1966 L72 running hot

[Joe T.]

I am running hot and sometimes to boiling during in town driving. Changes made: New DeWitt replacement radiator and hoses, Zerex G-05, no oil in antifreeze, no white foam in oil, full mechanical timing at 36 deg advance, new wires, older AC R45XLS plugs set at 35, fan clutch is working fine, fuel mixture seems fine, running aviation gas. Car runs fantastic until it starts to overheat. At that time I may get some vapor lock and it wants to stall unless RPM's are kept up. Some say, it's the nature of the beast. I can't agree with that. I should be able to drive on 85 to 90 degree days. Only related items I know of that are not new, are the plugs. Had a 327 350HP and never had a heat problem.

[Michael J.]

Re: 1966 L72 running hot

What number VAC are you running?

[Joe T.]

Re: 1966 L72 running hot

Not sure what you mean. I have a new K66 Ignition and distributor. Where do I find the vac number and what should I have?

[Jim D.]

Re: 1966 L72 running hot

Sorry for the poor pic. but this is where the VAC numbers are stamped (this is from my 65 small block). On my L-72, I'm running a B28 (VC1810) VAC hooked to manifold vacuum.

[Michael J.]

Re: 1966 L72 running hot

Right, according to Duke, maybe he will chime in with his 2" Rule, the modern can should be a B28, like this one:

Typically, if an SHP (solid lifter, high performance) engine is running hot, and other issues have been settled, best to check the advance timing starting with how much vacuum advance you have, as these engine have low vacuum in the low end and need more advance to not overheat.

Ps, just did this this afternoon with my L84 to solve the same problem.

[Leif A.]

Re: 1966 L72 running hot

One thing that gets little attention when true overheating occurs is the radiator cap. Make sure yours is holding the proper pressure (should be a 15# cap). A local parts store should be able to check it for you. If your cooling system is not properly pressurized, it can't do it's job as designed.

[Chris H.]

Re: 1966 L72 running hot

Duke's paper. Full of great information.

http://stlouisncrs.org/news_files/DukeWilliamsEngineTuningPerformance%26EconomySeminar.pdf

[Timothy B.]

Re: 1966 L72 running hot

The 327 and 427 have different size radiators, if your car was originally a small block that may explain the cooling problem.

[Jim D.]

Re: 1966 L72 running hot

The 327 and 427 have different size radiators, if your car was originally a small block that may explain the cooling problem.

Good point. When the OP stated - "Had a 327 350HP and never had a heat problem", I assumed he was talking about a different car. We need a clarification.

[Joe T.]

Re: 1966 L72 running hot

Sorry for confusing my question on the vacuum can. I was thinking of a different type of vacuum can. I will check mine out tomorrow. I purchased the distributor and K66 ignition from Chicago Corvette and the can was what was included with the distributor. I don't know the vacuum or number on the can. When I said I had a 327 350HP it was before I got the 427 425HP corvette. This 427 is a numbers and date coded car. I also have a date coded new carburetor. Sounds like I need a B28 VC1810. I will have the radiator cap checked also.

[Chris H.]

Re: 1966 L72 running hot

2 inch rule description starts on slide 17.

[Duke W.]

Re: 1966 L72 running hot

You need to report the ID number of the VAC and the start and stop points measured with a Mighty Vac or equivalent. Also report manifold vacuum at actual idle speed.

The OE L-72 carb is set up for ported vacuum advance. This should be converted to full time by teeing into the choke vacuum break line.

Duke

[Michael J.]

Re: 1966 L72 running hot

Here is another Duke article on this:

https://www.crankshaftcoalition.com/wiki/images/e/e4/Vacuum_Advance_Specs.pdf

[Joe T.]

Re: 1966 L72 running hot

Ok. I have read the articles and and replies. My 427 425 HP motor was rebuilt before I purchased the car. It sounds very healthy. Not sure of the cam used. I have installed numbers and date coded parts. I have the new Transistorized Ignition (K66) along with a date coded new distributor for that ignition and the 4150 carburetor. Have changed to full manifold vacuum using a tee in the choke vacuum break line. With this information, should I use a B26 or B28 vacuum can? I do not have a vacuum gauge.

[Chris H.]