Opinion on '68 overflow tank & cap BB427

[Gary K.]

My 68 is a great driver, originally Harrison copper but now fitted with DeWitts aluminum radiator w/dual fans which works great here in Phoenix, and a cheapo Stant 15lb cap. From searching archives I see 1968 L71 had no tank - just dumps on the street which is what is happening now from time to time.

I'm not looking to win awards, but in keeping the car true to form I need advice on what I should do for an expansion tank for the simple reason I don't want coolant on my garage floor. Aluminum tank? Brass? And the radiator cap itself - I would like to order one true to the year but am wondering if that cap would work well with the DeWitt's radiator, i.e. two different kinds of metal. Any suggestions much appreciated.

PS - Mecum's had at least two nice 68's go to 27k+, maybe this year is starting to get the respect it deserves. My own car doesn;t have any "engineering issues" beyond anyone elses' early C3.

[Timothy B.]

Re: Opinion on '68 overflow tank & cap BB427

Gary,

Get a radiator cap that's used with aluminum radiator, I think GM still sells one. The original copper radiator has the expansion space at the top of the radiator hence no overflow tank. Is this aluminum radiator made like the original copper in that the radiator cap is on the radiator?

If so, can you let the aluminum radiator overflow down to seek it's own level and see if the engine will still run cool. If not, how about a plastic tank but you have to do the plumbing to install and it's definately not going to look factory.

What timing are you running in the engine as that may help keep the engine cool. Do some reading in the archives on engine timing when you have some time.

[Peter L.]

Re: Opinion on '68 overflow tank & cap BB427

Gary - You'll probably want to get one newer stainless steel AC RC-26s or RC-15s. Both are 15 lb radiator pressure caps. In the 60s and 70s the RC-26 was the cap used on the aluminum radiator and aluminum over flow tank Corvettes and the RC-15 was used on the brass radiator Corvettes and GM passenger vehicles; but with the newer caps with the stainless steel "gut's and cover, the RC-26 and RC-15 are basically identical except for the embossed informtion on the top of the cap. In fact I've seen something somewhere that the RC-26 has been discontinued so you're to use the RC-15. BTW, you'll probably want to avoid the newest RC-15s with the TSV designation on the cap. Pete

[Gary K.]

Re: Opinion on '68 overflow tank & cap BB427

Thanks guys - through the archives and knowledge of NCRS members like yourselves my projects with this car are going great. I think I'll call DeWitts and see if they have something for the cap. Overflow tank we'll see.

[Jim T.]

Re: Opinion on '68 overflow tank & cap BB427

I use a plastic overflow tank on my 70 with the big brass radiator. I secured it to the fender well and it sits on the flat metal splash shield just behind the passenger front tire.
Run a hose from the tank to the radiator and it functions just like the factory installed plastic tank that was first used in I believe 1973.
What coolant the radiator expells is returned to the radiator when it cools down. No mess on the garage floor.
Very easy to remove for judging.

[Joe L.]

Re: Opinion on '68 overflow tank & cap BB427

My 68 is a great driver, originally Harrison copper but now fitted with DeWitts aluminum radiator w/dual fans which works great here in Phoenix, and a cheapo Stant 15lb cap. From searching archives I see 1968 L71 had no tank - just dumps on the street which is what is happening now from time to time.

I'm not looking to win awards, but in keeping the car true to form I need advice on what I should do for an expansion tank for the simple reason I don't want coolant on my garage floor. Aluminum tank? Brass? And the radiator cap itself - I would like to order one true to the year but am wondering if that cap would work well with the DeWitt's radiator, i.e. two different kinds of metal. Any suggestions much appreciated.

PS - Mecum's had at least two nice 68's go to 27k+, maybe this year is starting to get the respect it deserves. My own car doesn;t have any "engineering issues" beyond anyone elses' early C3.

Gary------


First of all, you're getting a SUPPLY ("expansion") TANK confused with a COOLANT RECOVERY TANK. A supply tank will not eliminate the the deposition of coolant overflow to the ground------they have an overflow hose just like most radiators with integral tanks. No Corvette prior to 1973 ever originally used a coolant recovery tank although many Corvettes during the 1960-72 period used coolant supply tanks.

It is possible to retrofit a coolant recovery tank to your application but, of course, it will not be an original-style tank since no original style tank ever existed for a 1968 Corvette. You would have to purchase an aftermarket kit for such an installation from a source like J. C. Whitney.

If your DeWitts Direct Fit radiator is the correct one for your 1968 big block (except L-88) application, it will have an integral filler neck and use no external supply tank. I would strongly recommend using an RC-26 cap with this radiator.

The problem will ensue if you decide to use an aftermarket coolant recovery tank. Most of these kits will include a specific radiator cap which has to be used with the kit. Generally, these will not be designed for use with an aluminum radiator. So, in that case you'll have to decide whether the anti-galvanic corrosion properties of the RC-26 is more important to you or if the coolant recovery system is more important.

[Gary K.]

Note: '68 coolant supply tank details from 1967

I have enough info to solve my issue, but for information only I found it interesting that the supply tank system, associated brackets and hoses is clearly shown in the '68 assembly manual, detail UPC# 11-13, B-6, sheet H241. Revisions of various kinds are 8/5, 8/28 and 10/12/67. Maybe this is for small block cars>

[Jim T.]

Re: Note: '68 coolant supply tank details from 1967

I have enough info to solve my issue, but for information only I found it interesting that the supply tank system, associated brackets and hoses is clearly shown in the '68 assembly manual, detail UPC# 11-13, B-6, sheet H241. Revisions of various kinds are 8/5, 8/28 and 10/12/67. Maybe this is for small block cars>

Gary with a one owner 68 327/350 L79 I can verify that this car came with the small aluminum radiator and supply tank. Just recently changed the coolant over to the ZEREX G-5 and only way to install coolant is through the supply tank, no pressure cap on the radiator.

[Joe L.]

Re: Note: '68 coolant supply tank details from 1967

I have enough info to solve my issue, but for information only I found it interesting that the supply tank system, associated brackets and hoses is clearly shown in the '68 assembly manual, detail UPC# 11-13, B-6, sheet H241. Revisions of various kinds are 8/5, 8/28 and 10/12/67. Maybe this is for small block cars>

Gary------


For 1968 small blocks with manual transmission used an aluminum radiator with an external aluminum supply tank. L-88 used a different aluminum radiator but the same aluminum supply tank.

All other 1968 applications used a copper/brass radiator with NO external supply tank.

1969 is different in many respects so one can't "lump the two year models together".

[Patrick B.]

Re: Opinion on '68 overflow tank & cap BB427

Gary: Your posts say that you are looking for an early 321 block. I have a complete 435 hp CE short block with a 321 block dated H-18-7. The only problem is that I live in Virginia and I don't know if shipping to Arizona is practical. Call me at 703-919-4294 if you have any interest.