Coolant coming out of over flow
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From: Hurley, VA
Coolant coming out of over flow I’ve got a LS swapped 2nd gen with a heads cam carbed LS1. New stock 4th gen radiator and cap. I don’t have an overflow tank on the car but when the cars running coolant will squirt from the over flow port on the radiator with throttle. I replaced the cap and same thing. It never boils over, never gets hot just shoots coolant out with throttle. It’s a 18 psi cap and the hoses do get hard. The coolant crossover is jumped from the water pump spacer to the coolant tube. If it was a head gasket issue wouldn’t it overheat? Has to be the radiator right?
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From: Central Cal.
Thread Starter
10 Second Club
Joined: Jan 2010
Posts: 2,317
Likes: 20
From: Hurley, VA
It’s not just a little bit from expansion. I do fill it to the top but the radiator has leaked down to half full on several occasions. Whether it’s 3 inches down or filled to the neck under pressure it still pushes antifreeze out at the same rate. At idle they’re no leakage but if I rev the car it will shoot a 6 inch stream from the port.
There is an important distinction to make here, which is that there is a big difference between an overflow bottle and a surge tank. An overflow bottle is an unpressurized chamber that is only designed to catch a little coolant when the volume of the coolant in the pressurized system (radiator, block, hoses) exceeds that of the system capacity. More commonly known as a puke tank. Here's an example:
A surge tank is a pressurized container and is probably what you're referring to for "every LS vehicle ever." It has a cap that is designed to open at a certain pressure and allows for thermal expansion of the coolant without removing it from the pressurized system. Modern Corvettes and many GM vehicles use it:
I actually had the same issue with coolant leaking from my system. 4th gen radiator with an 18psi cap that would dump out the cap vent every time I got into boost. Like you I suspected a headgasket issue but after a static compression and leakdown check I noticed no bubbles coming out of my surge tank. I even installed a cap with higher pressure rating (22psi) and made sure the gasket was good, locking tabs on cap were not loose, etc. Still no dice.
Eventually I threw in the towel and installed a C5 Vette radiator ($100 on rockauto) which eliminates the cap altogether (you can plop your 4th gen F body fans right onto this rad). You will need to put in a surge tank to give you a fill point and somewhere for the coolant to expand when hot. This solved my coolant leak issue entirely. A surge tank also has the benefit of self bleeding more efficiently - see my post here on cooling system design.
I'm using it because it's a more convenient fill point and allows breathing room in the cooling system for thermal expansion/contraction. Most of all, using a surge tank provides the benefits of deaeration which vastly increases cooling efficiency. Say certain areas of the heads get very hot and boil the coolant causing steam pockets - the steam will travel uphill out of the steam tubes and right into the surge tank, where the coolant has a chance to fall back down due to gravity and the steam can then condense back into liquid form. I suppose it could keep going downhill into the radiator vent port but even there it would be pumped across the radiator cooling it right off. Here is a great article/page that I have used as a guide since my first swap almost 10 years ago. The entire article is great but I use this diagram/section in particular the most.
http://www.billavista.com/tech/Artic...CoolingSystems
Since my surge tank doesn't have a separate overflow port and just dumps out the bottom in case of over pressurization, I don't use a traditional non-pressurized puke tank. For that reason this tank may not be a good option for someone running on a track where they require you to have a puke tank to collect coolant in case of overheating. I saw a neat trick by Truck Doug on here where he plumbed his overflow line to his passenger wiper fluid line so that he could see instantly if he was lifting a head or boiling over while making a pass under boost.
My radiator is an LT1 F-Body stock replacement that has a traditional radiator cap with its own overflow tube. Note: "If you add a surge tank to a system that already has a rad cap on the radiator, you need to permanently seal the radiator rad cap location, or at least install on the rad a cap with a rating significantly higher than the surge tank cap will have, so that the radiator mounted cap will not open before the surge tank cap." This seems more geared towards those running a surge tank AND a puke tank, so that you don't dump coolant on the ground out of the rad overflow before the extra overflow has a chance to collect it. Since I'm not running an overflow tank it doesn't really apply to me.
I modified the diagram to match my setup:
http://www.billavista.com/tech/Artic...CoolingSystems
Since my surge tank doesn't have a separate overflow port and just dumps out the bottom in case of over pressurization, I don't use a traditional non-pressurized puke tank. For that reason this tank may not be a good option for someone running on a track where they require you to have a puke tank to collect coolant in case of overheating. I saw a neat trick by Truck Doug on here where he plumbed his overflow line to his passenger wiper fluid line so that he could see instantly if he was lifting a head or boiling over while making a pass under boost.
My radiator is an LT1 F-Body stock replacement that has a traditional radiator cap with its own overflow tube. Note: "If you add a surge tank to a system that already has a rad cap on the radiator, you need to permanently seal the radiator rad cap location, or at least install on the rad a cap with a rating significantly higher than the surge tank cap will have, so that the radiator mounted cap will not open before the surge tank cap." This seems more geared towards those running a surge tank AND a puke tank, so that you don't dump coolant on the ground out of the rad overflow before the extra overflow has a chance to collect it. Since I'm not running an overflow tank it doesn't really apply to me.
I modified the diagram to match my setup:
