66 327 overheating - Chevelle Tech
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post #1 of 14 (permalink) Old Aug 19th, 19, 7:23 AM Thread Starter
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Location: Australia
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66 327 overheating

Hey guys, my 66 327 Malibu has an ongoing heat issue. I live in Queensland, Australia, the temps at this time are around 25 Celcius (74F). Car gets hot after 20 minutes or so of driving. Temp gauge creeps to 90+ Celcius (194F), which I know isn't too high, however at this temperate it is also causing a vapor lock issue and the car begins to hesitate and eventually stall.

This sounds like an airflow issue to me, the car is so hot under the hood. Car mainly gets hot in traffic, if I can keep it running on the highway the temp seems to sit steady around 80-85 Celcius, and no vapour lock. If I park the car and turn it off, the temp gauge keeps rising, highest I've seen is 110 Celcius. I have to turn the thermo fans on while the car is off to cool it down.

Current setup is:
327 with cam, headers, intake, carb, dizzy
Current timing is 18 initial, 38 total timing. Tuned 4 weeks ago, carby and dizzy all tuned
Aftermarket (eBay) triple core rad with 10" fans, thermatic controller kicks them in at 66 Celcius, I have tried various temparatures with no change.
160F Thermostat that it brand new, tried 185F and no change.
New long high flow water pump, runnig V belt setup
New coolant.
New temp gauge and sensor

I have checked the following.
Thermostat is working, I got the car up to temp with the rad cap off, hot coolant came into the rad spot on 160F.
Water pump flow is also good, checked and once the thermostat is open its flowing really well.
Fans are pulling and blow air the correct direction.
Water pump pulley is 6 1/4", which should be ok.

I am thinking of trying the following:
Remount the trans cooler with a gap between it and the radiator, or move it somewhere else altogether
Replace the dual 10" fans with Spal fans.
Wrap the headers (this will be a pain and don't really want to do it).
Replace with new radiator\shroud.

Any other suggestions? I believe in the 66 the air is supposed to travel down through the same place as the exhaust does, are the headers causing everything under the hood to get to hot, and as the fans blow back into the engine and headers, is the heat getting trapped under the hood with no where to go? Is the radiator size sufficient? Fan size ok? I don't want to run a clutch fan as I prefer the aesthetic of the thermo's, so that might be a last resort.
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post #2 of 14 (permalink) Old Aug 19th, 19, 8:22 AM
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Re: 66 327 overheating

Hows the fuel quality? To much alcohol will make the fuel boil out in the carb bowl and fuel line at prolonged idle or a hot soak in higher temps.I switched to premium fuel no ethanal,installed a phenolic carb spacer and made sure the pump to carb fuel line was routed properly and not to close to the engine anywhere on the way up.My car is a stock 327,never had the vapor lock hesitation or stall but hard start after a 20-30 minute hot soak,the fuel would boil out of the fuel bowl(Carter AVS carb)if you removed the air cleaner you could actually here it percolating.
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post #3 of 14 (permalink) Old Aug 19th, 19, 8:48 AM Thread Starter
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Re: 66 327 overheating

Hey Don, fuel quality is good, using 98 octane with no ethanol. I do have the fuel line running right against the engine, I'll look at some options to route it a different way without it sitting against the hot engine. I do have the issue of it hard starting after it sits due to the vapour lock and the heat buildup around the starter.
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post #4 of 14 (permalink) Old Aug 19th, 19, 8:57 AM
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Re: 66 327 overheating

Your coolant temps are not out of line. They seem fine. You can space your trans cooler out with rubber pads or brackets and avoid heat transfer between the cooler and radiator. Space it out even more and help the fans pull only through the radiator.

Insulate your fuel lines and install a phenolic carb spacer the insulates against heat. Use the best fuel you can find.

Headers, yes they make heat. Wrapping will help, but it also causes the headers to rust faster.

Install a cowl hood might help to pull more heat or offer more air for cooling. Plus give the heat a place to go when you shut down.

Put a timer on your fan circuit to keep the fans on for a period after shut down.

Your ambient temps are pretty low right now. Winter?

You might consider larger Spals with better cfm for summer use or all around better cooling.

I'm not too crazy about plastic or glass fuel filters. Might consider the Wix steel shell type as a safety factor. Insulate that and try to keep it out of the airflow from the radiator.

Install a heatshield on the starter or go pgmr starter.
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post #5 of 14 (permalink) Old Aug 19th, 19, 9:39 AM
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Re: 66 327 overheating

My 68 L79 which has all factory parts including 11 to 1 domed pistons runs cool as a cucumber with factory heavy duty cooling components that include 5 blade fan, fan clutch, shroud and pulleys. The radiator is a large tube two row aluminum made by Cold Case. Now to be fair it still isn't on the road aside of driving on my long driveway but it is also an AC car. As a test I left it idling for 20 minutes with the AC on during a 90 degree day and it stayed cool. I would certainly heat insulate your fuel lines as 194 degrees is not hot enough to cause a vapor lock. I once had a Z28 that had muffler drainage holes that blew hot exhaust and boiled my fuel tank in traffic. I would buy a laser heat probe and start scanning for hot spots. I would also move that cooler from being directory mounted to the radiator although my AC condenser is really close to my radiator. I have read many times that one inch wide tubes X 2 is superior to 3 or 4 core units.
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post #6 of 14 (permalink) Old Aug 19th, 19, 10:03 AM
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Re: 66 327 overheating

One thing you need to do it might not help the situation here is to put flaps in the shroud. At speed of 60 mph your fans are actually and inpediment to the cooling as more air is going through the radiator than fan cfm. The rubber flaps help disapate the flow at speed but close at idle when there is no flow. Dewitts, summit racing sells the flaps. See photos and those are two 12 inch fans.
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Last edited by Lew540; Aug 19th, 19 at 10:04 AM. Reason: adding stuff
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post #7 of 14 (permalink) Old Aug 19th, 19, 11:16 AM
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Re: 66 327 overheating

I agree with others. You may have an airflow problem. The job of the metal fan blade is not only to draw air through the heat exchanger, BUT it job is also to remove ( or PUSH) the SUPER HEATED AIR from the engine bay.
Example: both of my 1970s a 454 & 468 have fac. A/C along with the VO-1 type cooling system.
The engine bay has ALL the factory parts in place, Rubber seals, fender flaps(splash shields) Etc,Etc.
The factory fan & clutch system was not pretty. Why? The engine bay needed XXXX number of Cu. Ft. Per. Min. ( of HOT SUPERHEATED AIR removed. )
Both of my 70s have A/C and a 100% copy of the underhood items it had in 1970. My LS-5 4 speed one owner I have had no cooling issues in 50 years, My wagon is the same.
Bottom line is this: You need a TON of air to enter the front and exit by the lower left & lower right Exhaust manifolds. Missing any or part of the factory under hood items will cause " Air Burbles ", What the hell is that?
It is AIR that is spinning around under the hood, And " NOT EXITING ".
My thinking is you need more Cu. Ft. of air >>>>>> " IN " and more air >>>>>>OUT !
P.S. on my 70s, I had a gap between the core support and the heat exchanger. When the car is near a slow or static position, The SUPER HEATED AIR was being SUCKED back into the heat exchanger from the engine bay Adding to the heating problem. I closed off the gap!

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post #8 of 14 (permalink) Old Aug 19th, 19, 3:04 PM
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Re: 66 327 overheating

Follow Al's # 4 Post advise

That Trans Cooler should NOT be Sipped Tied tight to the Rad Core as the Efans will find it very hard to Pull Air Flow thru the 2 combined
Pic of mine with the Trans Cooler 3"at lest from Rad Core and Low Down away from the Hottest put of the Rad Top

I am not a Fan of Flat Metal Shrouds as they tend to hold the Heat/Hot Temperature at the Rad Core

A Cone shaped Shroud made out of Plastic/Fibre Glass is best for directing the Air Flow to the Efan Openings
Here is a Pic of mine

Are those Low Profile Efans ?
if they are they are not as Efficient as Regular Sized SPAL Dual 11" Efans/Shroud with Hwy Flaps that I have on my 67
My car's DF Rad Core is 23.5" Wide x 16" Hi https://www.dewitts.com/collections/...minum-radiator
Rad Support Panel Opening is 24"W x 16" Hi

Since you have a SBC there should be lots of Space for the Hot air to Travel it's normal Route out of the Engine Bay
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post #9 of 14 (permalink) Old Aug 19th, 19, 5:03 PM
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Re: 66 327 overheating

Is your vacuum advance hooked up on the distributor to manifold vacuum?

If not, that can cause it to overheat while idling.

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post #10 of 14 (permalink) Old Aug 19th, 19, 6:00 PM
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Re: 66 327 overheating

What radiator cap are you using? Ebay? Maybe it's not holding the pressure correctly, maybe try a new brand name cap at about 16 pounds or better. Just spit balling here, probably not your problem but a faulty radiator cap can cause over heating.

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post #11 of 14 (permalink) Old Aug 20th, 19, 1:03 PM
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Re: 66 327 overheating

Your vapor lock fuel issue is probably a separate issue. Cool can? put foam around your fuel lines.

Generally 10" fans are terrible. They pull so much less air than 12" fans. As much as 50% less! So unless you got some very high end, expensive, high amp fans, combine that with having to pull air through an inefficient 3 row radiator and that's your problem when sitting in stop and go driving.

I think you can solve the problem without upgrading the radiator. You should at least try. Ditch the 10" fans.

I also see merit in almost all of the suggestions from the balance of the contributors here.

The 3 row radiator is also 3 tiers below the best cooling from a volume and tube surface area standpoint. ie; 4 row aluminum, 2 1" big row, 2 1 1/4" big row. An upgrade in volume would help in both slow and high speed driving.

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post #12 of 14 (permalink) Old Aug 26th, 19, 1:05 AM Thread Starter
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Re: 66 327 overheating

Thanks everyone, some really good replies.

I started with the lowest denominator here as for changes, so I have done the following:
-Spaced the trans cooler out from the radiator, it now sits about 4 inches off the radiator.
-Replaced the fuel line with a thicker hose and removed the plastic fuel filter. This is temporary, I will install a billet fuel filter but removed the plastic one for testing as the walls of the filter are thin.

These changes look to have made a small impact, the temp now sits around 82-85 Celcius (180F-185), however it has resulted in the Vapour Lock kicking in at this lower temperature too, most likely as the second fan flows better now resulting in more hot air blowing into the engine bay. I witnessed bubbles coming through the fuel filter at this temp and thats when the car would start hesitating and stall. I used my laser thermometer and checking the fuel lines and mech fuel pump, they are sitting at around 65C (150F), which seems like it wouldn't be enough heat to cause vapour lock.

I am now going to do the following next:
-Source some new 98 Octane fuel from a different location.
-Install a 1" phenolic carb spacer, it should arrive tomorrow.
-Look into heat insulating the fuel lines with either foam, thermatic sleeve or silicon heat sleeve (anyone have any recommendations?)
-Look for hot spots around the fuel lines running under the car and also hot spots around the fuel tank

From there, if I still have the issue, I will look into:
-Installing some holes\flaps into the bottom of the shroud to dissipate heat at speed.
-Replace shroud\fans with better units, most likely the Spal 12" fans or a whole assembly with the Spal 12" and shroud.

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post #13 of 14 (permalink) Old Aug 26th, 19, 3:01 AM
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Re: 66 327 overheating

I think the spacer and insulating the fuel lines is probably going to help out. A cold air intake or tube to the air cleaner snout may help keep the carb cooler. While running it will keep the carb temp lower. Check your exhaust to see that it's not heating the fuel tank. I can't see what you have going on there, so just offering suggestions.

If you find a spot on the fuel line that is getting toasty and rerouting is not an option, a fabricated heat shield would work well in that location.
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post #14 of 14 (permalink) Old Aug 26th, 19, 8:22 AM Thread Starter
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Re: 66 327 overheating

Thanks Al,

I ran the car this afternoon, and checked around the exhaust and fuel tank, everything there seems fine it was cold enough I could put my hand all around the tank without getting burnt.

My best guess is that the metal fuel line that comes out at the frame in the engine bay is the culprit, the headers are close to the frame and heat it up so much that it was really hot to the touch today, i'm going to insulate around that part of the fuel line, and replace the rubber hoses with new, thicker hose. I also have ordered a new Carter mech fuel pump to replace the stock item on there, this new one has the right fuel pressure to match my Edelbrock 1406 and was something I have been wanting to change out for some time so may aswell do it now.
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