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I have a '65 327 300hp that was previously modified to a 350-365hp.
- I recently replaced the radiator (DeWitts), water pump (EMP/Stewart stage 1), 180* thermostat, all new hoses, etc.
- I also have timing dialed in using Duke/Lars method and I'm pretty sure she's running in tip top shape - very responsive, very smooth.
The only thing I haven't changed is my fan clutch, which I'm about to pull the trigger on.
Over the past few months, I've been venturing out farther and farther from home, and was under the impression that everything was "fine"...... until I went in for a state inspection.
They drove her around back for the inspection, and I waited up front. I know they left her on/idling the whole time as I could hear from where I was sitting.
The brought her back to the front, shut off the engine, and I was about to leave when she wouldn't start. I looked at the temp gauge, and she was ~220 - way hotter than I had ever seen it.
- the radiator cap never released, and I didnt have an infrared gun to check temp. I waited about an hour for her to cool down, occasionally cranking the starter to let the water pump do it's thing and move the water around. Temp gradually dropped to 160, and I got it started and rushed home.
- I checked the accelerator pump during the hour, and I never lost gas. However, I never checked for spark.
My questions:
What happens when the block gets hot that would prevent a restart? Do piston tolerances change with the heat to mess with compression?
or something much more simple like the coil overheating?
First, we need to define wouldn't start. I assume this means the starter does crank the engine over at near normal speed, but the electrical system doesn't fire the spark plugs. Or the starter cranks very slowly. Chevy put a larger starter on the high compression engines to compensate for the compression. If the starter is drawing a lot of voltage / amperage, it robs the ignition system enough it won't fire.
The pistons and rings do swell with a hot engine.and resistance is up. The starter is also hot and can take more voltage/amps to spin the engine. Timing can affect the hot starting as the plugs fire before TDC and try to drive the pistons backward, too much initial timing can prevent starting.
Also, what ignition system do you have? We need to know if you can safely pull the coil wire to check for spark without damaging the ignition module.
220*F is not fearfully hot, but can contribute to numerous problems.
I had a 302 with 12.3:1 pistons that I had to flip the kill switch off and get the engine rolling and flip it on to start it hot.
First, we need to define wouldn't start. I assume this means the starter does crank the engine over at near normal speed, but the electrical system doesn't fire the spark plugs. Or the starter cranks very slowly. Chevy put a larger starter on the high compression engines to compensate for the compression. If the starter is drawing a lot of voltage / amperage, it robs the ignition system enough it won't fire.
The pistons and rings do swell with a hot engine.and resistance is up. The starter is also hot and can take more voltage/amps to spin the engine. Timing can affect the hot starting as the plugs fire before TDC and try to drive the pistons backward, too much initial timing can prevent starting.
Also, what ignition system do you have? We need to know if you can safely pull the coil wire to check for spark without damaging the ignition module.
220*F is not fearfully hot, but can contribute to numerous problems.
I had a 302 with 12.3:1 pistons that I had to flip the kill switch off and get the engine rolling and flip it on to start it hot.
All great questions,
It would crank at normal speed, but wouldn't start.
I have a dual point distributor with points set at 29* each. This has a combined dwell of 34*
Initial timing is set at 14* (no vacuum)
Once everything cooled off, She begrudgingly started after a very long starter crank. I was able to drive home 2-3 miles without getting stopped at any stop lights.
Your explanation of piston rings swelling is where my head was at, but the hot starter stealing amps from the coil also makes a lot of sense.
I think your starting issue was related to fuel temperature, not engine temperature. 220 is not hot, it's just slightly over normal operating temperature for modern engines.
But when the coolant is at 220, the carb is pretty warm also, and fuel will boil, and do fun things.
I tend to leave the hood open on my 62 if I'm stopping for a little while, so it can cool off a bit. And the fresh air duct blowing on the carb trick also helps especially in summer (not so helpful in winter when you kinda need the heater working)
I'm glad I live where they don't bother inspecting our cars any more.
I think your starting issue was related to fuel temperature, not engine temperature. 220 is not hot, it's just slightly over normal operating temperature for modern engines.
But when the coolant is at 220, the carb is pretty warm also, and fuel will boil, and do fun things.
I tend to leave the hood open on my 62 if I'm stopping for a little while, so it can cool off a bit. And the fresh air duct blowing on the carb trick also helps especially in summer (not so helpful in winter when you kinda need the heater working)
I'm glad I live where they don't bother inspecting our cars any more.
I agree. It could likely have even percolated and flooded.
Sounds like vapor lock. Do you have a crossover under the carb on the intake manifold. If so, is it blocked off? Do you have the aluminum spacer under the carb? Jerry
The starter was spinning the engine normally, you had a pump shot when you moved the throttle lever and the engine was up to temperature. So it was cranking strongly, you had adequate fuel supply to the intake manifold, and there should have been no choke involvement.
Either it was fuel-flooded due to percolation or something in the ignition system failed intermittently (would likely have been heat related). Like Jack said, it sounds to me as though it was simply fuel-flooded. Over-rich A/F and dampened the plugs.
FWIW, the AFB in my '63 will percolate enough to require a bit of open-throttle cranking when hot-starting. I don't enjoy that, but it's a reality with the ethanol-laced fuel which is all that's available where I live. I plan to try lowering the float level slightly as an experiment to see if that will help without causing collateral issues, but haven't yet gotten around to that.
And as others have commented, 220*F is a tad warmer than I like to see, but it is by no means overheated.
Looks like everyone is giving you good guidance. Now that I review your initial post: 1) Idle for a long time, 2) shut the engine off assuming the hood was closed trapping the heat 3) sits shut off for 3 or more minutes, 4) the normal rise in temperature due to the engine off = no circulation - 240*F would not surprise me 5) heat soak boils the cheap fuel out of the carburetor and into the intake flooding the engine and emptying the fuel bowls. 6) starter is also absorbing the heat and will draw more off of the battery. Points systems seem to require more voltage to work properly than some electronic ignitions.
I have the same problem with the R66 mouse if it is >80 degrees F out, the car is just shut off, and setting in the sun with the sun beating down on the hood. I have to open the hood and wait a few minutes to normalize the temperature. Then, I still have to hold the accelerator to the floor and crank the engine to clear the fuel in the cylinders and refill the bowls on the Holley. Then after quite a few revolutions, it will fire and start. There are many posts on this forum and others with heat shields and fans and other attempted remedies that have been attempted, some with limited success. One simple remedy is to pop the hood when you park it and leave it up 2 inches or so.
You have normal operation for an old car with a carburetor in summer weather (temperatures) and today's fuel.
So much great info. I love learning as much as I can about this beast!
Here's a little more interesting info.
- I've been rolling without a hood ever since the radiator swap - I feel like it's kind of like a badass flex move
- it was a beautiful 70 degrees outside here in Houston.
- I'm running non-ethanol fuel, 91 octane.
I'm relived to know that even ~240 wouldn't have done any damage to the block.
@R66 in a different thread, you mentioned various kinds of fan clutches (165 vs 180). Is there a particular one you would recommend?
I'm just a dumb redneck and don't have the data base for recommending a clutch for your fan. However, there are several guys on here that do and have replaced theirs with a equivalent clutch. It think it was a HAYDEN Thermal Fan Clutch if you want to do a search or wait on their replies.
Sorry, being DUMB is better than opening my mouth and being STUPID.
OK, so you hit me with some new data:
1, No hood to trap the heat,
2, 70 degrees outside, I envy you.
3, Non ethanol fuel - slower evaporation.
As I recall from your prior posts:
1, No heat riser, you have a spacer?
2, Cast iron intake with heat passages in the smiley face under the carburetor are plugged but passages at the head / intake still open allowing heat under the carburetor, just not directly on the base.
I assume you have the correct fan shroud on the new radiator? A new radiator is almost worthless without air flow directed by a shroud even with a good fan when the engine is idling or driven in town.
the flow rate of the new SW water pump is equal to stock, not high flow?
What kind of fuel filter and location?
What is the carburetor? Holley or Carter?
Don't know how long it idled, but I wouldn't worry about the temperature if it only went to 220*F after it was off for a couple of minutes. I don't know that you need a clutch on the fan. I would test it first.
Extra information from Holley:
"All 4150 and 4160 style Holley carburetors use the standard 30cc pump reservoir. This capacity rating is not the amount of fuel delivered per full stroke of the accelerator pump system but instead is the volume after 10 strokes. This is the total reservoir capacity. Depending upon the pump cam, the volume delivered after 10 strokes is usually less than 30cc. As an example, the white accelerator pump cam will deliver less than 20 cc of fuel after 10 strokes."
Thus, follow me here: The fuel in the accelerator pump well is held in by a check ball should it expand and try to reenter the bowl. The discharge from the pump well is closed at the nozzle with a ball that acts as a check valve and thus helps retain fuel at that level. The discharge of the pump is at the very bottom of the bowl and metering block, and the fuel in the accelerator pump well is the last thing to go dry in case of heat related evaporation and fuel expansion.
Hypothesis: Even with the bowl completely dry below the main jets, the accelerator well can remain full and still supply up to 10 strokes to the nozzle making it appear you have fuel in the bowl. In this case, I don't accept fuel from the nozzles as a reliable indicator of a full bowl of fuel.
Reference: https://www.holley.com/blog/post/acc...y_carburetors/
14* initial advance seems high and could contribute to cranking resistance when hot. How much centrifugal advance do you get from that distributor, what is your total advance?
As I recall from your prior posts:
1, No heat riser, you have a spacer?
2, Cast iron intake with heat passages in the smiley face under the carburetor are plugged but passages at the head / intake still open allowing heat under the carburetor, just not directly on the base.
I assume you have the correct fan shroud on the new radiator? A new radiator is almost worthless without air flow directed by a shroud even with a good fan when the engine is idling or driven in town.
the flow rate of the new SW water pump is equal to stock, not high flow?
What kind of fuel filter and location?
What is the carburetor? Holley or Carter?
Heat riser is wired open.
Heat passages in the intake are not plugged under the carb. This is on my to-do list....
Stock fan shroud with new rubber seal on the bottom when I replaced the radiator.
If it was cranking fine, timing is not your problem. I was on the dyno Sunday and a 408 BBC (396 with a 4.155 piston, street, 10.72:1) needed 21 initial and 42 total. My dirt stuff is locked, so the initial is essentially 31-38 depending on the piston/chamber design. Do you have headers? 220 is not too hot, as said above. On a street engine, I tend to try and keep them at the 190-210 range. Hot enough to burn moisture and allow the oil to do what it's supposed to, yet plenty cool. Carb percolation could happen, but at 220 degrees, you wouldn't expect it. I would look close at the fuel line near any heat source (hence the header question) for vapor lock, and I would examine the coil. They don't like heat and take a long time to cool off. Is it leaking? Ballast resistor (if still there) breaking down? As said above, measure your voltage after heat soak at the coil. MSD and Daytona Sensors won't fire below 10.5V. (or won't fire reliably) If you have a big draw because your starter is not exactly up to snuff, this will occur.
It might just be camera angle, but it looks like your fan blades are significantly farther from the shroud than I see on my 67. Not that it matters a lot with your hood being off. This also might be a model year difference.
Wow! Just looking at the clearance of your fan blades to the inner edge of your (rad-man) shroud. I had half that clearance on my C1 and had hot idle issues. I got a larger diameter fan (reducing that clearance to 1/4") and now it actually runs cooler when at idle than cruising. Just sayin'.
I don't know if this was suggested--given the number of responses that I didn't read in total--but do you have a phenolic spacer between the carb and the manifold? That is a two-minute upgrade and worth the effort.
02-13-2024, 12:35 PM
What exactly happens during engine overheat?
