I know that high engine temperture can be caused by improper ignition timing. Which condition causes high tempertures, to advanced or to retarded? How many degrees either way will cause overheating.

 

Both can cause overheating. Too early makes detonation, this heats the chamber, valves and pistons. Too late leaves a fire still burning as it exits the exhaust, wastes power and heats the exhaust valve and valve guide. Late timing will sometimes start to turn the manifold cherry red from the flame hitting the exhaust. Sometimes 2 additonal advance degree's is enough to start the engine pinging and headed into detonation.
I suspect you would need 5 to 10 retarded to really start heating up. Never tried to cause your symtems so this is hard to answer. Find TDC and time it correctly. Good Luck

 

Most often - having too little timing in the engine (retarded) will cause an overheating problem. This is why working vacuum advance plugged into a non-ported vacuum outlet will often help cool a motor down.

 

Late timing will increase exhaust gas temperature which will eventually throw heat into the cooling system.

On the other hand, I have yet to see late ignition timing be the main reason for an overheating engine. Late meaning up to 8-10 degrees. That is enough timing deficiency that the engine not being responsive would be the primary concern, not overheating. If your engine is overheating, clean up the cooling system.

Like anything else, I haven't seen them all.

Why do you ask, may I ask?

 

This is why many of the over heating issues discussed here are suggested to check the vacuum advance canister. I know from my own experience. I had an "high temp" problem and took the advice from fellow forum memebers and checked my vac canister. Found it not holding any vacuum. Changed it, set the timing at factory specs and now I can drive in 85+ degree weather and hold steady at 180 degrees. That's in my '66, stock 327 and a copper/brass replacement radiator.

 

I believe the root cause of your alleged high temperature problem was the coper radiator. Slow timing just aggravated the condition. I have a copper radiator in my '65. Timing is set 2* BTDC. It'll run 180* in 85* weather too.

What do you think about the '67 California emmision cars that had factory timing set at 2-4* ATDC (as opposed to 49 states 10* BTDC)? That's a big difference. Do you think the California cars overheated when new?

 

Agree with Sweet 66 and not sure the copper is the villain. I have an aluminum radiator and when my vacuum advance can goes out, my car will start to heat up when sitting at a light during the summer. It is REAL obvious. Fix the can and it's a sweetheart. But I do have a question Mike. Why are you timing at 2 degrees BTDC for initial? Did you mean 12 degrees?

Just wonderin'

G

 

What kind of shape is your aluminum radiator and the rest of your cooling system in? Unknown?

'65 250 hp timing spec is 2*-6* BTDC. If I set it any faster, it'll surge at low engine speed in gear. Original vacuum can on mine is working fine but I can't keep the temp at 180* if I'm in stop/go driving on a 90* day. Goes to about 200*. No problem.

All I'm saying, if your cooling system is in "as new", oem condition, slow timing won't make it run hot unless you have the timing way slow from spec. But, how many of these cars have a cooling system in that condition.

When the '73 models came out, the timing was severely restricted at low engine speeds and even earlier '71 models had transmission controlled spark which meant no vacuum spark advance until you got in high gear. At the same time, the oem's went to 195* thermostat and that's where they ran.

 

What kind of shape is your aluminum radiator and the rest of your cooling system in? Unknown?

'65 250 hp timing spec is 2*-6* BTDC. If I set it any faster, it'll surge at low engine speed in gear.

All I'm saying, if your cooling system is in "as new", oem condition, slow timing won't make it run hot unless you have the timing way slow from spec. But, how many of these cars have a cooling system in that condition.

When the '73 models came out, the timing was severely restricted at low engine speeds and even earlier '71 models had transmission controlled spark which meant no vacuum spark advance until you got in high gear. At the same time, the oem's went to 195* thermostat and that's where they ran.

I have a '63 FI car. Stock, the vacuum advance is hooked to ported vacuum. No advance at idle. If you run it like this, it has an unstable idle, high underhood temperature and engine response is a little lazy.

Hooked to straight manifold vacuum, the idle is stable, underhood temp is noticeably less and engine response is much improved.

Regardless of the above changes in engine behaviour, the temperature gauge stays the same regardless of where the vacuum is hooked. That's because the cooling system on this car is working like it's supposed to.

 

Ahhh... there's my answer. I did not consider the 250HP version and right you are on the timing. Nowhere near what the L79 times in at. Thanks.

As for my radiator? Honestly it was in the car when I got it and while it "tests" good, I wouldn't say it's perfect. I will admit to being tempted when DeWitts has a sale or forum special. My intent was only to communicate that when my car dumps a vacuum can (done it three times in 8 years) it communicates that quickly through the temp gauge when I sit at a stoplight. My temp goes up and I go home to check the can.

Thanks for the reply.

g

 

Mike, I had a 350 270HP in a 71 Nova SS in California back in 1975, they ran terrible with the smog stuff hooked up. We would leave the smog shop and take that stuff off till the next smog test. I don't know what they thought they were fixing with those early smog devices. Gas mileage and power went in the dumper with that stuff connected.
I do not recall the actuall timing setting.

 

California had different emmission standards than the rest of the country back then. The 49 state cars weren't much better. Everything got much worse on the '73 models when they started using the EGR valve.

The car companies used the late ignition timing to raise the exhaust gas temperature to burn the residual fuel out of the exhaust. That in itself didn't really raise engine coolant temperature though. They also used a 195* thermostat to raise engine coolant temperature to help vaporize the leaner fuel mixtures they started using.

 

Good explanation Thanks

 

I always have to think twice when cooling issues are automatically directed towards the cheap copper replacement radiator.
Now, I am no expert, but didn't the big block cars ( most anyway at least according to my NCRS manual ) come with copper radiators? Now I know there is an argument for overall size/capacity and additional core rows adding to the performance of the copper radiator. My '71 is a factory AC car and has the original copper radiator.

All I'm saying is once I diagnosed that my vac advance can was bad and I replaced it my high temp issues went away. The copper rad in my '66 was in the car when I got it and I just can't see spending $600+ to change something that works just fine. It gets pretty hot here in the south and I have been in plenty of traffic situations when it's 85 degrees out and the engine barely gets over 180 in traffic, always 180 on the highway.
No argument that a proper aluminum radiator with factory style shroud, fan and everything else in place is the way to go but sometimes it's not always the obvious.

 

Well, you just made my point. Your copper radiator in your car is very marginal at best. The OEM aluminum radiator had some margin of reserve. All else equal, if you'd had a properly functioning OEM aluminum radiator in your car, you may have never known your advance wasn't working.

Don't forget, a very large percentage of C-1 Corvettes didn't have vacuum advance. You don't see those guys complaining about them overheating much either.

Another example: I once had a '56 Bel Air with a 327/340 engine in it using the stock 265 radiator. 283 rams horn exhaust. I used a Chevy dual point distributor with no vacuum advance, just like C-1's

I could run that thing hard coming home at night and when I'd get in the driveway, I could see the exhaust manifolds were glowing a dull red. Later, I used a vacuum advance distributor for awhile and it didn't matter how hard you ran it, the manifolds wouldn't get that hot again. With either distributor, the engine coolant temperature ran right on 180* which was the calibration of the thermostat. So, the slow(er) timing of the mechanical distributor was heating the exhaust but the cooling system had the capacity to absorb and throw off the extra heat. Therefore, no rise in engine coolant temperature.

 

PSS. I forgot to mention, the '63 FI cars had ported vacuum advance so there's 15* degrees of timing they didn't have at idle that the 340 hp cars had. They didn't overheat either.