actual temp. 50 year old gauge and sender? or possibly worse, a new sender that isn't right for the gauge? pump rotation. serpentines run backwards. the spoiler-diverter-splitter under front bumper. is it there? lastly go bubba. remove the thermostat to see what temp you get without.
With everything he has checked it may be the wrong water pump. March Serpentine system uses a reverse rotation pump.
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Old 05-18-2019, 05:10 PM
  #23  
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heats up at 45 mph or so. drive home warm. let it idle. temp comes down? if it is a straight blade pump, it runs same either direction. if curved blades running wrong way will provide some but not much coolant flow. removable plate on back of pump? or cheap bluetooth borescope.. edit. take off the bypass hose from top of water pump. shine flashlight in...

Last edited by derekderek; 05-18-2019 at 05:16 PM.
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Old 05-18-2019, 05:19 PM
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Originally Posted by BigBill94 View Post
I have the Dakota set to spin up the first fan at 185 and the second at 195. Both fans on full blast the temperature still climbs. Said another way, once it hits 185 the first fan comes on (5 degrees over the thermostat) then the second one comes on 10 degrees later..... It still easily passes 210 with both fans running full blast.

The radiator doesn't "know" it has a surge tank or an overflow tank, can you explain?

What I've noticed is that the heater outlet on the intake manifold "pressurizes" the surge tank, and then coolant is forced into the radiator via the small overflow hose on the surge. The radiator cap does act as a "one way" until it opens, meaning coolant can flow into the radiator via the small discharge tube on the surge tank but not out of the radiator discharge until the cap opens.

Am I missing something?

An overflow system has a reservoir that has coolant in it and is connected to the radiator via the fill cap. The radiator has a pressure cap (about 15psi). As the engine temperature rises, coolant is pushed under pressure past the cap and into the overflow tank. As the engine cools the coolant is sucked back into the radiator through a valve in the radiator cap, keeping the coolant level full in the radiator.

A surge system is connected to heater hose and to a hose that is connected to the radiator. The pressure cap is on the surge tank and there is constant flow of coolant from the radiator to the tank. The tank becomes a part of the cooling process. (OEM SYSTEM for a 70 big block Vette)

What you have is a disabled surge system by having the flow of coolant from the radiator to the tank blocked. This may or may not cause an issue.

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Old 05-18-2019, 05:43 PM
  #25  
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Originally Posted by BigBill94 View Post
Hi, yes, it's the specific serpentine for the c3 corvette.

It's this one:

https://marchperformance.com/chevy/c...ntine-kit.html

I've had the "fortunate" experience of taking it all out and putting it all back in there.
my bad... They also have the kit they sold me which is totally different and was listed in the catalog as C3 at the time (4-5 years ago) and has a lot more room in front. Regardless, not the source of your problem.


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Old 05-18-2019, 05:47 PM
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heater hose pressurizes Be Cool tank? does another hose leave the tank and go to the firewall? what does the other heater hose do?
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Old 05-18-2019, 05:54 PM
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Originally Posted by derekderek View Post
heater hose pressurizes Be Cool tank? does another hose leave the tank and go to the firewall? what does the other heater hose do?
It's a DeWitts Surge tank, I just used a be-cool radiator cap, and put an OEM radiator cap on the radiator.

The surge tank has 4 hose connections, it goes inline on the outlet for the heater on the intake manifold. It has one small puke hose if the tank is over pressurized that goes to the ground and the other connects from the tank to the radiator overflow connection. OEM hose routing.
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Old 05-18-2019, 05:58 PM
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Originally Posted by Gunfighter13 View Post
An overflow system has a reservoir that has coolant in it and is connected to the radiator via the fill cap. The radiator has a pressure cap (about 15psi). As the engine temperature rises, coolant is pushed under pressure past the cap and into the overflow tank. As the engine cools the coolant is sucked back into the radiator through a valve in the radiator cap, keeping the coolant level full in the radiator.

A surge system is connected to heater hose and to a hose that is connected to the radiator. The pressure cap is on the surge tank and there is constant flow of coolant from the radiator to the tank. The tank becomes a part of the cooling process. (OEM SYSTEM for a 70 big block Vette)

What you have is a disabled surge system by having the flow of coolant from the radiator to the tank blocked. This may or may not cause an issue.
Yep, constant flow in. It can flow in from the heater connection on the intake manifold, or in from the radiator. The way the radiator cap works Tank -> Radiator functions, Radiator -> Tank only when the radiator cap opens, which it does. That hose will get hot, which means coolant is flowing through it.

This isn't my at least main issue however, as it's getting hot enough to puke the coolant out of the surge tank.
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Old 05-18-2019, 06:16 PM
  #29  
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I've relocated the temperature sender back into the driver's side head, I'd moved it to the heater discharge tube to see what was going on (no change). I also re-filled the radiator, half filled the surge tank, and took the topmost coolant plug out of the intake manifold and used a funnel to pour coolant in there to be sure the heads are full.

It's rainy here this weekend, so will wait until the radiator seals come in.

I've had the water pump off the car as I'd had to pull the whole serpentine system to put it back together. I don't recall a part number on it.

The water pump for the March C3 Corvette kit is a "Aluminum Edelbrock standard rotation short water pump and pulley with nose cover." https://marchperformance.com/chevy/c...ntine-kit.html



Short of pulling the heads to check for a wrong head gasket type, I'm at a loss...
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Old 05-18-2019, 07:54 PM
  #30  
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the extra puke hose. i don't like it. if not behind a pressure cap, it will stop cooling system from pressurizing. just boil everything out. try capping the hose off tight.
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Old 05-18-2019, 08:42 PM
  #31  
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All overheating diagnosis BEGINS with pressure testing the system.

You can't have a single drip, a single leak. It's a pressurized system --- think of it like a balloon. There's no such thing as a pinhole in a balloon!

If coolant isn't kept pressurized, then it will boil inside the heads and the car overheats. Steam or coolant VAPOR cannot transfer heat like liquid coolant.

All it takes is one loose hose clamp, a drippy heater core, a radiator cap gasket that's split, anything that KEEPS the system from holding pressure and you've got overheating. Those
hoses TO the heater core are often old, brittle on this car, hard to access so they seldom get changed.

Buy or borrow a pressure tester. You should be able to pump it up to 12-18 psi and the needle not move a BIT for an hour or more. If not, you've got
a pressure leak. Now your job is to find it. It may take UV dye and some work!

You can buy the biggest electric fans in the industry, shroud 'em, everything, but if the system ain't holding pressure it won't fix your problem.

Everybody's installing bigger fans, drilling t-stats, using lower temp t-stats, changing radiators, when the problem, 80% of the time is the cooling system
simply isn't holding pressure.

Find and fix your leak and miraculously all your overheating issues go away and you can drive without your eyes glued to the temperature gauge.
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Old 05-18-2019, 08:59 PM
  #32  
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I think it is the vent hose on the add on tank..
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Old 05-18-2019, 09:09 PM
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Originally Posted by wadenelson View Post
All overheating diagnosis BEGINS with pressure testing the system.

You can't have a single drip, a single leak. It's a pressurized system --- think of it like a balloon. There's no such thing as a pinhole in a balloon!

If coolant isn't kept pressurized, then it will boil inside the heads and the car overheats. Steam or coolant VAPOR cannot transfer heat like liquid coolant.

All it takes is one loose hose clamp, a drippy heater core, a radiator cap gasket that's split, anything that KEEPS the system from holding pressure and you've got overheating. Those
hoses TO the heater core are often old, brittle on this car, hard to access so they seldom get changed.

Buy or borrow a pressure tester. You should be able to pump it up to 12-18 psi and the needle not move a BIT for an hour or more. If not, you've got
a pressure leak. Now your job is to find it. It may take UV dye and some work!

You can buy the biggest electric fans in the industry, shroud 'em, everything, but if the system ain't holding pressure it won't fix your problem.

Everybody's installing bigger fans, drilling t-stats, using lower temp t-stats, changing radiators, when the problem, 80% of the time is the cooling system
simply isn't holding pressure.

Find and fix your leak and miraculously all your overheating issues go away and you can drive without your eyes glued to the temperature gauge.
This is good advice, I believe I have one, and I'd forgotten about it. I bought it when I built my cobra replica. I'll go dig it out and give it a shot.
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Old 05-18-2019, 11:33 PM
  #34  
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Just a thought,
Could the high flow pump and thermostat be flowing coolant too quickly through the radiator and not allowing it to cool before returning to the engine?
Another thought,
Have you verified that the temp is actually 230 using an independent gauge or tester?
One more question,
I read that you verified the serpentine system is correct, but did the prior owner install it with the correct size pulleys?
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Old 05-19-2019, 06:42 AM
  #35  
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OCB. No. that is an old wives tale. the faster the coolant travels past a block or a radiator, the higher the temp diff between the coolant and the surface. the higher temp diff results in higher heat transfer rate.
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Old 05-19-2019, 10:38 AM
  #36  
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I get it, however this is an issue that is beat to death on the forum so I threw it out there just as a suggestion.
Both sides of the argument seem to make sense.

Last edited by OldCarBum; 05-19-2019 at 10:45 AM.
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Old 05-19-2019, 12:56 PM
  #37  
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Is the radiator saturated with heat (is the temp the same on the inlet and outlet) if so then its one of 2 issues, to much heat for the radiator to dissipate or not enough air flow.

If the radiator is not saturated with heat then you have something else going on.

Have you checked the engine oil temp? Excess oil temp can overwhelm the radiator but can be managed by adding a sufficient engine oil cooler.

Neal
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Old 05-19-2019, 03:40 PM
  #38  
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if you have the bypass hose from the water pump to the front of the intake manifold install a restrictor in the hose with a 1/8" hole. that hose allows too much water to bypass the rad and go straight back into the block. on BBC race engines I remove that hose completely.
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Old 05-19-2019, 04:40 PM
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Originally Posted by PAmotorman View Post
if you have the bypass hose from the water pump to the front of the intake manifold install a restrictor in the hose with a 1/8" hole. that hose allows too much water to bypass the rad and go straight back into the block. on BBC race engines I remove that hose completely.
Interesting. For a street motor you definitely want the bypass to eliminate steam pockets. Restricting it though would still allow for the function without all the bypass flow.

Not sure I've seen a bypass hose restrictor however..... I suppose you could use a 1/2 NPT -> -3 or -4 AN, sort of an exotic way around it however.... Any suggestions?
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Old 05-19-2019, 04:54 PM
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go to the auto parts and buy a brass cup type expansion plug that is a snug slip fit in the hose and drill a 1/8" hole in the center. https://www.clipsandfasteners.com/7-...gs-p/a3952.htm. not the correct size just to show what to buy

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