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1968 DeVille radiator overflow tank

Started by Giant Jason, January 17, 2018, 11:37:09 AM

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Giant Jason

 My 1968 Deville did not come with a radiator overflow tank. What overflow tank fits best? I have found one for 70 to 71 Eldo and one for a 72 to 76 Eldo. $10 price difference.  The earlier one mounts to the radiator, and the later one has a bracket.  They are shaped completely different.

TJ Hopland

Its interesting that the line is 72, not 73.  73 was when they seem to have redesigned the whole front end apparently to deal with the impact bumpers.  72 there was a lot more space in front of the radiator and the whole core support structure was different.   In the 73 the tank was in the area opposite the battery which was behind the 'core support'.   Earlier the battery was in front of that.

I'm thinking perhaps one reason for the odd shape is maybe it gets pretty close to the horns?  I can't think of anything else in that area that would cause clearance issues.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Giant Jason

Here's pics of the 2 styles. The cube one with the 2 hoses is from the 73-76.


bcroe

Along with big fan, shroud, and upgraded radiator, I found the
overflow tank to be an excellent upgrade to all my 60s cars.  Besides
the usual traffic/heat problems, some found their way to Death Valley. 
You need that app specific radiator cap too.  I used a conversion kit
for some, yard parts for others.  And one tank was created to fit a
really odd shaped space, from fiberglass. 
good luck, Bruce Roe

cadillacmike68

!968s had NO overflow tank.

Best is to get the 69-76 one and bolt it to the inside of the wheel well up front on the driver side. That's where I put mine. Or get a shorter bottle and put in the well where the Guide-Matic would go on the driver side behind the turn signal. Of course you can't do this if you have Guidematic - or a 2nd battery like I have...
Regards,
"Cadillac" Mike

The Tassie Devil(le)

Don't forget to turn your cooling system into a Recovery System, and to do this, you will have to change your radiator cap for one that is designed for a recovery system.

The Bottle will have to have the hose reaching the bottom so it can flow back as the system cools down.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

Bentley

I bought a generic tank from the auto parts store and installed it where the second battery would go. What was the second battery for? Was that an option in 68?
Wes Bentley
CLC # 30183

bcroe

Some cars had the starter on the left, some on the right.  The battery would
be on the same side.  Multiple engine options would give dual battery positions,
they were both used on diesel cars.  On an Olds it would be on the left, except
a Toronado trans forced it to be moved to the right.  I think the same applied
to Cads.  Bruce Roe

Giant Jason

Thanks so much. I ordered the one to go in the spare battery tray. Do I just need to order a radiator cap from a 69 DeVille?

cadillacmike68

^^^ Yes. ACDelco RC-27 is the correct cap.
Regards,
"Cadillac" Mike

gkhashem

 I have 4 vehicles that came with no overflow tank. You know how many times I had it overflow?  Once or twice and only when I changed the coolant, now that I am more alert I know how much to fill the radiator or am patient when filling it as not to over fill it.

When you do that it should not overflow.

So what's the point of adding a tank?

Educate me or is this I want to add a tank? Just curious as to the reason.
1959 Oldsmobile 98 Holiday Sports Sedan
1960 Cadillac Coupe Deville (CLC Sr #72)
1964 Oldsmobile 98 Town Sedan (OCA 1st)
1970 GMC C1500
1977 Oldsmobile 98 Regency Coupe
1978 Cadillac Coupe Deville (CLC Sr Crown #959)*
1992 Oldsmobile 98 (OCA 1st)
1996 Oldsmobile 98
*CLC Past President's Preservation

Past Cadillacs
1959 Coupe Deville
1966 Coupe Deville (Sr #861)*
1991 Eldorado Biarritz (Sr #838)

35-709

#11
When they were introduced, overflow tanks were touted to increase cooling capacity by xxx%, because the radiator could be completely full at all times and the overflow tank received the expanded coolant when hot and returned it when cool.  The radiator was always full instead of down a certain amount to allow for expansion.  Coolant could be added without removing the radiator cap, I remember that radiator caps were round and smooth back then with no finger holds to help in the cap's removal.
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

bcroe

It appears to me, the overflow tank became mandatory with the use of
cross flow radiators.  These have no reserve coolant space, so they need
to be filled completely to use all the tubes.  That condition can only be
maintained by an overflow tank that moves fluid back and forth with heating
and cooling cycles, without losing it. 

That said, the vertical flow cooling systems of the early 60s had less
capacity.  Air conditioning wasn't standard, electrical systems took less
energy.  And maybe owners were a bit more tolerant of hot engines when
all the stars aligned wrong.  When fluid blew out, it got replaced.  That is
not acceptable today.  If it wasn't replaced, the next overheat cycle would
happen a lot easier.  Bruce Roe

The Tassie Devil(le)

And the main reason everyone went to cross-flow radiators was to get the hood line down low, creating a lower looking vehicle, and therefore less wind resistance.

When Ford did it, in the Thunderbirds, they found that they had to use a Header Tank to keep the engine blocks full of coolant.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

67caddyLA

Quote from: cadillacmike68 on January 23, 2018, 05:46:19 PM^^^ Yes. ACDelco RC-27 is the correct cap.

This is a great thread. I want to add a 67 deville overflow tank where the second battery is. When I go seriiously uphill, I get a nice puke of fluid.  My radiator also maybe overfilled.

Do you have a link to the one you bought where it goes in the 2nd battery space?

Also the radiator cap you installed, should that work on a 67 as well?
Ryan Zeimen
1967 Cadillac Deville Topless

Scott Nellis

   I agree this is a very informative thread. Thanks for reviving it Ryan. I will put in my two cents. I currently own two 1968 Cadillacs. One is a hearse which does not have an overflow tank and the other is a Fleetwood Brougham which I purchased this spring that the previous owner had put an overflow tank in the battery well on the drivers side. I live in Canada and the hearse has always been a northern car. The Fleetwood came from Arizona and originally California so it has always been a southern car. I think it depends on the climate you live in as to whether it is necessary to install the overflow tank. I have never had an overheating problem with my hearse. My Fleetwood was in a much hotter climate and had A/C so the previous owner may have had issues before he had the overflow tank installed. I will leave it on, but it probably isn't necessary because of where I live. I will note that my hearse coolant level likes to be just at the level stripe on the rad or even a hair below or it will barf any excess out. I think many people are used to seeing the coolant sit much higher when they open the cap so they tend to overfill. The correct level recommended by the factory actually seems quite low, but I trust Cadillac knew what they were doing. I have never had a problem.
   I am certainly not trying to talk anyone out of installing an overflow tank, just relating my personal experiences and observations on the subject.
1957 Eureka Hearse
1965 Miller-Meteor Hearse
1968 Miller-Meteor Hearse
1968 Fleetwood Brougham
1970 Superior Hearse

67caddyLA

Quote from: Scott Nellis on December 29, 2022, 10:02:07 PMI agree this is a very informative thread. Thanks for reviving it Ryan. I will put in my two cents. I currently own two 1968 Cadillacs. One is a hearse which does not have an overflow tank and the other is a Fleetwood Brougham which I purchased this spring that the previous owner had put an overflow tank in the battery well on the drivers side. I live in Canada and the hearse has always been a northern car. The Fleetwood came from Arizona and originally California so it has always been a southern car. I think it depends on the climate you live in as to whether it is necessary to install the overflow tank. I have never had an overheating problem with my hearse. My Fleetwood was in a much hotter climate and had A/C so the previous owner may have had issues before he had the overflow tank installed. I will leave it on, but it probably isn't necessary because of where I live. I will note that my hearse coolant level likes to be just at the level stripe on the rad or even a hair below or it will barf any excess out. I think many people are used to seeing the coolant sit much higher when they open the cap so they tend to overfill. The correct level recommended by the factory actually seems quite low, but I trust Cadillac knew what they were doing. I have never had a problem.
   I am certainly not trying to talk anyone out of installing an overflow tank, just relating my personal experiences and observations on the subject.

Apprecaite the info! Maybe I need to learn to see what the regular level of my 67 Deville is, instead of tyring to add an overflow tank!
Ryan Zeimen
1967 Cadillac Deville Topless

The Tassie Devil(le)

The only way to check just how much the level should be when cold is to fill the radiator, go for a drive, and the next morning when the car has cooled down and everything has settled, open the cap, and see where the level it.

You will be surprised just how low it is.

In my '70 Ranchero Squire, which has a cross-flow radiator, the level is down around 5 Inches below the top.   Always tempted to fill it a bit more, but the next day, it is always back low.   I have a catch tank, but not a recovery system.   I use the catch tank to simply limit the water onto the ground.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

Joe G 12138

    If you are fortunate to own or have a chance to look at an original " GM Harrison" radiator of this vintage, there is usually a stamped line in the tank on the fill side. Sometimes marked "full" sometimes not. It is about 5" down. But as others have said it will seek it's own level after a few drives if overfilled.    Joe Gibeault

bcroe

My 62 turbo had a crossflow radiator, before coolant
recovery tanks were common.  I see the tanks as a
cooling capacity upgrade on any crossflow radiator,
besides the other advantages.  Bruce Roe