Ok folks - 1967 327 with a 700R4 - engine rebuilt from bare block stock with 350 HP cam and ported heads and runs great - rebuilt water pump - new radiator cap- new Dewitt radiator - new fan clutch (tried both old OEM and NAPA replacement) - new hoses - new thermostat (verifyed operation ) - stock fan - the car runs cool when moving. If I idle in traffic it starts to rise. Continued idleing will put it into overheat. (not the guage since it will puke fluid). One other thing to mention when it gets hot on ocasion I can hear a whistle. I tightened all the intake manifold bolts and carb bolts and it seemed to reduce but not eliminate the noise. The car is almost done and this overheating is driving me nuts. Any suggestions short of a match?

 

How many lbs is your rad cap? If the system can't pressurize due to an under rated cap then it would boil and puke. Sounds like you also may have a leak in your intake manifold. Possibly a crack. I assume you checked your oil for traces of water?

Bob

 

Low speed overheating causes

Insufficient idle timing-are you using full time vacuum advance w. the proper VAC? You need about 28* idle timing ( initial timing+ timing provided by VAC) to minmize EGT. Idealy the EGT should read about 450*F at the exhaust port.

Insufficient air flow thru the radiator- do you have a fan shroud and are the proper seals in place? Is the fan half way in the shroud?

 

The intake is a edlebbock - no water in the oil - tried 17# cap and 13 pound cap - the timing light is out on the bench as it was my next adjustment - I was going to check the timing with the vac adv bloacke then re connect. Correct? - I am looking for 28 degree idle timing - I will also check the exaust gas temp - thanks for thet bit - the shroud is in place and the fan is half in half out - I am going to put the OEM part back on - no AC so no additional seals on the shroud I was thinking about installing the AC bits for extra help - one more thing, the Dewitt radiator is handeling the cooling duty for the trans instead of the stock xternal cooler which is on the shelf. I did this to control Trans fluid temp.

 

Idle timing should be read with the VAC connected to full time vacuum source.

 

Thanks Donald- company today so I will not have a chance to check until tomorow. I will report back then in case someone else has a similar problem.

 

Checked the timing. 8* with the VAC disconected. 8* with it connected. Increased idle speed from 700 to 900 in park (700R4) and I have 20*. I will check it in gear this weekend when I have someone to assist.

I also noticed the radiator has left a new wet spot in the shroud.

Can not seem to find the source. It is a Dewitt purchased in 2005 with under 3,000 miles on it. Very small spot and only seems to leak when the engine is shut down. I will continue to drive the car and pull the rad this winter. It still heats up if left to idle so I will continue to troubleshoot( diferent VAC?) until I resolve the problem (a electric fan is still a posibility - I do not wan to ever worry about the temp)

 

sounds like the vacuum advance is connected to ported vacuum. It is preferrable to have it connected to a full manifold vacuum source that gives full vacuum advance will at idle.
Not only will full manifold vacuum give typically better driving characteristics, it also helps to keep operating temps lower (ported vacuum was done in later years ONLY for the use of emissions control and one aspect of that was to increase operating temps so they lowered initial timing and went to ported vacuum.

I'd find a full manifold vacuum connection on your carb and run your vacuum advance off of that instead

 

Here is a picture of my '66 300hp Holley carb. Should be similar to the '67 carb. I see that you have an Ebelbrock manifold. This is a stock cast iron manifold but the set up should be about the same.



The vacuum source that BarryK references for the advance canister is the line in the lower right of the pic. Rubber to hard line.
Also check to see if your vacuum advance canister is working properly. Found mine not working last year. With an AutoZone replacement the car ran much better and cooler at idle. Worth checking into.
With 8* both connected and disconnected the canister may be the problem.

 

You found the culprit. 8 degrees at idle with the vacuum advance hooked up is going to result in overheating symptoms. Barry is right that you need to hook up to manifold vacuum vice ported and then buy a vacuum advance canister that corresponds to your measured manifold vac.

Geek

 

Two primary causes of SB (small block) mid-year overheating complaints are the temp sender not calibrated properly and overfilling the surge tank. Have you verified actual temperature with an IR gun OR a surface temp thermometer?

In any case, take your distributor rotor off and tie your centrifugal weights back by wrapping them with a rubber band and then check your timing at the idle speed you prefer, set it and lock it down. Check it again at the idle speed you prefer with the rubber band removed. You may be suprised to find your timing has changed. Be that as it may, the initial set with the rubber band on it is where you should start as a baseline before you go fiddling around with vacuum hoses. The next step is to rev the engine until the timing quits advancing and see how much mechanical advance you have. Then hook the vacuum advance up, recheck the timing and see what your total is. Only then can you determine if your timing is causing your heating problem. A dial back timing light or timing tape is required here to determine the amount of advance.

If you search the archives of SB mid-year overheating, you probably won't find one single case of an overheating complaint being resolved soley by hooking up the vacuum advance, either to ported or manifold vacuum. That is, if the rest of the system is in like new, OEM condition. If you have part of your cooling system that is marginal or compromised, the timing could make a difference. I have no idea how much influence the transmission cooler in your new radiator is contributing to your problem.

 

Try this, I made this adjustment on my NAPA fan clutch and had great results: http://www.stl-vettes.com/65Vette/co...tch_Adjust.pdf

 

Respectfully I would not agree with the above given the symptoms of heating only when stopped AND his 8 degrees of timing with the vacuum hooked up at idle. My car had the same basic overheating symptoms twice and both times it was a bad vacuum can on the distributor letting my idle timing drop to about 10 degrees. I think his vacuum can is either bad or it's the wrong can for his vacuum. (I do wonder about that whistle he describes and if that is bleeding off his vacuum so that the can can't really work)

That being said I think the advice for checking the timing starting with holding back the centrifugal advance is solid gouge. Looks like centrifugal is working since he gets an additional 12 degrees with only a 200RPM in idle speed but checking and determining max mechanical (hopefully all 24 to 26 degrees or so in at about 2800 RPM for a total of 34 to 36 degrees) is the right way to set it. Once you have it set there, you should be able to see what you have at idle without the the can connected and then I would expect to see it jump up about 16 or so degrees when you connect the can.

Geek

 

He may have a broken or missing centrifugal weight spring. If that's the case, what do you think his static timing really is?

With what I've read, the OP doesn't really know what the initial is.

 

I swapped the Vac Can over the weekend and the timing at Idle is now 28 degrees with the Vac Adv. (Thanks to Lars for his excelent guide on Vac Cans) The temp has come down but the Exaust gas temp is still close to 700 degrees after idleing for 20 - 30 minutes. I am considering trying playing with the jets and going through the entire advance curve set up this weekend. Thanks for all the help and advice...