Overflow Tank question

Archrms · #1 (**permalink**) 07-06-2010, 11:24 AM

The Over Flow Tank is the black canister with the small hose from the expansion tank at the top and the pet cock valve at the bottom. There is a small hole at the top of the tank that spewed out some coolant the other day shortly after start up. I assume that this is the only way for excess coolant to escape the cooling system.

Is the leakage considered normal (even though it was a small amount)? The engine did get up to temp as it idled. I did not take it for a drive until I could locate the source of the leak. I finally traced the coolant leak to the hole at the top, which then got blown around the engine compartment by the fans.

While inspecting the over flow tank, I noticed that the pet cock valve was in the closed position. However, the entire valve rotated when twisted by hand when I checked to see if the fitting was tight. Is there any way to tighten this connection, or is this normal?

patrickt · #2 (**permalink**) 07-06-2010, 06:12 PM

Can you post a pic of the tank you're talking about?

Excaliber · #3 (**permalink**) 07-06-2010, 06:35 PM

That is a rather confusing word picture....

The shiny tank at the front of this engine is not an "over flow" tank, it is a "surge tank" (OK, expansion tank then). No water should leave this tank, period, under any circumstances at any port, when the engine is cold. When the engine is HOT and the water has expanded enough to totally fill this surge tank beyond it's capacity AND pressure rating of it's "radiator" cap, THEN it will expell a certain volume of water to the "over flow tank". Assuming you have an overflow tank, not all cars do. If you don't, the water is simply lost to the atmosphere (hit's the fan and is blown all over the engine) and will not be returned by "suction" when the engine cools back down.

IF water is leaving the SURGE TANK (see the shiny tank in the picture) when the engine is cold, the reason is elementary, my dear Watson: The radiator cap isn't holding pressure.

timsullivan · #4 (**permalink**) 07-06-2010, 08:56 PM

Yes, you're right, the plastic overflow tank mounted on the right side fender well undoubtedly is the only source for the cooling system to literally and figuratively blow off some steam. Most likely you have the expansion tank (that sits directly above and in front of your thermostat housing) overfilled. They should only be filled to the midpoint of the expansion tank when the car is cold. That or you have some very serious overheating problems going on. Normal cooling system pressure relief shouldn't see water coming out of that very tiny breather hole on top of the overflow tank unless you have the puppy filled to the brim! Drain it all out of the oveflow tank and reset your coolant level in the expansion tank to the midpoint.

The valve on the bottom of the overflow tank should only move about 180 degrees to open or close the drain. If memory serves me it's just a press fit into the bottom of the tank.

PANAVIA · #5 (**permalink**) 07-07-2010, 01:42 AM

Note: The overflow tank should be able to vent to air and not create a backup of pressure into the cooling system.

Archrms · #6 (**permalink**) 07-07-2010, 07:43 AM

Ernie: That is why I differentiated between the black over-flow canister and the expansion tank in my original post.

Tim: Thanks for the input. I don't fill the expansion tank to full, however, it is possible it may have been slightly over-filled, and if the overflow tank was full already, it would have spewed out as it did. The valve at the bottom moves 90º open/close to drain the overflow tank, but the entire assembly rotates 360º. If is is press fit as you noted and not screwed in, it would explain the rotation.

Archrms · #7 (**permalink**) 07-07-2010, 07:46 AM

Tim, Does the overflow tank have an internal hose to the bottom of the tank so that it can siphon back into the expansion tank? I haven't taken it apart, and can only see the hose connected at the top of the tank. Otherwise, any coolant that is expelled into the overflow can not get back into the cooling system, eventually resulting in a full overflow tank that will spew out the relief hole at the top.

Archrms · #8 (**permalink**) 07-07-2010, 07:52 AM

I will try to get pics tonight for those without an SPF for reference.

Excaliber · #9 (**permalink**) 07-07-2010, 08:06 AM

Ah, I see what you mean now, black tank vs shiny tank, makes sense.

I keep my over flow tank about a 1/3rd full and my surge tank about 1/2 full. The overflow typically fills up almost to the top when the engine gets to full temp following a good drive. Then as it cools that water is drawn back into the engine, works out real nice. On occasion I've put to much water in the overflow and then it filled and overflowed.

Before I ran an overflow tank I would have to add water to the radiator on occasion as it would eventually get to low from the water being pushed out and lost.

My surge tank hose goes into the bottom of my overflow tank, but some use a hose that goes in the top and then reaches down to the bottom of the tank inside.

An overflow tank is required at some race tracks, as are various "puke" tanks, all in an effort to keep fluids off the race track.

patrickt · #10 (**permalink**) 07-07-2010, 08:30 AM

Quote:

Originally Posted by Excaliber

My surge tank hose goes into the bottom of my overflow tank, but some use a hose that goes in the top and then reaches down to the bottom of the tank inside.

Yep, that's how I do mine.

Excaliber · #11 (**permalink**) 07-07-2010, 08:37 AM

Looks good Pat!

Eh eh, I was running an old Gatorade bottle for awhile. The SAAC-35 requirements are the overflow tank has to be bolted to something. I had the Gatorade bottle just sitting on the lower frame, so I went with a "store bought" plastic tank and actual bolts.

timsullivan · #12 (**permalink**) 07-07-2010, 09:01 PM

Archms: No, the overflow tank does not come with a hose inside it running down to the bottom. It literally was intended for race applications where the track wants you to have a container to catch coolant overflow. But here is a link to a site (under Craig's "tips" section of his website) that shows how easy it is to convert the plastic overflow tank to include the hose such that the tank will act like a true recovery system and draw overflow back into the cooling system as the car cools down. I did the conversion on my tank and it was quite easy to do.

http://craigscobras.com/

-Tim

patrickt · #13 (**permalink**) 07-08-2010, 05:46 AM

Quote:

Originally Posted by timsullivan

But here is a link to a site (under Craig's "tips" section of his website) that shows how easy it is to convert the plastic overflow tank to include the hose such that the tank will act like a true recovery system and draw overflow back into the cooling system as the car cools down. I did the conversion on my tank and it was quite easy to do.

http://craigscobras.com/

Tim, I didn't see any mention of the use of a "recovery type cap." There are two types of radiator caps, recovery caps and overflow caps. If you try and run your recovery system with an overflow only cap you're not going to get very far. I would venture to say that most of our Cobras probably have the "overflow only" cap (mine does), so when buying your new cap, make sure it specifies that it is a "recovery type" cap, like this:

Excaliber · #14 (**permalink**) 07-08-2010, 07:06 AM

Well thats news to me!! I've always just walked into the auto parts store and bought whatever cap of the correct pressure they laid on the counter. Said caps have always been able to draw the fluid back into the radiator from the overflow.

I've never seen any radiator cap that wasn't capable of drawing the fluid back in? So Pat, are you saying YOUR cap does NOT draw your overflow fluid back in when the engine cools?

Come to think of it, I always specify a manual pressure relief type cap, one I can lift the little handle on and release pressure if I choose to. Perhaps that is the difference, as opposed to a cap that the only way to release pressure is to turn it to take it off. I always considered those a dangerous type cap and never use them.

patrickt · #15 (**permalink**) 07-08-2010, 07:29 AM

Quote:

Originally Posted by Excaliber

Well thats news to me!! I've always just walked into the auto parts store and bought whatever cap of the correct pressure they laid on the counter.

That's why I'm here looking out for you, Ernie.

All caps are NOT recovery capable. Some lever caps are recovery capable, some aren't. Here, this is a nice page that shows a lot of caps, some of which are, and some of which aren't, recovery capable:
http://www.cpcauto.com.au/radiator_caps.aspx

patrickt · #16 (**permalink**) 07-08-2010, 07:55 AM

This should not be news to anyone, we talked about it almost nine years ago.... Radiator Caps - they're all not the same ya know? So Ernie, as per Bob P.'s advice in that thread, put your mouth on your radiator cap and start sucking....

Excaliber · #17 (**permalink**) 07-08-2010, 08:07 AM

I think I'll pass on the personal sucking of the radiator cap to determine it's status.

So the last time this was an issue was nine years ago? From that I would speculate that about every 10 years, or less, someone manages to find the one cap that is not a recovery type.

Archrms, you best choose your cap wisely, the nine year window says it is time again for someone to choose a non-recovery type cap!

patrickt · #18 (**permalink**) 07-08-2010, 08:18 AM

Quote:

Originally Posted by Excaliber

So the last time this was an issue was nine years ago? From that I would speculate that about every 10 years, or less, someone manages to find the one cap that is not a recovery type.

No, that was the last time someone realized that it was an issue, and then a discussion ensued.

I think I've posted on it since then, frankly. Honestly, I find it easier to just open the surge tank, eyeball the coolant condition, maybe even use one of these handy dandy little test strips I have sitting around here, and then top off as necessary.

Archrms · #19 (**permalink**) 07-08-2010, 08:22 AM

Tim, thanks for the link on the recovery conversion. I am amazed that it is such a simple procedure, and costs virtually nothing.

I also did not know there were recovery vs non-recovery radiator caps, but it is something I will look for now. Thanks Patrick.

Jim Norris · #20 (**permalink**) 07-19-2010, 08:54 AM

After reading this thread I went out to check my own setup. On mine, the small hose from the expansion tank (shiny tank) runs directly to the bottom of the overflow tank (the petcock is in the open position) and another small hose is attached to the upper overflow tank fitting and run down the side of the tank. This hose is open to the ground.
Does this setup possibly act as a recovery system allowing accumulated coolant resting at bottom of the tank to be drawn back up the hose and into the expansion tank, assuming I have a recovery type cap?