my 68 327 4 speed with air runs fine,except in hot weather. at idle, temp. ga. will peg after maybe 20 mins. then it will just shut down.probably fuel perculation.it will restart,but it hates idling in 80+ degrees.all raditor rubber gaskets to shroud are in great shape,even the top gasket of rad. to hood is perfect. everything looks to be in great shape. i believe i have the heavy duty big block rad.with the steel shroud,because of the ac.looking inside the rad.,all looks like brand new,,no deposits of scale anywhere,and i can see down,about 16 inches.it most likely is the original rad. harrison stamp,pertruding on side.no leaks.everything is as it should be from factory.really clean car.so im wondering,how much btu loss can occur over 43 years. the dewitts a66m, i believe has two rows vrs. four of my copper,brass rad. but 25 percent more cooling power. i know i need air flow at idle,but do you guys think the dewitts will cure my problem,assuming all other components are working as they should. sure hate to spend 5 hundred.but i would in a split second,to be able to idle in hot weather..also, clutch is firm,and stops spinning after a few revolations,thanks everyone,,tom, in cleveland.

 

If I thought it was the radiator, I'd visit an old radiator shop and let them have a look at it before popping on $500 for a new one.

 

Airflow issue if it cools at high speed ok.

 

Did you ck for loose or sliping belts, thermostat not opening all the way, bad hose, interior hose rot, bad cap?

 

What's your idle timing?

 

What you probably have is a defect vacuum advance can or it's plumbed up wrong. When checking the timing you typically set it at about 8 degrees advanced (static timing) but when you reconnect the vacuum advance line it should add another 12-18 degrees or so.
The vacuum line should be connected to a full vacuum source, not a reduced (ported) vacuum off the carb. Try this easy test...with the engine cold, hook up a timing light and get a 9/16 wrench to loosen the distributor clamp bolt. Start the motor and check the timing with the vacuum connected and disconnected. If the timing doesn't jump up when connecting the vacuum line, crank the timing up 10-15 manually by turning the distributor. I think you will find the car will idle without overheating but DO NOT drive the car like this. It is only a test to prove the timing is the issue. Back the timing back to static timing specs and replace the vacuum can. Somewhere in the 68 SB specification book there is a spec for exactly how many degrees the can should advance and with what vacuum, typically measured in inches. That should fix it but when that old c/b radiator does die, give us a call

 

thank you all,,i will have the rad. checked soon.its still considered winter here in cleveland.so i must wait. and i did not check the thermostat,ive been assuming that if it runs good at speed,that it probably would be ok.ill get a 180 robertshaw soon.belts and hoses look and feel real nice.but could change belts,,,unsure of age,,,thow motor was rebuilt 2 years ago by p. o. ive been researching this problem,for what seems like 2 years now.and always came back to the rad.,,at least in my mind.except untill recently,where lars and others,, like tom dewitt,,who say to check where your vacuum is coming from..well i just took off the air cleaner,and the hose from the vac.adv.is run to the ported vacuum port on my 1406 edelbrock carb. sooo we are getting somewhere i see..thanks tom,,now im looking at the edelbrock carb. manual. manual shows ported vacuum port on-lets say-the passenger side of carb.or right side.and the full time vacuum port on the left.which has a rubber plug over it.should i switch them..but let also say that the dizzy was changed over to an hei,so might there be a reason they went to the ported side of carb. which brings me back to tom dewitts test,in above reply.its just that im afraid to play with timing.actually i just paid to have the timing set 2 months ago,now im thinking he overlooked the-correct-porting.or is it correct porting to the ported side,for hei.shwooo,thats a mouthful. i suppose i could switch the porting,and see how it runs,,but id have to wait till summer,when its hot out,to really know if it would overheat at idle. and 69427 im not sure what he set the idle timing at,but i could call and ask,he may remember.now i ask,should i switch from ported vac. to full time vac.,,with hei...p.s. tom, i did call your company 2 days ago,spoke to a very nice young lady.she knew exactly what i needed.i want this raditor so bad, i can taste anti-freeze.thank you, to all hows replyed.love this forum,read it everyday,and sometimes at night,,tom in cleveland.

 

I would double check the fan clutch which is a very common problem involving overheating at idle. You don't need a special radiator as I assure you the problem was not there when the car was new. You just need to find what part(s) is not functioning properly.

 

hi jud,the clutch fan feels good to the touch,no wobble at all,from moving it front to back.it has slight resistance to turning it when cold.then it loosens up a bit more after turning it awhile.i remember,the last time i drove it,while engine was at temp.,then shut off engine while watching the fan,,it probably spun about 3-to-5 revolutions.im thinking its ok.well i just got off the phone with edelbrock,tech. says my porting to the ported side is correct.humm.of course he says air flow issues....we all know that. also says try more idle timing,,plus fatten up the gas mixture abit.set timing correctely.thanks jud. i guess ill have to look deeper into the timing-total timing-carb. settings.possible vac.adv. can issues...when i find the problem,ill let you all know,then some of us can sleep at night,thanks,tom.

 

oh ya,edel.tech. also said,try a carb.spacer....which was on my list too.

 

Have you cleaned the radiator? If you cannot see a flashlight shining through it, the core is gunked up, especially with an AC condensor sitting in front of it. Water pressure from the garden hose might be enough to clean it out.

 

I don't think the fan should have 3-5 revolutions after shut off... especially if it is up to temp. Replace the fan clutch and I'll bet your problems are solved...

 

clutch fan not pulling air? does it cool down after reving engine while still parked and not moving?

timing retarded? do you get hesitation off idle?

lean mixture at idle causes overheating too, turn your idle screws to enrich your mixture at idle. extra fuel cools the engine.

get you a 1/4 inch phenolic carb insulator, it will cool your carb considerably.

the stock system from the factory should work with plenty of room to spare.

butterfly valve in your exhaust manifold stuck closed, forcing exhaust thru your intake out the other side will overheat the top end?

 

The reason I asked about your idle timing is to see if your engine's combustion/thermal efficency is where it's supposed to be. Retarded timing causes excessive heat to be dumped into the coolant. If the major complaint is at idle then there's a good chance that you're not getting any vacuum advance, whether by the use of ported vacuum, or as Tom mentioned, a possible defective vacuum canister. Check this out first, as it's a free diagnostic at a minimum, and a free solution if retarded timing is the problem.

 

Clutch fan maybe water pump....

 

Just swap the vacuum advance hose to manifold vacuum and plug the ported side. You will need to turn down the idle speed, as your vacuum advance will now be in effect at idle. You gonna like it...

 

On a warmed up engine mine stops in less than 1 revolution.

 

If the vacuum advance can on the dist. is connected to a 'timed' or 'ported' vacuum fitting on the carb (rather than manifold vacuum), there will be NO vacuum signal getting to that advance can. Thus, the engine will be running with retarded timing, which results in running hot. Just what the EPA wanted! Lower emissions at idle. But, they really don't care if the car runs or not. In fact, if it isn't running it's making ZERO emissions!

Check to see if that is the case. If so, switch it to manifold vacuum and your problem should go away.

[On '70-74 cars, the CEC system had a "dual" temp switch that would defeat the "ported" vacuum feed to the dist advance can if the engine was too cold OR if the engine was too hot.]

 

tomgallucci57:
I had the same problem in my SB 68, I put big aluminum radiator new water pump 160* thermostat flex fan nothing help, still I had the same problem, only when I put a big shroud instead of the round metal shroud the problem gone.
Thanks
Avner

 

I hate to restate the obvious... but your fan should NOT rotate 3-5 times after you shut the engine off (even with the engine cold). So you know that your fan clutch is bad, and if that isn't the entire problem, it is a major contributor. A $30 fan clutch and 15 minutes of your time should solve the problem.