I am getting ready to restore the cooling system on my very early 1968 427/400 no A\C car. I know GM had overheating problems with the 68's and made a number of running changes to correct the problem. I even have the hand cut holes under the nose that the dealers were told to make to help with overheating. I like to keep things as stock as possible, but am I asking for trouble if I put the early cooling system parts on the car? It overheats at idle now, but it is missing a number of things like seals, fan shroud, etc., so I've got to do something.

I'm interested in any opinions or experiences.

Thanks,
Rick L.

 

Usel a Flowkooler or similar water pump. Use a Stewart or similar high performance wide mouth thermostat. Install/replace the thermostatic fan clutch.

 

What changes did they make?

 

Cutting holes under the nose, different fan shrouds and a couple of other things I've read about over the last few days but that I can't remember right off-hand.

 

I've never heard of early 68 overheating problems. Did you have overheating problems before? Or just now that half the parts are missing?

 

I am running the re-cored original Harrison radiator and shroud. I did use a 7 blade AC fan with a Flex-A-Lire thermo-clutch and a FlowKooler pump. No problems. My car is a 68 L36 Roadster, mid-year production.

 

I have an early 68 427/390 and yes the factory did handcut rectangular openings under the nose in an effort to cool them. They run plenty cool in stock form with a Dewitt's aluminum radiator (they came with copper/brass), with a stock clutch fan, proper vacuum advance and all your seals and factory shroud in place.

 

Are the rubber seals in place around the radiator and the air deflector under the front end? If not, that can guarantee overheating. They're critical to cooling.

 

While not on a 427/400 Vette, have put together a few performance builds that tend to gulp air into the cooling system. Usually start the car from cold and everythings fine. Shut off a bit for a gas stop, then runs hot after that. This is a real happening, as elevated burp tank kits are availible for a reason. No cooling system expert, but maybe some here will add a bit more on this.

 

For those of you interested, I found this on the NCRS forum:

after VIN 00720, new pulley to increase fan speed; add slots in front valance panel

after VIN 01344 added new fan clutch to increase the slip speed.

after VIN 02469, added full fan shroud.

 

Rick
Close to stock as possible is good. So is being able to enjoy driving the car in summertime south Florida bumper to bumper traffic, without staring at the temperature gauge.

I went with a new Dewitts Direct Fit aluminum radiator for my '69 L36 and put the original in the box for the next caretaker. Dewitts will paint it black and only an NCRS judge will know the difference. They claim that their aluminum radiator cools 30% better than the stock copper brass radiator. I believe it. My temperature gauge NEVER goes above 190.

Check the '68 AIM to see if there is a stapled air dam in front of the bottom edge of the core support. Doc Rebuild sells all the seals and air dams, including the one between the top of the radiator and hood. It works best to pull the entire radiator package as a unit, disassemble on the bench, restore the support, clean the shroud and reassemble with the seals on the bench. Then install the entire assembly in the car. The more air that you can direct thru the core, rather than around it, the more heat will be removed from the coolant.

If your fan clutch is not doing it's job, they can be rebuilt ($ and time) or Eaton makes a good replacement.

Remove your front license plate bracket and save it for the next caretaker as well. No need to block any air flow.
Dennis

 

Shrouds and seal are key to lowering temps. Get that air flowing through the radiator not around it.. that alone lowered my temps by 15 degrees on the street. Removing the license plate bracket also helps but depends on what state your in, whether they require a front plate.

 

My cooling experience with a 1968 bb Vette is completely stock and no overheating ever....reading the numerous posts complaining with over heating is to return the car to new stock cooling sustem parts....I have never witnessed the so called '68`s had a factory right out of the box heating problem...hell they also had a 5 year warantee....and in those 5 years I never went back for any cooling problems

Opinions about trick aftermarket cooling parts can make a situation worse.....the trick stuff is not an improvement over what GM had in mind when they released the BB`s....so getting back to my experiences with BB`s, I have a half dozen BB cars consisting of all stock parts and none overheat all over the horsepower range from high to low....

 

My '68 Early L71 435hp Tri-Power Vette (s/n: ...2000) has just completed a complete frame-off restoration. It has all of the NCRS changes outlined by FlaVert and the shroud seals mentioned by several others.

In addition, my engine was bored/honed .030 over (normal engine re-build), the fan-clutch was completely restored and I have a New GM Restoration Radiator made by DeWitts which is identical to the original "4-row" Copper/Brass Harrison model. I'm using 104 RON leaded fuel to eliminate the engine knocking detonation.

All of that said, My car also OVERHEATS!....and has since I purchased it long ago. Many Chevy dealers have tried to fix it but none have succeeded.

Here's what my various "expert" sources have told me to do:
1. Change the radiator to a DeWitts aluminum model.
2. Change the radiator to a '69 radiator that is 5" wider.
3. Replace the metal shroud used in the early '68s with the better sealing plastic one used after Nov 1967. Supposedly, it forces more air through the radiator than the metal shroud.
4. Change the radiator to a DeWitts model that has two 12 Volt fans mounted to the rear of the radiator; then remove the 5-blade fan and fan clutch.
5. Remove the front license plate bracket.

I'm trying to get the car NCRS Top-Flighted so any advice would be welcomed.

 

I DID THE SAME / and a shroud will certainlly help but not 100% solve your issue at hand. No need for fans !

 

 

I guess I'm agreeing with myself on an old thread The aluminum Dewitt's is your answer My 68 runs 180 all day long with it.

 

There is a thread about this over on the NCRS forum that I started. It may give you some more info. I haven't had a chance to start on my 68, my 66 decided it needed my undivided attention for a while.

If your engine was rebuilt to stock specs and you still have to use 104 octane to stop detonation then your timing may be off. That can cause overheating as well.

 

I had the same problem. I did everything new shroud, shroud extension, seals, thermostat (with hole drilled in it), new fan clutch... Nothing worked, some things made a little difference but nothing that would make the car stop over heating. I would stop at a light in the summer and i would watch the temp gauge rise. Also if i held on to the shifter, not the ball at the top the shaft that comes up through the floor, it was hot. All the time talking to a friend who owns a restoration shop and he was telling me the timing is not right and i need to advance it. Long story short I email Lars to get his paper on timing read it until i understood it. I then set the timing up per his recommendations and it's like night and day. It's running cool, I can grab the shifter and it's just warm. So far so good one more test today it's supposed to be in the upper ninety's i will go for a ride tonight when i get home from work. I'm confident that the problem is pretty much resolved.

 

another bad information quote with BB 1968`s overheating....they are all right as long as aftermarket engineers keep there hands off.....I have several BB powered pieces and everyone is a stock factory cooling system. No fancy high dollar back alley mechanics and bench jockeys suggested parts necessary......the principal reason is that some of these cars have had several owners and who knows what or how they were cared for with OE parts long removed.....One sure way to correct them is to keep them all OE, .......