Coolant overflow tank

[Johnnymike]

I have a pretty standard Roadster [complete kit] with a 1966 iron block 427 built by a professional
engine builder. Not radical about 500HP. Very streetable.
If you can believe the temp gauge it runs between 80 and 90 C all day even in hot weather and stop and go traffic.
I never loose any coolant when driving but occasionally I get about a half cup of coolant leak out of the overflow tank
when I park it after driving. It doesn't happen every time and after I park it I will lift the hood and take a look at the engine
and no leaking anywhere. No bad noises not a drop, nothing unusual. Some times when I return later there is a small puddle
and I am sure it is coming out of the overflow tank overflow[I have seen it dripping]. Everything is tight and after it cools I look in the tank and it is empty.
The problem happens infrequently so I cant always get a read on all the details.

I would like some ideas as to why this occurs. I could live with it but would like to know what is happening. It almost seems to me that the overflow tank is too small for the cooling system. Any ideas or advice would be greatly appreciated.

JMS

[stang_killer]

What size overflow tank? I had to go to a larger overflow tank on my 33 hot rod (one supplied with kit wasnt large enough 351w motor), I had same type of issue and it was case of not enough room in overflow to handle the expansion of fluid when up to temp. Larger tank solved the issue.

[Johnnymike]

Yes
It is the small tubular one supplied with the original kit.
Thanks

[68GT500MAN]

The condition is called "heat soak" and a larger overflow tank will solve the problem.
Doug

[Johnnymike]

Thanks
Do you know where I can buy a new tank that resembles the original 427 tanks?
JMS

[skullandbones]

I looked for days to find the proper volume and price for my tank. I wanted something between 1 and 1.5 quarts. I found a Moroso brand that looked perfect but had was about an inch too tall. We cut the bottom and replaced the bungs so it fit perfectly on top of the passenger foot box. It cycles regularly but no overflow. With your big block it might require a little more volume than my sbf. I also use a 12 lbs cap. WEK.

[68GT500MAN]

I am running one from Kirkham that is machined from billet aluminum, a true piece of art.
Doug

[fireman2343]

I have two tanks sir. A large one on bottom and a small on top. I have barely just "cracked" the top of the small overfill tank with coolant. My car runs between 80-90 degrees c even here in AZ. Maybe replace your thermostat first, they will most likely be the problem.

[fireman2343]

Also check the clamps on the bottom of the radiator hose, might be a lose clamp.
Good luck.

[CraigS]

Be sure to get a tank that is at least 1.5 qt and preferably 2 qts. It's just not worth it to mess w/ a tank that is too small. Every time that tank is dry you sucked air into the system. Hoping it will purge by itself isn't a good plan.

[Jeff Kleiner]

I used the FFR one on a Mk4 build I did a couple of years ago and feel that the capacity (28 ounces if memory serves) is a little short of ideal. It works but takes a bit of trial and error to hit the sweet spot of not too much/not too little. I recently did another roadster and used this one from Jegs:

http://i269.photobucket.com/albums/jj43/jkleiner/Aaron5171/100_3825.jpg

JEGS Performance Products 511036 JEGS Stainless Steel Recovery/Recirculating Tanks (http://www.jegs.com/i/JEGS+Performance+Products/555/511036/10002/-1)

Looks very similar but with a larger diameter allowing for about twice the capacity. Works perfectly and a good price too :)

Cheers,
Jeff

[Johnnymike]

Thanks guys.
Great ideas.

[edwardb]

I installed this Moroso 63766 1.25 quart (40 oz) in my Mk4 build. With everything going on in the engine compartment, this one fit the best. It's a bit smaller than the 2 quart Canton I installed in the Mk3. But so far through multiple engine starts, go-kart, etc. where the engine has been fully heat cycled, it has enough capacity for my 347.

http://i867.photobucket.com/albums/ab234/edwardb123/Factory%20Five%20Mark%204%20Roadster%20Build/Engine/IMG_2472_zps72468c12.jpg (http://s867.photobucket.com/user/edwardb123/media/Factory%20Five%20Mark%204%20Roadster%20Build/Engine/IMG_2472_zps72468c12.jpg.html)

[Dan Babb]

Best bet to finding an original expansion tank will be ebay. They come up often. I have one that I modified to work on my small block.

If you can't find one there, do a google search for "big block expansion tank". Here's a manufacturer I found doing that, but I think his price is pretty high.
http://classicfordradiator.com/overflowtanks.aspx.

Not sure if this one will fit your motor...but it's less money.
http://www.dearbornclassics.com/61-64-radiator-surge-tank-352-390-406-427.html


Other places might still make them too.