With no shroud you have a Reversion issue at idle meaning you are recirculating air that has already gone through your radiator, another thing you need to look is you said the Electric fan is running with the engine speed, you only need an electric fan at idle. What brand of electric fan do you have and how much CFM does it pull? It might help if you can take some pics of the Engine Bay.
Engine temp on chevy small block
- Thread starter Carburetor1
- Start date
Agreed, but before he deals with something like this he needs to get his lack of air flow issue addressed.
Worth trying, sure, but it could also be possible that the current air flow is sufficient, and he's dumping too much heat into the coolant to begin with.
Had a buddy with this issue a couple years ago in a Bronco with a 351W. He put over $1,000 into the cooling system with a big 4 core radiator, big fan with shroud that turned on at 200°F, high volume water pump, etc... and it would still creep up to 215+°F idling in traffic. I switched his vacuum advance from ported to manifold, (12° --> 22° at idle) and steady 185-190°F.
I would just make sure there's not a reason for it overheating on the engine side before I started throwing money at the cooling side.
I happen to know for a fact, based on personal experience with a 56, that the way his fan is set-up is not going to function adequately at idle or slow speeds. He needs substantially more air flow and he is for sure having a reversion issue. I also went through this problem with my Tiger (well know for overheating issues), and as you mentioned, I finally solved the heating issue with ignition timing changes, only I used more advance on it than you mentioned, but first I had to get the cooling system up to snuff, and air flow was key. Earlier Ford Windsor small block engines are notorious for having cooling problems.
Last edited:
Do you have a short or long WP? A long one with a healthy clutch fan from a Buick or similar BB will get you close to the RAD and would help.
I never ran hot Idling at 650 rpm. I hate fast idling cars with small cams. Not good for carburetion - or my ears
I never ran hot Idling at 650 rpm. I hate fast idling cars with small cams. Not good for carburetion - or my ears
I have personal experience with a '55 Bel-Air with a 355ci SBC that doesn't overheat with a stock replacement radiator and fan with no shroud. I got to know that car very well, as detailed on here a while back. How he describes it is exactly the symptoms of late spark timing.
https://bobistheoilguy.com/forums/threads/roadkill-trip-in-a-55-chevy-belair-wagon.351447/
The 50's engines ran at 180 deg f. In the manual in front of me, for 1957 chevrolet truck, thermostat starts to open at 157 to 163, Fully open at 183, for all except Powermatic models. Radiator caps 7 to 9 pounds per sq in depending on truck model. Fans where 19 to 20 inch depending on truck model. 4 blades for smaller trucks and 5 for larger.
- Joined
- Feb 7, 2022
- Messages
- 121
Update.... purchased a shroud and replacing bottom hose to move closer to fan and adding new coolant.
Job should be done this week and will post an update. Thanks for all the info and knowledge.
Job should be done this week and will post an update. Thanks for all the info and knowledge.
- Joined
- Feb 7, 2022
- Messages
- 121
Installed a shroud but didn't help at idle..still 210 215. Currently have a 195f thermostat might try something like 180. Maybe back timing a bit
With a shroud, the fan blades need not be close to the resistance of the radiator.
The blades are likely stalled, pulling a fraction of the air they would, if not stalled, or if movement was assisting the flow.
Im a bit of a fan nazi. All my axial fans,, both the 1500 rpm ones and the 7500 rpm ones, the closer their impeller intake side is to the resistance, the more noise they make, and less air they move.
They have difficulty scavenging when too close, to the point of near uselessness.
The blades of these fans, are a nice aerofoil too, not just bent flat metal relying on angle of attack alone for lift, like most water pump belt driven fans.
Also, the air pushed into engine bay, needs an escape route.
I recently took off some wheel well shrouds that I made yeats ago, that quieten engine noise to the sides, but restrict escaping airflow.
Even though it has been hotter than ever recently, my coolant temp gauge has been reading half a hatch mark lower, always, and the skirt removal is the only variable I changed.
I know tstat should keep coolant temp same as before, with an uncompromised radiator.
I suspect increased around engine airflow, from wheel well skirt removal, is cooling the one wire temp sender, and lowering gauge reading.
I dont have much faith in this hypothesis, but unless some other variable has changed unbeknownst to me......
My sender used to be tucked tightly under an ac compressor, and when i installed wheel well skirts, i noticed no difference in coolant temp readings.
But now, a dual internal fan alternator resides there, spewing air radially at the coolant temp sender, which now reads half a hatch mark lower with skirts removed, and air from radiator fan having an easier escape from engine compartment.
This second alternator has not been worked hard since skirt removal, spewing its own heat at temp Sender. I have a k type temp sensor on it, and t stat housing, but have not bothered checking, yet.
The blades are likely stalled, pulling a fraction of the air they would, if not stalled, or if movement was assisting the flow.
Im a bit of a fan nazi. All my axial fans,, both the 1500 rpm ones and the 7500 rpm ones, the closer their impeller intake side is to the resistance, the more noise they make, and less air they move.
They have difficulty scavenging when too close, to the point of near uselessness.
The blades of these fans, are a nice aerofoil too, not just bent flat metal relying on angle of attack alone for lift, like most water pump belt driven fans.
Also, the air pushed into engine bay, needs an escape route.
I recently took off some wheel well shrouds that I made yeats ago, that quieten engine noise to the sides, but restrict escaping airflow.
Even though it has been hotter than ever recently, my coolant temp gauge has been reading half a hatch mark lower, always, and the skirt removal is the only variable I changed.
I know tstat should keep coolant temp same as before, with an uncompromised radiator.
I suspect increased around engine airflow, from wheel well skirt removal, is cooling the one wire temp sender, and lowering gauge reading.
I dont have much faith in this hypothesis, but unless some other variable has changed unbeknownst to me......
My sender used to be tucked tightly under an ac compressor, and when i installed wheel well skirts, i noticed no difference in coolant temp readings.
But now, a dual internal fan alternator resides there, spewing air radially at the coolant temp sender, which now reads half a hatch mark lower with skirts removed, and air from radiator fan having an easier escape from engine compartment.
This second alternator has not been worked hard since skirt removal, spewing its own heat at temp Sender. I have a k type temp sensor on it, and t stat housing, but have not bothered checking, yet.
What is your spark timing? Late spark timing is what causes it to overheat so you would be wanting to advance it if that's the issue. Need to know where it is though.
A 180°F stat will do nothing.
- Joined
- Feb 7, 2022
- Messages
- 121
Not sure on spark timing a shop set it when capacitor was changed, but said it was hard to get the timing set for some reason. It has backfired a few times at low speeds then shut off and had to wait 10min to start it.
Like RDY4WAR said in post #43, you need to make sure that your vacuum timing is connected to manifold vacuum. Static advance needs to be set to at least 12 degrees BTDC (with the vacuum advance disconnected) and that you are getting at least 10 degrees of vacuum advance (after reconnecting it) at idle. Aim for 22-24 degrees of total advance (BTDC) at idle. Doing this will noticeably reduce your heating problem at idle.
Take the car to someone who is familiar with and experienced at tuning pre-emissions system engines (probably an old-timer like me). Tell them what RDY4WAR and I said, he should know what we are talking about.
If you are going to try doing this yourself you are going to need an adjustable timing light and a vacuum gauge. The ignition system needs to have an adjustable vacuum advance pot (most point-style ignition systems do). Read about how to do this and/or watch some YouTubes on how to do this.
Last edited:
- Joined
- Feb 7, 2022
- Messages
- 121
I don't have a light but will get one the screw was set around 8 I think.
The guy who set it is an old timer and knows what he is doing but said it was a pain to get timing accurate. Could a slight nudge advanced help a little to get it up there.
The guy who set it is an old timer and knows what he is doing but said it was a pain to get timing accurate. Could a slight nudge advanced help a little to get it up there.
This. If it has standard points ignition the dwell needs to be set at 30 degrees first before attempting to adjust ignition timing. Always disconnect vacuum advance when setting the initial timing. Always have the advance connected to manifold “live” vacuum when connected. You can spend an ass load of money on fans and shrouds when proper timing may be the issue…
- Joined
- Feb 7, 2022
- Messages
- 121
Getting a light and gauge tonight and will update...
If it has an original harmonic damper, the timing marks may be worn off or the damper could've moved slightly. Something like that could be why it was difficult to set.
If it's installed at 8° with no vacuum advance (or set to ported vacuum) then that is your issue. Idle likes the timing in the 20-25° range, sometimes higher. At idle, you have low cylinder pressure and a good bit of reversion. This means a slower flame propagation requiring more spark advance. When timing is late, the mixture is still burning when the exhaust valve opens which causes exhaust gas temperatures (EGTs) to spike. The coolant in the heads flows around the exhaust ports so a good bit of that heat ends up going in the coolant. The late burn also means a higher amount of exhaust reversion into the intake port during overlap and a higher amount of residual exhaust gases on the next intake cycle. That means less efficient combustion with dilutes further and so on. Average cylinder temperatures are higher, dumping more heat through the cylinder walls.
My process for finding ideal timing is similar to what is stated above. I like to use a 15° vacuum canister and set the initial timing at 5°. I like to get the initial timing as low as I can so it'll crank over easier. Then let the vacuum advance add the timing once it's fired up. Starting at 5° initial, I hook up the vacuum advance to manifold and verify 20°. (5° initial + 15° vacuum) Then I hook up the vacuum gauge and gradually bump the timing until I find the highest vacuum and/or smoothest idle. I let the engine tell me what it wants. I then unhook the vacuum advance to see where the initial timing is so I can start mapping the mechanical curve.
When moving the timing around, the idle rpm is likely to change as well. This is due to the change in combustion efficiency and vacuum. You'll likely have to adjust the idle rpm and possibly the idle screws on the carb to compensate. You may need to move the timing a couple degrees, adjust the carb, move the timing, adjust the carb, etc... to keep things consistent. It requires some patience to dial it in, but it'll run so much better and cooler once you do.
If it's installed at 8° with no vacuum advance (or set to ported vacuum) then that is your issue. Idle likes the timing in the 20-25° range, sometimes higher. At idle, you have low cylinder pressure and a good bit of reversion. This means a slower flame propagation requiring more spark advance. When timing is late, the mixture is still burning when the exhaust valve opens which causes exhaust gas temperatures (EGTs) to spike. The coolant in the heads flows around the exhaust ports so a good bit of that heat ends up going in the coolant. The late burn also means a higher amount of exhaust reversion into the intake port during overlap and a higher amount of residual exhaust gases on the next intake cycle. That means less efficient combustion with dilutes further and so on. Average cylinder temperatures are higher, dumping more heat through the cylinder walls.
My process for finding ideal timing is similar to what is stated above. I like to use a 15° vacuum canister and set the initial timing at 5°. I like to get the initial timing as low as I can so it'll crank over easier. Then let the vacuum advance add the timing once it's fired up. Starting at 5° initial, I hook up the vacuum advance to manifold and verify 20°. (5° initial + 15° vacuum) Then I hook up the vacuum gauge and gradually bump the timing until I find the highest vacuum and/or smoothest idle. I let the engine tell me what it wants. I then unhook the vacuum advance to see where the initial timing is so I can start mapping the mechanical curve.
When moving the timing around, the idle rpm is likely to change as well. This is due to the change in combustion efficiency and vacuum. You'll likely have to adjust the idle rpm and possibly the idle screws on the carb to compensate. You may need to move the timing a couple degrees, adjust the carb, move the timing, adjust the carb, etc... to keep things consistent. It requires some patience to dial it in, but it'll run so much better and cooler once you do.
Before doing this everything else has to be set to spec, including the dwell. If the total timing can't be accurately set you might have a vacuum leak and/or miss-adjusted carburetor, either one can cause the idle vacuum to be out of spec or fluctuating. Furthermore, if the static timing is fluctuating/jumping you could have a worn distributor or timing chain.
When you get the timing set properly you are going to have to readjust the carburetor, not just the idle speed, the idle mixture as well. You can use the vacuum gauge to do this. Then you need to go back and check the timing. You may need to do the back and forth routine a few times to get a steady idle.
Make sure you get an adjustable timing light. It doesn't have to be a fancy digital type, a dial type will work fine. I'm assuming that you have a tachometer so you can accurately set the idle RPMs.
Last edited:
My personal preferred method with small block and aftermarket cam is to adjust timing higher until starter “grunts” once to turn over the engine. Has always been a great starting point when adjusting-tuning without a timing light. Engine needs to be at operating temp. Carb adjustments always after timing is set.
Grumpy Jenkins liked high timing until 4th gear on the big end of the track. He had a switch to kill one set of ignition points (dual point dist.) to effectively lower timing in high gear. Said it would pull harder at the finish line…
Good point. Furthermore, the harmonic balancer could be bad, I have run across this before.
Similar threads
