I am having an issue with my 63 Corvette 327/300HP engine overheating. I have tried all of the things (or think I have) that have been posted without results. I have a powerglide transmission. Everything is stock. Carter AFB carb. When the engine was rebuilt, it was bored out 30 over. All parts are either rebuilt or new on the car.

I suspect timing, but could be wrong. So far, I have done the following:

Change to an Aluminum Dewitts radiator from copper
replaced the thermostat
new waterpump
new fan clutch
radiator seals

The engine runs at about 215 to 220 degrees. I checked the vacuum and at idle am running about 10-12". I have a B28 vacuum advance installed now. I did have a B22 installed, but at idle, the advance did not kick in so the idle was not very good. The B28 seems to have helped. Currently, I have the full advance at about 36 degrees. I have tried it from there to about 50 degrees, but can't seem to find an advance setting that has helped either the heat or the performance.

The engine seems to run pretty well when you drive it after the initial launch. It bogs down when you push the pedal down fast. I have considered putting a spacer on the fan so it would be further into the shroud and pull more air. Seems like that would help, but certainly not stock. Currently, the blades on the fan are about 1/2 in the shroud.

Any help would be appreciated. I am at a loss to cool this car. I have done a ground up restoration and certainly can't afford to run this car hot.

 

Did you confirm the guage readings with an IR gun. If not, do so.
Sounds like you know what your doing so you must have heard about the bad sending units.

 

Thanks for the response. I did check it with a gun and changed the sending unit as a result. It seems to reflect the correct temp now. unfortunately, still too high. Appreciate any advice.

 

What is your initial timing advance? And what is your advance curve set for in the distributor? When does all of the centrif. advance come all in, at what rpm? IMO that may be your problem also, you want the distributor advance to come all on at around 2500-3000 repm....

There are a ton of articles about this on this forum...The timing could be your issue!

Maybe the initial timing needs to be increased a bit more......?

In many of the articles I have read on this forum, The B28 vac can and a few more initial advance degrees and faster distrib. curve will help the temp at idle and cruise etc.

And of course the enevitable vacuum source to the B28 can should be on a FULL maniforld vacuum port

With the Aluminum, radiator you should see a major decrease in running temp, IMO I suspect this to be a timing issue...

imo Your present temps are way too high your motor....

 

Right now I have it at about 12-15 degress initial (with the vacuum adv disconnected). The vacuum advance take it at idle to about 30. All in at about 3000 RPM. I have tried it at higher initial timings, but it does not seem to make a difference. The engine seems to prefer about 40-50 total at high RPM, sitting in the driveway. There is a pretty significant hesitation when you take off from a standstill. Pretty strong power at 2000+ RPM after the initial launch.

 

imo sounds like the ignition is set up correctly, are you connected to full maifold vacuum to the can, sounds like it is...

The 300 hp motor should run very cool with your present setup. Are you sure the water pump is working ok?

Could this be a fuel related issue???? running too lean??

 

I checked the air/fuel mix with a machine a friend of mine gave me. It measures CO2 output from the tailpipe. It appears I am running at about 13.5 to 1. I adjusted the idle/air mix with this machine to get to this level.

The only other thing I can think of is to try and increase the airflow through the radiator. Hate to put a spacer in there to push the fan further in the shroud.

 

Forgot to reply to the vacuum source. The AFB Carter has a connection at the base of the carb in the front of the carb that hooks up the vacuum. That source feeds the Vac. can as well as the auto transmission.

 

a high performance fan and a Dewitts radiator helped mine with overheating at idle. As JohnZ said on a previous thread here, overheating at idle is usually an air flow problem.

 

What High Perf fan did you put on and from where? I would like to keep the original look if I can.

 

Are you located in the mountain states at high altitude? If not, 10-12" of Hg is a very low vacuum reading for 327/300HP engine.

My 327/300/p-glide pulls 19.5" in P/N (500' elevation) & it loses about 2.5" when selecting D range. Thus, using a B20 vacuum can (fully deployed = 16 degrees at crank at 12" Hg) works well for me with similar centrifical/initial as you describe. Never had any overheating problems & have verified temp gage with IR thermometer (normally 180-185F summer cruise conditions). My temp sending unit is OEM and measures ~685-700 ohms between the tip & the threads at 72F ambient.

You have not mentioned physical evidence of overheating such as coolant overcoming the pressure cap, etc, which makes me suspicious of the actual running temps. On my IR thermometer, the sensor spot size is 1" at 6" distance, 2" at 12, etc. Perhaps yours is similar. If so, be careful to shoot your black radiator hose as a target from close-up, aiming just forward of the thermostat outlet, kind of level, from passenger side towards drivers side. In other words, don't allow a bunch of background IR contribution into your readings by being too far away & having engine's mass heat influence the shot.

Perhaps you could describe your fan clutch as well. In my case, the clutch is OEM Switzer (?) type recently remanfactured by Fred Oliva. If you have the NORS replacement clutch (GM 3916141), they clutch-in at a higher temperature.

Lots of stuff to chase on these situations, but I'd suggest resisting the tempation to re-engineer things, find out why the vacuum is so low, & examine sending unit/gage accuracy as a start. Good luck.

 

Agee with Vark- waso. Your vacuum is way too low for a 300 Hp engine.
Sure there isnt a vacuum leak? One other area not mentioned is the timing cover the correct one? Latter covers have a different timing mark location and the timing may actually be retarded.

 

I have checked TDC to make sure the timing mark is accurate and it is. I do agree that the vacuum seem low. I have checked all over the intake and made sure the intake bolts are tight and tha the carb bolts are tight.

 

I have the GM replacement clutch. Even if it kicks in later at 195, seems like the car should not run at 215-220.

 

Putting the fan further into the shroud will reduce airflow, not improve it - the blades should be half-in/half-out of the rear edge of the shroud for maximum fan efficiency. Your abnormally low idle vacuum reading indicates a significant vacuum leak somewhere (modulator?), which will cause an excessively lean condition at cruise - I'd go after the vacuum leak first.

 

For one thing it's no longer a 327/300 - not even close! Someone put a a "big cam" in it - one with WAAAAAAAAY too much overlap, and high overlap is especially ill-suited to Powerglide. The 300 HP cam should pull about 15-16" idling in Drive at 475.

The B28 can and as quick a centrifugal curve as the engine can handle without detonation is your best bet assuming everything in the cooling system is to OE spec and performance.

IMO you should have the guy who put the dumb cam in replace it with a proper 300 HP cam, or take him out and shoot him.

I recently did some work on a '62 with a 30-30 cam and 700R4. Don't even ask how this configuration was established! It pulls 7.5" idling in Drive at 700, and it overheats. The vacuum can was a B1, which doesn't even start to pull until 8", which is less vacuum than the engine pulls at idle so it may as well have ported vacuum advance. The 30-30 cam was in the engine when he bought the car, but he had the 700R4 installed in place of the four-speed manual. The distributor was set up by an "expert" after the transmission change.

A B28 cam was a vast improvement in both heating and driving quality, but the centrifugal curve still needs work. The dist is from a '67 L-79 according to the tag, and should have 30 degrees centrifugal, but only shows about 20, so it's apparently been brainlessly diddled. The owner had somewhat agreed to have the cam changed back to the proper 300 HP cam, but is now so pleased with the engine characteristics (compared to before) that he may not do so, which is okay - his choice if he can live with it.

At least the 700R4 with its stump-pulling 3.06:1 first gear somewhat masks the poor low end torque, but a PG with its 1.76:1 first gear and a high overlap cam that kills all the low end torque is going to be a poor driver no matter what you do.

Unfortunately most "engine builders" are utterly clueless when it comes to "engine system engineering", which is the installation of complementary components including cam, spark advance map, and carburetion, that are properly suited to the car and drivetrain and yield a torque curve that is well matched to the owner's typical driving profile.

Duke

 

Other than pulling the cam out, how can I tell that the cam is the problem?

 

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Does it idle nice and smooth, or is it rough & lumpy ??? A 327-300 HP engine should develop at least 18" of vacuum at idle, and idle as smooth as your grandmother's Cadillac. Can you get it to idle down to about 450-500 RPM ??? Ask the shop that rebuilt it if they remember what cam they put in it.

 

By comparing your idle vacuum to what a real 300 HP cam should pull - several examples listed above.

It was suggested your car has a vacuum leak. I agree, and the source of this vacuum leak (assuming all other potential sources such as brake booster, vacuum can, carb/manifold gaskets, etc. have been checked and eliminated as a cause) is the length of time that the valves are simultaneously open - commonly known as "overlap".

Duke

 

I think I like Duke's explanation of the source of the vacuum leak here Nice to have your wisdom!